Abstract:
A novel process is provided for the efficient preparation of an asymmetric compound of structural formula I: 
     
       
                 
         
             
             
         
       
     
     employing dynamic kinetic resolution (DKR). The DKR process involves an enzymatic enantioselective amination reaction catalyzed by transaminases. The process can be used to manufacture key intermediates in the preparation of poly (ADP-ribose) polymerase (PARP) inhibitors which may be useful for the treatment of cancer.

Description:
REFERENCE TO SEQUENCE LISTING 
       [0001]    A sequence listing text file is submitted via EFS-Web in compliance with 37 CFR §1.52(e)(5) concurrently with the specification. The sequence listing has the file name “23370-PCT-SEQTXT-31JUL2017”, was created on Jul. 31, 2017, and is 470,397 bytes in size. The sequence listing is part of the specification and is incorporated in its entirety by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention describes the preparation of chiral compounds by employing dynamic kinetic resolution (DKR) involving an enzymatic enantioselective amination reaction catalyzed by a transaminase. This enzyme-catalyzed transaminase reaction allows convenient access to chiral compounds from an achiral starting material with high stereoselectivity. 
         [0003]    Koszelewski et al. (2009, J. Mol. Catal. B-Enzym. 60:191-194) describes preparation of an enantiomerically enriched 4-phenylpyrrolidin-2-one using dynamic kinetic resolution involving an enzymatic enantioselective amination reaction catalyzed by ω-transaminases. 
         [0004]    Wallace et al. (2011, Organic Process Research and Development 15:831-840) describes large-scale synthesis (up to 5 kg) routes of 2-{4-[(3S)-Piperidin-3-yl]phenyl}-2H-indazole-7-carboxamide relying on either classical resolution or chiral separation. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides an efficient process for the preparation of an asymmetric compound of formula I: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    wherein:
   R 1  is a leaving group, a protected amino group, NO 2 , or OH or its protected form;   R 2  is hydrogen;   R 3  is (C═O)OR 5 , CH 2 R 6 , or a protected aldehyde; or,   R 2  and R 3  are combined to form a nitrogen containing heterocyclyl selected from   
 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    R 4  is hydrogen or an amino protecting group;
   R 5  is C 1-6  alkyl, C 3-10  cycloalkyl, C 4-10  heterocyclyl, aryl, or heteroaryl; and,   R 6  is a leaving group or OH or its protected form.   
 
         [0012]    The process of the present invention relates to a method for the preparation of an asymmetric compound of formula I in an efficient enantioselective fashion via transaminase-catalyzed dynamic kinetic resolution (DKR) of a compound of formula II: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    wherein:
   R 1  is a leaving group, a protected amino group, NO2, or OH or its protected form;   R 2′  is an aldehyde or an aldehyde equivalent; and,   R 3′  is (C═O)OR 5 , CH 2 R 6 , or a protected aldehyde; or   R 2′  and R 3′  are combined to form   
 
         [0000]    
       
                 
         
             
             
         
       
