Synthesis of a Spiroindolinone Pyrrolidinecarboxamide MDM2

Article pubs.acs.org/OPRD

Synthesis of a Spiroindolinone Pyrrolidinecarboxamide MDM2 Antagonist Lianhe Shu,* Zizhong Li, Chen Gu, and Dan Fishlock Process Research and Synthesis, Pharma Research and Early Development (pRED), Hoffmann-La Roche, Inc., 340 Kingsland Street, Nutley, New Jersey 07110, United States S Supporting Information *

ABSTRACT: A practical synthesis of a spiroindolinone pyrrolidinecarboxamide MDM2 antagonist 2 is reported. Cycloaddition of dipolarophile 3 with imine 30 afforded a complex mixture of diastereomers that were isomerized to the desired stereoisomer 31 by heating the mixture in the presence of DBU. After hydrolysis, the resulting product was resolved with a chiral amine to give an enantiopure acid which was converted to the target product 2. The process has been scaled up to a multihundred-gram scale. In addition, an asymmetric synthesis of 31 catalyzed by AgOAc and a chiral phosphine ligand was developed to give enantiomerically enriched 31, which was also converted to enantiopure 2.

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INTRODUCTION MDM2 is an important negative regulator of the tumor suppressor, p53.1 The overexpression of MDM2, which impairs p53 functions, has been found in many human tumors.2 Inhibition of MDM2−p53 binding would reactivate the p53 activities, thus providing a potential treatment for cancer.3 Since the discovery of the Nutlin series compounds (e.g., 1) in 2004,4 intensive research has been conducted searching for smallmolecule MDM2 antagonists. 5 Besides Nutlin and its analogues, representative compounds from the pyrrolidine series,6 such as 2 (Chart 1), have also demonstrated excellent

scaled up to the multihundred-gram scale. An asymmetric synthesis is also described.

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RESULTS AND DISCUSSION Synthesis of Racemic Pyrrolidinecarboxylic Acid Core. The synthesis of tert-butyl ester 5 was the most problematic step in the original synthesis.6b The silver-promoted cycloaddition between 3 and 4, followed by treatment with DBU at an elevated temperature, gave a complex mixture of various isomers. The desired isomer 5 was obtained in 20−33% yield by flash column chromatography or SFC. The use of 1 equiv of silver fluoride is clearly not suitable for scale-up in fixed equipment as the formation of a silver mirror on the wall of glassware has been observed. Asymmetric [3 + 2] cycloaddition of azomethine ylides with electron-deficient alkenes, that has been studied extensively over several decades,7 is a powerful method for the synthesis of pyrrolidinecarboxylic acid derivatives. In a typical reaction, a dipolarophile reacts with an imine, either preformed or generated in situ, in the presence of a chiral Lewis acid catalyst to give the cycloaddition product. With a concerted transition state, the relative stereochemistry between C-3 and C-4 is determined by the geometry of the double bond in the dipolarophile, and selectivity at the C-2 and C-5 positions is controlled by the catalyst. While a silver salt catalyst would prefer the endo product, reactions catalyzed by a copper salt usually proceed via the exo transition state.7 As the proton on C-2 is relatively acidic, we envisioned that 8 could be prepared via epimerization of 9, which could be obtained from a silver-catalyzed concerted [3 + 2] cycloaddition between imine 4 and dipolarophile 10 or its analogues such as 12 (Scheme 2). The preparation of Z-isomer 10 was challenging, however. While the undesired E-isomer 3 can be readily isolated in pure form by condensation of 13 with aldehyde 16, 10 was only observed in solution that predominantly contained 3.

Chart 1

efficacy in xenograft mouse models and desirable pharmacological properties. In order to support toxicology studies, process research was initiated to create a scalable synthesis of 2. In the original synthesis,6b 2 was prepared in four steps and 1.3−2.2% overall yield from 3 (Scheme 1). The pyrrolidine core 5 was obtained in modest yield from a cycloaddition reaction of 3 with 4 promoted by stoichiometric amount of silver fluoride. Due to the lack of selectivity, the reaction gave a complex mixture, and the isolation of 5 was very tedious. The subsequent steps to 2 also suffered from low yields and inconsistency. Moreover, chiral supercritical fluid chromatography (SFC) was required for the isolation of the desired enantiomer from the racemate. This synthesis was clearly not suitable for the preparation of 2 in bulk quantities. Herein, we describe a practical synthesis of enantiopure 2, which has been © XXXX American Chemical Society

