Convergent Synthesis of the Renin Inhibitor ... - ACS Publications

Subscriber access provided by UNIV OF NEBRASKA - LINCOLN

Full Paper

Convergent Synthesis of Renin Inhibitor Aliskiren Based on C5-C6 Disconnection And CO2H - NH2 Equivalence Elena Cini, Luca Banfi, Giuseppe Barreca, Luca Carcone, Luciana Malpezzi, Fabrizio Manetti, Giovanni Marras, Marcello Rasparini, Renata Riva, Stephen Roseblade, Adele Russo, Maurizio Taddei, Romina Vitale, and Antonio Zanotti-Gerosa Org. Process Res. Dev., Just Accepted Manuscript • DOI: 10.1021/acs.oprd.5b00396 • Publication Date (Web): 05 Jan 2016 Downloaded from http://pubs.acs.org on January 6, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Organic Process Research & Development is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Organic Process Research & Development

Convergent Synthesis of Renin Inhibitor Aliskiren Based on C5-C6 Disconnection And CO2H − NH2 Equivalence Elena Cini,† Luca Banfi,¢ Giuseppe Barreca††, Luca Carcone††, Luciana Malpezzi,§ Fabrizio Manetti†, Giovanni Marras,†† Marcello Rasparini,††,±,* Renata Riva,¢ Stephen Roseblade,¶ Adele Russo,† Maurizio Taddei,†* Romina Vitale,¢ Antonio Zanotti-Gerosa¶ †Dipartimento di Biotecnologie, Chimica e Farmacia, Università degli Studi di Siena, Via A. Moro 2, 53100 Siena, Italy ††

Chemessentia srl, Via Bovio 6, 28100 Novara, Italy

¢

Dipartimento di Chimica e Chimica Industriale, Università degli Studi di Genova, Via

Dodecaneso 31, 16146 GENOVA §

Dipartimento di Chimica, Materiali e Ingegneria Chimica “G. Natta”, Politecnico di Milano, Via

Mancinelli 7, 20131 Milano, Italy ¶

Johnson Matthey Catalysis and Chiral Technologies, 28 Cambridge Science Park, Milton Road,

Cambridge, CB4 0FP, United Kingdom ±Present address: Janssen Pharmaceutica PR&D, Turnhoutseweg 30, B-2340 Beerse (Belgium)

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 45

Toc graphic

Enzyme resolution

Catalytic enantioselective hydrogenation Curtius rearrangement

Kg ALISKIREN


2

Page 3 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ABSTRACT. A novel synthesis of renin inhibitor Aliskiren was developed, based on an unprecedented disconnection between C5 and C6, where the C5 carbon acts as nucleophile and the amino group is introduced by Curtius rearrangement. Followed by simultaneous stereocontrolled generation of C4 and C5 stereogenic centres by an asymmetric hydrogenation. Operational simplicity, step economy and a good overall yield makes this synthesis amenable to manufacture on scale.

Keywords: Aliskiren, asymmetric catalysis, asymmetric hydrogenation, generic APIs INTRODUCTION The renin-angiotensin system (RAS) is the primary player of a complex process responsible for the rapid increase of blood pressure, inflammation, kidney fibrosis, heart hypertrophy and vasoconstriction.1-3 The classic therapeutic intervention is based on ACE (Angiotensin Converting Enzyme) inhibitors to block the conversion of angiotensin I into angiotensin II or on angiotensin II receptor blockers, and several drugs belonging to these classes are nowadays available on the market.4 5-7 However, the RAS breakdown leads to a feedback increase of renin production with the activation of a “non-ACE mediated” mechanism to produce angiotensin II. Thus, long-term treatment with ACE inhibitors may result in a general increase of plasmatic renin activity with uncontrolled increasing blood pressure and other side effects.8 As renin is the protease enrolled in the angiotensinogen cleavage to generate the angiotensin cascade, its inhibition appeared as the most direct way to suppress the uncontrolled plasmatic renin increase and prevents the problem related to the use of ACE inhibitors. However, although research towards renin inhibitors started as early as in the late '70s of the last century, formidable


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 45

pharmacokinetic issues slowed down the discovery of efficient oral drugs. Only when the drug candidates moved away from the typical peptide-like systems were these problems solved, at least in part, leading to Aliskiren 1, the first successful renin inhibitor.9,10 Marketing of Aliskiren was also slowed down by the complexity of its structure, which makes the total synthesis rather challenging. Contrary to most peptidomimetics, Aliskirien is characterized by a nearly all-carbon chain, apart from the amide group at its right terminus, and encompasses four stereogenic centres. Poor bioavailability necessitates a relatively high dosage (typically 150 mg/day), compared to ACE inhibitors (Ramipril: 5 mg/day) or angiotensin receptor blockers (Losartan: 50 mg/day), and thus the development of a cost-effective synthesis was particularly important since a high yearly tonnage was expected. In 2007, Aliskiren was licensed by Novartis in the US with the brand name Tekturna and in Europe with the name Rasilez. The introduction of this new hypertension therapy raised expectations for a pathology affecting more than 25% people worldwide, with a population of patients expected to rise to > 1.5 billion people in 2025.11 Starting from the first Novartis-Speedel synthesis,12-17 several research groups, both from academy and industry, have reported brilliant solutions to the problem of Aliskiren synthesis.18-33 At the outset of this work, in view of an industrial scale preparation suitable for sale as a generic drug, we looked for a proprietary, original approach endowed with these features: a) good overall yield (> 10%); b) step-economy (< 15 steps); c) amenable for large scale synthesis; d) cost-effective; e) using, as much as possible, catalytic methods for the control of the stereogenic centres (or allowing efficient recycling of any chiral auxiliary); f) avoidance of the use of stoichiometric organometallic reagents; g) (and last but not least) non infringing previous patents. The latter was probably the most challenging issue, considering the many previous


4

Page 5 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


patent applications regarding Aliskiren synthesis, both from Novartis and competitor generic producers. Partial reports on our efforts have been already published.34,35 Here we give a full account of the successful accomplishment of a synthesis that completely satisfies our initial objectives.


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 45

RESULTS AND DISCUSSION Retrosynthesis. Our retrosynthetic plan is shown in Scheme 1. Most of the previous approaches to the synthesis of Aliskiren are based on the aminolysis of lactone 2: we also decided to aim at this advanced intermediate for two main reasons. First, from the available literature, it was clear that 2 is one of the few crystalline Aliskiren late intermediates, thus providing opportunity for efficient purification. Second, interception of Novartis synthesis at this stage would be advantageous from a regulatory point of view, since the last steps of our synthesis would coincide with those of the originator. For the preparation of 2, we chose to rely on the synthetic equivalence between a carboxylic acid and an amine, which is granted by the stereospecific Curtius rearrangement. The use of a carboxylate as masked amino group brings about another advantage: the possibility to exploit ester enolates as nucleophiles in the crucial carbon-carbon bond formation that joins the two fragments to build up the eight carbon skeleton. Having established C-5 as the nucleophilic carbon for this C-C bond forming event, two disconnections in principle are possible: between C-4 and C-5 (route A, described by Novartis27) or C-5 and C-6 (route B). Therefore, looking for a practical and original approach, we decided to follow route B, relying on an unprecedented C5-C6 disconnection where C5 acts as the nucleophilic counterpart.36 Route B can be further divided in two branches: B1 and B2. They are differentiated by the way the stereogenic centres at C-5 and C-4 are introduced, and by the timing of Curtius rearrangement. In route B1 the two stereogenic centres are generated stepwise, by reduction of the keto group and of the double bond on intermediate 10, whereas the Curtius rearrangement is planned after formation of lactone 3. In route B2 the stereogenic centres are generated


6

Page 7 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


simultaneously, by reduction of enol derivative 8 and the conversion of carboxylate into Boc amine is carried out before lactonization.

Scheme 1. Retrosyntheses. R1 = MeO(CH2)3-


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 45

The key intermediates of the two routes are 9 and 10. The latter may derive from a Knoevenagel condensation between ketoester 12 and aldehyde 11. On the other hand, 9, can result from reduction of 10, or from an alkylation of 12 with iodide 13. Synthesis of chiral building blocks 11 and 13. For the preparation of enantiopure aldehyde 11 and iodide 13 we envisioned as a common precursor alcohol 19, in turn derived from reduction of acid 16 (Scheme 2). For the preparation of 1637-39 we first explored a catalytic methodology, based on enzymatic kinetic resolution of esters 15.40,41 A series of esters were initially produced by Fischer esterification of racemic 16 and a thorough study was carried out in order to find the best conditions for this resolution. Initially, being concerned by the bulkiness of our substrate, we chose methyl ester 15b (R2 = Me) because of the known higher reactivity in enzyme mediated hydrolysis. A considerable number of lipases, proteases and esterases were tested, but none of them was able to efficiently catalyse the reaction. Since traces of product were detected with esterases from pig liver or from Mucor miehei, we concentrated on this class of enzymes, eventually finding a good activity for Horse Liver Acetone Powder (HLAP)42,43 a crude preparation, that was previously proved by us to be particularly efficient on sterically encumbered substrates.44 However, conversion after 48 h was only 43.5% and the E factor45 (= 35) was too low for achieving a high ee of the formed acid 16, which, by comparison with literature data, had the desired (R) configuration.38 Several other parameters were thus varied: a) the nature of R2 group (Me, Et, CF3CH2, nPr, nBu); b) the addition of cosolvents; c) the type and concentration of buffer; d) the substrate concentration; e) the temperature. Complete details of this optimization may be found in the Supporting Information. We eventually found that with the butyl ester 17a, a great increase in E value was observed and unexpectedly, also the reaction rate increased. At a temperature of 40 °C, a substrate concentration of 0.043 M, with 0.3 M TRIS


8

Page 9 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


buffer and no organic cosolvent, an excellent E value of 147 was achieved. This allowed, with a 25 h reaction time, to obtain, at a 47.5% conversion, an ee of 96.2% for (R) 16. Separation of (R) 16 from unreacted (S) ester 15a was trivial and the latter could be racemized by treatment with NaOH in EtOH, allowing a quantitative conversion of the unwanted enantiomer into racemic 16. Esterification of the latter to 15a completed the full recycle of unwanted enantiomer. The ee of acid 16 could be raised to 99.5% by neutralization with dry ammonia in isopropanol, filtration of the solid and extractive recovery of the acid (95% yield).