     
         [0017]    The process described as part of the present invention can be used to manufacture key intermediates in the preparation of poly (ADP-ribose) polymerase (PARP) inhibitors disclosed in U.S. Pat. No. 8,071,623, which may be useful for the treatment of cancer. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    The present invention provides processes for the preparation of an asymmetric compound of formula I: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    wherein:
   R 1  is a leaving group, a protected amino group, NO 2 , or OH or its protected form;   R 2  is hydrogen;   R 3  is (C═O)OR 5 , CH2R 6 , or a protected aldehyde; or,   R 2  and R 3  are combined to form a nitrogen containing heterocyclyl selected from   
 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    R 4  is hydrogen or an amino protecting group;
   R 5  is C 1-6  alkyl, C 3-10  cycloalkyl, C 4-10  heterocyclyl, aryl, or heteroaryl; and,   R 6  is a leaving group or OH or its protected form;   comprising a biocatalytic transamination of a compound of formula II:   
 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    wherein:
   R 1  is as defined above;   R 2′  is an aldehyde or an aldehyde equivalent; and,   R 3′  is R 3 ; or   R 2′  and R 3′  are combined to form   
 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    in the presence of a transaminase polypeptide, a coenzyme, and an amino donor. 
         [0030]    In one embodiment of the process of the present invention, R 1  is a leaving group. In a further embodiment, R 1  is Br. 
         [0031]    In another embodiment of the process of the present invention, R 2  and R 3  are combined to form a nitrogen containing heterocyclyl selected from 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    and R 4  is hydrogen. In a further embodiment, R 2  and R 3  are combined to form 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    and R 4  is hydrogen. 
         [0032]    In a still further embodiment of the process of the present invention, R 1  is Br, R 2  and R 3  are combined to form 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    and R 4  is hydrogen. 
         [0033]    In another embodiment of the present invention, R 2  is hydrogen, R 3  is CH 2 R 6 , R 4  is hydrogen, and R 6  is OH. 
         [0034]    The present invention provides a process for the preparation of an asymmetric compound of formula III by transaminase-catalyzed DKR: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    comprising a biocatalytic transamination of a compound of formula IV or a compound of formula V: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    in the presence of a transaminase polypeptide, a coenzyme, and an amino donor. 
         [0035]    The present invention further provides a process for the preparation of an asymmetric compound of formula VI: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    by transaminase-catalyzed DKR, wherein Prot is an amino protecting group comprising: 
         [0036]    (a) a biocatalytic transamination of a compound of formula IV or a compound of formula V: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0037]    in the presence of a transaminase polypeptide, a coenzyme, and an amino donor, forming the compound of formula III: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0038]    (b) reducing the lactam of the compound of formula III, forming the compound of formula VII: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    and, 
         [0039]    (c) protecting the piperidine nitrogen of the compound of formula VII to form the compound of formula VI. 
         [0040]    In one embodiment of the processes of the invention, the biocatalytic transamination provides a compound of formula I having an enantiomeric excess of at least about 95% e.e., at least about 96% e.e., at least about 97% e.e., at least about 98% e.e., at least about 99% e.e., or at least about 99.9% e.e. In another embodiment of the process of the present invention, the transaminase-catalyzed DKR of a compound of formula II as described provides a compound of formula I having an enantiomeric excess of at least 95%. In a further embodiment of the process of the present invention, the transaminase-catalyzed DKR of a compound of formula II as described provides a compound of formula I having an enantiomeric excess of at least 99%. 
         [0041]    In one embodiment of the instant processes, the transaminase polypeptide is a naturally occurring transaminase. In another embodiment, the transaminase polypeptide is a synthetic variant of a naturally occurring transaminase. In a further embodiment, the transaminase polypeptide is selected from SEQ ID NO: 18 or SEQ ID NO: 180. In a further embodiment, the transaminase polypeptide is SEQ ID NO: 180. 
         [0042]    In one embodiment of the instant process, isopropylamine is used as an amino donor. 
         [0043]    In another embodiment of the instant process, pyridoxal-phosphate is used as a coenzyme. 
         [0044]    “Amino donor” or “amine donor” refers to an amino compound which donates an amino group to an amino acceptor, thereby becoming a carbonyl species. Amino donors are molecules of general formula shown below, 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    in which each of R 3* , R 4* , when taken independently, is an alkyl, an alkylaryl group, or aryl group which is unsubstituted or substituted with one or more enzymatically non-inhibiting groups. R 3*  can be the same or different from R 4*  in structure or chirality. In some embodiments, R 3*  and R 4* , taken together, may form a ring that is unsubstituted, substituted, or fused to other rings. Typical amino donors that can be used with the embodiments of the present disclosure include chiral and achiral amino acids, and chiral and achiral amines. 
         [0045]    “Chiral amine” refers to amines of general formula R α —CH(NH 2 )—R β  and is employed herein in its broadest sense, including a wide variety of aliphatic and alicyclic compounds of different, and mixed, functional types, characterized by the presence of a primary amino group bound to a secondary carbon atom which, in addition to a hydrogen atom, carries either (i) a divalent group forming a chiral cyclic structure, or (ii) two substituents (other than hydrogen) differing from each other in structure or chirality. Divalent groups forming a chiral cyclic structure include, for example, 2-methylbutane-1,4-diyl, pentane-1,4-diykhexane-1,4-diyl, hexane-1,5-diyl, 2-methylpentane-1,5-diyl. The two different substituents on the secondary carbon atom (R α  and R β  above) also can vary widely and include alkyl, arylalkyl, aryl, halo, hydroxy, lower alkyl, lower alkyloxy, lower alkylthio, cycloalkyl, carboxy, carbalkyloxy, carbamoyl, mono- and di-(lower alkyl) substituted carbamoyl, trifluoromethyl, phenyl, nitro, amino, mono- and di-(lower alkyl) substituted amino, alkylsulfonyl, arylsulfonyl, alkylcarboxamido, arylcarboxamido, etc., as well as alkyl, arylalkyl, or aryl substituted by the foregoing. 
         [0046]    Exemplary amino donors that can be used with the embodiments herein include, by way of example and not limitation, isopropylamine (also referred to as 2-aminopropane, and referred to elsewhere herein as “IPM”), α-phenethylamine (also termed 1-phenylethanamine), and its enantiomers (S)-1-phenylethanamine and (R)-1-phenylethanamine, 2-amino-4-phenylbutane, glycine, L-glutamic acid, L-glutamate, monosodium glutamate, L-alanine, D-alanine, D,L-alanine, L-aspartic acid, L-lysine, D,L-ornithine, β-alanine, taurine, n-octylamine, cyclohexylamine, 1,4-butanediamine (also referred to as putrescine), 1,6-hexanediamine, 6-aminohexanoic acid, 4-aminobutyric acid, tyramine, and benzyl amine, 2-aminobutane, 2-amino-1-butanol, 1-amino-1-phenylethane, 1-amino-1-(2-methoxy-5-fluorophenyl)ethane, 1-amino-1-phenylpropane, 1-amino-1-(4-hydroxyphenyl)propane, 1-amino-1-(4-bromophenyl)propane, 1-amino-1-(4-nitrophenyl)propane, 1-phenyl-2-aminopropane, 1-(3-trifluoromethylphenyl)-2-aminopropane, 2-aminopropanol, 1-amino-l-phenylbutane, 1-phenyl-2-aminobutane, 1-(2,5-dimethoxy-4-methylphenyl)-2-aminobutane, 1-phenyl-3-aminobutane, 1-(4-hydroxyphenyl)-3-aminobutane, 1-amino-2-methylcyclopentane, 1-amino-3-methylcyclopentane, 1-amino-2-methylcyclohexane, 1-amino-1-(2-naphthyl)ethane, 3-methylcyclopentylamine, 2-methylcyclopentylamine, 2-ethylcyclopentylamine, 2-methylcyclohexylamine, 3-methylcyclohexylamine, 1-aminotetralin, 2-aminotetralin, 2-amino-5-methoxytetralin, and 1-aminoindan, including both (R) and (S) single isomers where possible and including all possible salts of the amines. 
         [0047]    “Amino acceptor” and “amine acceptor,” “keto substrate,” “keto,” and “ketone” are used interchangeably herein to refer to a carbonyl (keto, or ketone) compound which accepts an amino group from a donor amine. Amino acceptors are molecules of general formula shown below, 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    in which each of R l* , R 2* , when taken independently, is an alkyl, an alkylaryl group, or aryl group which is unsubstituted or substituted with one or more enzymatically acceptable groups. R l*  may be the same or different from R 2*  in structure or chirality. In some embodiments, R l*  and R 2* , taken together, may form a ring that is unsubstituted, substituted, or fused to other rings. Amino acceptors include keto carboxylic acids, alkanones (ketones), and alkanals (aldehydes). 
         [0048]    “Coenzyme,” as used herein, refers to a non-protein compound that operates in combination with an enzyme in catalyzing a reaction. As used herein, “coenzyme” is intended to encompass the vitamin B 6  family compounds PLP, PN, PL, PM, PNP, and PMP. 
         [0049]    “Pyridoxal-phosphate,” “PLP,” “pyridoxal-5′-phosphate,” “PYP,” and “P5P” are used interchangeably herein to refer to a compound that acts as a coenzyme in transaminase reactions. In some embodiments, pyridoxal phosphate is defined by the structure 1-(4′-formyl-3′-hydroxy-2′-methyl-5′-pyridyl)methoxyphosphonic acid, CAS number [54-47-7]. Pyridoxal-5′-phosphate can be produced in vivo by phosphorylation and oxidation of pyridoxol (also known as Vitamin B 6 ). In transamination reactions using transaminase enzymes, the amine group of the amino donor is transferred to the coenzyme to produce a keto by-product, while pyridoxal-5′-phosphate is converted to pyridoxamine phosphate. Pyridoxal-5′-phosphate is regenerated by reaction with a different keto compound (the amino acceptor). The transfer of the amine group from pyridoxamine phosphate to the amino acceptor produces an amine and regenerates the coenzyme. In some embodiments, the pyridoxal-5′-phosphate can be replaced by other members of the vitamin B 6  family, including pyridoxine (PN), pyridoxal (PL), pyridoxamine (PM), and their phosphorylated counterparts; pyridoxine phosphate (PNP), and pyridoxamine phosphate (PMP). 
         [0050]    “Leaving group” is defined as a term that would be understood by one of ordinary skill in the art; that is, a group on a carbon where, upon reaction, a new bond is to be formed and the carbon loses the group upon formation of the new bond. A typical example employing a suitable leaving group is a nucleophilic substitution reaction, e.g., on a sp 3  hybridized carbon (S N 2 or S N 1), e.g. where the leaving group is a halide, such as a bromide, the reactant might be benzyl bromide. Another typical example of such a reaction is a nucleophilic aromatic substitution reaction (SNAr). Another example is an insertion reaction (for example by a transition metal) into the bond between an aromatic reaction partner bearing a leaving group followed by reductive coupling. “Leaving group” is not limited to such mechanistic restrictions. Examples of suitable leaving groups include halogens (fluorine, chlorine, bromine or iodine), optionally substituted aryl or alkyl sulfonates, phosphonates, azides and —S(O) 0-2 R where R is, for example optionally substituted alkyl, optionally substituted aryl, or optionally substituted heteroaryl. Those of skill in the art of organic synthesis will readily identify suitable leaving groups to perform a desired reaction under different reaction conditions. Non-limiting characteristics and examples of leaving groups can be found, for example in Organic Chemistry, 2nd ed., Francis Carey (1992), pages 328-331; Introduction to Organic Chemistry, 2d ed., Andrew Streitwieser and Clayton Heathcock (1981), pages 169-171; and Organic Chemistry, 5th Ed., John McMurry, Brooks/Cole Publishing (2000), pages 398 and 408; all of which are incorporated herein by reference. 
         [0051]    “Protecting group” refers to a group of atoms that mask, reduce or prevent the reactivity of the functional group when attached to a reactive functional group in a molecule. Typically, a protecting group may be selectively removed as desired during the course of a synthesis. Examples of protecting groups can be found in Wuts and Greene, “Greene&#39;s Protective Groups in Organic Synthesis,” 4 th  Ed., Wiley Interscience (2006), and Harrison et al., Compendium of Synthetic Organic Methods, Vols. 1-8, 1971-1996, John Wiley &amp; Sons, NY. Functional groups that can have a protecting group include, but are not limited to, hydroxy, amino, and carboxy groups. 
         [0052]    Representative amino protecting groups include, but are not limited to, formyl, acetyl (Ac), trifluoroacetyl, benzyl (Bn), benzoyl (Bz), carbamate, benzyloxycarbonyl (“CBZ”), p-methoxybenzyl carbonyl (Moz or MeOZ), tert-butoxycarbonyl (“Boc”), trimethylsilyl (“TMS”), 2-trimethylsilyl-ethanesulfonyl (“SES”), trityl and substituted trityl groups, allyloxycarbonyl, 9-fluorenylmethyloxycarbonyl (“FMOC”), nitro-veratryloxycarbonyl (“NVOC”), p-methoxybenzyl (PMB), tosyl (Ts) and the like. 
         [0053]    Representative hydroxyl protecting groups include, but are not limited to, those where the hydroxyl group is either acylated (e.g., methyl and ethyl esters, acetate or propionate groups or glycol esters) or alkylated such as benzyl and trityl ethers, as well as alkyl ethers, tetrahydropyranyl ethers, trialkylsilyl ethers (e.g., TMS or TIPS groups) and allyl ethers. Other protecting groups can be found in the references noted herein. 