Received: November 7, 2012

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dx.doi.org/10.1021/op3003213 | Org. Process Res. Dev. XXXX, XXX, XXX−XXX

Organic Process Research & Development

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Scheme 1. Original synthesis of 2a

a Reagents and conditions: a) i. AgF (1.0 equiv), NEt3, MeOH; ii. DBU, n-BuOH, 120 °C, chromatography, 20−33% yield. b) TFA, CH2Cl2, 93% yield. c) Ph2POCl, 4-amino-3-methoxybenzonitrile, chromatography, 35% yield. d) i. NaOH, H2O2, 63% yield; ii. chiral SFC, 32% yield.

Scheme 2. Retrosynthetic analysis of the pyrrolidinecarboxylic acid core 8

Scheme 3. Attempted preparation of Z-substrates

gave predominantly the desired Z-isomer 23 (Scheme 4). Treatment of 23 with hydrogen chloride in methanol afforded 24, in which the configuration of double bond was retained. The subsequent cycloaddition reaction of nitrile 23 with imine

Reactions of aldehyde 16 with 14, 15, or 20 also gave the undesired E-isomers as shown in Scheme 3. On the contrary, the condensation of 16 with compound 22, which contains a nitrile group instead of the carbonyl function, B



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Scheme 4. Silver-catalyzed [3 + 2] cycloaddition of Z-substrates with 25

Scheme 5. Catalytic hydrogenation of 26

Scheme 6. Preparation of 6-TFA via an N-lithiated azomethine ylide

DIPEA, DABCO) at temperatures ranging from 0 to 60 °C (Scheme 6). While mixtures of isomers were obtained under all conditions according to LC−MS analysis, reactions promoted with LiCl/DABCO or LiOH at 40 °C gave the best selectivity overall (∼45%) for the desired stereoisomer 5. After solvent exchange to methanol−water, the resulting precipitate was collected by filtration; LC−MS analysis indicated the presence of 5 (∼57%) and two other unidentified isomers. This material was then treated with trifluoroacetic acid in dichloromethane. Upon solvent exchange to methyl tert-butyl ether (MTBE), the desired isomer 6-TFA crystallized as an MTBE solvate and was collected by filtration in 35% yield (Scheme 6). Although the lithium-promoted process consistently gave 6-TFA in good quality without chromatographic purification, the subsequent coupling of 6 with an aniline remained problematic due to significant homocoupling of 6. Therefore, a convergent approach, that introduces the aniline component prior to the cycloaddition, was considered.

25 in the presence of a catalytic amount of silver acetate and triphenylphosphine proceeded smoothly, and 26 was obtained in up to 66% yield. On the other hand, ester 24 failed to undergo the cycloaddition with imine 25. The reduction of the nitro group in 26 was challenging. A variety of transition metal-catalyzed hydrogenation conditions were studied, but none of them afforded the desired product 29 or its cyclization product. Interestingly, when platinum on charcoal and VO(acac)2 were used as the catalyst, a C−H insertion product 28 was obtained instead of the desired product 29 (Scheme 5). As attempts to use a silver-catalyzed, concerted cycloaddition process were unsuccessful, a stepwise process via an N-lithiated azomethine ylide was investigated (Scheme 6). Unlike the concerted process, the reaction of an N-lithiated azomethine ylide is believed to proceed through a zwitterionic intermediate.8 Consequently, the relative stereochemistry of the product is difficult to predict. The reaction of 3 and 4 in THF was examined in the presence of a lithium salt (e.g., LiCl) paired with a base (e.g., triethylamine, C



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Synthesis of 2 via Chiral Resolution. Imine 30, a crystalline solid, was prepared in three steps from methyl 3-methoxy-4-aminobenzoate. The reaction of 3 with 30 was initially examined under conditions identical to those used for the synthesis of 5. While HPLC analysis showed the presence of a mixture of isomers, the isolation of the desired stereoisomer 31 was surprisingly easy; after solvent exchange to methanol, 31 was obtained by filtration in 33% yield (Scheme 7).