Scheme 2. Synthesis of building blocks 11 and 13. R1 = MeO(CH2)3Although in preliminary studies the racemic ester 17a was prepared from racemic acid 16 by Fischer esterification, we later found that it could be directly obtained in good overall yield from


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 45

known aldehyde 1417, 18 by a sequence of aldol reaction with butyl isovalerate, acid promoted dehydration, and hydrogenation.Enantiomerically pure acid (R)-16 was then reduced to the alcohol 19, which was in turn oxidized to aldehyde 11 or converted into iodide 13 in excellent overall yields. Although the enzymatic resolution enabled us to produce the first gram-scale batches of 19, which were crucial to prove the downstream chemistry, when we started to upscale this enzymatic methodology, we found that its major drawbacks (low dilution, sourcing of the enzyme and laborious work-up) made it unsuitable on multi-Kg scale. Therefore we draw our attention on an alternative route based on Evans' auxiliary. Thus, Knoevenagel condensation of Evans' oxazolidinone 18 with aldehyde 14, followed by hydrogenation and removal of the chiral auxiliary, gave acid (R)-16 in good overall yield. However, the ee (80%) was too low for our purposes. Therefore we draw our attention on an alternative route based on alkylation of oxazolidinone 18 with 4-(bromomethyl)-1-methoxy-2-(3methoxypropoxy)benzene. This methodology was already known17,18 and would have been freely operable at product patent expiry. Indeed, after the necessary fine-tuning to adapt it to our plants, this route was eventually selected for the large scale preparation of acid (R)-16. Synthesis of the C1-C5 fragment. Enantiopure fragments 12 (Scheme 1; unambiguously identified as 21 or 24-25 in Scheme 3) were prepared starting from the known isovaleryl oxazolidinone (S)-18,46 derived from (S)-phenyl alanine, that was alkylated with tertbutylbromoacetate in the presence of LDA at -78 °C. The reaction gave known product 2046-48 in 80% yield as a single diastereomer. The tert-butyl protection was then removed with TFA and the corresponding acid subjected to homologation with carbonyldiimidazole and magnesium mono-ethyl malonate49 to produce the β-keto ester 21 in 72% overall yield. In order to simplify


10

Page 11 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the recovery of the chiral auxiliary, we also studied the conversion of 20 into an appropriate ester. Using lithium benzyloxide, the benzyl ester 23 was obtained in high yield. Moreover, under these reaction conditions, the recovery of the chiral auxiliary (89% yield) was exceptionally efficient: a simple filtration was needed. As above, selective removal of the tertbutyl protection followed by the homologation with Mg mono-ethyl or mono-tert-butyl malonate worked well giving β-ketoesters 24 and 25 in 72% and 82% yields.

Scheme 3. Synthesis of C1-C5 fragment and union of C1-C5 and C6-C8 fragments. R1 = MeO(CH2)3Union of C1-C5 and C6-C8 fragments. For exploitation of the retrosynthetic route B1 we needed to perform a Knoevenagel reaction between β-ketoesters 21, 24 or 25 and aldehyde 11 (Scheme 3). This reaction was first tested on compound 21. Unexpectedly, classic conditions


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 45

using piperidine in DMF at 60 °C afforded the anticipated adduct 22a only in very low yields. The major product was 22b, where piperidine had displaced the Evans auxiliary (70% overall yield and 8:1 ratio between 22b and 22a). Both adducts were obtained as E:Z mixtures. Although compound 22b could in principle, act as an effective intermediate for our plan, we were concerned about the possibility of a challenging lactonization reaction, since previous Aliskiren syntheses have shown that the lactone - amide equilibrium is normally shifted towards the amide. Therefore we carried out a thorough investigation in order to find optimal conditions to obtain 22a. Details of this optimization are reported in the SI. The optimal solution was a Lewis acid promoted Knoevenagel reaction: using TiCl4/pyridine in equimolar amount (1.2 eq respect to aldehyde 11),50 compound 22a could be obtained in 46% yield, as a 60/40 mixture of E and Z isomers. Our optimized Knoevenagel reaction of benzyl ester 24 with aldehyde 11 produced the desired 26, however, in unsatisfactory yields and with low purity due to extensive TiCl4 catalyzed transesterification. The unsuccessful Knoevenagel reaction prompted the search for a different approach, using iodide 13 for the alkylation of β-ketoester 24. Unfortunately, this reaction also proved to be troublesome. With K2CO3 in acetone, the expected compound 27 was obtained together with another product having the same mass that was attributed to the corresponding Oalkylated derivative. An extensive optimization of the reaction conditions were carried out in order to prevent the formation of the O-alkylated impurity. After a long optimization process, we discovered that the product distribution was highly influenced by the polarity of the solvent and by the counterion of the base. We used the counterion effect and solvent dependence to our advantage and selected LiH in DMA at 60 °C for 18 h to provide a highly efficient C alkylation with complete retention of the original fragment configuration and produced exclusively the C-


12

Page 13 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


alkylated product 27 in 71% isolated yield. Under these optimised conditions, the corresponding tert-butyl ester 28 was also obtained in 80% yield. Investigation of B1 route. Having secured derivatives 22a and 22b, enabled us to explore the feasibility of route B1 (Scheme 4). Carbonyl reduction of 22b with NaBH4 in the presence of CeCl3 proceeded with complete stereoselection and compound 29 was isolated in 54% yield after column chromatography. Further double bond hydrogenation under standard conditions gave 30 as a 4:1 diastereomeric mixture (non-optimized conditions).

Scheme 4. Attempted synthesis through retrosynthetic route B1. R1 = MeO(CH2)3To our surprise, working on compound 30, we noted that lactonization to give 31 occurred very easily, upon treatment with even mild acids or bases. Therefore, it was not possible to selectively hydrolyze the ester without promoting lactonization.


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 45

At first we were pleased by this result, that demonstrated that our concerns about difficult lactonization of the piperidine derivative were not substantiated, and that 22b could be a valid intermediate. However, after separation of the desired major stereoisomer from the minor one, we were unable to remove the ethyl ester without affecting the lactone fragment. This outcome made it impossible to carry out a Curtius rearrangement selectively on the carboxylic acid appended to C-5 without touching also the C-1 carboxy group. The facile lactonization of amide 30, which prevented all attempts to protect the hydroxy group, was unexpected. The equilibrium between esters and amides is normally shifted towards the latter, although notable exception are reported in the literature in the case of tertiary amides.51 We therefore reasoned that with a secondary amide the equilibrium position could be reversed, and installed the amidic part of the final target at this level, with the goal of converting the CO2Et group in 32 into the free carboxylic acid. However, when lactone 31 was treated with 3-amino-2,2-dimethylpropanamide in the presence of AlMe3, although ES/MS of the crude reaction mixture showed the formation of the expected compound 32, all attempts to purify it by column chromatography generated again lactone 31 that was isolated as the main component of the reaction mixture. An analogous behavior was observed also when we tried to prepare 33 by reaction of lactone 31 with benzylamine/AlMe3. This strong propensity to lactonize of compounds 30, 32, and 33 depends on the presence of the carboxylic ester in position 4, since no example of spontaneous lactonization was reported with other intermediates used in Aliskiren synthesis, having a Boc protected amino group in place of the CO2Et group at C-4. To understand the effect of the CO2Et group, a systematic Monte Carlo Multiple Minimum (MCMM) conformational search was performed. The problem was subjected to MacroModel software,52 by using the OPLS_2005 force field53 and the Polak-Ribiere conjugate gradient


14

Page 15 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(PRCG) minimizer on simplified models (with R1 = Me) of 30, 32, 33, and of the analogue of 30 having a NHBoc instead of a CO2Et group. Details on these computations are reported in the SI. One of the decisive steps for the lactonization reaction is the adoption of an optimal conformation, where the distance between the carbonyl atoms of the amide moiety is reduced to approximately 3 Å from the oxygen atom of the hydroxy group. Moreover, according to the Bürgi-Dunitz trajectory hypothesis,54 the angle between the approaching nucleophile and the carbonyl group (O--C=O) should be about 105 degrees. An analysis of conformer population resulting from the calculations shows that the global minimum of the simplified model of benzyl derivative 33 possesses both these optimal geometric requirements for a nucleophilic attack onto the amide carbonyl. In fact, the distance between the hydroxyl oxygen and the carbonyl carbon atoms is about 3.1 Å and the HO---C=O angle is 108 degrees (Figure 1).

Figure 1. Graphical representation of the minimum energy conformer of the benzyl derivative 33 (R1 = Me). The molecule is arranged in a folded conformation stabilized by a hydrogen bond (upper black line) between the hydroxyl group and the carboxyl oxygen of the ester moiety, as well as by a parallel stacked and displaced π-π interaction between the two terminal aromatic rings. Distance between the hydroxyl oxygen (nucleophile) and the carbonyl carbon atom is 3.1 Å, while the Ohydroxyl---C=O angle is 108 degrees.


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 45

This conformation is stabilized by a hydrogen bond between the hydroxyl group and the carbonyl oxygen of the ester moiety. Moreover, π-π interaction (parallel stacked and displaced) is also found between the two terminal aromatic rings. Although, for the simplified models of 30 and 32, the global minimum does not possess the above cited optimal requirements, a significant number of conformations with energy close to the minimum endowed with these features could be found. On the contrary, replacement of the ester side chain with a NHBoc group led to a significant modification of conformational behaviour, due to a hydrogen bond between the secondary amide NH and the Boc carbonyl. This bond causes the global minimum to be characterized by a distance of 3.8 Ǻ and an angle of about 131 degrees. None of the other conformations with energy close to the global minimum satisfy the geometric requirements for cyclization. Investigation of B2 route and accomplishment of total synthesis of Aliskiren. From the above described outcomes it was clear that in order to prevent lactonization, a protected alcohol must be generated before the carboxylic acid/amine transformation. Therefore, the alternative retrosynthetic route B2, depicted in Scheme 1, was pursued. According to this strategy, the two stereogenic centres at C-4 and C-5 would be simultaneously generated by hydrogenation of an enol derivative, providing an intermediate already protected at the hydroxy group, and thus unable to lactonize. The transformation into enol acetates 34-35 (Scheme 5) was of paramount importance, since the correct setting of the relative stereochemistry can be obtained only from an E-enol ether, in view of the fact that both heterogeneous and homogeneous hydrogenations occur largely as syn additions. With regard to the absolute stereochemistry of positions 4 and 5, we hoped to capitalize on the stereochemical bias created by the two isopropyl groups flanking the C=C bond to be reduced.


16

Page 17 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


We investigated this approach first on the ethyl ester 27 (Scheme 5). After conversion into enol acetate 34, it was submitted, without purification, to a panel of hydrogenation conditions.34

Scheme 5. Completion of Aliskiren synthesis along retrosynthetic route B2. R1 = MeO(CH2)3Good conversion into product 34 was observed using [Rh(S)-Phanephos(cod)]BF4 and [Rh(dipf)(cod)]BF4 but a significant amount of the other diastereomers, as well as of by-products was still evident by HPLC and no improvements in the dr was observed modifying the reaction


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 45

conditions. In order to minimize the amount of by-products and increase the stereoselectivity through a stronger coordinative center located on the substrate, the free acid 36 was prepared starting from tert-butyl ester 28. The possibility of working with a free acid also has the advantage to avoid the problem of ester hydrolysis in the presence of the acetate. In this case enolacetate 35 was isolated and we could verify that it was a single diastereomer.55 On subsequent upscaling we found out that enol acetate 35 could be prepared in 80% overall yield from β-ketoester 25, without isolation of the alkylated product 28. Removal of the t-butyl protection with TFA in DCM at 0 °C gave free acid 36, that was directly hydrogenated, without any purification, using [Rh(S)-Phanephos(cod)]BF4 (10 mol %) in CH2Cl2 at 60 °C and 30 bar H2 over 18 hours. Unfortunately, only moderate conversion to product 38 was observed, in contrast to the hydrogenation of the corresponding ester 34, which was more reactive under these conditions. However, the addition of 0.7 equiv. of NEt3 dramatically increased the rate, permitting high conversion into 38 (99% yields) with excellent diastereoselectivity (99:1:0:0; d.r. = 98%). Further extensive optimization during scale-up allowed decreasing the catalyst loading to 0.05% mol working on 1.00 Kg of 36. On this scale, complete conversion was observed in 24 hours (TON = 2115, TOF = 88 h-1) with no erosion in the diastereoselectivity. Acid 38 has all the characteristics for a correct application of the Curtius rearrangement without lactonization risk: a free CO2H and the contiguous protected OH. Thus, 38 was reacted with DPPA in the presence of t-BuOH or benzyl alcohol. Only in the second case the reaction proceeded giving the NHCbz derivative 39 in good yields. Acidic removal of the acetate resulted in spontaneous lactonization to compound 40. This was the first crystalline intermediate of the synthetic sequence following the alkylated β-keto ester 25, and its structure was determined by X-ray crystallography, confirming the correct stereochemistry postulated after the hydrogenation