         [0054]    A “protected aldehyde” is defined as the term would be understood by one of ordinary skill in the art; that is, the aldehyde is protected with a group such that it may be converted under assays conditions to an unprotected aldehyde. Examples of protected aldehydes include, but are not limited to, an acetal or hemiacetal which can be converted into a free aldehyde group by treatment with acids (organic or inorganic acids), such as acetal groups formed with a polyalcohol such as propane diol or ethylene glycol, or hemiacetal groups in a sugar or in a sugar-related compound such as an aldose sugar, e.g. glucose or galactose. Further examples of protected aldehydes are imino groups (e.g., ═NH groups), which give aldehyde groups upon treatment with acids; thioacetal or dithioacetal groups (e.g., C(SR) 2  groups wherein R may be an alkyl radical), which give aldehyde groups upon treatment with mercury salts; oxime groups (e.g., ═NOH groups), which give aldehyde groups upon treatment with acids; hydrazone groups (e.g., ═N—NHR groups wherein R may be an alkyl radical), which give aldehyde groups upon treatment with acids; and imidazolone or imidazolidine groups or benzothiazole or dihydrobenzothiazole groups, which give aldehydes upon hydrolysis, e.g. with acid. 
         [0055]    As used herein except where noted, “alkyl” is intended to include both branched- and straight-chain saturated aliphatic hydrocarbon groups having the specified number of carbon atoms. For example, “C 1 —C 6 ” or “C 1-6 ,” as in “C 1 —C 6  alkyl” or “C 1-6  alkyl,” is defined to include groups having 1, 2, 3, 4, 5, or 6 carbons in a linear or branched arrangement. C 1-6  alkyl includes all of the hexyl alkyl and pentyl alkyl isomers as well as n-, iso-, sec- and t-butyl, n- and isopropyl, ethyl and methyl. As another example, C 1-4  alkyl means n-, iso-, sec- and t-butyl, n- and isopropyl, ethyl and methyl. As another example, C 1 —C 10  alkyl specifically includes methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl, i-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, and so on. If no number is specified, 1-10 carbon atoms are intended for linear or branched alkyl groups. Commonly used abbreviations for alkyl groups are used throughout the specification, e.g. methyl may be represented by conventional abbreviations including “Me” or CH 3  or a symbol that is an extended bond without defined terminal group, e.g. ,          , ethyl may be represented by “Et” or CH 2 CH 3 , propyl may be represented by “Pr” or CH 2 CH 2 CH 3 , butyl may be represented by “Bu” or CH 2 CH 2 CH 2 CH 3 , etc. The term “cycloalkyl” means a monocyclic saturated aliphatic hydrocarbon group having the specified number of carbon atoms. For example, “cycloalkyl” includes cyclopropyl, methyl-cyclopropyl, 2,2-dimethyl-cyclobutyl, 2-ethyl-cyclopentyl, cyclohexyl, cyclopentenyl, cyclobutenyl and so on. 
         [0056]    “Aryl,” unless otherwise indicated, is intended to mean any stable monocyclic or bicyclic carbon ring of up to 7 atoms in each ring, wherein at least one ring is aromatic. Examples of such aryl elements include phenyl, naphthyl, tetrahydronaphthyl, indanyl and biphenyl. In cases where the aryl substituent is bicyclic and one ring is non-aromatic, it is understood that attachment is via the aromatic ring. In an embodiment, aryl is phenyl. 
         [0057]    The term “heteroaryl,” as used herein, represents a stable monocyclic or bicyclic ring of up to 7 atoms in each ring, wherein at least one ring is aromatic and contains from 1 to 4 heteroatoms selected from the group consisting of O, N and S. Heteroaryl groups within the scope of this definition include but are not limited to: acridinyl, carbazolyl, cinnolinyl, quinoxalinyl, pyrrazolyl, indolyl, benzotriazolyl, furanyl, thienyl, benzothienyl, benzofuranyl, benzimidazolonyl, benzoxazolonyl, quinolinyl, isoquinolinyl, dihydroisoindolonyl, imidazopyridinyl, isoindolonyl, indazolyl, oxazolyl, oxadiazolyl, isoxazolyl, indolyl, pyrazinyl, pyridazinyl, pyridinyl, pyrimidinyl, pyrrolyl, tetrahydroquinoline. As with the definition of heterocycle below, “heteroaryl” is also understood to include the N-oxide derivative of any nitrogen-containing heteroaryl. In cases where the heteroaryl substituent is bicyclic and one ring is non-aromatic or contains no heteroatoms, it is understood that attachment is via the aromatic ring or via the heteroatom containing ring, respectively. 
         [0058]    The term “heterocycle” or “heterocyclyl,” as used herein, is intended to mean a 3- to 10-membered aromatic or nonaromatic heterocycle containing from 1 to 4 heteroatoms selected from the group consisting of O, N and S, and includes bicyclic groups. For the purposes of this invention, the term “heterocyclic” is also considered to be synonymous with the terms “heterocycle” and “heterocyclyl” and is understood as also having the definitions set forth herein. “Heterocyclyl” therefore includes the above mentioned heteroaryls, as well as dihydro and tetrahydro analogs thereof. Further examples of “heterocyclyl” include, but are not limited to the following: azetidinyl, benzoimidazolyl, benzofuranyl, benzofurazanyl, benzopyrazolyl, benzotriazolyl, benzothiophenyl, benzoxazolyl, carbazolyl, carbolinyl, cinnolinyl, furanyl, imidazolyl, indolinyl, indolyl, indolazinyl, indazolyl, isobenzofuranyl, isoindolyl, isoquinolyl, isothiazolyl, isoxazolyl, naphthpyridinyl, oxadiazolyl, oxooxazolidinyl, oxazolyl, oxazoline, oxopiperazinyl, oxopyrrolidinyl, oxomorpholinyl, isoxazoline, oxetanyl, pyranyl, pyrazinyl, pyrazolyl, pyridazinyl, pyridopyridinyl, pyridazinyl, pyridyl, pyrimidyl, pyrrolyl, quinazolinyl, quinolyl, quinoxalinyl, tetrahydropyranyl, tetrahydrofuranyl, tetrahydrothiopyranyl, tetrahydroisoquinolinyl, tetrazolyl, tetrazolopyridyl, thiadiazolyl, thiazolyl, thienyl, triazolyl, 1,4-dioxanyl, hexahydroazepinyl, piperazinyl, piperidinyl, pyridin-2-onyl, pyrrolidinyl, morpholinyl, thiomorpholinyl, dihydrobenzoimidazolyl, dihydrobenzofuranyl, dihydrobenzothiophenyl, dihydrobenzoxazolyl, dihydrofuranyl, dihydroimidazolyl, dihydroindolyl, dihydroisooxazolyl, dihydroisothiazolyl, dihydrooxadiazolyl, dihydrooxazolyl, dihydropyrazinyl, dihydropyrazolyl, dihydropyridinyl, dihydropyrimidinyl, dihydropyrrolyl, dihydroquinolinyl, dihydrotetrazolyl, dihydrothiadiazolyl, dihydrothiazolyl, dihydrothienyl, dihydrotriazolyl, dihydroazetidinyl, dioxidothiomorpholinyl, methylenedioxybenzoyl, tetrahydrofuranyl, and tetrahydrothienyl, and N-oxides thereof. Attachment of a heterocyclyl substituent can occur via a carbon atom or via a heteroatom. 
         [0059]    “Protein,” “polypeptide,” and “peptide” are used interchangeably herein to denote a polymer of at least two amino acids covalently linked by an amide bond, regardless of length or post-translational modification (e.g., glycosylation, phosphorylation, lipidation, myristilation, ubiquitination, etc.). Included within this definition are D- and L-amino acids, and mixtures of D- and L-amino acids. 
         [0060]    “Stereoselectivity” refers to the preferential formation in a chemical or enzymatic reaction of one stereoisomer over another. Stereoselectivity can be partial, where the formation of one stereoisomer is favored over the other, or it may be complete where only one stereoisomer is formed. When the stereoisomers are enantiomers, the stereoselectivity is referred to as enantioselectivity, the fraction (typically reported as a percentage) of one enantiomer in the sum of both. It is commonly alternatively reported in the art (typically as a percentage) as the enantiomeric excess (e.e.) calculated there from according to the formula [major enantiomer−minor enantiomer]/[major enantiomer+minor enantiomer]. Where the stereoisomers are diastereoisomers, the stereoselectivity is referred to as diastereoselectivity, the fraction (typically reported as a percentage) of one diastereomer in a mixture of two diastereomers, commonly alternatively reported as the diastereomeric excess (d.e.). Where a mixture contains more than two diastereomers it is common to report the ratio of diastereomers or “diastereomeric ratio” rather than diastereomeric excess. Enantiomeric excess and diastereomeric excess are types of stereomeric excess. “High stereoselectivity,” in reference to the process of the present invention, refers the capability of converting a substrate to the asymmetric amine product with at least about 85% stereomeric excess. 
         [0061]    “Transaminase,” “transaminase polypeptide” and “transaminase enzyme,” as used interchangeably herein, refer to a polypeptide having an enzymatic capability of transferring an amino group (NH 2 ), a pair of electrons, and a proton from a primary amine of an amino donor to a carbonyl group (C═O; i.e., a keto group) of an amino acceptor molecule. Transaminases as used herein include naturally occurring (wild-type) transaminases, as well as non-naturally occurring engineered polypeptides generated by human manipulation. In an embodiment of the instant process, a transaminase polypeptide having the amino acid sequence as set forth in SEQ ID NO: 18 or SEQ ID NO: 180 is used. In an embodiment of the instant process, a transaminase polypeptide having a polynucleotide sequence as set forth in SEQ ID NO: 17 or SEQ ID NO: 179 is used. 
       Transaminase Polypeptides 
       [0062]    Transaminases have been identified from various organisms, such as  Alcaligenes denitrificans, Arthrobacter, Bordetella bronchiseptica, Bordetella parapertussis, Brucella melitensis, Burkholderia malle, Burkholderia pseudomallei, Chromobacterium violaceum, Oceanicola granulosus  HTCC2516,  Oceanobacter  sp. RED65,  Oceanospirillum  sp. MED92,  Pseudomonas putida, Ralstonia solanacearum, Rhizobium meliloti, Rhizobium  sp. (strain NGR234),  Bacillus thuringensis, Vibrio fluvialis  and  Klebsiella pneumoniae  (see, e.g., Shin et al., 2001, Biosci. Biotechnol. Biochem. 65: 1782-1788). Both R-selective and S-selective transaminases are known. The wild-type transaminase from  Arthrobacter  sp. KNK168 is an R-selective, pyridoxal 5′-phosphate (PLP)-dependent enzyme that produces R-amines from some substrates (see, e.g., Iwasaki et al., 2006, Appl. Microbiol. Biotechnol., 69:499-505; U.S. Pat. No. 7,169,592). 
         [0063]    U.S. application Ser. No. 12/714,397, filed Feb. 26, 2010 (published as US20100285541), and PCT International application serial no. PCT/US2010/025685, filed Feb. 26, 2010 (published as WO 2010/099501), disclose engineered transaminase polypeptides derived from the naturally occurring transaminase of  Arthrobacter  sp. KNK168. These transaminase polypeptides have increased stability to temperature and/or organic solvent and have been adapted to have enzymatic activity towards structurally different amino acceptor molecules (see also, e.g., Savile et al., 2010, Science 329(5989):305-9). PCT International patent application serial no. PCT/US2011/046932, filed Aug. 8, 2011 (published as WO 2012/024104), further describes non-naturally occurring transaminase polypeptides derived from  Arthrobacter  sp. KNK168 engineered to have improved properties, such as increased stereoselectivity. These synthetic variants of the naturally occurring  Arthrobacter  sp. KNK168 transaminase comprise amino acid sequences that have one or more residue differences as compared to the wild-type sequence. For example, the residue differences may occur at residue positions that affect one or more functional properties of the enzyme, including but not limited to stereoselectivity, substrate and/or product binding (e.g., resistance to substrate and/or product inhibition), activity (e.g., percent conversion of substrate to product), thermostability, solvent stability, expression, or various combinations thereof. 
         [0064]    In one embodiment of the present invention, the asymmetric synthesis of compounds of formula I from compounds of formula II via biocatalytic transamination utilizes a naturally occurring transaminase polypeptide. In another embodiment, the synthesis reaction of the invention utilizes a synthetic variant of a naturally occurring transaminase. In a further embodiment, the synthetic, engineered transaminase polypeptide is derived from a transaminase of  Arthrobacter  sp. KNK168, including the  Arthrobacter  sp. KNK168 transaminase polypeptide as set forth in SEQ ID NO: 2, wherein the synthetic variant comprises an amino acid sequence having one or more residue differences as compared to the wild-type sequence of SEQ ID NO: 2. 
         [0065]    In a further embodiment, the transaminase polypeptide comprises or consists of an engineered transaminase polypeptide as described in PCT International application serial no. PCT/US2011/046932, filed Aug. 8, 2011 (published as WO 2012/024104), which is hereby incorporated by reference herein, having among other things a high stereoselectivity. These engineered polypeptides are non-naturally occurring transaminases engineered to have improved properties, such as increased stereoselectivity, increased activity, increased thermostability, and tolerance of increased substrate and/or product concentration (e.g., decreased product inhibition). 
         [0066]    As described in detail in PCT International application serial no. PCT/US2011/046932, engineered transaminases were previously identified by optimizing the reported wild-type omega transaminase polypeptide from  Arthrobacter  sp. KNK168 of SEQ ID NO: 2. First, a transaminase polypeptide derived from SEQ ID NO: 2 having a single amino acid change relative to the wild-type sequence (1306V) was generated having the amino acid sequence as set forth in SEQ ID NO: 4 (encoded by the polynucleotide sequence as set forth in SEQ ID NO: 3). The synthetic polynucleotide of SEQ ID NO: 3 was optimized for increased expression and thermostability by inserting active and silent mutations which are described in U.S. application Ser. No. 12/714,397, filed Feb. 26, 2010, which is incorporated herein by reference. This optimization resulted in the synthetic polynucleotide of SEQ ID NO: 5, which encodes the engineered polypeptide of SEQ ID NO: 6, having the following 24 amino acid differences relative to the naturally occurring transaminase of  Arthrobacter  sp. KNK168 (SEQ ID NO: 2): S8P; Y60F; L61Y; H62T; V65A; V69T; D81G; M94I; I96L; F122I; G136F; A169L; V199I; A209L; G215C; G217N; S223P; L269P; L273Y; T282S; A284G; P297S; 1306V; and S321P. The engineered transaminase polypeptide of SEQ ID NO: 6 was used as the starting backbone for further optimization to generate polynucleotides encoding additional engineered transaminase polypeptides (see PCT/US2011/046932; supra). 
