Communication pubs.acs.org/OPRD
Practical Manufacture of 4‑Alkyl-4-aminocyclohexylalcohols Using Ketoreductases Susana García-Cerrada,* Laura Redondo-Gallego, Francisco Martínez-Olid, Juan A. Rincón, and Pablo García-Losada* Centro de Investigación Lilly S.A., Avda. de la Industria, 30, Alcobendas-Madrid 28108, Spain S Supporting Information *
2. RESULTS AND DISCUSSION The synthesis of the corresponding starting ketones for the alcohol preparation was performed following the synthetic route described below (Scheme 1). Starting from commercially available ethyl 4-oxocyclohexanecarboxylate (1), and after protection of the ketone group with ethylene glycol,5 the alkylation at the α-carbonyl position was performed by treatment of the lithium enolate with the corresponding halo-alkyl derivative at low temperature6 to afford 4-substituted intermediate compounds 3a−g. Ethyl ester hydrolysis followed by the Curtius rearrangement in the presence of allyl alcohol7 installed the desired quaternary amine functionality onto the cyclohexyl ring, protected as the allyl carbamate (compounds 4a−g). Finally, acid-catalyzed ketone deprotection led to the desired 4-substituted cyclohexyl ketones 5a−g with good yields.8 Our main purpose was the preparation of the cis alcohols 6a−g as pure isomers. However, synthesis by conventional methods typically afforded a mixture of the two diastereomers that was difficult to separate by chromatographic methods. In fact, the absence of ultraviolet (UV) chromophore, low molecular weight, and poor mass spectroscopy (MS) ionization negatively impacted on detection. Therefore, nuclear magnetic resonance (NMR) was chosen for evaluation of conversion and selectivity. The comparison of the integrals from the alkyl group resonances of the ketone starting materials (compounds 5a−g), and the final alcohols (compounds 6a−g and 7a−g), was taken as reference to measure the conversion. Cis/trans assignation was achieved through combination of proton−proton coupling constants and NOE correlations, as described in the characterization section. The cis/trans selectivity was determined by using the integration of the H1 signal of each isomer in reaction mixtures samples (around 3.63 ppm for the cis isomer and 3.85 ppm for the trans isomer). As a first approach, we tested the reduction of the ketones using standard hydride reducing agents. Substrate 5a was treated with sodium borohydride, sodium triacetoxyborohydride, lithium borohydride, zinc borohydride, and L-selectride as reducing agents (MeOH or THF as solvent, 0−22 °C and then 16 h at 22 °C). Under these conditions, a mixture of two compounds (6a/7a) was obtained in moderate yield but low selectivity, and only freshly generated zinc borohydride in
ABSTRACT: The diastereoselective preparation of cis- or trans-4-substituted-4-aminocyclohexyl alcohols by conventional chemical processes reported in the literature requires long synthetic sequences and is not amenable to scale-up. In the past decade, ketoreductases (KREDs) have emerged as a powerful approach for the preparation of chiral secondary alcohols from prochiral ketones. This paper describes the diastereoselective preparation at the kilo scale of cis-allyl N-(4-hydroxy-1-methyl-cyclohexyl)carbamate (6a) via ketoreductase transformation. The methodology was also applicable to a set of different analogous cyclic ketones.