18

Page 19 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


process (see SI). Unfortunately, the Cbz group was unstable under the further aminolysis conditions, giving rise to the corresponding mixed urea, which proved to be very difficult to purge by crystallization. A Cbz/Boc exchange (benzyl hydrogenolysis in the presence of Boc2O) was therefore carried out to give known N-Boc lactone 41.56 Aminolysis with 3-amino-2,2dimethylpropanamide in the presence of etylhexanoic acid as the catalyst was greatly improved with respect to the prior art56 shifting the equilibrium towards the product by crystallizing it while it is formed,57 by adding heptane as solvent in aminolysis reaction in Scheme 5, providing 42 in 92 % yield and with the same [α]D value (− 19.45, c 1.45 in MeOH) described in the literature for N-Boc Aliskiren.30,56 Finally, Boc removal and crystallization with fumaric acid gave the active principle 1 as the hemifumarate (m.p. = 110-112 °C). CONCLUSIONS The synthesis of Aliskiren presented herein was designed around two conditions: 1) the chemistry needed to be scalable in common multi-purpose plants and 2) must not infringe product and process patents from other parties. Our synthesis was based on the unprecedented C5-C6 disconnection, where C5 acts as the nucleophilic counterpart, and was carried out on a multigram scale in 9 steps58 and 20% overall yield starting from enantiomerically pure known compound 20. Our synthesis is intended for production of a generic API, and the route capitalized on known intermediates whenever intellectual property issues allowed, and where it was convenient from a process chemistry or regulatory perspective. The key points of the synthesis are: the use of the CO2H - NH2 synthetic equivalence, that permitted the exploitation of the typical ketoester enolate reactivity in the formation of C-C bonds under mild conditions; the C-selective alkylation of the β-keto ester 25; and the highly enantioselective catalytic hydrogenation of enol acetate 36, that allowed the full control of relative and absolute


19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 45

stereochemistry of the internal 1,2-syn amino alcohol. In the final industrial synthesis, the absolute configuration of two out of four stereogenic centers was controlled by catalytic methods, whereas for the other two we used chiral auxiliaries. To improve the efficiency of the process for building block 16, we had to move from a highly enantioselective, but not efficient enough at the industrial scale, enzymatic resolution to a more robust chiral auxiliary based preparation. However, as for 20, the chiral auxiliary was recovered in high yield. However, if we consider the enzymatic kinetic resolution and the fact that catalytic enantioselective synthesis of esters like 20 have been recently published,59-61 a fully catalytic synthesis is in principle possible. Notwithstanding the several brilliant previously reported syntheses of Aliskiren, we believe that the here described methodology compares well in terms of operational simplicity, avoidance of harsh conditions or toxic reagents, green-metric values, and overall cost. This process was indeed scaled-up in our development laboratories for the production of this active pharmaceutical ingredient in several Kg batches, with an analytical profile adequate for use in a drug product.

EXPERIMENTAL General methods. All reagents were used as purchased from commercial suppliers without further purification. The reactions were carried out in oven dried or flamed vessels and performed under nitrogen. Solvents were dried and purified by conventional methods prior use.62 Flash column chromatography was performed with silica gel 60, 0.040-0.063 mm (230-400 mesh). Al backed plates pre-coated with silica gel 60 (UV254) were used for thin layer chromatography and were visualized by staining with KMnO4. NMR spectra were recorded under conditions that are specified for each spectrum (temperature 25 °C unless specified). Splitting patterns are designated as s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet; br,


20

Page 21 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


broad. Chemical shifts (δ) are given in ppm relative to the resonance of their respective residual solvent peak, CHCl3 (7.27 ppm, 1H; 77.16 ppm, the middle peak, 13C). High and low resolution mass spectroscopy analyses were recorded at 70 eV by electrospray ionization using a triple quadrupole mass spectrometer. Specific rotations were measured with a 10 cm cell with a Na 589 nm filter: values are given in 10-1 deg.cm3.g-1. Details of the molecular modeling are reported in the SI. General remark: flash chromatography was used during the route scouting studies for the purpose of obtaining analytically pure materials for spectroscopic characterization. In the scaled up synthesis the final building blocks (13) and (25) as well as all the intermediates described in Scheme 5 were used as such, without any chromatographic purification. Butyl 2-(4-methoxy-3-(3-methoxypropoxy)benzyl)-3-methylbutanoate (15a). General procedure. A solution of 2-(4-methoxy-3-(3-methoxypropoxy)benzyl)-3-methylbutanoic acid (11.20 g, 36.08 mmol) in dry CH2Cl2 (120 ml) and DMF (34 µl, 439 µmol) is cooled to 0°C. Then oxalyl chloride is added dropwise (4.3 ml, 50.5 mmol). The reaction is stirred at room temperature until complete (usually 1.5 h). The solvent is evaporated under reduced pressure and the crude taken up twice with CH2Cl2 and concentrated again. The acyl chloride is dissolved in 1-butanol (120 ml) and stirred overnight at room temperature. After concentration under reduced pressure, the crude is partitioned between toluene and 5% aqueous NaHCO3 and extracted with toluene. The organic layer is washed with brine, dried over Na2SO4 and concentrated to give 15 as an oil (9.24 g, 70%). 1H NMR (400 MHz, CDCl3): δ 6.77-6.67 (m, 3H), 4.08 (t, J = 6.5,2H), 3.94 (t, J = 6.6, 2H), 3.82 (s, 3H), 3.57 (t, J = 6.2, 2H), 3.35 (s, 3H), 2.78 (d-like, J = 7.8, 2H), 2.42 (q, J = 7.5,1H), 2.09 (quintuplet, J = 6.3, 2H), 1.92 (octuplet, J = 6.9,1H), 1.41-1.51 (m, 2H), 1.22 (m, 2H), 1.02 (d, J = 6.9, 3H), 0.97 (d, J = 6.6, 3H), 0.85 (t, J = 7.2, 3H).

13

C NMR (100 Mhz,


21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 45

CDCl3): δ 175.0, 148.1, 147.7, 132.5, 120.9, 113.9, 111.6, 69.3, 65.9, 63.7, 58.6, 55.9, 54.9, 35.5, 30.7, 30.6, 29.5, 20.4, 20.2, 19.0, 13.6. HRMS (EI) calcd for C21H34O5Na [M+Na]+ 389.2304. Found 389.2301. Methyl 2-(4-methoxy-3-(3-methoxypropoxy)benzyl)-3-methylbutanoate (15b). (10.77 g, 92% yield). 1H NMR (400 MHz, CDCl3, δ 6.78-6.668 (m, 3H), 4.08 (t, J = 6.6,2H), 3.82 (s, 3H), 3.57 (t, J = 6.2, 2H), 3.54 (s, 3H), 3.56 (s, 3H), 2.81 and 2.77 (AB part of an ABX system, JAB = 13.6, JAX = 7.9, JBX = 0.8,2H), 2.44 (dt, Jd = 9.0, Jt = 6.8, 1H), 2.09 (m, 2H), 1.92 (m, 1H), 1.02 (d, J = 6.9, 3H), 0.96 (d, J = 6.6, 3H).

13

C NMR (100 MHz, CDCl3): δ, 175.4, 148.2, 147.8,. 132.5,

120.9, 114.0, 111.7, 69.4, 66.0, 58.6, 56.0, 54.9, 51.1, 35.5, 29.6, 20.5, 20.1. HRMS (EI) calcd for C18H28O5Na [M+Na]+ 347.1835. Found 347.1832. (2R)-2-{[4-Methoxy-3-(3-methoxypropoxy)phenyl]methyl}-3-methylbutyric

acid

(R)-16.

Racemic 15a (15.24 g, 41.58 mmol) is dispersed in 0.3 M TRIS buffer (500 ml, 83 mmol/ml) and vigorously stirred for 5 min. Then HLAP (10.40 g, 250 mg/mmol respect to 15a, (enzyme purchased from Sigma L9627) is added and the mixture stirred at 40 °C for 80 h. An aqueous solution of citric acid (0.5 M) is added to adjust pH to 3-4 and the aqueous phase saturated with solid NaCl. The crude is filtered over a Celite pad, washed wit Et2O/MeOH 9:1, brine and again with Et2O/MeOH 9:1. This biphasic system is poured into a separatory funnel and 3 additional extractions with Et2O (200 mL each) are performed. After drying on Na2SO4 and solvent removal a red oil is obtained, which was purified by chromatography (AcOEt) to give known (R)-16 as a white solid. The process gives (S)-15a (9.43 g, 62%) and (R)-30 (2.96 g, 23%) with 35% conversion and 52.7% and 97.8% ee respectively; [α]D + 41.2 (c 1, EtOH). Lit63 [α]D +42.1 (c 1, EtOH). The spectroscopic properties are analogues to those reported in the literature.64


22

Page 23 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


General procedure for HPLC analysis. A solution from enzymatic resolution (typically 10 mg, 32.2 mol) in CH2Cl2 (1 ml) is treated dropwise, at 0 °C, with a CH2N2 solution (0.25 M in Et2O) until the yellow color persists. After 30 min the excess of CH2N2 is quenched with few drops of AcOH. The solution is concentrated in vacuum and the last traces of AcOH azeotropically removed with heptane. The sample is dissolved in MeOH ad submitted to HPLC analysis. Regeneration of ester 15a A solution of (S)-15a(12.62 g, 37.29 mmol) in ethanol (95%, 50 ml) was treated with NaOH (4.47 g, 111.9 mmol) previously dissolved in water (8 mL) and refluxed overnight. After concentration under reduced pressure the residue was partitioned between water and toluene and extracted twice. The aqueous phase was acidified with 1 M HCl (to pH 2) and saturated with solid NaCl. Then the acid was extracted with toluene (or AcOEt). After drying on Na2SO4 and solvent removal a red oil was obtained, which was purified by chromatography (AcOEt) to give known racemic 2-(4-methoxy-3-(3-methoxypropoxy)benzyl)-3-methylbutanoic acid as a white solid (10.42 g). Rf 0.32 (hexane/AcOEt 8:2 + 3% AcOH,) The acid was further transformed into the butyl ester 15a following the general procedure described above. (R)-2-(4-Methoxy-3-(3-methoxypropoxy)benzyl)-3-methylbutanal (11). To a solution of (R)-2-(4methoxy-3-(3-methoxypropoxy)benzyl)-3-methylbutanoic acid (R)-16 (2 g, 6.44 mmol) in THF (20 mL), under nitrogen at 0 °C, LiAlH4 (0.488 g, 12.88 mmol) is added. The reaction mixture is stirred vigorously at r.t. for 3 hours, then at 0 °C water is added. The salts are filtered through a pad of Celite and the organic phase concentrated under reduced pressure to give the desired alcohol (1.8 g, 5.63 mmol, 87% yield). The crude product is dissolved in CH2Cl2 (5 mL) and aqueous solutions of NaHCO3 0.5M (2.5 mL) and K2CO3 0.5M (2.5 mL) added. Next, TEMPO (0.016 g, 0.104 mmol), TBACl (0.029 g, 0.104 mmol) and NCS (0.2 g, 1.49 mmmol) are added.