The use of a stoichiometric amount of lithium hydroxide was found unnecessary. When 1 equiv of lithium hydroxide was used, 3 was consumed within 5 min, and a mild exotherm was observed in a reaction run on a 1-g scale. In order to better control the exotherm, which could become significant upon scale-up, the amount of lithium hydroxide was lowered to 0.1 equiv. Under this condition, 3 was consumed after ∼30 min, and at this point, LC−MS analysis showed a mixture of two major isomers (31 and 32 in essentially 1:1 ratio), three minor isomers (33, 34, and 35) (Figure 1), and a number of additional small peaks. Most of these peaks exhibited molecular weight and mass fragmentation patterns identical to those of 31. As shown in Figure 2, while the minor isomers 34 and 35 remained constant after 30 min, 32 gradually converted to the desired product 31, which was isolated in 70−74% yield by crystallization. The isomerization of 32, which involves the inversion of two stereocenters, is likely a retro-Mannich reaction followed by a Mannich ring-closure process (Scheme 8).9 It was postulated that such a conversion could be possible for other diastereomers, such as 33 and 34. To test this potential interconversion, 31, 33, and 34 were individually treated with DBU in toluene, and the reaction mixtures were carefully monitored by LC−MS. After being stirred at reflux overnight, all three reactions gave a mixture of 31, 32, 33, and 34, in an identical ratio, together with trace amounts of a few other isomers, with the formation of the desired isomer 31 clearly favored (Scheme 9). To take advantage of this equilibrium, after a mixture of 3, 30 and lithium hydroxide (0.1 equiv) in THF was stirred at 60 °C

Scheme 7. Preparation of 31 by LiOH-promoted cycloaddition

Encouraged by this result, solvent and temperature effects were investigated. The reaction was screened using a number of common solvents at temperature ranges from 0 °C to reflux. In all cases, LC−MS analysis showed many peaks with the desired molecular weight of 628, but the product distribution profiles were different and changed over time. Overall, THF gave the best profile after the reaction mixture was stirred at 40 °C overnight.

Figure 1. Isomers of 31. D



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Scheme 9. Interconversion of isomers 31, 32, 33, and 34, and isomerization of 35 to 39a

a Reagents and conditions: a) LiOH (cat.), THF, 40−60 °C. b) DBU (1 equiv), toluene, reflux.

Figure 2. Plot of the composition of isomers against reaction time. • 31, ▲ 32, × 34, ∗ 35.

overnight and HPLC analysis indicated no further ongoing isomerization; DBU (0.1 or 1 equiv) was added, and the mixture was heated to reflux. HPLC analysis indeed showed an increased level of 31 accompanied by a reduction of 33 and 34. The regioisomer 35 was converted mainly to another regioisomer, 39, as judged by LC−MS analysis. The cycloaddition of azomethine ylides primarily proceeds via the favored pathway (a) as shown in Figure 3. The unusually high level of regioisomer (i.e., 35) could be explained by a chelation effect of lithium with the enolate and the carbonyl group of the dipolarophile (Figure 3b).10 We envisioned that such an undesired reaction could be suppressed by running the cycloaddition under metal-free conditions. The cycloaddition of 3 and 30 was thus run with DBU as the only catalyst. In the beginning of the reaction at room temperature, a more complex mixture of isomers was observed; the desired isomer 31 was present only as a minor component. From this reaction mixture, three additional diastereomers, 36, 37, and 38, were isolated by chromatography. Compound 40 was the only diastereomer that was not identified. The formation of regioisomers was indeed significantly inhibited, and only a trace amount of 35 was detected as compared to ∼9% in reactions catalyzed by lithium hydroxide. The conversion of the undesired diastereomers to 31 proceeded smoothly after heating the reaction mixture to reflux; 31 became the major product after stirring at reflux overnight. Under optimized conditions (Scheme 10), a mixture

Figure 3. Two different pathways for the cycloaddition of 3 and 30.