         [0067]    Therefore, in a further embodiment of the present invention, the asymmetric synthesis of compounds of formula I from compounds of formula II via biocatalytic transamination utilizes a transaminase polypeptide that is a synthetic variant of a naturally occurring transaminase and comprises the acid sequence as set forth in SEQ ID NO: 6. 
         [0068]    In another embodiment of the instant process, the transaminase polypeptide comprises an amino acid sequence having at least 80% sequence identity (e.g., at least 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity) to the reference polypeptide of SEQ ID NO: 6. 
         [0069]    In a further embodiment of the present invention, the transaminase polypeptide used in a process of the invention comprises an amino acid sequence having at least 80% sequence identity to the reference polypeptide of SEQ ID NO: 6 and an amino acid residue difference as compared to SEQ ID NO: 6 at one or more of the following positions: X2; X4; X5; X7; X8; X9; X10; X11; X14; X22; X28; X37; X38; X41; X42; X44; X52; X54; X55; X56; X58; X69; X94; X99; X108; X124; X126; X135; X136; X141; X142; X150; X155; X156; X157; X164; X165; X171; X182; X199; X209; X210; X213; X215; X217; X218; X223; X245; X257; X265; X267; X296; and X328. In some embodiments of the instant process, the amino acid residue differences of the transaminase polypeptide as compared to SEQ ID NO: 6 are selected from the following: X2K; X2Q; X2S; X41; X4L; X5H; X5I; X5L; X5N; X5S; X5T; X5V; X7A; X8T; X9N; X9Q; X9S; X10V; X11K; X14R; X221; X28P; X37R; X38G; X41F; X42A; X44Q; X44V; X52K; X54K; X54N; X54P; X54R; X55L; X56G; X56L; X56S; X58L; X69C; X69V; X69W; X94L; X99L; X108V; X124F; X124I; X124L; X124R; X124V; X126A; X126T; X135Q; X136W; X141L; X142R; X142T; X150A; X150F; X150N; X155A; X156A; X156F; X156G; X156S; X156T; X157L; X164A; X165N; X171A; X182T; X199F; X199R; X199Y; X209C; X209D; X209E; X210S; X213P; X215F; X215Y; X217S; X218M; X223I; X223L; X223M; X223N; X245S; X257F; X265T; X267V; X296S; and X3281. 
         [0070]    In some embodiments of the instant process, the transaminase polypeptide comprises one or more combinations of amino acid differences as compared to SEQ ID NO: 6 selected from the following: (a) X124V and X210S; (b) X124V, X136W and X210S; (c) X69V and X136W; (d) X69V and X215Y; (e) X69V and X217S; (0 X69V, X124I and X136W; (g) X69V, X136W and X257F; (h) X44V and X223N; (i) X56S, X69V, X136W and X265T; and (j) X28P, X69V and X136W. 
         [0071]    Exemplary engineered polypeptides having various combinations of amino acid differences resulting in improved properties are provided in the sequence listing incorporated by reference herein and include the polypeptides as set forth in SEQ ID NO: 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 130, 132, 134, 136, 138, 140, 142, 144, 146, 148, 150, 152, 154, 156, 158, 160, 162, 164, 166, 168, 170, 172, 174, 176, 178, 180, 182, 184, 186, 188, 190, 192, 194, 196, 198, 200, 202, 204, and 206. Exemplary polynucleotide sequences encoding these transaminases are provided in the sequence listing incorporated by reference herein and include the polynucleotides as set forth in SEQ ID NO: 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99, 101, 103, 105, 107, 109, 111, 113, 115, 117, 119, 121, 123, 125, 127, 129, 131, 133, 135, 137, 139, 141, 143, 145, 147, 149, 151, 153, 155, 157, 159, 161, 163, 165, 167, 169, 171, 173, 175, 177, 179, 181, 183, 185, 187, 189, 191, 193, 195, 197, 199, 201, 203, and 205. 
         [0072]    Thus, in another embodiment, a transaminase polypeptide utilized in the process of the present invention comprises the amino acid sequence as set forth in SEQ ID NOs: 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 130, 132, 134, 136, 138, 140, 142, 144, 146, 148, 150, 152, 154, 156, 158, 160, 162, 164, 166, 168, 170, 172, 174, 176, 178, 180, 182, 184, 186, 188, 190, 192, 194, 196, 198, 200, 202, 204, or 206. 
         [0073]    In a further embodiment of the instant process, a transaminase polypeptide having an amino acid sequence as set forth in SEQ ID NO: 18 is used. SEQ ID NO: 18 has the following amino acid differences relative to SEQ ID NO: 6: T69V, S124I and F136W 
         [0074]    In a further embodiment of the instant process, a transaminase polypeptide having a polynucleotide sequence as set forth in SEQ ID NO: 17 is used. 
         [0075]    In a further embodiment of the instant process, a transaminase polypeptide having an amino acid sequence as set forth in SEQ ID NO: 180 is used. SEQ ID NO: 180 has the following amino acid differences relative to SEQ ID NO: 6: A2S, ASH, T69V, S124I, F136W and C215F. 
         [0076]    In a further embodiment of the instant process, a transaminase polypeptide having a polynucleotide sequence as set forth in SEQ ID NO: 179 is used. 
         [0077]    In addition to the exemplary engineered polypeptides described herein, the process of the present disclosure can be carried out using engineered transaminase polypeptides having improved enzymatic properties (e.g., as disclosed above) and comprising further modifications of the amino acid sequence. Such engineered polypeptides can be derived from the exemplary polypeptides and have amino acid sequences retaining some percent identity to the exemplary engineered polypeptides and one or more of the amino acid differences relative to SEQ ID NO: 6 that are associated with the improved enzymatic property. Techniques and methods for deriving further engineered polypeptides are known in the art and include the methods of directed evolution as described herein. For example, any of the exemplary engineered polypeptides can be used as the starting amino acid sequence (i.e., the “backbone” sequence) for subsequent rounds of evolution in which a library of genes encoding additional amino acid differences in the backbone is synthesized, expressed, and screened in high-throughput for particular improved properties (e.g., thermostability, total substrate conversion, stereoselectivity, etc.). The design of the libraries can be controlled such that only certain amino acid positions are allowed to change, while others are not. Thus, a backbone set of amino acid differences that are associated with improved properties can be maintained throughout the directed evolution process. The most improved engineered polypeptides from each round could then be used as the parent “backbone” sequence for subsequent rounds of evolution. The resulting engineered transaminase polypeptides, having further improvements in its properties, will retain some or all of the starting backbone amino acid differences and include new amino acid differences, typically while retaining an overall sequence identity to the starting backbone of at least 80%. It is contemplated, however, that one or more of the backbone amino acid differences can be changed during the directed evolution process leading to further improved properties in the engineered polypeptides. Further improvements at later rounds of evolution such as “fine tuning” an engineered polypeptide for certain process conditions (e.g., solvent conditions/concentrations, increased substrate and/or coenzyme loading, pH, and temperature changes) may be generated by including amino acid differences at positions that had been maintained as unchanged throughout earlier rounds of evolution. 
         [0078]    In some embodiments, the engineered transaminase polypeptides useful in the process of the instant invention comprise an amino acid sequence having at least 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity to a reference amino acid sequence selected from any one of SEQ ID NO: 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 130, 132, 134, 136, 138, 140, 142, 144, 146, 148, 150, 152, 154, 156, 158, 160, 162, 164, 166, 168, 170, 172, 174, 176, 178, 180, 182, 184, 186, 188, 190, 192, 194, 196, 198, 200, 202, 204, and 206. The amino acid sequence can include one or more residue differences as compared to SEQ ID NO:6 at the following residue positions: X2; X4; X5; X7; X8; X9; X10; X11; X14; X22; X28; X37; X38; X41; X42; X44; X52; X54; X55; X56; X58; X69; X94; X99; X108; X124; X126; X135; X136; X141; X142; X150; X155; X156; X157; X164; X165; X171; X182; X199; X209; X210; X213; X215; X217; X218; X223; X245; X257; X265; X267; X296; and X328. The amino acid sequence can include one or more residue differences as compared to SEQ ID NO:6 selected from the following: X2K; X2Q; X2S; X41; X4L; X5H; X5I; X5L; X5N; X5S; X5T; X5V; X7A; X8T; X9N; X9Q; X9S; X10V; X11K; X14R; X221; X28P; X37R; X38G; X41F; X42A; X44Q; X44V; X52K; X54K; X54N; X54P; X54R; X55L; X56G; X56L; X56S; X58L; X69C; X69V; X69W; X94L; X99L; X108V; X124F; X124I; X124L; X124R; X124V; X126A; X126T; X135Q; X136W; X141L; X142R; X142T; X150A; X150F; X150N; X155A; X156A; X156F; X156G; X156S; X156T; X157L; X164A; X165N; X171A; X182T; X199F; X199R; X199Y; X209C; X209D; X209E; X210S; X213P; X215F; X215Y; X217S; X218M; X2231; X223L; X223M; X223N; X245S; X257F; X265T; X267V; X296S; and X3281. 
         [0079]    In some embodiments, the engineered transaminase polypeptides useful in the process of the instant invention comprise an amino acid sequence having at least 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity to a reference amino acid sequence selected from any one of SEQ ID NO: 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 130, 132, 134, 136, 138, 140, 142, 144, 146, 148, 150, 152, 154, 156, 158, 160, 162, 164, 166, 168, 170, 172, 174, 176, 178, 180, 182, 184, 186, 188, 190, 192, 194, 196, 198, 200, 202, 204, and 206; and further comprises one or more combinations of amino acid differences as compared to SEQ ID NO: 6 selected from the following: (a) X124V and X210S; (b) X124V, X136W and X210S; (c) X69V and X136W; (d) X69V and X215Y; (e) X69V and X2175; (f) X69V, X124I and X136W; (g) X69V, X136W and X257F; (h) X44V and X223N; (i) X56S, X69V, X136W and X265T; and (j) X28P, X69V and X136W. In addition to one or more of the above combinations, the engineered polypeptide amino acid sequence can further comprise one or more amino acid residue differences as compared to SEQ ID NO: 6 selected from the following: X2K; X2Q; X2S; X41; X4L; X5H; X5I; X5L; X5N; X5S; X5T; X5V; X54K; X54N; X54P; X54R; X56G; X94L; X124I; X126A; X126T; X150A; X150N; X156S; X215F; and X267V. 
         [0080]    In some embodiments, the engineered transaminase polypeptides useful in the process of the instant invention comprise an amino acid sequence having at least 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity to a reference amino acid sequence selected from any one of SEQ ID NO: 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 130, 132, 134, 136, 138, 140, 142, 144, 146, 148, 150, 152, 154, 156, 158, 160, 162, 164, 166, 168, 170, 172, 174, 176, 178, 180, 182, 184, 186, 188, 190, 192, 194, 196, 198, 200, 202, 204, and 206; comprises an amino acid difference as compared to SEQ ID NO: 6 at one or more of the following positions: X28; X69; X124; X126; X136; X150; X156; X199; X209; X215; X217; and X223; and further comprises an amino acid difference as compared to SEQ ID NO: 6 at one or more of the following positions: X2; X4; X5; X7; X8; X9; X10; X11; X14; X22; X37; X38; X41; X42; X44; X52; X54; X55; X56; X58; X94; X99; X108; X126; X135; X141; X142; X155; X157; X164; X165; X171; X182; X210; X213; X218; X245; X257; X265; X267; X296; and X328. In some embodiments, the amino acid differences as compared to SEQ ID NO: 6 at positions X28; X69; X124; X126; X136; X150; X156; X199; X209; X215; X217; and/or X223, are selected from the following: X28P; X69C; X69V; X69W; X124F; X124I; X124L; X124R; X124V; X126A; X126T; X136W; X150A; X150N; X1565; X199F; X199R; X199Y; X209C; X209D; X209E; X215F; X215Y; X2175; X2231; X223L; X223M; and X223N. In other embodiments, the amino acid differences of the transaminase polypeptide as compared to SEQ ID NO: 6 at positions X28; X69; X124; X126; X136; X150; X156; X199; X209; X215; X217; and/or X223 are selected from the following: X28P; X69C; X136W; X150N; X1565; X199F; X199Y; and X217S. In some embodiments of the process, the amino acid differences of the transaminase polypeptide as compared to SEQ ID NO: 6 at positions X2; X4; X5; X7; X8; X9; X10; X11; X14; X22; X37; X38; X41; X42; X44; X52; X54; X55; X56; X58; X94; X99; X108; X135; X141; X142; X155; X157; X164; X165; X171; X182; X210; X213; X218; X245; X257; X265; X267; X296; and X328 are selected from: X2K; X2Q; X2S; X41; X4L; X5H; X5; X5L; X5N; X5S; X5T; X5V; X7A; X8T; X9N; X9Q; X9S; X10V; X11K; X14R; X221; X37R; X38G; X41F; X42A; X44Q; X44V; X52K; X54K; X54N; X54P; X54R; X55L; X56G; X56L; X56S; X58L; X94L; X99L; X108V; X135Q; X141L; X142R; X142T; X155A; X156A; X156F; X156G; X1565; X156T; X157L; X164A; X165N; X171A; X182T; X2105; X213P; X218M; X2455; X257F; X265T; X267V; X296S; and X328I. 
         [0081]    In some embodiments, the instant process uses a non-naturally occurring polypeptide comprising an amino acid sequence having at least 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 130, 132, 134, 136, 138, 140, 142, 144, 146, 148, 150, 152, 154, 156, 158, 160, 162, 164, 166, 168, 170, 172, 174, 176, 178, 180, 182, 184, 186, 188, 190, 192, 194, 196, 198, 200, 202, 204, and 206; and further comprises the set of one or more amino acid residue differences as compared to SEQ ID NO:6 found in any one of SEQ ID NO: 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 130, 132, 134, 136, 138, 140, 142, 144, 146, 148, 150, 152, 154, 156, 158, 160, 162, 164, 166, 168, 170, 172, 174, 176, 178, 180, 182, 184, 186, 188, 190, 192, 194, 196, 198, 200, 202, 204, and 206. 
         [0082]    Amino acid residue differences at other positions relative to the wild-type sequence of SEQ ID NO: 2 and the affect of these differences on enzyme function are provide by other engineered transaminase polypeptides disclosed in U.S. application Ser. No. 12/714,397, filed Feb. 26, 2010. One or more of the amino acid differences as compared to the wild-type sequence of SEQ ID NO: 2, provided in the engineered transaminase polypeptide amino acid sequences of U.S. application Ser. No. 12/714,397, filed Feb. 26, 2010 (see e.g., Table 2 of U.S. application Ser. No. 12/714,397), could also be introduced into a engineered transaminase polypeptide of the present disclosure. 
         [0083]    The abbreviations used for the genetically encoded amino acids are conventional and are as follows: 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 Three-Letter 
                 One-Letter 
               