1. INTRODUCTION The diastereoselective synthesis of cis- and trans-4-substituted4-aminocyclohexyl alcohols and their analogues is in demand due to their application as building blocks in the pharmaceutical industry for the synthesis of more complex structures.1 Unfortunately, synthetic routes toward these compounds still remain challenging. Other than chromatographic separation of the cis/trans isomer mixtures, some interesting examples involving sequential reactions have been developed, but neither the isolated yields neither the selectivity were completely satisfactory.2 A highly efficient system based on allyl addition to alkyl aldehydes and ketones catalyzed by rhenium oxide has also been reported to afford excellent selectivity (98%) for alkyl ketones, but the selectivity decreased for cyclic ketones.3 Biocatalysis is well-matched to chemical synthesis in the pharmaceutical industry.4 A significant number of pharmaceutical products are optically active, and many compounds have multiple chiral centers. The efficient generation of chiral centers often requires the use of different catalytic systems including enzymes, which possess a unique mechanistic action. Catalytic ketone reductions using enzymes (KREDs) are a reliable method of accessing optically enriched alcohols in a highly stereoselective way and often exceed the ability of conventional chemical catalysts to perform the same transformations. In our ongoing research focused on the diastereoselective preparation of protected cis- or trans-4-alkyl-4-aminocyclohexyl alcohols, we have successfully executed a selective enzymatic ketone reduction to generate the cis and trans isomers at kilogram scale. © 2017 American Chemical Society
Received: February 9, 2017 Published: April 20, 2017 779
DOI: 10.1021/acs.oprd.7b00048 Org. Process Res. Dev. 2017, 21, 779−784
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Scheme 1. General Scheme for the Preparation of the 4-Amino-4-substituted Ketonesa
Reagents and conditions: (i) ethylene glycol, p-TsOH; (ii) LDA, −78 °C, R-I or R-Br (60−99%); (iii) NaOH, EtOH; (iv) Ph3PON3, TEA, CH3CN, allyl alcohol (60−95%); (v) HCl, Acetone (58−93%); R = Me (a), Et (b), n-Pr (c), Propargyl (d), MOM (e), n-Pentyl (f), i-Bu (g).
a
Table 1. KRED Screening Results with Compound 5a
Scheme 2. General Mechanism for KREDs
KRED
cofactor
conversiona (%)
6aa (%)
7aa (%)
d.e.b (%)
P1−A04 P1−A12 P1−B02 P1−B05 P1−B10 P1−B12 P1−C01 P1−H08 P2−B02 P2−C02 P2−C11 P2−D03 P2−D11 P2−D12 P2−G03 P2−H07 P3−B03 P3-G09 P3−H12 101 119 130 NADH101 NADH110
NADP NADP NADP NADP NADP NADP NADP NADP NADP NADP NADP NADP NADP NADP NADP NADP NADP NADP NADP NAD NAD NAD NAD
93 97 99 85 91 98 99 99 99 92 97 95 96 91 93 93 93 96 98 98 89 82 83 >98 >98 97 c c 4 c
17 6 8 3
3 c c 96 c
66 (c) 88 (c) 84 (c) 94 (c) >98 (c) >98 (c) 94 (c) 90 (c) 96 (c) 72 (c) 50 (c) 40 (c) >98 (c) 78 (c) 84 (c) 86 (c) >98 (c) >98 (c) 96 (c) c c 92 (t) c
NAD
90
24
76
52 (t)
entry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
tetrahydrofuran9 afforded a 3:1 mixture enriched in cis isomer 6a (72% yield). Since these conventional methods provided moderate yields and poor stereoselectivity, we decided to explore biocatalysis for the preparation of our target compounds. Ketoreductases (KREDs) are well-established as very useful enzymes for the selective preparation of chiral secondary alcohols from prochiral ketones under mild conditions (Scheme 2).10 In an initial set of experiments, a screen of a kit of 24 KREDs was carried out for the selective reduction of ketone 5a following a similar protocol to the reference procedure reported by the supplier.11 As result of this