of 3, 30 (1.06 equiv), and DBU (0.2 equiv) in toluene was stirred under gentle reflux for 16 h, when LC−MS analysis indicated that an equilibrium had been reached. The reaction mixture was cooled to room temperature and then diluted with methanol and n-heptane. The resulting solid was collected by filtration to give 31 in 90−92% yield and greater than 99% purity. This process has been successfully scaled up to produce over a kilogram of 31. Since attempts to resolve 31 with chiral acids were unsuccessful, 31 was hydrolyzed, and the resolution of the corresponding acid, rac-42, was investigated with both chiral acids and chiral amines. (R)-N,N-Dimethyl-1-phenylethylamine (43), a readily available resolving agent, formed a crystalline salt of the desired enantiomer of 42. The resolution with this reagent was further examined in various solvents with varied stoichiometry. Under optimized conditions, a mixture of rac-42 and 43 (1.40 equiv) in ethyl acetate was heated to reflux and then

Scheme 8. retro-Mannich/Mannich isomerization of 32 to 31

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Scheme 10. Preparation of 2 from 3 and 30

Scheme 11. Potential asymmetric synthesis of 31

for preparative purposes. A reasonable reaction rate could be achieved in DMF, but no sign of chiral induction was observed. The [3 + 2] process using silver acetate and a chiral biphosphine ligand was then evaluated. As shown in Scheme 12, when ligand 46 was used, the reaction gave a 1:1 mixture of 32 and regioisomer 35, the stereochemistry of which suggested that the concerted transition state was predominant. Despite the poor regioselectivity, an encouraging 40% ee was observed for diastereomer 32, which could be converted to an enantiomerically enriched 31 when treated with DBU, as described above. Encouraged by this result, a number of other chiral ligands were examined. A mixture of silver acetate (0.09 equiv) and chiral ligand (0.10 equiv) in toluene was stirred at room temperature until a clear solution was obtained. Then, 3, 30, and triethylamine (1 equiv) were added, and the reaction mixtures were stirred at room temperature for 48 h. The results are summarized in Table 1. With chiral ligands 50−52 (entries 4−6, Table 1; see also Chart 2), high levels of regioisomer 35 were generated. On the other hand, the formation of 35 was significantly reduced with ligands 47−49 (entries 1−3, Table 1; Chart 2). Interestingly, the exo/endo-selectivity also changed. It should be noted that diastereomers 32 and 36, as well as regioisomer 35, are the expected products via concerted transition states.

gradually cooled to room temperature overnight. The resolved 42 salt was obtained in 96−98% de and 39−42% yield from rac-42. The amidation of 42-salt to 2 was straightforward. Treatment of 42-salt with CDI in THF followed by addition of ammonium hydroxide cleanly gave 2, which was isolated in 97% yield and >99% ee. Asymmetric Synthesis of 2. While the synthesis of 2 via resolution has been successfully scaled up to produce multihundred gram quantities of enantiopure 2, the overall yield was limited by the resolution, and half of the material was wasted at the penultimate step. Thus, an asymmetric synthesis would be highly desirable. Inspired by the discovery that all of the diastereomers could be converted to 31 by treatment with DBU (illustrated in Scheme 11), we shifted the focus to fixing the stereochemistry at C-3 in 44 or 45, which might be possible either by an enantioselective stepwise cycloaddition or a concerted [3 + 2] process. Initial attempts to catalyze the reaction of 3 and 30 with a lithium salt in the presence of chiral amines11 did not show any signs of chiral induction. The reaction was further examined with chiral organic bases, such as chiral guanidines,12 chiral thiourea,13 and chiral amines including alkaloids, or inorganic bases (e.g., sodium hydroxide, potassium carbonate, etc.) in the presence of chiral phase transfer catalysts.14 In nonpolar solvents, such as toluene, the reactions were simply too slow to be meaningful F



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Scheme 12. Asymmetric cycloaddition of 3 and 30 catalyzed by AgOAc/46

Table 1. Chiral ligand screening for the preparation of 31

Table 2. Optimization of cycloaddition reaction

HPLC area (%) after cycloaddition reaction

entry ligand 1 2 3 4 5 6

47 48 49 50 51 52

diastereomers

cycloaddition reaction conditions

regioisomer

conv. (%)

31

32

36

38

35

ee (%) of 31 after DBU treatment

71 66 80 61 58 100

15 7 11 18 9 7

0 15b >15b 2.5 3 4 4 15 6 1.5 1 1 4

a

ee (%) of 31 after isomerization − 48 − − 53 50 52 60 55 52 55 55 65 40

a Reactions were stopped whenever conversion reached ≥95%. bThe reaction was too slow and did not achieve ≥95% conversion in 15 days. cDABCO was used as the base for entry 2. For all other reactions, triethylamine was used.