23


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 45

The reddish mixture is stirred vigorously at rt for three hours, then the mixture is diluted with dichloromethane (20 mL) and water (20 mL). The phases are separated and the organic phase washed with brine, dried over sodium sulfate and concentrated to give the desired compound 11 (0.279 g, 91% yield) as a yellow oil. An analytical sample was obtained by column chromatography on silica gel (eluent hexane: AcOEt 3: 4). The spectroscopic properties are analogues to those reported in the literature.26 HRMS (EI) calcd for C17H27O4 [M+H]+ 295.1909, found 295.1910. (R)-4-(2-(Iodomethyl)-3-methylbutyl)-1-methoxy-2-(3-methoxypropoxy)benzene

(13)

To

a

solution of (R)-16(3.500 g, 11.27 mmol) in THF (35 mL), under nitrogen at 0 °C, LiAlH4 (0.854g, 22.50 mmol) was added. The reaction mixture was stirred vigorously at r.t. for 3 h, water (0.85 mL) was added at 0 °C, followed by 15% NaOH (0.85 g) and water (2.55 mL), the aluminum salts were filtered through a pad of Celite and the filtrate was concentrated under reduced pressure. The residue was dissolved in toluene (15 mL), Et3N (1.64 mL, 11.77 mmol) was added and, after cooling to 0 °C under nitrogen, mesyl chloride (0.87 mL, 11.2 mmol) was added dropwise. The resulting solution was stirred for 1.5 h at 20 °C, then water was added (10 mL), the phases were separated, the organic phase was washed with brine, dried over Na2SO4 and concentrated to residue. The mesylate was taken up in acetonitrile (20 mL), NaI was added (4.50 g, 30.00 mmol) and the solution was heated under reflux and under nitrogen for 12 h. Then the solvent was evaporated and the residue was taken up in toluene (25 mL), the organic phase was washed twice with water, dried over Na2SO4 and concentrated to residue. The product was obtained as a white solid that did not require further purification (4.05 g, 9.97 mmol, 88% yield). The spectroscopic properties are analogues to those reported in the literature.34 HRMS (EI) calcd for C17H27IO3Na [M+Na]+ 429.0903, found 429.0905


24

Page 25 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(S)-tert-Butyl 3-((S)-4-benzyl-2-oxooxazolidine-3-carbonyl)-4-methylpentanoate (20) A solution of hexyllithium 2.3 M in hexane (18.3 mL, 42.1 mmol) is added at 0 °C and under nitrogen to a solution of diisopropylamine (5.19 mL, 42.1 mmol) in anhydrous THF (10 mL). After 15 minutes the solution is cooled to -78 °C and a solution of (S)-4-benzyl-3-(3methylbutanoyl)oxazolidin-2-one (S)-18 (10 g, 38.3 mmol), in THF (5 mL) is added dropwise. After 45 minutes at -78 °C, t-butyl bromoacetate (10.7 mL, 72.7 mmol) is added. The temperature is raised to 20 °C during 4 hours, then a saturated solution of ammonium chloride (50 ml) is added, the THF evaporated and the suspension thus obtained is extracted twice with ethyl acetate (2 x 100 mL). The combined organic phases are washed with 0.5 N HCl, brine and dried over anhydrous sodium sulfate. After evaporating the solvent under reduced pressure, the residue was purified by flash column chromatography (cyclohexane/ethyl acetate 8:2) to give 20 (11.5 g, 90% yield) as a white solid. [a]D25 = + 69.0 (c = 1 in CDCl3). Literature65 [a]D25 = + 69.9 (c= 1 in CH2Cl2). 1H NMR (300 MHz, CDCl3,) δ 7.37-7.20 (m, 5H), 4.70-4.60 (m, 1H), 4.204.08 (m, 3H), 3.35-3.25 (dd, J = 13.5 Hz, 3.1 Hz,1H), 2.85-2.75 (dd, J = 28.9, 10.1 Hz, 1H), 2.75-2.65 (dd, J = 13.8, 10.11 Hz, 1H), 2.47-2.37 (dd, J = 16.8 Hz, 3.1 Hz, 1H), 2.01-1.91 (m, 1H), 1.45-1.35 (s, 9H),1.05-0.95 (d, J = 6.7 Hz, 3H), 0.95-0.85 (d, J = 6.7 Hz, 3H). 13C NMR (75 MHz, CDCl3) δ 176.9, 174.5, 172.2, 137.3, 130.7, 130.5, 128.5, 81.1, 66.9, 57.1, 45.4, 38.5, 34.5, 31.1, 29.3, 21.7, 19.5. HRMS (EI) calcd for C21H29NO5Na [M+Na]+ 398.1944, found 398.1948. (S)-Ethyl 5-((S)-4-benzyl-2-oxooxazolidine-3-carbonyl)-6-methyl-3-oxoheptanoate (21). A 100mL flask is charged with potassium ethyl malonate (7.99 g, 46.9 mmol), anhydrous THF (20 mL) and anhydrous magnesium chloride (2.24 g, 23.5 mmol). The suspension is heated under


25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 45

reflux under nitrogen for 12 hours and then cooled to 20-22 °C. Compound 20 (5.87 g, 15.65 mmol) is dissolved into CH2Cl2 (10 mL) and the solution cooled to 0 °C. TFA (4.56 g, 40 mmol) is slowly added and the solution stirred at 0°C for 12 h. The solvent is evaporated and the crude dissolved in anhydrous THF (15 mL). At 0 °C, carbonyldiimidazole (2.79 g, 17.2 mmol) is added to this solution and the mixture stirred at 20 °C for 2 hours. After cooling again to 0 °C, this solution is added to the suspension containing the magnesium ethyl malonate. The resultant mixture is stirred at 20-22 °C for 3 hours, then 10% w/w aqueous solution of HCl (about 80 mL) is added to pH = 2. THF is evaporated at reduced pressure and the mixture extracted with toluene (80 mL); the organic phase is washed twice with a saturated solution of NaHCO3 (80 mL), dried over anhydrous sodium sulfate and concentrated. The product is obtained in the form of viscous oil that does not require further purification (5.5 g, 14.1 mmol, 90% yield). An analytical sample was obtained by column chromatography on silica gel (eluent hexane: AcOEt 2: 1). 1H NMR (300 MHz, CDCl3) δ 7.30-7.10 (m, 5H), 4.62-4.52 (m, 1H), 4.15-4.00 (m, 5H), 3.48-3.32 (q, J = 13.20 Hz, 2H), 3.22-3.12 (dd, J = 13.2, 2.8 Hz ,1H), 3.12-3.02 (dd, J = 18.4, 11.6 Hz, 1H), 2.752.65 (m, 2H), 1.97-1.87 (m, 1H), 1.22-1.15 (t, J = 6.7 Hz, 3H), 0.95-0.90 (d, J = 6.7 Hz, 3H), 0.83-0.78 (d, J = 6.7 Hz, 3H). 13C NMR (75 MHz, CDCl3) δ 202.6, 176.5, 168.2, 154.2, 137.2, 130.3, 128.5, 67.1, 57.0, 50.8, 44.9, 42.9, 38.8, 30.9, 22.1, 21.2, 15.3 HRMS (EI) calcd for C21H27NO6Na [M+Na]+ 412.1736, found 412.1737. (S)-1-Benzyl 4-tert-butyl 2-isopropylsuccinate (23) To a solution of 20 (25.0 g, 66.6 mmol) in anhydrous THF (100 mL), at 0 °C, a solution of benzyl alcohol (9.36 g 86.6 mmol) in anhydrous THF (40 mL) is added. The mixture is cooled to –10 °C and a 2.3 M solution of hexyllithium in hexane (31.8 mL, 73.2 mmol) added dropwise. The resultant solution was stirred for 6 hours at 0 °C, then water (250 mL) and AcOEt (150 mL) added. The phases are separated, the organic


26

Page 27 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


phase washed with water, dried over sodium sulfate and concentrated under reduced pressure. The residue is taken up in AcOEt (40 mL) and hexane (200 mL); the mixture is stirred for 30 minutes and the precipitated Evan’s auxiliary filtered (recovery 9.9 gr, 85% yield). The filtrate solution is concentrated to residue and purified by flash column chromatography (eluent hexane/AcOEt 7:3) to give the desired compound 23 (16.0 g, 52.25 mmol, 79% yield) as a colorless oil. 1H-NMR 300 MHz (CDCl3) δ (ppm): 7.35-7.23 (m, 5H); 5.09 - 5.14 (system AB, 2H); 2.79-2.60 (m, 2H); 2.38-2.28 (m, 1H); 1.97 (m, 1H); 1.40 (s, 9H); 0.90 (d, J = 7.4 Hz, 3H); 0.87 (d, J = 7.4 Hz, 3H). 13C-NMR (100 MHz, CDCl3) 173.8, 171.1, 135.6, 128.0, 127.8, 127.6, 80.1, 65.7, 47.2, 33.9, 29.7, 27.5, 19.6, 19.1. HRMS (EI) calcd for C18H26O4Na [M+Na]+ 329.1729, found 329.1727. (S)-1-Benzyl-6-ethyl

2-isopropyl-4-oxohexanedioate

(24)

(S)-1-Benzyl

4-tert-butyl

2-

isopropylsuccinate 23 (20.0 g, 65.3 mmol) is dissolved in 100 mL of a 1:2 v/v solution of TFA and CH2Cl2 and the mixture stirred at room temperature overnight. The reaction mixture is evaporated under reduced pressure to give the acid as a yellow oil. The acid is dissolved in anhydrous THF and carbonyldiimidazole (10.50 g, 65.3 mmol) added at 0 °C. The solution is added to a suspension of magnesium ethyl malonate, prepared from potassium ethyl malonate (28.0 g, 165 mmol) and MgCl2 (7.85 g, 82.5 mmol) in THF stirred at 20 °C. The mixture is refluxed 12 h, then stirred at 20 °C for other 3 h. A 10% w/w aqueous solution of HCl is then added up to pH = 2 (80 mL). THF is evaporated under reduced pressure and the mixture extracted with toluene (80 mL); the organic phase is washed twice with a saturated solution of NaHCO3 (80 mL), dried over Na2SO4 and concentrated. The product is obtained as a viscous oil that does not require further purification (15.04 g, 72% yield). An analytical sample is obtained by flash column chromatography (heptane/AcOEt 1:2). 1H-NMR (400 MHz, CDCl3) δ 7.34 (m,


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 45

5H), 5.15-5.05 (AB system, J = 12.2 Hz, 2H), 4.15 (q, J = 7.0 Hz, 2H), 3.52-3.37 (AB system, J = 15.3 Hz, 2H), 3.02-2.86 (m, 2H), 2.59 (dd, J = 17.4, 3.0, 1H), 2.03 (m, 1H), 1.26 (t, J = 7.0, 3H), 0.90 (d, J = 7.4 Hz, 3H), 0.87 (d, J = 7.4 Hz, 3H). 13C-NMR (100 MHz, CDCl3) δ 201.0, 176.2, 169.0, 137.8, 129.5, 128.4, 67.2, 59.4, 48.2, 39.8, 30.3, 20.6, 16.0. HRMS calcd for C18H24O5Na [M+Na]+ 343.1522; found 343.1518. (S)-1-Benzyl-6-t-butyl 2-isopropyl-4-oxohexanedioate (25). This product is prepared following the procedure already described for 24. The product is obtained as a viscous oil that does not require further purification (18.3 g, 82% yield). An analytical sample is obtained by flash column chromatography (heptane/AcOEt 1:1). 1H NMR (400 MHz, CDCl3) δ 7.30 (m, 5H), 5.08 (m, 2H), 3.40 – 3.25 (m, 2H), 2.95 (m, 2H), 2.60 (dd, J = 17.8, 3.3 Hz, 1H), 1.99 (dp, J = 13.1, 6.6 Hz, 1H), 1.44 (s, 9H), 0.87 (dd, J = 12.0, 6.9 Hz, 6H).