screening (Table 1), high selectivity for the cis isomer 6a was observed with most of the enzymes tested, and five gave the cis isomer with very high conversion and complete diastereoselectivity (entries 5, 6, 13, 17, and 18). Only one enzyme showed good selectivity for the trans isomer 7a (entry 22). With these preliminary results, an optimization campaign was initiated to find the best enzyme for the kilogram-scale synthesis of cis-allyl N-(4-hydroxy-1-methyl-cyclohexyl)carbamate (6a). The five hits identified in the screening were tested at 100 mg substrate scale, under similar conditions but using 5% (w/w) enzyme loading.12 All gave complete conversion in 24 h, but two of them, KRED-P1-B10 and KRED-P2-D11, reached complete conversion with a cleaner impurity profile. With these two enzymes, a second optimization campaign was carried out. Further changes in temperature, concentration, and enzyme and NADP+ loading were explored. KRED-P1-B10 performed as the best enzyme for the reduction of allyl N-(1-methyl-4-oxo-cyclohexyl)carbamate (5a) to the corresponding cis-allyl N-(4-hydroxy-1methyl-cyclohexyl)carbamate (6a). A great advantage of this enzyme at scale is that it tolerates isopropanol (IPA) in high concentration as recycling system (as do all of the enzymes 1− 19 in the kit), which also function as cosolvent at the same time, simplifying the process and reducing the cost, since the GDH/glucose recycling system is not required. Once KRED-P1-B10 had been selected as the best enzyme, a multigram-scale proof of concept run was conducted at 30 g
24
3 5 3 14 25 30 11 8 7
a
Conversion as percentage, checked by 1H NMR, considered 99% when the starting material was not detected. bd.e. purity as percentage, checked by 1H NMR, considered >98% when the other isomer was not detected. (c) for cis isomer, (t) for trans isomer. cd.e. was not measured due to low conversion observed by TLC.
scale under more concentrated conditions, to optimize the concentration and to characterize the reaction progress (Table 2 and Figure 1). The analysis showed that, after just 4 h of reaction the conversion was 50%, while 24 h was required for total conversion, no erosion in diastereoselectivity was observed, giving pure desired compound in up to 95% isolated yield. Table 2. KRED-P1-B10 NMR Conversion
780
entry
time (h)
conversion (% 6a)
1 2 3 4 5
1.25 2 4 7 23
21 30 51 64 99 DOI: 10.1021/acs.oprd.7b00048 Org. Process Res. Dev. 2017, 21, 779−784
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selective in the case of substrates 5c, 5e, and 5g (entry 7). The pentyl substrate 5f was the example in which lowest trans selectivity was observed. Interesting results were obtained with ketoreductase KREDP3-H12, which showed dramatic changes in selectivity as a function of the substituent, from the cis isomer (96% d.e. in the case of methyl group 6a) to the trans isomer (86% d.e. in the case of the methoxymethyl group 7e). To further demonstrate the synthetic applicability and scalability of these procedures, we also ran the KRED reduction of substrate 5b on larger scale. After some optimization efforts, including, as previously, variations of enzyme and NADP+ loading, temperature, and concentration conditions, the reaction was performed at 50 g scale of ketone starting material 5b,15 obtaining cis-isomer (6b) in 97% isolated yield, with d.e. > 98% (the trans isomer was not detected).
Figure 1.
A successful 1 kg scale campaign was finally performed using substrate 5a in a 20 L reactor.13 Compound 6a was isolated in 99% yield and 98% purity (>98% d.e., trans isomer not detected) by simple direct extraction of the crude mixture.