               
                   
                 Amino Acid 
                 Abbreviation 
                 Abbreviation 
               
               
                   
                   
               
             
             
               
                   
                 Alanine 
                 Ala 
                 A 
               
               
                   
                 Arginine 
                 Arg 
                 R 
               
               
                   
                 Asparagine 
                 Asn 
                 N 
               
               
                   
                 Aspartate 
                 Asp 
                 D 
               
               
                   
                 Cysteine 
                 Cys 
                 C 
               
               
                   
                 Glutamate 
                 Glu 
                 E 
               
               
                   
                 Glutamine 
                 Gln 
                 Q 
               
               
                   
                 Glycine 
                 Gly 
                 G 
               
               
                   
                 Histidine 
                 HIS 
                 H 
               
               
                   
                 Isoleucine 
                 Ile 
                 I 
               
               
                   
                 Leucine 
                 Leu 
                 L 
               
               
                   
                 Lysine 
                 Lys 
                 K 
               
               
                   
                 Methionine 
                 Met 
                 M 
               
               
                   
                 Phenylalanine 
                 Phe 
                 F 
               
               
                   
                 Proline 
                 Pro 
                 P 
               
               
                   
                 Serine 
                 Ser 
                 S 
               
               
                   
                 Threonine 
                 Thr 
                 T 
               
               
                   
                 Tryptophan 
                 Trp 
                 W 
               
               
                   
                 Tyrosine 
                 Tyr 
                 Y 
               
               
                   
                 Valine 
                 Val 
                 V 
               
               
                   
                   
               
             
          
         
       
     
         [0084]    When the three-letter abbreviations are used, unless specifically preceded by an “L” or a “D” or clear from the context in which the abbreviation is used, the amino acid may be in either the L- or D-configuration about α-carbon (C α ). For example, whereas “Ala” designates alanine without specifying the configuration about the α-carbon, “D-Ala” and “L-Ala” designate D-alanine and L-alanine, respectively. When the one-letter abbreviations are used, upper case letters designate amino acids in the L-configuration about the α-carbon and lower case letters designate amino acids in the D-configuration about the α-carbon. For example, “A” designates L-alanine and “a” designates D-alanine. When polypeptide sequences are presented as a string of one-letter or three-letter abbreviations (or mixtures thereof), the sequences are presented in the amino (N) to carboxy (C) direction in accordance with common convention. 
         [0085]    The abbreviations used for the genetically encoding nucleosides are conventional and are as follows: adenosine (A); guanosine (G); cytidine (C); thymidine (T); and uridine (U). Unless specifically delineated, the abbreviated nucleotides may be either ribonucleosides or 2′-deoxyribonucleosides. The nucleosides may be specified as being either ribonucleosides or 2′-deoxyribonucleosides on an individual basis or on an aggregate basis. When nucleic acid sequences are presented as a string of one-letter abbreviations, the sequences are presented in the 5′ to 3′ direction in accordance with common convention, and the phosphates are not indicated. In addition, the following terms are defined as: 
         [0086]    “Naturally-occurring” or “wild-type” refers to the form found in nature. For example, a naturally occurring or wild-type polypeptide or polynucleotide sequence is a sequence that can be isolated from a source in nature and which has not been intentionally modified by human manipulation. 
         [0087]    “Derived from” as used herein in the context of engineered transaminase enzymes, identifies the originating transaminase enzyme, and/or the gene encoding such transaminase enzyme, upon which the engineering was based. For example, the engineered transaminase enzyme of SEQ ID NO:34 was obtained by artificially evolving, over multiple generations the gene encoding the  Arthrobacter  sp. KNK168 transaminase enzyme of SEQ ID NO:2. Thus, this engineered transaminase enzyme is “derived from” the wild-type transaminase of SEQ ID NO:2. 
         [0088]    “Control sequence” is defined herein to include all components, which are necessary or advantageous for the expression of a polynucleotide and/or polypeptide of the present disclosure. Each control sequence may be native or foreign to the nucleic acid sequence encoding the polypeptide. Such control sequences include, but are not limited to, a leader, polyadenylation sequence, propeptide sequence, promoter, signal peptide sequence, and transcription terminator. At a minimum, the control sequences include a promoter, and transcriptional and translational stop signals. The control sequences may be provided with linkers for the purpose of introducing specific restriction sites facilitating ligation of the control sequences with the coding region of the nucleic acid sequence encoding a polypeptide. 
         [0089]    “Recombinant” or “engineered” or “non-naturally occurring” when used with reference to, e.g., a cell, nucleic acid, or polypeptide, refers to a material, or a material corresponding to the natural or native form of the material, that has been modified in a manner that would not otherwise exist in nature, or is identical thereto but produced or derived from synthetic materials and/or by manipulation using recombinant techniques. Non-limiting examples include, among others, recombinant cells expressing genes that are not found within the native (non-recombinant) form of the cell or express native genes that are otherwise expressed at a different level. 
         [0090]    “Percentage of sequence identity” and “percentage homology” are used interchangeably herein to refer to comparisons among polynucleotides and polypeptides, and are determined by comparing two optimally aligned sequences over a comparison window, wherein the portion of the polynucleotide or polypeptide sequence in the comparison window may comprise additions or deletions (i.e., gaps) as compared to the reference sequence for optimal alignment of the two sequences. The percentage may be calculated by determining the number of positions at which the identical nucleic acid base or amino acid residue occurs in both sequences to yield the number of matched positions, dividing the number of matched positions by the total number of positions in the window of comparison and multiplying the result by 100 to yield the percentage of sequence identity. Alternatively, the percentage may be calculated by determining the number of positions at which either the identical nucleic acid base or amino acid residue occurs in both sequences or a nucleic acid base or amino acid residue is aligned with a gap to yield the number of matched positions, dividing the number of matched positions by the total number of positions in the window of comparison and multiplying the result by 100 to yield the percentage of sequence identity. Those of skill in the art appreciate that there are many established algorithms available to align two sequences. Optimal alignment of sequences for comparison can be conducted, e.g., by the local homology algorithm of Smith and Waterman, 1981, Adv. Appl. Math. 2:482, by the homology alignment algorithm of Needleman and Wunsch, 1970, J. Mol. Biol. 48:443, by the search for similarity method of Pearson and Lipman, 1988, Proc. Natl. Acad. Sci. USA 85:2444, by computerized implementations of these algorithms (GAP, BESTFIT, FASTA, and TFASTA in the GCG Wisconsin Software Package), or by visual inspection (see generally, Current Protocols in Molecular Biology, F. M. Ausubel et al., eds., Current Protocols, a joint venture between Greene Publishing Associates, Inc. and John Wiley &amp; Sons, Inc., (1995 Supplement) (Ausubel)). Examples of algorithms that are suitable for determining percent sequence identity and sequence similarity are the BLAST and BLAST 2.0 algorithms, which are described in Altschul et al., 1990, J. Mol. Biol. 215: 403-410 and Altschul et al., 1977, Nucleic Acids Res. 3389-3402, respectively. Software for performing BLAST analyses is publicly available through the National Center for Biotechnology Information website. This algorithm involves first identifying high scoring sequence pairs (HSPs) by identifying short words of length W in the query sequence, which either match or satisfy some positive-valued threshold score T when aligned with a word of the same length in a database sequence. T is referred to as, the neighborhood word score threshold (Altschul et al, supra). These initial neighborhood word hits act as seeds for initiating searches to find longer HSPs containing them. The word hits are then extended in both directions along each sequence for as far as the cumulative alignment score can be increased. Cumulative scores are calculated using, for nucleotide sequences, the parameters M (reward score for a pair of matching residues; always &gt;0) and N (penally score for mismatching residues; always &lt;0). For amino acid sequences, a scoring matrix is used to calculate the cumulative score. Extension of the word hits in each direction are halted when: the cumulative alignment score falls off by the quantity X from its maximum achieved value; the cumulative score goes to zero or below, due to the accumulation of one or more negative-scoring residue alignments; or the end of either sequence is reached. The BLAST algorithm parameters W, T, and X determine the sensitivity and speed of the alignment. The BLASTN program (for nucleotide sequences) uses as defaults a wordlength (W) of 11, an expectation (E) of 10, M=5, N=−4, and a comparison of both strands. For amino acid sequences, the BLASTP program uses as defaults a wordlength (W) of 3, an expectation (E) of 10, and the BLOSUM62 scoring matrix (see Henikoff and Henikoff, 1989, Proc. Natl. Acad. Sci. USA 89:10915). Exemplary determination of sequence alignment and % sequence identity can employ the BESTFIT or GAP programs in the GCG Wisconsin Software package (Accelrys, Madison, Wis.), using default parameters provided. 
         [0091]    “Reference sequence” refers to a defined sequence used as a basis for a sequence comparison. A reference sequence may be a subset of a larger sequence, for example, a segment of a full-length gene or polypeptide sequence. Generally, a reference sequence is at least 20 nucleotide or amino acid residues in length, at least 25 residues in length, at least 50 residues in length, or the full length of the nucleic acid or polypeptide. Since two polynucleotides or polypeptides may each (1) comprise a sequence (i.e., a portion of the complete sequence) that is similar between the two sequences, and (2) may further comprise a sequence that is divergent between the two sequences, sequence comparisons between two (or more) polynucleotides or polypeptide are typically performed by comparing sequences of the two polynucleotides or polypeptides over a “comparison window” to identify and compare local regions of sequence similarity. A “reference sequence” can be based on a primary amino acid sequence, where the reference sequence is a sequence that can have one or more changes in the primary sequence. For instance, a “reference sequence based on SEQ ID NO:2 having at the residue corresponding to X9 a threonine” refers to a reference sequence in which the corresponding amino acid residue at X9 in SEQ ID NO:2, which is an alanine, has been changed to threonine. 
         [0092]    “Comparison window” refers to a conceptual segment of at least about 20 contiguous nucleotide positions or amino acids residues wherein a sequence may be compared to a reference sequence of at least 20 contiguous nucleotides or amino acids and wherein the portion of the sequence in the comparison window may comprise additions or deletions (i.e., gaps) of 20 percent or less as compared to the reference sequence (which does not comprise additions or deletions) for optimal alignment of the two sequences. The comparison window can be longer than 20 contiguous residues, and includes, optionally 30, 40, 50, 100, or longer windows. 
         [0093]    “Corresponding to,” “reference to” or “relative to” when used in the context of the numbering of a given amino acid or polynucleotide sequence refers to the numbering of the residues of a specified reference sequence when the given amino acid or polynucleotide sequence is compared to the reference sequence. In other words, the residue number or residue position of a given polymer is designated with respect to the reference sequence rather than by the actual numerical position of the residue within the given amino acid or polynucleotide sequence. For example, a given amino acid sequence, such as that of an engineered transaminase, can be aligned to a reference sequence by introducing gaps to optimize residue matches between the two sequences. In these cases, although the gaps are present, the numbering of the residue in the given amino acid or polynucleotide sequence is made with respect to the reference sequence to which it has been aligned. 
         [0094]    “Amino acid difference” or “residue difference” refers to a change in the amino acid residue at a position of a polypeptide sequence relative to the amino acid residue at a corresponding position in a reference sequence. The positions of amino acid differences generally are referred to herein as “Xn,” where n refers to the corresponding position in the reference sequence upon which the residue difference is based. For example, a “residue difference at position X3 as compared to SEQ ID NO: 2” refers to a change of the amino acid residue at the polypeptide position corresponding to position 3 of SEQ ID NO:2. Thus, if the reference polypeptide of SEQ ID NO: 2 has a glutamine at position 3, then a “residue difference at position X3 as compared to SEQ ID NO:2” is an amino acid substitution of any residue other than glutamine at the position of the polypeptide corresponding to position 3 of SEQ ID NO: 2. In most instances herein, the specific amino acid residue difference at a position is indicated as “XnY” where “Xn” specified the corresponding position as described above, and “Y” is the single letter identifier of the amino acid found in the engineered polypeptide (i.e., the different residue than in the reference polypeptide). In some instances, the present disclosure also provides specific amino acid differences denoted by the conventional notation “AnB”, where A is the single letter identifier of the residue in the reference sequence, “n” is the number of the residue position in the reference sequence, and B is the single letter identifier of the residue substitution in the sequence of the engineered polypeptide. In some instances, a polypeptide can include one or more amino acid residue differences relative to a reference sequence, which is indicated by a list of the specified positions where changes are made relative to the reference sequence. The present process may use engineered polypeptide sequences which comprise one or more amino acid differences that include either/or both conservative and non-conservative amino acid substitutions. 
         [0095]    “Conservative amino acid substitution” refers to a substitution of a residue with a different residue having a similar side chain, and thus typically involves substitution of the amino acid in the polypeptide with amino acids within the same or similar defined class of amino acids. By way of example and not limitation, an amino acid with an aliphatic side chain may be substituted with another aliphatic amino acid, e.g., alanine, valine, leucine, and isoleucine; an amino acid with hydroxyl side chain is substituted with another amino acid with a hydroxyl side chain, e.g., serine and threonine; an amino acids having aromatic side chains is substituted with another amino acid having an aromatic side chain, e.g., phenylalanine, tyrosine, tryptophan, and histidine; an amino acid with a basic side chain is substituted with another amino acid with a basis side chain, e.g., lysine and arginine; an amino acid with an acidic side chain is substituted with another amino acid with an acidic side chain, e.g., aspartic acid or glutamic acid; and a hydrophobic or hydrophilic amino acid is replaced with another hydrophobic or hydrophilic amino acid, respectively. Exemplary conservative substitutions are provided in Table 1 below: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Residue 
                 Possible Conservative Substitutions 
               