13

C-NMR (100 MHz, CDCl3) 201.7,

172.2, 166.2, 136.6, 128.5, 127.9, 127.6, 82.1, 66.5, 51.3, 46.5, 41.1, 29.9, 28.4, 20.1, 19.3. HRMS calcd for C20H28O5Na [M+Na]+ 371.1835. Found 371.1833. (S)-Ethyl-5-(((S)-4-benzyloxazolidin-2-on-3-yl)carbonyl)-2-((R)-2-(4-methoxy-3-(3methoxypropoxy)benzyl)-3-methylbutylidene)-6-methyl-3-oxoheptanoate, E/Z mixture (22a). Dry titanium tetrachloride (18.40 g, 9.7 mmol) is dissolved in dichloromethane (24 mL) and to this solution, cooled to 0 °C, a solution containing aldehyde 11 (14.3 g, 48.5 mmol) and keto ester 21 (18.9 g, 48.5 mmol) in THF (67 mL) is added. A solution of pyridine (15.3 g, 194 mmol) in THF (26 mL) is added, during 2 h, to the resultant solution, under vigorous stirring. In the further 14 hours of stirring, the reaction mixture is allowed to reach the temperature of 15 °C. Then it is cooled again to 0 °C and water and methyl-t-butyl ether (200 mL) are added. The phases are separated, the aqueous phase is extracted with methyl-t-butyl ether, the combined organic phases are washed with brine, dried over sodium sulfate and concentrated under reduced pressure. The


28

Page 29 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


residue is purified by flash column chromatography (petroleum ether/ethyl acetate 7:3) to give the desired compound 22a (15.0 g, 46% yield) as a yellow oil. 1H-NMR (400 MHz, CDCl3) δ 7.28-7.19 (m, 5H), 6.79-6.67 (m, 3H), 6.59 (d, J = 16.8 Hz, 1H), 4.64-4.62 (m, 1H), 4.18-3.99 (m, 6H), 3.72 (s, 3H), 3.49 (t, J = 6 Hz, 2H); 3.27 (s, 3H); 3.1-3.0 (m, 2H); 2.77-2.68 (m, 2H); 2.55-2.30 (m, 2H); 2.02-1.97 (m, 2H); 1.88-1.77 (m, 1H); 1.72-1.55 (m, 1H); 1.27-1.17 (m, 4H); 0.96-0.77 (m, 13H). HRMS (EI) calcd for C38H51NO9Na [M+Na]+ 688.3462, found 688.3463. (S)-Ethyl 2-((R)-2-(4-methoxy-3-(3-methoxypropoxy)benzyl)-3-methylbutyldene)-6-methyl-3-oxo5-(piperidine-1-carbonyl)heptanoate (E/Z mixture) (22b). To a solution of (R)-2-(4-methoxy-3(3-methoxypropoxy)benzyl)-3-methylbutanal 11 (0.304 g, 1.03 mmol) in DMF (3 mL), (S)ethyl-5-(((S)-4-benzyloxazolidin-2-on-3-yl)carbonyl)-6-methyl-3-oxoheptanoate 21 (0.684 g, 1.758 mmol) and piperidine (0.509 mL, 5.15 mmol) are added. The resulting solution is stirred at 60 °C for two hours, then Et2O is added, the organic phase washed with water, dried over sodium sulfate and concentrated under reduced pressure. The residue is purified by flash column chromatography (petroleum ether/ethyl acetate 8:2) to give the desired compound 22b (0.413 g, 70% yield) as a pale yellow oil. 1H-NMR (400 MHz, CDCl3) δ 6.74-6.62 (m, 3H); 4.19-4.02 (m, 5H); 3.78 (s, 3H); 3.55-3.48 (m, 8H); 3.32 (s, 3H); 3.17-3.0 (m, 3H); 2.77-2.52 (m, 4H); 2.192.03 (m, 3H); 1.84-1.42 (m, 12H); 1.27-1.18 (m, 6H); 0.94-0.78 (m, 15H). HRMS (EI) calcd for C33H51NO7Na [M+Na]+ 596.3563, found 596.3562. (2R,S)(5S)-6-Benzyl 1-ethyl 5-isopropyl-2-((R)-2-(4-methoxy-3-(3-methoxypropoxy)-benzyl)-3methylbutyl)-3-oxohexanedioate (27). Keto ester 24 (0.910 g, 2.841 mmol) is dissolved in dry dimethylacetamide (1.8 mL) and LiH (21.6 mg, 2.717 mmol) added. The mixture is heated to 60 °C for 1 hour, then iodide 13 (1.050 g, 2.584 mmol)28 added and the mixture stirred at 60 °C for 48 hours, then diluted with toluene (30 mL) and washed with water. The organic phase is


29


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 45

separated, dried over Na2SO4 and concentrated under reduced pressure. The residue is purified by flash column chromatography (hexane/ethyl acetate 7:3) to give 27 (1.155 g, 1.929 mmol, 71% yield) as a yellow oil. The following data refer to a 1: 1 mixture of diastereomers. 1H-NMR (300 MHz, CDCl3) δ 7.31 (m, 5H), 6.76-6.63 (m, 3H), 5.07 (m, 2H), 4.14-4.05 (m, 4H), 3.80 (s, 3H), 3.55 (t, J = 6.4 Hz, 2H), 3.42-3.32 (m, 1H+3H), 2.79-2.76 (m, 2H), 2.52-2.46 (m, 3H), 2.07 (m, 2H), 2.09-1.90 (m, 2H), 1.76-1.52 (m, 2H), 1.50-1.36 (m, 1H), 1.22 and 1.16 (2 x t, J = 7.1 Hz, 3H), 0.86-0.81 (m, 12H).

13

C-NMR (75 MHz, CDCl3) δ 205.7, 205.5, 175.9, 175.4, 171.6,

171.4, 150.2, 149.5, 137.8, 135.8, 135.6, 130.2, 130.2, 129.9, 129.8, 123.0, 122.9, 116.1, 113.6, 71.2, 68.0, 67.9, 63.1, 63.0, 60.4, 59.6, 59.2, 57.8, 47.8, 47.7, 45.3, 45.0, 41.9, 41.6, 38.7, 38.3, 31.7, 31.6, 31.4, 31.1, 31.0, 21.8, 21.4, 21.3 20.9, 20.4, 20.3, 19.7, 15.9, 15.8. HRMS (EI) calcd for C35H50O8Na [M+Na]+: 621.3403, found 621.3407. (5S)-6-Benzyl

1-tert-butyl

5-isopropyl-2-((R)-2-(4-methoxy-3-(3-methoxypropoxy)benzyl)-3-

methylbutyl)-3-oxohexanedioate (28). The product was prepared following the procedure used for 27. Yield isolated after flash chromatography 50%. The following data refer to an inseparable 1 : 1 mixture of diastereomers. 1

H-NMR (300 MHz, CDCl3) δ 7.35-7.25 (m, 5H), 6.77-6.62 (m, 3H), 5.14-5.04 (m, 2H), 4.08 (t,

J = 5.2 Hz, 2H), 3.82 (s, 3H), 3.56 (t, J = 4.9 Hz, 2H), 3.34 (s, 3H), 3.35-3.32 (m, 1H), 3.04-2.71 (m, 2H), 2.58-2.27 (m, 3H), 2.09-2.02 (m, 2H), 2.01-1.81 (m, 2H), 1.75-1.65 (m, 1H), 1.60-1.40 (m, 2H), 1.44 (s, 6H), 1.37 (s, 3H), 0.94-0.78 (m, 12H).

13

C NMR (75 MHz, CDCl3) δ 204.27,

174.41, 174.21, 169.25, 168.97, 148.49, 147.81, 136.21, 134.26, 134.09, 128.62, 128.58, 128.34, 128.24, 128.17, 121.32, 114.42, 111.93, 81.93, 81.86, 69.57, 66.42, 66.32, 66.22, 58.93, 58.80, 58.56, 56.24, 56.18, 46.13, 45.99, 43.52, 43.35, 40.33, 39.89, 36.92, 36.54, 30.19, 30.07, 29.80,


30

Page 31 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


29.22, 28.89, 28.52, 28.06, 27.90, 20.24, 19.82, 19.67, 18.79, 18.56, 17.67. HRMS (EI) calcd for C37H54O8Na [M+Na]+ 649.3716, found 649.3717. 5S)-Ethyl

3-hydroxy-2-((R)-2-(4-methoxy-3-(3-methoxypropoxy)benzyl)-3-methylbutylidene)-6-

methyl-5-(piperidine-1-carbonyl)heptanoate (29). To a solution of 22b (0.362 g, 0.632 mmol) in MeOH (6 mL), CeCl3 (0.353 g, 0.948 mmol) is added. The reaction mixture is cooled to 0 °C and NaBH4 (0.026 g, 0.695 mmol) is added. The resultant solution is stirred for 1 hour at r.t, then a solution of HCl 1M is added to reach pH = 6-7. The aqueous solution is extracted with dichloromethane and the organic phase dried over sodium sulfate and concentrated under reduced pressure. The residue is purified by flash column chromatography (heptane/AcOEt 1:1) to give the two isomers E and Z. Isomer Z (196 mg, 54%): 1H-NMR (400 MHz, CDCl3) δ 6.726.62 (m, 3H); 5.93 (d, J = 10.8 Hz, 1H); 4.15-4.02 (m, 5H); 3.78 (s, 3H); 3.55-3.52 (m, 6H); 3.32 (s, 3H); 3.15-3.03 (m, 1H); 2.73-2.70 (m, 1H); 2.55-2.35 (m, 3H); 2.06-2.03 (m, 2H); 1.89-1.84 (m, 2H); 1.66-1.53 (m, 8H); 1.24-1.18 (m, 3H); 0.95-0.85 (m, 12H). ).