After heating to reflux overnight, HPLC analysis indicated that an equilibrium was reached with 31 becoming the predominant product. Crude 31 obtained in 65% ee was directly hydrolyzed in THF with 50% aqueous sodium hydroxide. The chiral purity of 42 was upgraded by resolution with chiral amine 43. The crystalline salt of 42 was obtained in 99% chemical purity, 99.5% de, and 60% overall yield from 3. This resolved salt was then converted to the target product 2 following the same amidation process described above.

The crude products obtained from the reactions for entries 1−3 (Table 1) were then treated with DBU in toluene at reflux to convert the diastereomers to 31, the chiral purity of which was then determined by chiral HPLC analysis. With the encouraging results obtained with these ligands (entries 1−3), the reaction was further evaluated with the Roche ligands, 47 and 48,15 and (R)-BINAP, an inexpensive analogue of 49. As shown in Table 2, 48 gave consistently higher ee than 47 or (R)BINAP. The reaction rate was significantly improved by switching the solvent to THF or MeTHF and running the reaction at 40 °C. Interestingly, raising the temperature from 22 to 40 °C seemed to have only a minor impact on the enantioselectivity. Under optimized conditions (entry 13, Table 2), silver acetate (2.45 mol %) and 48 (2.50 mol %) were mixed in MeTHF to form a solution of the chiral complex. Then, 3 and 30 (1.1 equiv) were added, followed by triethylamine (1.0 equiv) (Scheme 13). The reaction mixture was heated to 40 °C for 28 h; HPLC analysis indicated complete consumption of 3. The solvent was then exchanged to toluene, and DBU (0.2 equiv) was added.

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CONCLUSION We have described a practical synthesis of a spiroindolinone pyrrolidinecarboxamide MDM2 antagonist. Cycloaddition reactions of 3 with 30 catalyzed by anhydrous lithium hydroxide or DBU gave a mixture of isomers. Upon treatment with DBU at elevated temperatures, all the diastereomers were converted to the desired product 31 via a retro-Mannich/Mannich isomerization process. The formation of undesired regioisomers 35 and 39 could be suppressed by running the reaction under metal-free conditions. Hydrolysis of 31, followed by resolution with N,Ndimethyl-((R)-1-phenylethyl)amine (43) produced enantiopure acid, 42. Amidation of 42 with ammonium hydroxide then provided the title compound 2. The optimized four-step process gave enantiopure 2 in 33% overall yield, and was successfully scaled up to produce multihundred gram quantities of 2. Asymmetric synthesis of 2 was also investigated. Promising G



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Scheme 13. Asymmetric synthesis of 2