               
                   
                   
               
             
             
               
                   
                 A, L, V, I 
                 Other aliphatic (A, L, V, I) 
               
               
                   
                   
                 Other non-polar (A, L, V, I, G, M) 
               
               
                   
                 G, M 
                 Other non-polar (A, L, V, I, G, M) 
               
               
                   
                 D, E 
                 Other acidic (D, E) 
               
               
                   
                 K, R 
                 Other basic (K, R) 
               
               
                   
                 N, Q, S, T 
                 Other polar 
               
               
                   
                 H, Y, W, F 
                 Other aromatic (H, Y, W, F) 
               
               
                   
                 C, P 
                 None 
               
               
                   
                   
               
             
          
         
       
     
         [0096]    “Non-conservative substitution” refers to substitution of an amino acid in the polypeptide with an amino acid with significantly differing side chain properties. Non-conservative substitutions may use amino acids between, rather than within, the defined groups and affects (a) the structure of the peptide backbone in the area of the substitution (e.g., proline for glycine) (b) the charge or hydrophobicity, or (c) the bulk of the side chain. By way of example and not limitation, an exemplary non-conservative substitution can be an acidic amino acid substituted with a basic or aliphatic amino acid; an aromatic amino acid substituted with a small amino acid; and a hydrophilic amino acid substituted with a hydrophobic amino acid. 
         [0097]    In some embodiments, the present process uses engineered transaminase polypeptides that comprise a polypeptide fragment of any of the engineered transaminase polypeptides described herein that retains the functional activity and/or improved property of that engineered transaminase. A polypeptide fragment that may be capable of asymmetric synthesis of compounds of formula I from compounds of formula II via biocatalytic transamination include fragments comprising at least about 80%, 90%, 95%, 98%, or 99% of a full-length amino acid sequence of an exemplary engineered transaminase polypeptide of SEQ ID NO: 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 130, 132, 134, 136, 138, 140, 142, 144, 146, 148, 150, 152, 154, 156, 158, 160, 162, 164, 166, 168, 170, 172, 174, 176, 178, 180, 182, 184, 186, 188, 190, 192, 194, 196, 198, 200, 202, 204, and 206. 
         [0098]    In some embodiments, the process of the instant invention uses an engineered transaminase polypeptide having an amino acid sequence comprising a deletion as compared to any one of the engineered transaminase polypeptides described herein, such as the exemplary engineered polypeptides of SEQ ID NO: 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 130, 132, 134, 136, 138, 140, 142, 144, 146, 148, 150, 152, 154, 156, 158, 160, 162, 164, 166, 168, 170, 172, 174, 176, 178, 180, 182, 184, 186, 188, 190, 192, 194, 196, 198, 200, 202, 204, and 206. Thus, for each and every embodiment of the engineered transaminase polypeptides of the present process, the amino acid sequence can comprise deletions of one or more amino acids, 2 or more amino acids, 3 or more amino acids, 4 or more amino acids, 5 or more amino acids, 6 or more amino acids, 8 or more amino acids, 10 or more amino acids, 15 or more amino acids, or 20 or more amino acids, up to 10% of the total number of amino acids, up to 20% of the total number of amino acids, or up to 30% of the total number of amino acids of the transaminase polypeptides, where the associated functional activity and/or improved properties of the engineered transaminase is maintained. The deletions can comprise, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-15, 1-20, 1-21, 1-22, 1-23, 1-24, 1-25, 1-30, 1-35, 1-40, 1-45, 1-50, 1-55, or 1-60 amino acid residues. The number of deletions can be 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, 30, 30, 35, 40, 45, 50, 55, or 60 amino acids. In some embodiments, the deletions can comprise deletions of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 18, 20, 21, 22, 23, 24, 25 or 30 amino acid residues. 
         [0099]    In some embodiments, the process uses an engineered transaminase polypeptide having an amino acid sequence comprising an insertion as compared to any one of the engineered transaminase polypeptides described herein, such as the exemplary engineered polypeptides of SEQ ID NO: 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 130, 132, 134, 136, 138, 140, 142, 144, 146, 148, 150, 152, 154, 156, 158, 160, 162, 164, 166, 168, 170, 172, 174, 176, 178, 180, 182, 184, 186, 188, 190, 192, 194, 196, 198, 200, 202, 204, and 206. Thus, for each embodiment of the transaminase polypeptides utilized in the instant process, the insertions can comprise one or more amino acids, 2 or more amino acids, 3 or more amino acids, 4 or more amino acids, 5 or more amino acids, 6 or more amino acids, 8 or more amino acids, 10 or more amino acids, 15 or more amino acids, or 20 or more amino acids, where the associated functional activity and/or improved properties of the engineered transaminase described herein is maintained. The insertions can be to amino or carboxy terminus of the transaminase, or internal portions of the transaminase polypeptide. 
         [0100]    “Deletion” refers to modification to the polypeptide by removal of one or more amino acids from the reference polypeptide. Deletions can comprise removal of 1 or more amino acids, 2 or more amino acids, 5 or more amino acids, 10 or more amino acids, 15 or more amino acids, or 20 or more amino acids, up to 10% of the total number of amino acids, or up to 20% of the total number of amino acids making up the reference enzyme while retaining enzymatic activity and/or retaining the improved properties of an engineered transaminase enzyme or polypeptide. Deletions can be directed to the internal portions and/or terminal portions of the polypeptide. The deletion can comprise a continuous segment or can be discontinuous. 
         [0101]    “Insertion” refers to modification to the polypeptide by addition of one or more amino acids from the reference polypeptide. The improved engineered transaminase enzymes comprise insertions of one or more amino acids to the naturally occurring transaminase polypeptide as well as insertions of one or more amino acids to other improved transaminase polypeptides. Insertions can be in the internal portions of the polypeptide, or to the carboxy or amino terminus. Insertions as used herein include fusion proteins as is known in the art. The insertion can be a contiguous segment of amino acids or separated by one or more of the amino acids in the naturally occurring polypeptide. 
         [0102]    “Fragment” as used herein refers to a polypeptide that has an amino-terminal and/or carboxy-terminal deletion, but where the remaining amino acid sequence is identical to the corresponding positions in the sequence. Fragments can be at least 14 amino acids long, at least 20 amino acids long, at least 50 amino acids long or longer, and up to 70%, 80%, 90%, 95%, 98%, and 99% of the full-length transaminase polypeptide, for example the polypeptide of SEQ ID NO:2 or an engineered transaminase. 
         [0103]    In some embodiments, the transaminase polypeptides of the instant process can be in the form of fusion polypeptides in which the engineered polypeptides are fused to other polypeptides, such as, by way of example and not limitation, antibody tags (e.g., myc epitope), purification sequences (e.g., His-tags for binding to metals), and cell localization signals (e.g., secretion signals). Thus, the engineered polypeptides described herein can be used with or without fusions to other polypeptides. 
         [0104]    The engineered transaminase polypeptides described herein are not restricted to the genetically encoded amino acids. In addition to the genetically encoded amino acids, the polypeptides described herein may be comprised, either in whole or in part, of naturally-occurring and/or synthetic non-encoded amino acids. Certain commonly encountered non-encoded amino acids of which the polypeptides described herein may be comprised include, but are not limited to: the D-stereomers of the genetically-encoded amino acids; 2,3-diaminopropionic acid (Dpr); α-aminoisobutyric acid (Aib); ε-aminohexanoic acid (Aha); δ-aminovaleric acid (Ava); N-methylglycine or sarcosine (MeGly or Sar); ornithine (Orn); citrulline (Cit); t-butylalanine (Bua); t-butylglycine (Bug); N-methylisoleucine (MeIle); phenylglycine (Phg); cyclohexylalanine (Cha); norleucine (Nle); naphthylalanine (Nal); 2-chlorophenylalanine (Ocf); 3-chlorophenylalanine (Mcf); 4-chlorophenylalanine (Pcf); 2-fluorophenylalanine (Off); 3-fluorophenylalanine (Mff); 4-fluorophenylalanine (Pff); 2-bromophenylalanine (Obf); 3-bromophenylalanine (Mbf); 4-bromophenylalanine (Pbf); 2-methylphenylalanine (Omf); 3-methylphenylalanine (Mmf); 4-methylphenylalanine (Pmf); 2-nitrophenylalanine (Onf); 3-nitrophenylalanine (Mnf); 4-nitrophenylalanine (Pnf); 2-cyanophenylalanine (Ocf); 3-cyanophenylalanine (Mcf); 4-cyanophenylalanine (Pcf); 2-trifluoromethylphenylalanine (Otf); 3-trifluoromethylphenylalanine (Mtf); 4-trifluoromethylphenylalanine (Ptf); 4-aminophenylalanine (Paf); 4-iodophenylalanine (Pif); 4-aminomethylphenylalanine (Pamf); 2,4-dichlorophenylalanine (Opef); 3,4-dichlorophenylalanine (Mpcf); 2,4-difluorophenylalanine (Opff); 3,4-difluorophenylalanine (Mpff); pyrid-2-ylalanine (2pAla); pyrid-3-ylalanine (3pAla); pyrid-4-ylalanine (4pAla); naphth-1-ylalanine (1nAla); naphth-2-ylalanine (2nAla); thiazolylalanine (taAla); benzothienylalanine (bAla); thienylalanine (tAla); furylalanine (fAla); homophenylalanine (hPhe); homotyrosine (hTyr); homotryptophan (hTrp); pentafluorophenylalanine (5ff); styrylkalanine (sAla); authrylalanine (aAla); 3,3-diphenylalanine (Dfa); 3-amino-5-phenypentanoic acid (Afp); penicillamine (Pen); 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic); β-2-thienylalanine (Thi); methionine sulfoxide (Mso); N(w)-nitroarginine (nArg); homolysine (hLys); phosphonomethylphenylalanine (pmPhe); phosphoserine (pSer); phosphothreonine (pThr); homoaspartic acid (hAsp); homoglutanic acid (hGlu); 1-aminocyclopent-(2 or 3)-ene-4 carboxylic acid; pipecolic acid (PA), azetidine-3-carboxylic acid (ACA); 1-aminocyclopentane-3-carboxylic acid; allylglycine (aOly); propargylglycine (pgGly); homoalanine (hAla); norvaline (nVal); homoleucine (hLeu), homovaline (hVal); homoisolencine (hIle); homoarginine (hArg); N-acetyl lysine (AcLys); 2,4-diaminobutyric acid (Dbu); 2,3-diaminobutyric acid (Dab); N-methylvaline (MeVal); homocysteine (hCys); homoserine (hSer); hydroxyproline (Hyp) and homoproline (hPro). Additional non-encoded amino acids of which the polypeptides described herein may be comprised will be apparent to those of skill in the art (see, e.g., the various amino acids provided in Fasman, 1989, CRC Practical Handbook of Biochemistry and Molecular Biology, CRC Press, Boca Raton, Fla., at pp. 3-70 and the references cited therein, all of which are incorporated by reference). These amino acids may be in either the L- or D-configuration. 
         [0105]    Those of skill in the art will recognize that amino acids or residues bearing side chain protecting groups may also comprise the polypeptides described herein. Non-limiting examples of such protected amino acids, which in this case belong to the aromatic category, include (protecting groups listed in parentheses), but are not limited to: Arg(tos), Cys(methylbenzyl), Cys (nitropyridinesulfenyl), Glu(δ-benzylester), Gln(xanthyl), Asn(N-δ-xanthyl), His(bom), His(benzyl), His(tos), Lys(fmoc), Lys(tos), Ser(O-benzyl), Thr (O-benzyl) and Tyr(O-benzyl). 
         [0106]    Non-encoding amino acids that are conformationally constrained of which the polypeptides described herein may be composed include, but are not limited to, N-methyl amino acids (L-configuration); 1-aminocyclopent-(2 or 3)-ene-4-carboxylic acid; pipecolic acid; azetidine-3-carboxylic acid; homoproline (hPro); and 1-aminocyclopentane-3-carboxylic acid. As described above the various modifications introduced into the naturally occurring polypeptide to generate an engineered transaminase enzyme can be targeted to a specific property of the enzyme. 