13

C NMR (100 MHz,

CDCl3) δ 174.3, 167.6,. 148.1, 147.6, 142.7, 135.6, 133.1, 121.5, 114.5, 111.6, 71.2, 69.4, 66.0, 60.6, 60.1, 58.6, 56.0, 47.2, 46.4, 43.5, 43.5, 43.1, 43.0, 38.3, 36.5, 36.1, 31.3, 30.8, 30.4, 29.6, 26.7, 26.0, 24.8, 21.4, 20.7, 19.9, 19.1, 14.1. HRMS (EI) calcd for C33H53NO7Na [M+Na]+ 598.3720, found 598.3721. (5S)-Ethyl

3-hydroxy-2-((R)-2-(4-methoxy-3-(3-methoxypropoxy)benzyl)-3-methylbutyl)-6-

methyl-5-(piperidine-1-carbonyl)heptanoate (30). To a solution of 29 (100 mg, 0.174 mmol) in MeOH (5 mL), 10% Pd/C (0.009 g, 0.0087 mmol) is added. The suspension is stirred at r.t. and under H2 (1 Atm) for 16 h. The catalyst is filtered and washed several times with MeOH. The solvent is removed under reduced pressure to give 30 as a colorless oil (100 mg, 99%). 1H-NMR (400 MHz, CDCl3) δ 6.76 (d, J = 8Hz, 1H); 6.66-6.64 (m, 2H); 4.18-3.81 (m, 4H); 3.80 (s, 3H);


31


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 45

3.56-3.53 (m, 6H); 3.32 (s, 3H); 2.80-2.75 (m, 1H); 2.57-2.40 (m, 4H); 2.10-2.03 (m, 2H); 1.921.78 (m, 3H); 1.68-1.48 (m, 7H); 1.42-1.32 (m, 2H); 1.25-1.12 (m, 4H); 0.95-0.82 (m, 13H). HRMS (ESI) calcd. for C33H55NO7Na [M+Na]+: 600.3876: Found 600.3879. (4R)-Ethyl

2-((2S,4S)-4-isopropyl-5-oxotetrahydrofuran-2-yl)-4-(4-methoxy-3-(3-

methoxypropoxy)benzyl)-5-methylhexanoate (31). To a solution of 30 (100 mg, 0.173 mmol) in CH2Cl2 (2 mL) TFA (59 mg, 40 µL, 0.519 mmol) is added. The reaction mixture is stirred at rt for 12 h, the solvent removed under reduced pressure and the crude mixture purified by column chromatography on silica gel (petroleum ether/AcOEt 3:7) to give compound 31 as a colorless oil (0.058 g, 68 % yield). 1H-NMR (400 MHz, CDCl3) δ 6.73-6.60 (m, 3H), 4.43-4.38 (m, 1H), 4.11 (q, J = 7.2 Hz, 2H), 4.02 (t, J = 6.4 Hz, 2H), 3.76 (s, 3H), 3.51 (t, J = 6.4 Hz, 2H), 3.28 (s, 3H), 2.43-2.32 (m, 3H), 2.06-1.99 (m, 5H), 1.80-1.39 (m, 2H), 1.20 (t, J = 7.2 Hz, 3H) 0.95-0.74 (m, 16 H). 13C-NMR (100 MHz, CDCl3) 177.2, 172.3, 147.9, 147.4, 133.0, 120.8, 114.0, 111.4, 78.5, 68.8, 65.7, 60.3, 58.1, 55.6, 49.5, 44.6, 43.1, 36.9, 29.2, 28.6, 28.4, 28.1, 27.0, 19.8, 19.3, 18.1, 16.7, 13.8. HRMS (ESI) calcd for C28H45O7 [M+H]+: 493.3166, found 493.3163. (2S,3S,5S)-6-Benzyl

1-ethyl

3-acetoxy-5-isopropyl-2-((R)-2-(4-methoxy-3-(3-

methoxypropoxy)benzyl)-3-methylbutyl)hexanedioate (37). Keto ester 27 (3.71 g, 6.196 mmol) is dissolved in acetic anhydride (12 mL), and 4-dimethylaminopyridine (0.361 g, 2.96 mmol) and Et3N (6.59 mL, 47.28 mmol) added. The reaction mixture is stirred for 3 h at rt. The solvent is evaporated and the residue taken up in toluene and washed with a saturated solution of NaHCO3, water and brine. The organic phase is dried over Na2SO4 and concentrated under reduced pressure. The residue is dissolved in DCE (20 mL) and this solution added to a 50 mL steel autoclave filled with nitrogen and charged with [((S)-Phanephos)Rh(cod)]BF4 (271 mg, 0.31


32

Page 33 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


mmol) in DCE (5 mL). After 3 cycles of vacuum/nitrogen and 3 cycles of vacuum/hydrogen, the autoclave is pressurized to 30 bar of hydrogen and heated at 60 °C for 16 h. After cooling, the solution is concentrated and the residue taken up in CH2Cl2 (30 mL) and washed with HCl 1M (20 mL). The organic phase is separated and dried over Na2SO4 and evaporated to dryness, obtaining the desired product as a yellow oil (3.40 gr, 90% yield). HPLC data: LC Column: Diacel AD-H 0.46 x 15 cm, 5 µm; flow rate: 1 mL/min; injection volume: 10 µL; wavelength: 205 nm; column temperature: 40 °C; mobile phase: hexane/isopropanol 95:5 ; run time: 20 minutes: Retention times (S,R,R,S)-isomer (minor), 8.63 min; (S,S,S,S)- isomer (major) 9.56 min. 1H-NMR (400 MHz, CDCl3) δ (ppm): 7.37-7.35 (m, 5H), 6.77-6.67 (m, 3H), 5.16-5.02 (AB system, J = 12.5 Hz, 2H), 5.08–4.98 (m, 1H), 4.13-4.07 (m, 4H), 3.82 (s, 3H), 3.57 (t, J = 6.1 Hz, 2H), 3.35 (s, 3H), 2.63-2.58 (m, 1H), 2.55-2.33 (m, 2H), 2.26-2.15 (m, 1H), 2.11-2.07 (m, 2H), 2.02-1.80 (m, 2H), 1.92 (s, 3H), 1.76-1.47 (m, 4H), 1.47-1.31 (m, 1H), 1.24 (t, J = 7.20 Hz, 3H), 0.88-0.80 (m, 12H).

13

C-NMR (100 MHz, CDCl3) δ. 172.9, 171.6, 170.3, 149.5, 148.7, 137.6,

132.3, 129.0, 128.5, 128.0, 127.8, 127.4, 121.2, 116.9, 114.9, 72.6, 69.7, 69.0, 67.5, 61.6, 58.0, 57.0, 49.4, 48.2, 40.2, 39.7, 33.6, 32.9, 30.3, 29.9, 27.9, 25.1, 20.3, 18.6, 15.6. HRMS calcd for C37H54O9Na [M+Na]+ 665.3666. Found 665.3661. (S,E)-3-Acetoxy-5-((benzyloxy)carbonyl)-2-((S)-2-(4-methoxy-3-(3-methoxy-propoxy)benzyl)-3methylbutyl)-6-methylhept-2-enoic acid (36). Compound 28 (7.68 g, 12.27 mmol) is dissolved in acetic anhydride (12 mL), and 4-dimethylaminopyridine (0.361 g, 2.96 mmol) and Et3N (6.59 mL, 47.28 mmol) added. The reaction mixture is stirred for 3 h at r.t. The solvent is evaporated and the residue was taken up in toluene and washed with a saturated solution of NaHCO3, water and brine. The residue is dissolved in TFA (25 mL) and the mixture stirred at room temperature for 1 hour. The solvent is evaporated under reduced pressure and the product is obtained as a


33


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 45

yellow oil (7.36 g, 98% yield). 1H-NMR (300 MHz, CDCl3) δ 7.32 (m, 5H), 6.75-6.64 (m, 3H), 5.15-5.02 (AB system, J = 12.3 Hz, 2H), 4.20-4.05 (m, 2H), 3.81 (s, 3H), 3.59 (t, J = 6.1 Hz, 2H), 3.38 (s, 3H), 3.03 (dd, J = 14.5, 3.5 Hz, 1H), 2.80 (dd, J = 14.4, 11.2, 1H), 2.50-2.45 (m, 2H), 2.25-2.01 (m, 5H), 2.00 (s, 3H), 1.95-1.82 (m, 2H), 1.78-1.69 (m, 2H), 0.93-0.82 (m, 12H). 13

C-NMR (75 MHz, CDCl3) δ 177.3, 173.2, 170.3, 160.3, 150.2, 149.9, 138.1, 136.3, 130.7,

130.4, 130.3, 126.0, 123.8, 117.0, 114.0, 71.6, 68.5, 68.4, 60.7, 58.3, 53.0, 47.4, 38.0, 34.1, 33.3, 31.5, 30.4, 30.3, 22.7, 22.2, 22.1, 21.0, 20.6. HRMS (EI) calcd for C35H48O9Na [M+Na]+ 635.3196, found 635.3194. (2S,3S,5S)-3-Acetoxy-5-(benzyloxycarbonyl)-2-((R)-2-(4-methoxy-3-(3-methoxypropoxy)benzyl)-3-methylbutyl)-6-methylheptanoic acid (38). A 1 L steel hydrogenation apparatus was charges with a solution of 36 (120.0 g, 0.196 mol) in methanol (480 mL) and Et3N (19.3 mL, 0.138 mol). The mixture is carefully degassed with nitrogen, then [((S)-PhanePhos)Rh(cod)]BF4 (71 mg, 8.1 10

-5

mol, substrate : catalyst ratio = 2100:1) is added. After 3 cycles of

vacuum/nitrogen and 3 cycles of vacuum/hydrogen the autoclave is pressurized to 30 bar of hydrogen and heated at 60 °C for 24 h. After complete conversion, the reactor is cooled to rt, depressurized and purged with nitrogen. The reaction mixture is concentrated to a residue which is taken up in toluene (500 mL) and washed with 5% AcOH in water until pH = 5. The organic phase is washed with water, azeotropically dried and concentrated to give 118.9 gr of 38 (99% yield) as a pale brown oil that can be used in the further steps without any purification. An analytical sample is obtained after flash chromatography on silica gel (eluent hexane: AcOEt : MeOH 1: 2: 0.01). Chiral HPLC analysis after reaction with diazomethane showed a diastereomeric ratio > 99:1.1H-NMR (300 MHz, CDCl3) δ (ppm): 7.36-7.26 (m, 5H), 6.75-6.63 (m, 3H), 5.18-5.02 (AB system, J = 12.2 Hz, 2H), 5.18-5.03 (m, 1H), 4.15-4.08 (m, 2H), 3.81 (s,


34

Page 35 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3H), 3.61-3.51 (m, 2H), 3.36 (s, 3H), 2.72-2.59 (m, 1H), 2.55-2.33 (m, 2H), 2.27-2.15 (m, 1H), 2.14-1.76 (m, 4H), 1.91 (s, 3H), 1.68-1.58 (m, 5H), 1.30-1.18 (m, 1 H), 0.87-0.79 (m, 12H). 13CNMR (75 MHz, CDCl3) δ 177.0, 174.6, 170.2, 148.3, 147.8, 136.1, 134.1, 128.6, 128.5, 128.2, 121.3, 114.2, 111.7, 72.7, 69.7, 66.5, 66.2, 60.6, 58.7, 56.2, 48.3, 47.8, 44.1, 36.9, 31.1, 29.4, 29.0, 28.7, 20.9, 20.4, 19.9, 19.8, 17.5. HRMS (EI) calcd for C35H50NaO9+ [M+Na]+ 637.3353, found 637.3351. Derivatization: Concentrate 1 mL of hydrogenation mixture, weigh 25 mg of residue in a 25 mL volumetric

flask

and

dilute

with

5

mL

of

absolute

ethanol;

add

dropwise

trimethylsilildiazomethane (2.0 M in diethyl ether) until yellow persistent color. After about 10 minutes, add acetic acid up to a colorless solution, then dilute up to 25 mL with hexane. HPLC Method: column: Chiralpak OD 250 x 4.6 mm 5 µm; flow rate: 1.0 mL/min; injection volume: 10 µL; wavelength: 205 nm; column temperature: 40 °C; mobile phase: 95% hexane/5% isopropanol; run time: 25 minutes.; Retention times: (S,R,R,S) hydrogenation product: 7.80 min (S,S,S,S) hydrogenation product: 9.07 min. (2S,4S,5S,7S)-Benzyl