3. EXTENSION TO ANALOGOUS ALKYL GROUPS With the excellent results obtained in optimization and scale-up in the case of allyl N-(1-methyl-4-oxo-cyclohexyl)carbamate (5a), the study was extended to other analogues, to better understand the scope of ketoreductases for the preparation of allyl N-(4-hydroxy-1-alkyl-cyclohexyl)carbamates (Scheme 3). In general, most of the enzymes were selective for the cis isomer (6) and only a few of them for the trans isomer (7) (Table 3).14 Conversion under the screening conditions (25% enzyme loading w/w, rt, 24 h) was typically high, especially with the propargyl (d) and methoxymethyl (e) substituents, but pentyl (f) and isobutyl (g) afforded lower conversion. The enzymes that tolerate IPA as recycling system (from 1 to 19 in the Codexis screening kit) were the most reactive and almost always showed selectivity for the cis isomer 6. On the other hand, the enzymes that required GDH/glucose as recycling system (from 20 to 24 in the Codexis screening kit) were less reactive and were selective for the trans isomer 7 in almost all the examples. Similar behavior was observed for some KREDs across the different substrates. Enzymes KREDP1-B10, KRED-P1-B12, and KRED-P2-D11 were completely selective for the cis isomer 6 in substrates 5a, 5b, and 5d (R: methyl, ethyl, and propargyl, entries 1, 2, and 4) and showed very high cis selectivity (>90%) in substrates 5c (R: propyl, in this case KRED-P2-D11 was completely selective) and 5e (R: methoxymethyl). The alkyl size negatively impacted selectivity, being slightly or significantly reduced for 5f (R: pentyl group), in which the d.e. was 80%, 74%, and 46% with enzymes KREDP1-B10, KRED-P1-B12, and KRED-P2-B02 (entries 1, 2, 3) and 5g (R: isobutyl group; d.e. 76% and 32% with enzymes KRED-P1-B12 and KRED-P2-D11 (entries 2 and 4). Substrate 5f (R: pentyl) was the only example in which the selectivity for the cis isomer was lower than 96% with all of the enzymes tested. Regarding the trans isomer, enzyme KRED-130 showed very good selectivity for the trans isomer in the case of substrates 5a, 5b, and 5d (entry 6), and KRED-NADH-110 was the most
4. CIS/TRANS ISOMER ASSIGNATION BY NMR The cis/trans assignment of the 4-hydroxycyclohexylcarbamates 6 and 7 was performed (NMR) through proton−proton coupling constants (3JHH) and confirmed by NOE experiments. The isomer assignment is described in detail for isomer pairs 6a and 7a, the approach being similar for the rest of the compounds in this communication. The assignment of the cis/trans isomers was achieved through the combination of NOEs and proton−proton coupling constants. In both derivatives, the NH of the carbamate substituent shows NOEs to H2ax and H3eq, whereas the methyl protons show NOEs to H3eq but not to H2ax, indicating that both isomers adopt a chair conformation in which the carbamate is in an axial and the methyl group is in an equatorial position (Figure 2). The position of the hydroxyl group was determined based on the NOEs observed for H1. In 7a, H1 shows NOEs with H2eq and H2ax, whereas in 6a this proton shows NOEs to H2eq and H3ax, indicating that H1 occupies an equatorial position in 7a and an axial position in 6a and, therefore, the hydroxyl is axial in 7a (trans) and equatorial in 6a (cis). The use of the dihedral angle dependence of vicinal proton coupling constants (3JHH) for structural studies of organic compounds is widely accepted and was used to confirm the cis/ trans assignation. The magnitude of the coupling constant between vicinal protons is related to the dihedral angle between them via the Karplus equation.16 The position of the hydroxy group was confirmed based on the coupling constants between H1 and the vicinal H2 protons. In the isomer 6a, H1 appears as a triplet of triplets with a large coupling constant of 10 Hz and a small coupling constant of 4.5 Hz, corresponding to two axial−axial couplings and to two axial−equatorial couplings, respectively (Figure 3). Therefore, these coupling constants reveal that H1 is axial and the hydroxy group equatorial, as expected for the cis isomer. In contrast, in the isomer 7a, H1 appears as a broad signal involving small
Scheme 3. General Scheme for Biocatalytic Amino Alcohol Preparation
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Table 3. KRED Screening Summary with Substrates 5a−g13
a
Conversion as a percentage, checked by 1H NMR, considered 99% when the starting material was not detected. bd.e. as a percentage, checked by H NMR, considered >98% when the other isomer was not detected. (c) for cis isomer, (t) for trans isomer. cd.e. was not measured due to low reactivity observed by TLC.