with MeOH (24 mL) at room temperature. To the resulting solution was added n-heptane (120 mL) dropwise over 20 min. The resulting suspension was stirred for an additional 2 h and then filtered. The filter cake was washed with toluene/ n-heptane/MeOH (36 mL, 5:5:1), followed by n-heptane (36 mL), and then dried to give 31 (22.0 g, 90% yield) as an off-white solid, mp 256−259 °C; 1H NMR (300 MHz, DMSOd6) δ 10.79 (s, 1H), 10.48 (s, 1H), 8.42 (d, J = 8.4 Hz, 1H), 7.71 (d, J = 8.1 Hz, 1H), 7.65−7.54 (m, 3H), 7.37 (m, 1H), 7.16 (m, 1H), 7.01 (dd, J = 8.1, 1.9 Hz, 1H), 6.68 (d, J = 2.9 Hz, 1H), 4.67 (t, J = 9.6 Hz, 1H), 4.48 (d, J = 10.6 Hz, 1H), 3.91 (s, 3H), 3.85 (m, 1H), 3.84 (s, 3H), 3.72 (m, 1H), 1.29 (dd, J = 13.7, 9.7 Hz, 1H), 0.91 (s, 9H), 0.76 (d, J = 13.7 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 177.3, 171.9, 166.8, 157.6, 155.1, 147.9, 141.5, 134.2, 131.5, 129.5, 127.2, 125.1, 124.8, 124.4, 124.3, 124.0, 123.4, 123.1, 121.2, 118.2, 110.7, 110.3, 66.7, 66.3, 65.4, 55.6, 52.1, 49.9, 42.9, 30.3, 29.8; HRMS (ESI) m/z calcd for C32H33O5N3Cl2F [M + H]+ 628.1781, found 628.1777. rac-4-{[(2′S,3′R,4′S,5′R)-6-Chloro-4′-(3-chloro-2-fluorophenyl)-2′-(2,2-dimethylpropyl)-2-oxo-1,2dihydrospiro[indole-3,3′-pyrrolidine]-5′-carbonyl]amino}-3-methoxybenzoic Acid (rac-42). To a solution of 31 (37.0 g, 58.9 mmol) in THF (185 mL) and water (37 mL) was added 50% NaOH (15.5 mL). After stirring at 60 °C for 4 h, the reaction mixture was diluted with water (37 mL) and then acidified to pH 6 with 55% citric acid (44 g, 105 mmol). After stirring at room temperature for 30 min, the mixture was filtered, and the collected solids were washed with water (2 × 100 mL) and dried to give rac-42 (36.2 g, 96% yield) as a white solid, mp 200 °C dec; 1H NMR (300 MHz, DMSO-d6) δ 12.85 (br s, 1H), 10.77 (s, 1H), 10.48 (s, 1H), 8.40 (d, J = 9.1 Hz, 1H), 7.71 (d, J = 7.9 Hz, 1H), 7.65−7.53 (m, 3H), 7.37 (m, 1H), 7.16 (t, J = 8.6 Hz, 1H), 7.01 (dd, J = 7.9, 1.9 Hz, 1H), 6.68 (d, J = 1.9 Hz, 1H), 4.67 (d, J = 9.8 Hz, 1H), 4.48 (d, J = 8.5 Hz, 1H), 3.91 (s, 3H), 3.85 (m, 1H), 1.29 (dd, J = 14.0, 9.3 Hz, 1H), 0.91 (s, 9H), 0.76 (d, J = 14.0 Hz, 1H); 13 C NMR (100 MHz, DMSO-d6) δ 176.9, 172.1, 167.1, 156.8, 154.3, 147.5, 143.4, 132.4, 131.4, 129.0, 128.4, 126.7, 126.6, 125.8,

results were obtained from a silver acetate and chiral phosphine ligand catalyzed cycloaddition, which provided 31 in 65% ee upon treatment with DBU. After hydrolysis, the chiral purity of acid 42 was further upgraded by resolution, and enantiopure 42 was obtained as a salt in 60% overall yield from 3. This process has been demonstrated on a 10-g scale.

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EXPERIMENTAL SECTION General. HRMS (ESI, positive mode) was obtained by TOF or orbittrap mass analyzer. Structures of 31, 42, and 2 were confirmed by comparison of the NMR spectra and chiral HPLC retention times with those of samples prepared previously as described in ref 6b. Relative stereochemistry of compounds 26 and 32−39 were determined by one-dimensional (1D) NOE experiments (see Supporting Information). Achiral HPLC analyses were performed on Agilent Eclipse XDB-C8 (100 mm × 3 mm, 3.5 μm) column with 30−100% CH3CN/H2O (+ 0.1% TFA) as mobile phase at a flow rate of 1 mL/min over 10 min. Chiral HPLC analyses were performed on Chiralpak IA (250 mm × 4.6 mm, 5 μm) column with CH3CN/iPrOH/H2O (20:55:25 + 0.1% TFA) as the mobile phase at a flow rate of 0.5 mL/min. rac-4-{[(2′S,3′R,4′S,5′R)-6-Chloro-4′-(3-chloro-2-fluorophenyl)-2′-(2,2-dimethylpropyl)-2-oxo-1,2-dihydrospiro[indole-3,3′-pyrrolidine]-5′-carbonyl]amino}-3-methoxybenzoic Acid Methyl Ester (31). LiOH-Catalyzed Process. To a suspension of 3 (20.0 g, 64.9 mmol) and freshly ground anhydrous lithium hydroxide (160 mg, 6.68 mmol) in THF (200 mL) at 40 °C was added 30 (22.0 g, 68.7 mmol). The mixture was stirred at 60 °C for 5 h and at room temperature overnight and then concentrated under reduced pressure to remove ∼140 mL of solvent. The residual thick slurry was diluted with 2-propanol (240 mL) and then further concentrated to remove ∼180 mL of solvent. After stirring at room temperature for 2 h, the resulting suspension was filtered, and the collected solids were washed with 2-propanol (60 mL) and dried to give 31 (30.4 g, 74% yield) as a white solid. DBU-Catalyzed Process. A mixture of 3 (12.0 g, 38.9 mmol), 30 (13.2 g, 41.2 mmol), and DBU (1.20 mL, 7.96 mmol) in toluene (120 mL) was stirred at reflux for 16 h and then diluted H