         [0107]    In some embodiments, the transaminase polypeptides used in the instant process are bound to a substrate. The transaminase polypeptide can be bound non-covalently or covalently. Various methods for conjugation to substrates, e.g., membranes, beads, glass, etc. are described in, among others, Hermanson, G. T., Bioconjugate Techniques, Second Edition, Academic Press; (2008), and Bioconjugation Protocols: Strategies and Methods, In Methods in Molecular Biology, C. M. Niemeyer ed., Humana Press (2004); the disclosures of which are incorporated herein by reference. 
         [0108]    The polynucleotides encoding the exemplary engineered transaminases useful in the present process are selected from SEQ ID NO: 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99, 101, 103, 105, 107, 109, 111, 113, 115, 117, 119, 121, 123, 125, 127, 129, 131, 133, 135, 137, 139, 141, 143, 145, 147, 149, 151, 153, 155, 157, 159, 161, 163, 165, 167, 169, 171, 173, 175, 177, 179, 181, 183, 185, 187, 189, 191, 193, 195, 197, 199, 201, 203, and 205. These polynucleotides may be manipulated in a variety of ways well-known in the art to provide for expression of the engineered polypeptides, including further sequence alteration by codon-optimization to improve expression, insertion in a suitable expression with or without further control sequences, and transformation into a host cell suitable for expression and production of the polypeptide, as further described in detail in PCT International application serial no. PCT/US2011/046932, supra. 
         [0109]    To make the transaminase polynucleotides and polypeptides for use in the present process, the naturally-occurring transaminase enzyme that catalyzes the transamination reaction can be obtained (or derived) from  Arthrobacter  sp. KNK168. In some embodiments, the parent polynucleotide sequence is codon optimized to enhance expression of the transaminase in a specified host cell. The parental polynucleotide sequence encoding the wild-type polypeptide of  Arthrobacter  sp. KNK168 has been described (see e.g., Iwasaki et al.,  Appl. Microbiol. Biotechnol.,  2006, 69: 499-505). Preparation of engineered transaminases based on this parental sequence are also described in U.S. application Ser. No. 12/714,397, filed Feb. 26, 2010 and International application PCT/US2010/025685, filed Feb. 26, 2010. The engineered transaminases can be obtained by subjecting the polynucleotide encoding the naturally occurring transaminase to mutagenesis and/or directed evolution methods, as discussed above. An exemplary directed evolution technique is mutagenesis and/or DNA shuffling as described in Stemmer, 1994, Proc Natl Acad Sci USA 91:10747-10751; WO 95/22625; WO 97/0078; WO 97/35966; WO 98/27230; WO 00/42651; WO 01/75767 and U.S. Pat. No. 6,537,746. Other directed evolution procedures that can be used include, among others, staggered extension process (StEP), in vitro recombination (Zhao et al., 1998, Nat. Biotechnol. 16:258-261), mutagenic PCR (Caldwell et al., 1994, PCR Methods Appl. 3:S136-S140), and cassette mutagenesis (Black et al., 1996, Proc Natl Acad Sci USA 93:3525-3529). Mutagenesis and directed evolution techniques useful for the purposes herein are also described in e.g., Ling, et al., 1997, Anal. Biochem. 254(2):157-78; Dale et al., 1996, Methods Mol. Biol. 57:369-74; Smith, 1985, Ann. Rev. Genet. 19:423-462; Botstein et al., 1985, Science 229:1193-1201; Carter, 1986, Biochem. J. 237:1-7; Kramer et al., 1984, Cell, 38:879-887; Wells et al., 1985, Gene 34:315-323; Minshull et al., 1999, Curr Opin Chem Biol 3:284-290; Christians et al., 1999, Nature Biotech 17:259-264; Crameri et al., 1998, Nature 391:288-291; Crameri et al., 1997, Nature Biotech 15:436-438; Zhang et al., 1997, Proc Natl Acad Sci USA 94:45-4-4509; Crameri et al., 1996, Nature Biotech 14:315-319; Stemmer, 1994, Nature 370:389-391; Stemmer, 1994, Proc Natl Acad Sci USA 91:10747-10751; PCT Publ. Nos. WO 95/22625, WO 97/0078, WO 97/35966, WO 98/27230, WO 00/42651, and WO 01/75767; and U.S. Pat. No. 6,537,746. All publications and patent are hereby incorporated by reference herein. 
         [0110]    The clones obtained following mutagenesis treatment can be screened for engineered transaminases having a desired improved enzyme property. Measuring enzyme activity from the expression libraries can be performed using the standard biochemistry techniques, such as HPLC analysis following OPA derivatization of the product amine (see, e.g., PCT/US2011/046932; supra). 
         [0111]    Where the improved enzyme property desired is thermostability, enzyme activity may be measured after subjecting the enzyme preparations to a defined temperature and measuring the amount of enzyme activity remaining after heat treatments. Clones containing a polynucleotide encoding a transaminase are then isolated, sequenced to identify the nucleotide sequence changes (if any), and used to express the enzyme in a host cell. 
         [0112]    “Improved enzyme property” refers to a transaminase polypeptide that exhibits an improvement in any enzyme property as compared to a reference transaminase. For the engineered transaminase polypeptides, the comparison is generally made to the wild-type transaminase enzyme, although in some embodiments, the reference transaminase can be another improved engineered transaminase. Enzyme properties for which improvement is desirable include, but are not limited to, enzymatic activity (which can be expressed in terms of percent conversion of the substrate), thermostability, solvent stability, pH activity profile, coenzyme requirements, refractoriness to inhibitors (e.g., substrate or product inhibition), stereospecificity, and stereoselectivity (including enantioselectivity). 
         [0113]    “Increased enzymatic activity” refers to an improved property of the engineered transaminase polypeptides, which can be represented by an increase in specific activity (e.g., product produced/time/weight protein) or an increase in percent conversion of the substrate to the product (e.g., percent conversion of starting amount of substrate to product in a specified time period using a specified amount of transaminase) as compared to the reference transaminase enzyme. Any property relating to enzyme activity may be affected, including the classical enzyme properties of K m , V max , or k cat , changes of which can lead to increased enzymatic activity. Improvements in enzyme activity can be from about 1.1 times the enzymatic activity of the corresponding wild-type transaminase enzyme, to as much as 2 times, 5 times, 10 times, 20 times, 25 times, 50 times, 75 times, 100 times, or more enzymatic activity than the naturally occurring transaminase or another engineered transaminase from which the transaminase polypeptides were derived. It is understood by the skilled artisan that the activity of any enzyme is diffusion limited such that the catalytic turnover rate cannot exceed the diffusion rate of the substrate, including any required coenzymes. The theoretical maximum of the diffusion limit, or k cat /K m , is generally about 10 8  to 10 9  (M −1 s −1 ). Hence, any improvements in the enzyme activity of the transaminase will have an upper limit related to the diffusion rate of the substrates acted on by the transaminase enzyme. 
         [0114]    Transaminase activity can be measured by any one of standard assays, such as by monitoring changes in spectrophotometric properties of reactants or products. The amount of products produced can be measured by High-Performance Liquid Chromatography (HPLC) separation combined with UV absorbance or fluorescent detection following o-phthaldialdehyde (OPA) derivatization. Comparisons of enzyme activities are made using a defined preparation of enzyme, a defined assay under a set condition, and one or more defined substrates, as further described in detail herein. Generally, when lysates are compared, the numbers of cells and the amount of protein assayed are determined as well as use of identical expression systems and identical host cells to minimize variations in amount of enzyme produced by the host cells and present in the lysates. 
         [0115]    “Conversion” refers to the enzymatic conversion of the substrate(s) to the corresponding product(s). “Percent conversion” refers to the percent of the substrate that is converted to the product within a period of time under specified conditions. Thus, the “enzymatic activity” or “activity” of a transaminase polypeptide can be expressed as “percent conversion” of the substrate to the product. 
         [0116]    “Thermostable” refers to a transaminase polypeptide that maintains similar activity (more than 60% to 80% for example) after exposure to elevated temperatures (e.g., 40-80° C.) for a period of time (e.g., 0.5-24 hrs) compared to the wild-type enzyme. 
         [0117]    “Solvent stable” refers to a transaminase polypeptide that maintains similar activity (more than e.g., 60% to 80%) after exposure to varying concentrations (e.g., 5-99%) of solvent (ethanol, isopropyl alcohol, dimethylsulfoxide (DMSO), tetrahydrofuran, 2-methyltetrahydrofuran, acetone, toluene, butyl acetate, methyl tert-butyl ether, etc.) for a period of time (e.g., 0.5-24 hrs) compared to the wild-type enzyme. 
         [0118]    “Thermo- and solvent stable” refers to a transaminase polypeptide that is both thermostable and solvent stable. 
         [0119]    Where the sequence of the engineered polypeptide is known, the polynucleotides encoding the enzyme can be prepared by standard solid-phase methods, according to known synthetic methods. In some embodiments, fragments of up to about 100 bases can be individually synthesized, then joined (e.g., by enzymatic or chemical litigation methods, or polymerase mediated methods) to form any desired continuous sequence. For example, polynucleotides and oligonucleotides of the disclosure can be prepared by chemical synthesis using, e.g., the classical phosphoramidite method described by Beaucage et al., 1981, Tet Lett 22:1859-69, or the method described by Matthes et al., 1984, EMBO J. 3:801-05, e.g., as it is typically practiced in automated synthetic methods. According to the phosphoramidite method, oligonucleotides are synthesized, e.g., in an automatic DNA synthesizer, purified, annealed, ligated and cloned in appropriate vectors. In addition, essentially any nucleic acid can be obtained from any of a variety of commercial sources. 
       Reaction Conditions 
       [0120]    As described further below, and illustrated in the Examples, the present process contemplates ranges of suitable reaction conditions that can be used in the enzymatic process disclosed, including but not limited to ranges of pH, temperature, buffer, solvent system, substrate loading, transaminase polypeptide loading, coenzyme loading, atmosphere, and reaction time. Further suitable reaction conditions for carrying out the method for the transaminase-catalyzed DKR of a compound formula II to form an asymmetric compound of formula I can be readily optimized by routine experimentation that includes, but is not limited to, contacting a transaminase polypeptide and substrate (compound of formula II) under experimental reaction conditions of concentration, pH, temperature, solvent conditions, and detecting the production of the compound of formula I, for example, using the methods described in the Examples provided herein. 
         [0121]    “Suitable reaction conditions” refers to those conditions in the biocatalytic reaction solution (e.g., ranges of enzyme loading, substrate loading, coenzyme loading, temperature, pH, buffers, co-solvents, etc.) under which a transaminase polypeptide is capable of converting a compound of formula II to a compound of formula I. Exemplary “suitable reaction conditions” are provided in the present disclosure and illustrated by the Examples. 
         [0122]    “Substrate” in the context of a biocatalyst mediated process refers to the compound or molecule acted on by the biocatalyst. For example, an exemplary substrate for the transaminase biocatalyst in the processes disclosed herein is a compound of formula II. 
         [0123]    The use of a lower concentration of transaminase polypeptide in a process of the invention may reduce the amount of residual protein that may need to be removed in subsequent steps for purification of the compound of formula I. In some embodiments of the process, the suitable reaction conditions comprise a transaminase polypeptide concentration of about 0.1 to about 15 g/L, about 0.5 to about 10 g/L, about 1.0 to about 5 g/L, about 2 to about 5 g/L, about 15 g/L, about 10 g/L, about 5, g/L, about 3 g/L, about 2 g/L, about 1.5 g/L, about 1.0 g/L, about 0.75 g/L, or even lower concentration. 