4-acetoxy-5-(benzyloxycarbonylamino)-2-isopropyl-7-(4-methoxy-3-(3-

methoxypropoxy)benzyl)-8-methylnonanoate (39). To a solution of 38 (5.35 g, 8.70 mmol) in 50 mL of toluene under N2, triethylamine (1.01 g, 9.98 mmol) is added. The solution is heated to 80 °C and a solution of diphenylphosphoryl azide (2.51 g, 9.12 mmol) in toluene (10 mL) added dropwise (evolution of N2 observed). The mixture is stirred at 80 °C for 1 h. The mixture is then brought to 50 °C and benzyl alcohol (1.88 g, 17.38 mmol) added; after complete addition the mixture is refluxed for 8 h. The reaction mixture is cooled to room temperature and water (100 mL) added, the organic layer separated, the aqueous phase extracted with toluene and the combined organic layers dried over Na2SO4. The solvent is removed under reduced pressure and


35


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 45

the crude mixture purified by column chromatography on silica gel (petroleum ether/EtOAc 7:3) to give compound 38 as a colorless oil (0.105 g, 71 % yield). 1H-NMR (300 MHz, CDCl3) δ 7.34-7.32 (m, 10H), 6.82-6.68 (m, 2H), 6.68-6.59 (m, 1H), 5.21-4.99 (m, 4H), 4.86 (m, 1H), 4.70-4.63 (m, 1H), 4.17-4.03 (m, 2H), 3.90-3.76 (m, 1H), 3.82 (s, 3H), 3.56 (t, J = 6.4 Hz, 2H), 3.32 (s, 3H), 2.52 (dd, J = 13.5, 6.2, 1H), 2.41 (dd, J = 13.4, 8.5, 1H), 2.24-2.14 (m, 1H), 2.142.01 (m, 2H), 1.97-1.75 (m, 2H), 1.83 (s, 3H), 1.77-1.46 (m, 5H), 1.33-1.06 (m, 2H), 0.91-0.72 (m, 12H).13C-NMR (75 MHz, CDCl3) δ 174.9, 170.9, 156.9, 148.7, 147.9, 137.1, 136.4, 134.3, 128.6, 128.5, 127.9, 127.6, 127.3, 121.7, 114.8, 112.1, 73.8, 69.9, 67.1, 66.7, 66.3, 65.6, 59.0, 55.5, 53.9, 53.3, 48.4, 42.3, 39.1, 33.2, 31.6, 28.1, 20.9, 20.4, 20.2, 20.1, 17.8. HRMS (ESI) calcd for C42H58NO9 [M+H]+: 720.4112, found 720.4109. Benzyl

(1S,3S)-1-((2S,4S)-4-isopropyl-5-oxotetrahydrofuran-2-yl)-3-(4-methoxy-3-(3-

methoxypropoxy)benzyl)-4-methylpentylcarbamate (40). To a solution of 39 (17.12 g, 23.8 mmol) in ethanol (342 mL) 10% w/w HCl in water (85.6 mL) is added. The mixture is stirred at 70 °C for 48 h, then cooled to 0 °C to induce crystallization, and the slurry is kept for 1 h at 0 °C, filtered and washed with cold ethanol to give the N-Cbz lactone 40 (11.31 g, 83%). 1H NMR (300 MHz,) δ 7.39-7.27 (m, 5H), 6.76-6.71 (m, 2H), 6.56 (m, 1H), 5.05 (s, 2H), 4.31 (m, 1H), 3.89 (m, 2H), 3.67 (s, 3H), 3.39 (t, J = 6.1 Hz, 2H), 3.27 (s, 3H), 2.56 (dd, J = 13.8, 5.5 Hz, 1H), 2.48-2.39 (m, 2H), 2.06-1.82 (m, 5H), 1.52-1.37 (m, 3H), 1.11 (m, 1H), 0.88 (d, J = 7.0 Hz, 3H), 0.80 (d, J = 6.7 Hz, 3H), 0.75-071 (m, 6H).

13

C NMR (75 MHz, DMSO-d6,) δ 177.9, 156.9,

147.9, 147.1, 137.4, 133.8, 128.3, 127.7, 127.3, 121.0, 114.0, 112.0, 80.3, 68.6, 65.2, 65.1, 57.9, 55.6, 52.6, 44.9, 41.8, 36.3, 30.5, 29.2, 28.5, 27.5, 26.1, 20.4, 20.0, 18.3, 16.5. HRMS (ESI) calcd. for C33H48NO7 [M+H]+: 570.3431. Found 570.3428.


36

Page 37 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


tert-Butyl

(1S,3S)-1-((2S,4S)-4-isopropyl-5-oxotetrahydrofuran-2-yl)-3-(4-methoxy-3-(3-

methoxypropoxy)benzyl)-4-methylpentylcarbamate (41) N-Cbz-lactone 40 (11.31 g, 21.11 mmol) is solubilized in MeOH 113 mL and to this solution Pd/C (10%, 50% H2O, 226 mg, 0.113 mmol) and Boc2O (5.20 g, 23.7 mmol) added. The reaction mixture is stirred at room temperature under H2 (balloon) for 12 h, then the system is purged with nitrogen and the catalyst removed by filtration on Celite. Imidazole (1.54 g, 22.6 mmol) is added to the filtrate and the mixture stirred for 2 h at room temperature (this procedure is necessary to decompose the unreacted Boc2O via N-Boc imidazole which is easily hydrolyzed during aqueous work-up). Then the solvent is evaporated and the residue taken up in toluene (226 mL), washed with 1N HCl (50 mL), water (50 mL) and brine (50 mL) and dried over Na2SO4. The solvent is removed under reduced pressure to give compound 41 as a low-melting colorless solid (10.5 g, 98%). Product 41 is known and the spectroscopic data (1H NMR, 13C NMR, IR [α]D, MS) correspond to the literature values. [α ]D23 = -6,17 (c=0,639 in MeOH) lit [α ]D23 = -6,18 (c=0,75 in MeOH).56 tert-Butyl

(3S,5S,6S,8S)-8-(3-amino-2,2-dimethyl-3-oxopropylcarbamoyl)-6-hydroxy-3-(4-

methoxy-3-(3-methoxypropoxy)benzyl)-2,9-dimethyldecan-5-ylcarbamate (42) To a solution of 41 (1.0 g, 1.87 mmol) in heptane (10 mL) heated to 70 °C, 3-amino-2,2-dimethylpropanamide (0.542 g, 4.67 mmol) and ethylhexanoic acid (0.135 g, 0.93 mmol) are added. The mixture is stirred at 70 °C for 8 h. Water is added and the precipitate filtered and washed with water and heptane and dried at 50-55 °C under vacuum to give to give 42 (1.12 g, 92%). The product thus obtained is known and the spectroscopic and optical data (1H NMR,

13

C NMR, IR MS)

correspond perfectly to the literature.56 (2S,4S,5S,7S)-5-amino-N-(3-amino-2,2-dimethyl-3-oxopropyl)-4-hydroxy-2-isopropyl-7-(4methoxy-3-(3-methoxypropoxy)benzyl)-8-methylnonanamide hemifumarate (1) Gaseous dry HCl


37


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 45

(generated form NaCl and H2SO4) was passed through a cooled (-10 °C) solution obtained dissolving 42 (1.83 g, 2.8 mmol) in dry CH2Cl2 (18 mL). The internal temperature rises to 0 °C during bubbling, the HCl addition stopped and the solution stirred for additional 3 h at 0 °C. The mixture was added to a Na2CO3 solution (880 mg. 16.8 mmol) in H2O (7 mL) cooled to 5 °C under vigorous stirring. The aqueous solution was extracted with CH2Cl2 and the organic phase concentrated under reduced pressure. The residue is taken up in toluene and washed with NH4OH (1 mL of a 28% solution in water). The organic layer is separated and the solvent removed under reduced pressure. Additional toluene is added and stripped away under vacuum to dry the residue. The withe vitreous residue is dissolved in dry t-BuOH and fumaric acid (163 mg, 1.405 mmol) added. The mixture is stirred until complete dissolution of the fumaric acid. The pH of the solution passes from 8 to 5. A small amount of original 1 (10 mg) is added to start the crystallization to give 1.45 g (85% yield) of a product with m.p. 110-112 °C (lit m. p. 108115)66 Spectral data are in accordance with the literature.56

ASSOCIATED CONTENT Supporting Information. Details on optimization of: a) kinetic resolution of esters 15; b) Knoevenagel reaction to give 22a,b; c) alkylation of β-ketoesters 24-25. Details on computational conformational study. Copy of 1H and 13C NMR of compounds 11, 20, 21, 22a, 22b, 23, 24, 25, 27, 29, 30, 31, 35, 36, 37, 38, 39, 40 and 1. AUTHOR INFORMATION Corresponding Author Marcello Rasparini: [email protected]. Maurizio Taddei: [email protected]


38

Page 39 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ACKNOWLEDGMENT Prof. Andrea Tafi is acknowledged for helpful discussion and technical suggestions. Dr. Jennifer Albaneze-Walker ia also acknowledged for the contribution to improve style of the manuscript. ABBREVIATIONS CSA: camphorsulfonic acid; HLAP: Horse Liver Acetone Powder; LHDMS: lithium hexamethyldisylazide; NCS: N-chlorosuccinimide; TEMPO: (2,2,6,6-Tetramethylpiperidin-1yl)oxyl radical; TFA: trifluoroacetic acid; CDI: carbonyl diimidazole; DMA: N,Ndimethylacetamide; DMAP: 4-dimethylaminopyridine.

REFERENCES (1)

van Thiel, B. S.; van der Pluijm, I.; Riet, L. t.; Essers, J.; Danser, A. H. J. Eur. J.

Pharmacol. 2015, 763, 3. (2)

Koh, K. K.; Sakuma, I.; Hayashi, T.; Kim, S. H.; Chung, W.-J. Expert Opin.

Pharmacother. 2015, 16, 949. (3)

Fournier, D.; Luft, F. C.; Bader, M.; Ganten, D.; Andrade-Navarro, M. A. J. Mol.

Med. 2012, 90, 495. (4)

Mercier, K.; Smith, H.; Biederman, J. Primary Care 2014, 41, 765.

(5)

Smith, C. G.; Vane, J. R. Faseb J. 2003, 17, 788.


39


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(6)

Page 40 of 45

Chang, C.-H.; Lin, J.-W.; Caffrey, J. L.; Wu, L.-C.; Lai, M.-S. Amer. J.

Hypertension 2015, 28, 823. (7)

Julius, S.; Kjeldsen, S. E.; Weber, M.; Brunner, H. R.; Ekman, S.; Hansson, L.;

Hua, T. S.; Laragh, J.; McInnes, G. T.; Mitchell, L.; Plat, F.; Schork, A.; Smith, B.; Zanchetti, A.; Grp, V. T. Lancet 2004, 363, 2022. (8)

Paulis, L.; Steckelings, U. M.; Unger, T. Nature Rev. Cardiol. 2012, 9, 276.

(9)

Jensen, C.; Herold, P.; Brunner, H. R. Nature Rev. Drug. Discov. 2008, 7, 399.