1
Figure 2. 2DNOESY expansion where the most important correlations are shown for 6a.
reproduced at kilogram scale for the preparation of cis-4substituted-4-aminocyclohexyl alcohols. This is the first example of this type of substrates being prepared in a totally selective manner.
equatorial−equatorial and equatorial−axial coupling constants, indicating that the hydroxy group occupies an axial position, as expected for the trans isomer. The same conclusions can be reached through the analysis of the multiplicity of H2ax as depicted in Figure 3.
6. EXPERIMENTAL SECTION Materials and Methods. All solvents were purchased from Sigma-Aldrich (Hy-Dry anhydrous solvents), and commercially available reagents were used as received. Codexis ketoreductase screening kit (KREDSK-000250P), NADP (nicotinamide adenine dinucleotide phosphate, oxidized form, monosodium salt, NADP-004669), and KRED-P1-B10 (D13083) were purchased from Codexis. Ketones 5a−g and alcohols 6a−g (as mixture of diastereomers, for reference) were synthesized and characterized following standard procedures described in refs 1, 5−9. All reactions were followed by TLC analysis (TLC
5. CONCLUSIONS In summary, we have developed an efficient sequence for the stereoselective reduction of a number of 4-substituted-4aminocyclohexanones, utilizing KRED reduction to set the absolute cis or trans configuration of these key intermediates. Initial batches of the intermediates were produced using a commercial KRED and IPA for cofactor regeneration to give near-quantitative yields of the alcohols with 98% d.e. The process was intensified to a point that showed sufficient robustness, efficiency regardless of scale, and was easily 782
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Figure 3. Proton NMR spectra for isomers trans (a) and cis (b) from the methyl hydroxycyclohexylcarbamate compounds and proton−proton coupling constants obtained for protons H2 and H3ax (m = multiplet, tt = triplet of triplets, cd = quadruplet of doublets, ax = axial disposition, eq = equatorial disposition).
H12) was added KRED Recycle Mix P (300 μL, 125 mM potassium phosphate, 1.25 mM magnesium sulfate, 1.0 NADP+, pH 7.0). KRED Recycle Mix N (300 μL, 250 mM potassium phosphate, 2 mM magnesium sulfate, 1.1 NADP+, 1.1 NAD+, 80 mM D-glucose, 10 U/mL glucose dehydrogenase, pH 7.0) was added to vials 20−24 (enzymes 101 to NADH-110). The corresponding ketone 5a−g (10 mg) was added to each vial as a solution in isopropanol (30 μL). The reactions were stirred for 24 h at room temperature. Then, 1 mL of ethyl acetate was added to each vial and shaken for 3 min. The organic phase was separated and dried. An initial check of conversion was made using TLC (hexane/MTBE 1:1). For reactions showing an approximate conversion higher than 50%, precise conversion was determined by 1H NMR (a,b,c,f,g), or GC/MS (d,e). Diastereoselectivity was checked by 1H NMR (a−g), compared to a previously prepared diastereomeric mixture of alcohols. The results from the screenings can be found in the Supporting Information. Scale-up of the Enzymatic Reduction Reactions. Ketone 5a (1 kg, 4.7 mol) was dissolved in isopropanol (3 L, 40.8 mol). Phosphate buffer (9 L, C = 0.1 M, pH 7.0), magnesium sulfate (3.43 g, 28 mmol), NADP+ (5 g, 5 mg/g), and KRED-P1-B10 (10 g, 10 mg/g, 1% w/w) were added to the solution. The reaction mixture was stirred at 35 °C for 24 h. Conversion and diastereomeric excess were checked by TLC and 1H NMR, compared to the ketone and a cis/trans mixture of alcohols, respectively. Then, ethyl acetate (3.5 L) was added to the mixture and stirred for 3 min. Once the layers were clearly defined, the phases were separated. This procedure was repeated a second time with 3.5 L of EtOAc and a third with 2 L. The organic layers were combined, dried over anhydrous MgSO4, filtered, and concentrated. Isolated yield 99%, diastereomeric excess >98% for pure cis isomer 6a. A similar procedure was applied for the preparation at scale of substrate 6b.17