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The crude 31 (32.5 mmol in theory) obtained above was dissolved in a mixture of THF (102 mL) and water (20 mL). Then 50% NaOH (8.6 mL) was added. The mixture was stirred at 65 °C for 4 h and then acidified with 6 M HCl (28.2 mL, 169 mmol) to pH ∼2. The organic phase was separated, washed with brine (3 × 20 mL), and filtered through a pad of Celite. The filtrate was diluted with water (204 mL), and the resulting suspension was filtered. The filter cake was washed with water and dried by suction to give crude 42 (22.0 g, overweight) as a light-yellow solid, which was directly used in the next step. The crude 42 (32.5 mmol in theory) from above was dissolved in ethyl acetate (80 mL), and then 43 (5.58 g, 37.4 mmol) was added. The mixture was stirred at 60 °C for 4 h, gradually cooled to room temperature, and stirred overnight. The resulting suspension was filtered, and the collected solids were washed with ethyl acetate (2 × 10 mL) to give crude 42-salt (16.4 g, 97% chemical purity and 98.5% de). This crude salt was triturated in methanol (40 mL) to give pure 42-salt (14.8 g, 99% chemical purity, 99.5% de, and 60% yield) as an off-white solid.

125.4, 125.3, 124.8, 122.8, 121.5, 119.3, 119.1, 117.0, 110.9, 109.2, 65.9, 65.05, 65.0, 55.7, 48.6, 42.7, 30.0, 29.6; HRMS (ESI) m/z calcd for C31H31Cl2FN3O5 [M + H]+ 614.1625, found 614.1619. 4-{[(2′S,3′R,4′S,5′R)-6-Chloro-4′-(3-chloro-2-fluorophenyl)-2′-(2,2-dimethylpropyl)-2-oxo-1,2-dihydrospiro[indole-3,3′-pyrrolidine]-5′-carbonyl]amino}-3-methoxybenzoic Acid Dimethyl-((R)-1-phenylethyl) Amine Salt (42-Salt). A mixture of 43 (1.12 g, 7.49 mmol) and rac-42 (4.00 g, 6.51 mmol) in ethyl acetate (80 mL) was stirred at 60 °C for 2 h, gradually cooled to room temperature over 5 h, and stirred at room temperature overnight. The resulting suspension was filtered. The collected solids were washed with cold ethyl acetate (2 mL) and dried to give 42-salt (2.06 g, 41% yield, 98% ee) as a white solid. 1H NMR (300 MHz, DMSO-d6) δ 10.75 (s, 1H), 10.51 (s, 1H), 8.39 (m, 1H), 7.70 (d, J = 7.9 Hz, 1H), 7.62 (m, 1H), 7.60−7.52 (m, 2H), 7.37 (m, 1H), 7.33−7.26 (m, 4H), 7.24 (m, 1H), 7.16 (t, J = 7.9 Hz, 1H), 7.01 (dd, J = 8.3, 1.5 Hz, 1H), 6.69 (d, J = 1.5 Hz, 1H), 4.67 (d, J = 9.2 Hz, 1H), 4.47 (d, J = 9.2 Hz, 1H), 3.90 (s, 3H), 3.85 (m, 1H), 3.34 (q, J = 6.6 Hz, 1H), 2.12 (s, 6H), 1.31 (m, 1H), 1.28 (d, J = 6.6 Hz, 3H), 0.91 (s, 9H), 0.77 (d, J = 14.0 Hz, 1H). (2′S,3′R,4′S,5′R)-6-Chloro-4′-(3-chloro-2-fluorophenyl)-2′-(2,2-dimethylpropyl)-2-oxo-1,2-dihydrospiro[indole-3,3′-pyrrolidine]-5′-carboxylic Acid (4-Carbamoyl-2-methoxyphenyl)amide (2). A mixture of 42-salt (30.0 g, 39.3 mmol) and CDI (12.7 g, 78.6 mmol) in THF (300 mL) was stirred at room temperature for 1.5 h. Ammonium hydroxide (53.1 mL, 786 mmol) was then added to the resulting suspension in one portion. The mixture was stirred at room temperature for 30 min and then