(10)

Wood, J. M.; Maibaum, J.; Rahuel, J.; Grutter, M. G.; Cohen, N. C.; Rasetti, V.;

Ruger, H.; Goschke, R.; Stutz, S.; Fuhrer, W.; Schilling, W.; Rigollier, P.; Yamaguchi, Y.; Cumin, F.; Baum, H. P.; Schnell, C. R.; Herold, P.; Mah, R.; Jensen, C.; O'Brien, E.; Stanton, A.; Bedigian, M. P. Biochem. Biophys. Res. Commun. 2003, 308, 698. (11)

Webb, R. L.; Schiering, N.; Sedrani, R.; Maibaum, J. J. Med. Chem. 2010, 53,

(12)

Herold, P.; Stutz, S.; Spindler, F. Process for the preparation of substituted

7490.

octanoyl amides. WO0202508A1, 2002. (13)

Stutz, S.; Herold, P. Process for the preparation of substituted octanoyl amides.

US2003181765A1, 2002. (14)

Herold, P.; Stutz, S. Process for the preparation of (R)-2-alkyl-3-phenyl-1-

propanols. WO0202487A1, 2002. (15)

Rueger, H.; Stutz, S.; Goschke, R.; Spindler, F.; Maibaum, J. Tetrahedron Lett.

2000, 41, 10085. (16)

Sandham, D. A.; Taylor, R. J.; Carey, J. S.; Fassler, A. Tetrahedron Lett. 2000,

41, 10091.


40

Page 41 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(17)

Goschke, R.; Stutz, S.; Heinzelmann, W.; Maibaum, J. Helv. Chimica Acta 2003,

86, 2848. (18)

Wang, F.; Xu, X.-Y.; Wang, F.-Y.; Peng, L.; Zhang, Y.; Tian, F.; Wang, L.-X.

Org. Process Res. Dev. 2013, 17, 1458. (19)

Hanessian, S.; Chénard, E.; Guesné, S.; Cusson, J.-P. J. Org. Chem. 2014, 79,

(20)

Kim, J. H.; Ko, S. Y. Bull. Korean Chem. Soc. 2013, 34, 3777.

(21)

Li, L.-L.; Ding, J.-Y.; Gao, L.-X.; Han, F.-S. Org. Biomol. Chem. 2015, 13, 1133.

(22)

Nam, G.; Ko, S. Y. Helv. Chimica Acta 2012, 95, 1937.

(23)

Pan, X.; Xu, S.; Huang, R.; Yu, W.; Liu, F. Org. Process Res. Dev. 2015, 19, 611.

(24)

Peters, B. K.; Liu, J.; Margarita, C.; Andersson, P. G. Chem. Eur. J. 2015, 21,

(25)

Pozgan, F.; Stefane, B.; Kidemet, D.; Smodis, J.; Zupet, R. Synthesis 2014, 46,

(26)

Rossi, S.; Benaglia, M.; Porta, R.; Cotarca, L.; Maragni, P.; Verzini, M. Eur. J.

9531.

7292.

3221.

Org. Chem. 2015, 2531. (27)

Slade, J.; Liu, H.; Prashad, M.; Prasad, K. Tetrahedron Lett. 2011, 52, 4349.

(28)

Lindsay, K. B.; Skrydstrup, T. J. Org. Chem. 2006, 71, 4766.

(29)

Dong, H.; Zhang, Z. L.; Huang, J. H.; Ma, R. J.; Chen, S. H.; Li, G. Tetrahedron

Lett. 2005, 46, 6337. (30)

Hanessian, S.; Guesne, S.; Chenard, E. Org. Lett. 2010, 12, 1816.

(31)

Dondoni, A.; De Lathauwer, G.; Perrone, D. Tetrahedron Lett. 2001, 42, 4819.


41


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(32)

Page 42 of 45

Heider, P. L.; Born, S. C.; Basak, S.; Benyahia, B.; Lakerveld, R.; Zhang, H.;

Hogan, R.; Buchbinder, L.; Wolfe, A.; Mascia, S.; Evans, J. M. B.; Jamison, T. F.; Jensen, K. F. Org. Process Res. Dev. 2014, 18, 402. (33)

Mascia, S.; Heider, P. L.; Zhang, H.; Lakerveld, R.; Benyahia, B.; Barton, P. I.;

Braatz, R. D.; Cooney, C. L.; Evans, J. M. B.; Jamison, T. F.; Jensen, K. F.; Myerson, A. S.; Trout, B. L. Angew. Chem., Int. Ed. 2013, 52, 12359. (34)

Arena, G.; Barreca, G.; Carcone, L.; Cini, E.; Marras, G.; Nedden, H. G.;

Rasparini, M.; Roseblade, S.; Russo, A.; Taddei, M.; Zanotti-Gerosa, A. Advanced Synthesis & Catalysis 2013, 355, 1449. (35)

Barreca, G.; Carcone, L.; Cini, E.; Marras, G.; Rasparini, M.; Russo, A.; Taddei,

M. Chim. Ind. (Milan) 2013, 129. (36)

C5-C6 disconnection was also used by others,12, 14-16, 31 but in all those cases the

nucleophilic carbon was C6, in the form of a Grignard reagent, whereas in our approach the nucleophilic carbon is C5, and as an easily produced enolate. Coupling between C5 (nucleophile) with C6 (electrophile) has been previously used in Aliskiren synthesis, but not to prepare the full 8-carbon skeleton.29 The most common disconnection in previous Aliskiren syntheses is between C-4 and C-5 or C-3 and C-4. (37)

(R) acid 16 can be also obtained by asymmetric hydrogenation of the

corresponding cinnamic acid derivative.38, 39 (38)

Li, S.; Zhu, S.-F.; Zhang, C.-M.; Song, S.; Zhou, Q.-L. J. Am. Chem. Soc. 2008,

130, 8584. (39)

Boogers, J. A. F.; Felfer, U.; Kotthaus, M.; Lefort, L.; Steinbauer, G.; de Vries, A.

H. M.; de Vries, J. G. Org. Process Res. Dev. 2007, 11, 585.


42

Page 43 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(40)

Woodmansee, D. H.; Müller, M.-A.; Tröndlin, L.; Hörmann, E.; Pfaltz, A. Chem.

Eur. J. 2012, 18, 13780. (41)

Sturm, T.; Weissensteiner, W.; Spindler, F. Adv. Synth. Cat. 2003, 345, 160.

(42)

This crude preparation was purchased from Sigma-Aldrich (cod. L9627).

Alternatively it can be easily prepared from horse liver following a reported procedure.43 Although now HPLAP is no longer sold by Sigma-Aldrich as acetone powder, the purified enzyme (horse liver esterase, cat. no. 46069), which displays a similar activity (obviously with higher U/mg than the acetone powder), is still available. (43)

Pacheco, A.; Luna, H.; Solis, A.; Perez, H. I.; Manjarrez, R. J. Mex. Chem. Soc.

2006, 50, 137. (44)

Guanti, G.; Banfi, L.; Powles, K.; Rasparini, M.; Scolastico, C.; Fossati, N.

Tetrahedron: Asymm. 2001, 12, 271. (45)

Sih, C. J.; Wu, S. H. Topics in Stereochemistry 1989, 63.

(46)

Evans, D. A.; Wu, L. D.; Wiener, J. J. M.; Johnson, J. S.; Ripin, D. H. B.;

Tedrow, J. S. J. Org. Chem. 1999, 64, 6411. (47)

Jiang, B.; Shi, H.-p.; Xu, M.; Wang, W.-j.; Zhou, W.-s. Tetrahedron 2008, 64,

(48)

Pratt, L. M.; Beckett, R. P.; Bellamy, C. L.; Corkill, D. J.; Cossins, J.; Courtney,

9738.

P. F.; Davies, S. J.; Davidson, A. H.; Drummond, A. H.; Helfrich, K.; Lewis, C. N.; Mangan, M.; Martin, F. M.; Miller, K.; Nayee, P.; Ricketts, M. L.; Thomas, W.; Todd, R. S.; Whittaker, M. Bioorg. Med. Chem. Lett. 1998, 8, 1359. (49)

Banfi, L.; Guanti, G.; Riva, R. Tetrahedron 1996, 52, 13493.

(50)

Lehnert, W. Tetrahedron Lett. 1970, 54, 4723.


43


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 44 of 45

(51)

Banfi, L.; Riva, R.; Basso, A. Synlett 2010, 23.

(52)

MacroModel/BatchMin, version 9.9, Schrödinger, LLC, New York, NY, 2011.

(53)

Banks, J. L.; Beard, H. S.; Cao, Y.; Cho, A. E.; Damm, W.; Farid, R.; Felts, A.

K.; Halgren, T. A.; Mainz, D. T.; Maple, J. R.; Murphy, R.; Philipp, D. M.; Repasky, M. P.; Zhang, L. Y.; Berne, B. J.; Friesner, R. A.; Gallicchio, E.; Levy, R. M. J. Comput. Chem. 2005, 26, 1752. (54)

Burgi, H. B.; Dunitz, J. D.; Shefter, E. J. Am. Chem. Soc. 1973, 95, 5065.

(55)

Brandange, S.; Leijonmarck, H. J. Chem. Soc., Chem. Commun. 1985, 1097.

(56)

Foley, M. A.; Jamison, T. F. Org. Process Res. Dev. 2010, 14, 1177.

(57)

Carcone, L.; Magrone, D.; Barreca, G.; Rasparini, M.; H., L. Chemical process

for opening ring compounds. US9067868, 2015. (58)

In this count, we have considered as a single step those transformations carried

out without isolating the intermediates, such as 23 → 24, 24 →35, 35 → 38 and 38 → 39. (59)

Chen, W.; Spindler, F.; Pugin, B.; Nettekoven, U. Angew. Chem., Int. Ed. 2013,

52, 8652. (60)

Andrushko, N.; Andrushko, V.; Thyrann, T.; Koenig, G.; Boerner, A.

Tetrahedron Lett. 2008, 49, 5980. (61)

Zirakzadeh, A.; Gross, M. A.; Wang, Y.; Mereiter, K.; Spindler, F.;

Weissensteiner, W. Organometallics 2013, 32, 1075. (62)

Armarego, W.; Chai, C. Purification of Laboratory Chemicals (Seventh Ed.)

Butterworth-Heinemann, Oxford (UK) 2003, 103–554. (63)

Li, S.; Zhu, S.-F.; Zhang, C.-M.; Song, S.; Zhou, Q.-L. J. Am. Chem. Soc. 2008,

130, 8584–8585.


44

Page 45 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(64)

Rosini, G.; Paolucci, C.; Boschi, F.; Marotta, E.; Righi, P.; Tozzi, F. Green Chem.

2010, 12, 1747-1757 (65)

Jakobsche, C. E.; Peris, G.; Miller, S. J. Angew. Chem. Int. Ed. Engl. 2008, 47,

6707–6711. (66)

Maibaum, J.; Stutz, S.; Göschke, R.; Rigollier, P.; Yamaguchi, Y.; Cumin, F.;

Rahuel, J.; Baum, H. P.; Cohen, N. C.; Schnell, C. R.; Fuhrer, W.; Gruetter, M. G.; Schilling, W.; Wood, J. M. J. Med. Chem. 2007, 50, 4832–4844


45

Convergent Synthesis of the Renin Inhibitor ... - ACS Publications

Recommend Documents