plates GF254, Merck) or liquid chromatography mass spectrometry (LC/MS) using an Agilent 1100 equipped with a solvent degasser, binary pump, autosampler, thermostated column compartment with 2-position/10-port valve, and a diode array detector (Agilent Technologies, Waldbronn, Germany). The UV wavelength was set at 214 nm. Electrospray mass spectrometry measurements were performed on a MSD quadrupole mass spectrometer (Agilent Technologies, Palo Alto, CA, USA) interfaced to the above HPLC system. MS measurements were acquired in positive ionization mode over the mass range of 100−700. Data acquisition and integration for LC/UV and LC/MS detection was performed using Chemstation software (Agilent Technologies). GC/MS measurements were acquired using an Agilent 7890A with HPChiral 30 m, 0.25 mm, 0.25 mm (β-cyclodextrin in (35% phenyl)-methylpolixiloxane) column, and mass measurements were performed in EI ionization mode over the mass range of 50−500. NMR spectra were recorded at ambient temperature using standard pulse methods on any of the following spectrometers and signal frequencies: Bruker Avance DPX 300 MHz (1H = 300 MHz, 13C = 75 MHz), Bruker Avance III HD 400 MHz (1H = 400 MHz, 13C = 100 MHz), Bruker Avance III HD 500 MHz (1H = 500 MHz, 13C = 125 MHz). Chemical shifts are reported in ppm and are referenced to the following solvent peaks: chloroform (1H = 7.26 ppm, 13C = 77.16 ppm), acetone (1H = 2.05 ppm, 13C = 29.84 ppm), methanol (1H = 3.31 ppm, 13C = 49.00 ppm), and DMSO (1H = 2.50 ppm, 13C = 39.52 ppm). Coupling constants are quoted to the nearest 0.1 Hz, and multiplicities are given by the following abbreviations and combinations thereof: s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet), br (broad). The purity of all compounds tested was determined by LC/MS and 1H NMR to be >95%. General Protocol for the Screening with KRED Codexis Kit. KREDs (2.5 mg) were weighted in 24 separate vials. To vials 1−19 (corresponding to enzymes P1-A04 to P3783
DOI: 10.1021/acs.oprd.7b00048 Org. Process Res. Dev. 2017, 21, 779−784
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(12) 100 mg scale conditions for 5a: 5% (w/w) enzyme loading, 1% NADP+, 15 mL/g of phosphate buffer pH 7, 8.6 equiv of isopropanol (3.3 mL/g), 35 °C, 24 h. (13) 1 kg scale conditions for 5a: 9 L of phosphate buffer pH 7, 3.1 L of isopropanol, 1% (w/w) enzyme loading, 0.5% (w/w) NADP+, 35 °C (inner temperature), 24 h. (14) The complete results from the screenings can be found in the Supporting Information. (15) 50 g scale conditions for 5b: 3% (w/w) enzyme loading, 0.5% (w/w) NADP+, 9 vol. of buffer phosphate pH 7, 8.6 equiv of IPA, 35 °C, 24 h. (16) Buys, H. R. Recl. Trav. Chim. Pays-Bas 1969, 88, 1003. Karplus, M. J. Am. Chem. Soc. 1963, 85, 2870. Karplus, M. J. Chem. Phys. 1959, 30, 11. Minch, M. J. Concepts Magn. Reson. 1994, 6, 41. (17) In the case of substrate 6b, the enzyme loading was 3% (w/w).
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.oprd.7b00048. Detailed 1H NMR characterization and enzyme screening results for compounds 5a−g, 6a−g, and 7a−g (PDF)
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
Pablo García-Losada: 0000-0002-8307-0033 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors want to thank Dr. Graham R. Cumming, Dr. Javier Mendiola, and Dr. Joshua R. Clayton for their assessment and helpful discussion. Laura Redondo-Gallego thanks the Fundación Universidad-Empresa (FUE) for a fellowship.