diluted with water (180 mL) and ethyl acetate (240 mL). The organic phase was separated, washed successively with brine, 1 M HCl, and water, and then concentrated. The resulting suspension was diluted with n-heptane and filtered. The filter cake was washed with n-heptane and dried to give 2 (23.3 g, 99% ee, 97% yield) as a white solid, mp 203 °C dec; 1H NMR (300 MHz, DMSO-d6) δ 10.69 (s, 1H), 10.47 (s, 1H), 8.33 (d, J = 10.3 Hz, 1H), 7.92 (s, 1H), 7.71 (d, J = 8.0 Hz, 1H), 7.61 (m, 1H), 7.58 (d, J = 1.9 Hz, 1H), 7.50 (dd, J = 8.5, 1.9 Hz, 1H), 7.38 (m, 1H), 7.29 (s, 1H), 7.17 (t, J = 7.9 Hz, 1H), 7.01 (dd, J = 8.1, 1.9 Hz, 1H), 6.68 (d, J = 1.8 Hz, 1H), 4.66 (t, J = 9.4 Hz, 1H), 4.47 (d, J = 9.4 Hz, 1H), 3.90 (s, 3H), 3.84 (m, 1H), 3.71 (m, 1H), 1.30 (dd, J = 14.0, 9.4 Hz, 1H), 0.91 (s, 9H), 0.76 (d, J = 14.0 Hz, 1H); 13C NMR (100 MHz, DMSO-d6) δ 176.9, 171.9, 167.2, 156.7, 154.3, 147.4, 143.4, 132.4, 129.9, 129.0, 128.9, 128.4, 126.7, 126.6, 125.8, 125.3, 124.8, 121.4, 120.4, 119.3, 119.1, 116.8, 109.8, 109.2, 65.9, 65.0, 55.7, 48.8, 42.7, 30.0, 29.6; HRMS (ESI) m/z calcd for C31H32Cl2FN4O4 [M + H]+ 613.1779, found 613.1779. Asymmetric Synthesis. A solution of ligand 48 (676 mg, 0.97 mmol) and AgOAc (131 mg, 0.78 mmol) in MeTHF (5.0 mL) was stirred at room temperature for 1 h. Then 3 (10.0 g, 32.5 mmol) and 30 (11.4 g, 35.7 mmol) were added, followed by triethylamine (4.5 mL, 32.5 mmol). After stirring at 40 °C for 28 h, the mixture was diluted with toluene (50 mL) and concentrated at 30 °C/90 mmHg to remove the solvent. The residual oil was diluted with toluene (150 mL), and then DBU (1.0 mL, 6.5 mmol) was added. The mixture was stirred at reflux overnight and then concentrated to remove 150 mL of solvent. The residue was diluted with n-heptane (200 mL), stirred at room temperature for 30 min, and then filtered. The filter cake was washed with n-heptane to give crude 31, which was directly used in the next step.

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ASSOCIATED CONTENT

* Supporting Information S

Detailed procedures for the preparation of 3, 6-TFA, 26, 28, and 30; 1H, 13C NMR data for 26, 28, 32−39; 1D NOE results for 26, 32−39, copies of NMR spectra for 2, 3, 6-TFA, 26, 28, precursor of 30, 30−39, and 42; LC−MS chromatograms for reactions of 3 with 30, and isomers interconversion experiments. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to Mr. Gino Sasso for structure identification of the isomers with NOE experiments, Dr. Hanspeter Michel for HRMS analysis, and Mr. Joseph Degasperi for analytical support. We thank Dr. Michelangelo Scalone of Roche Basel for providing ligands 47 and 48.

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REFERENCES

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Article

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Synthesis of a Spiroindolinone Pyrrolidinecarboxamide MDM2

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