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REFERENCES
(1) Czechtizky, W.; Weston, J.; Rackelmann, N.; Kraft, V.; Arndt, P.; Wirth, K.; Goegelein, H.; Ritzeler, O. Preparation of substituted chroman-6-yloxy-cycloalkanes and their use as pharmaceuticals. WO 2014135674. Romero, D. L.; Wessel, M. D.; Robinson, S.; Greenwood, J. R.; Watts, K. S.; Frye, L.; Harriman, G. C.; Corin, A. F.; Masse, C. Preparation of substituted 6,7-dihydro-5H-cyclopenta[4,5]thieno[2,3d]pyrimidines and analogs as IRAK inhibitors. WO 2012097013. Madar, D. J.; Djuric, S. W.; Michmerhuizen, M. J.; Kopecka, H. A.; Li, X.; Longenecker, K. L.; Pei, Z.; Pireh, D.; Sham, H. L.; Stewart, K. D.; Szczepankiewicz, B. G.; Wiedeman, P. E.; Yong, H. Preparation of cyanopyrrolidine derivatives and pharmaceutical compositions thereof as inhibitors of dipeptidyl peptidase-iv (DPP-IV). US 20050215784. (2) Zhang, X. Org. Lett. 2015, 17 (23), 5828. Kapat, A. J. Am. Chem. Soc. 2009, 131 (49), 17746. Ellman, J. Org. Lett. 2004, 6 (10), 1645. Panchaud, P. J. Org. Chem. 2004, 69 (8), 2755. (3) Pramanik, S. Chem. Commun. 2012, 48 (12), 1820. (4) Alcantara, A. R. Curr. Green Chem. 2014, 1 (2), 155. Reetz, M. J. Am. Chem. Soc. 2013, 135, 12480. Bornscheuer, U. T. Nature 2012, 485 (7397), 185. (5) Kitbunnadaj, R. Bioorg. Med. Chem. 2005, 13 (23), 6309. (6) Zheng, S. J. Med. Chem. 2012, 55 (10), 4837. (7) Ley, S. Org. Biomol. Chem. 2008, 6, 1577. Aicher, T. D.; Chicarelli, M. J.; Hinklin, R. J.; Tian, H.; Wallace, O. B.; Chen, Z.; Mabry, T. E.; Mccowan, J. R.; Snyder, N. J.; Winnerosky, L.; Allen, J. G. Preparation of cycloalkyl lactam derivatives, particularly N-substituted pyrrolidin-2-ones, as inhibitors of 11beta-hydroxysteroid dehydrogenase 1. WO2006049952. (8) Schunk, S.; Zemolka, S.; Saunders, D.; Gruss, M.; Graubaum, H. Preparation of spirocyclic indoles as ORL1 receptor inhibitors. WO2008101659. (9) Narasimhan, S. J. Org. Chem. 1995, 60, 5314. (10) Truppo, M. Comprehensive Organic Synthesis, 2nd ed.; 2014; Vol. 8, p 317. Huisman, G. W.; Liang, J.; Krebber, A. Curr. Opin. Chem. Biol. 2010, 14, 122. Kambourakis, S.; Rozzell, J. D. PharmaChem. 2006, 5 (9), 2−5. (11) Potassium phosphate buffer 0.1 M (pH 7), catalytic MgSO4, using NADP+ as a cofactor and isopropanol as a recycling system for the enzymes in entries 1−19, and NADP+ or NAD+ as a cofactor and GDH/glucose as a recycling system for the enzymes in entries 20−24. The enzyme loading was 25% w/w; the temperature was 25 °C, and the reaction time was 24 h. (http://www.codexis.com/productprotocols-and-faqs). 784
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