         [0124]    In some embodiments of the process, the amino donor is isopropylamine (also referred to herein as “IPM” or “iPrNH 2 ”), putrescine, L-lysine, α-phenethylamine, D-alanine, L-alanine, or D,L-alanine, or D,L-ornithine. In some embodiments, the amino donor is IPM, putrescine, L-lysine, D- or L-alanine. In some embodiments, the amino donor is IPM. In some embodiments, the suitable reaction conditions comprise the amino donor at a concentration of at least about 0.5 M, at least about 1.0 M, at least about 2.5 M, at least about 5.0 M, at least about 7.5 M, at least about 10.0 M, or more. 
         [0125]    Suitable reaction conditions for the process of the instant invention require a coenzyme. Engineered transaminases, as disclosed herein, may require far less coenzyme than reactions catalyzed with wild-type transaminase enzymes. Coenzymes useful in the disclosed methods include, but are not limited to, pyridoxal-5′-phosphate (also known as pyridoxal-phosphate, PLP, P5P). In some embodiments, the coenzyme is a member of the vitamin B6 family, selected from PLP, pyridoxine (PN), pyridoxal (PL), pyridoxamine (PM), and their phosphorylated counterparts; pyridoxine phosphate (PNP), and pyridoxamine phosphate (PMP). In some embodiments, the coenzyme is PLP. In some embodiments, the coenzyme is present naturally in the cell extract and does not need to be supplemented. In some embodiments of the methods, the suitable reaction conditions comprise coenzyme added to the enzyme reaction mixture. In some embodiments, the coenzyme is added either at the beginning of the reaction and/or additional coenzyme is added during the reaction. 
         [0126]    In some embodiments of the process, the suitable reaction conditions can further comprise the presence of the reduced coenzyme, nicotinamide adenine dinucleotide (NADH), which can act to limit the inactivation of the transaminase enzyme (see, e.g., van Ophem et al., 1998, Biochemistry 37(9):2879-88). In such embodiments where NADH is present, a coenzyme regeneration system, such as glucose dehydrogenase (GDH) and glucose or formate dehydrogenase and formate can be used to regenerate the NADH in the reaction medium. 
         [0127]    In some embodiments of the process, the suitable reaction conditions comprise a substrate compound of formula II loading of at least about 5 g/L, at least about 10 g/L, at least about 15 g/L, at least about 20 g/L, at least about 30 g/L, at least about 50 g/L, at least about 75 g/L, at least about 100 g/L, or even greater. 
         [0128]    In certain embodiments of the process, the temperature of the suitable reaction conditions can be chosen to maximize the reaction rate at higher temperatures while maintaining the activity of the enzyme for sufficient duration for efficient synthesis. Where higher temperatures are used, polypeptides with increased thermostability can be selected to carry out the process. For example, the engineered polypeptides of the present disclosure have increased thermal stability relative to naturally occurring transaminase polypeptide e.g., the wild type polypeptide of SEQ ID NO: 2. In some embodiments of the method the suitable reaction conditions comprise a temperature of between about 25° C. and about 75° C., between about 35° C. and about 65° C., between about 40° C. and about 60° C., at least about 30° C., at least about 35° C., at least about 40° C., at least about 45° C., or at least about 50° C., or about 60° C., or more. In certain embodiments, the temperature during the enzymatic reaction can be maintained at a temperature throughout the course of the reaction. In some embodiments, the temperature during the enzymatic reaction can be adjusted over a temperature profile during the course of the reaction. 
         [0129]    The methods for preparing compounds of formula I of the present disclosure are generally carried out in a solvent. Suitable solvents include water, aqueous buffer solutions, organic solvents, and/or co-solvent systems, which generally comprise aqueous solvents and organic solvents. The aqueous solvent (water or aqueous co-solvent system) may be pH-buffered or unbuffered. 
         [0130]    In certain embodiments, the process for preparing compounds of formula I of the present invention can be carried out with the pH of the reaction mixture and may be maintained at a desired pH or within a desired pH range by the addition of an acid or a base during the course of the reaction. In certain embodiments of the process, the pH of the reaction mixture may be allowed to change, or be changed during the course of the reaction. Thus, it is contemplated that in some embodiments the pH may be controlled by using an aqueous solvent that comprises a buffer. In some embodiments of the method, the suitable reaction conditions comprise a solution pH of between about pH 8.5 and about pH 11.5, between about pH 9.0 and about pH 11.5, between about pH 9.5 and about pH 11.0, at least about pH 8.5, at least about pH 9.0, at least about pH 9.5, at least about pH 10.0, or at least about pH 10.5. Suitable buffers to maintain desired pH ranges are known in the art and include, for example, phosphate buffer, triethanolamine buffer, and the like. Combinations of buffering and acid or base addition may also be used. In some embodiments, the buffer is TEA (e.g., about 0.025 M to about 0.25 M TEA). In some embodiments of the process the suitable reaction conditions comprise a buffer solution of about 0.05 M borate to about 0.25 M borate, or about 0.1 M borate. In some embodiments, the reaction conditions comprise water as a suitable solvent with no buffer present. 
         [0131]    In some embodiments, the process for preparing compounds of formula I are generally carried out in an aqueous co-solvent system comprising an organic solvent (e.g., ethanol, isopropanol (IPA), dimethyl sulfoxide (DMSO), ethyl acetate, butyl acetate, 1-octanol, heptane, octane, methyl t-butyl ether (MTBE), toluene, and the like), ionic liquids (e.g., 1-ethyl 4-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, and the like). The organic solvent component of an aqueous co-solvent system may be miscible with the aqueous component, providing a single liquid phase, or may be partly miscible or immiscible with the aqueous component, providing two liquid phases. Exemplary aqueous co-solvent systems comprises water and one or more organic solvent. In general, an organic solvent component of an aqueous co-solvent system is selected such that it does not completely inactivate the transaminase enzyme. Appropriate co-solvent systems can be readily identified by measuring the enzymatic activity of the specified engineered transaminase enzyme with a defined substrate of interest in the candidate solvent system, utilizing an enzyme activity assay, such as those described herein. In some embodiments of the process, the suitable reaction conditions comprise an aqueous co-solvent comprising DMSO at a concentration of at least about 5% (v/v), at least about 10% (v/v), at least about 20% (v/v), at least about 30% (v/v), or at least about 40% (v/v). 
         [0132]    In carrying out the transamination reactions described in the process of the instant invention, the transaminase polypeptide may be added to the reaction mixture in the form of a purified enzyme, whole cells transformed with gene(s) encoding the enzyme, and/or as cell extracts and/or lysates of such cells. Whole cells transformed with gene(s) encoding the transaminase enzyme or cell extracts, lysates thereof, and isolated enzymes may be employed in a variety of different forms, including solid (e.g., lyophilized, spray-dried, and the like) or semisolid (e.g., a crude paste). The cell extracts or cell lysates may be partially purified by precipitation (ammonium sulfate, polyethyleneimine, heat treatment or the like, followed by a desalting procedure prior to lyophilization (e.g., ultrafiltration, dialysis, and the like). Any of the cell preparations may be stabilized by crosslinking using known crosslinking agents, such as, for example, glutaraldehyde or immobilization to a solid phase (e.g., Eupergit C, and the like). In some embodiments where the transaminase polypeptide can be expressed in the form of a secreted polypeptide and the culture medium containing the secreted polypeptides can be used in the disclosed method. 
         [0133]    In some embodiments, solid reactants (e.g., enzyme, salts, etc.) may be provided to the reaction in a variety of different forms, including powder (e.g., lyophilized, spray dried, and the like), solution, emulsion, suspension, and the like. The reactants can be readily lyophilized or spray dried using methods and equipment that are known to those having ordinary skill in the art. For example, the protein solution can be frozen at −80° C. in small aliquots, then added to a pre-chilled lyophilization chamber, followed by the application of a vacuum. 
         [0134]    In some embodiments, the order of addition of reactants is not critical. The reactants may be added together at the same time to a solvent (e.g., monophasic solvent, biphasic aqueous co-solvent system, and the like), or alternatively, some of the reactants may be added separately, and some together at different time points. For example, the coenzyme, transaminase, and transaminase substrate may be added first to the solvent. For improved mixing efficiency when an aqueous co-solvent system is used, the transaminase, and coenzyme may be added and mixed into the aqueous phase first. The organic phase may then be added and mixed in, followed by addition of the transaminase substrate. Alternatively, the transaminase substrate may be premixed in the organic phase, prior to addition to the aqueous phase. 
         [0135]    The quantities of reactants used in the transamination reaction will generally vary depending on the quantities of product desired, and concomitantly the amount of transaminase substrate employed. Those having ordinary skill in the art will readily understand how to vary these quantities to tailor them to the desired level of productivity and scale of production. Transformation of substrate to product can be monitored using known methods by detecting substrate and/or product. Suitable methods include gas chromatography, HPLC, and the like. 
         [0136]    In some embodiments, the process can further comprise a step of removal of the carbonyl by-product formed from the amino group donor when the amino group is transferred to the transaminase substrate. Such removal in situ can reduce the rate of the reverse reaction such that the forward reaction dominates and more substrate is then converted to product. Removal of the carbonyl by-product can be carried in a number of ways. Where the amino group donor is an amino acid, such as alanine, the carbonyl by-product, a keto acid, can be removed by reaction with a peroxide (see, e.g., US 2008/0213845, incorporated herein by reference). Peroxides which can be used include, among others, hydrogen peroxide; peroxyacids (peracids) such as peracetic acid (CH 3 CO 3 H), trifluoroperacetic acid and metachloroperoxybenzoic acid; organic peroxides such as t-butyl peroxide ((CH 3 ) 3 COOH), or other selective oxidants such as tetrapropylammonium perruthenate, MnO 2 , KMnO 4 , ruthenium tetroxide and related compounds. Alternatively, pyruvate removal can be achieved via its reduction to lactate by employing lactate dehydrogenase to shift equilibrium to the product amine (see, e.g., Koszelewski et al., 2008, Adv. Syn. Catal. 350:2761-2766). Pyruvate removal can also be achieved via its decarboxylation to carbon dioxide acetaldehyde by employing pyruvate decarboxylase (see, e.g., Hohne et al., 2008, Chem BioChem 9:363-365). 
         [0137]    In some embodiments of the process, where the choice of the amino donor results in a carbonyl by-product that has a vapor pressure higher than water (e.g., a low boiling co-product such as a volatile organic carbonyl compound), the carbonyl by-product can be removed by sparging the reaction solution with a non-reactive gas or by applying a vacuum to lower the reaction pressure and removing the carbonyl by-product present in the gas phase. A non-reactive gas is any gas that does not react with the reaction components. Various non-reactive gases include nitrogen and noble gases (e.g., inert gases). In some embodiments, the non-reactive gas is nitrogen gas. 
         [0138]    In some embodiments, the amino donor used in the process is isopropylamine (IPM), which forms the carbonyl by-product acetone upon transfer of the amino group to the amino group acceptor. The acetone can be removed by sparging with nitrogen gas at elevated temperatures or applying a vacuum to the reaction solution and removing the acetone from the gas phase by an acetone trap, such as a condenser or other cold trap. Alternatively, the acetone can be removed by reduction to isopropanol using a ketoreductase. A nitrogen sweep can also be used to prevent formation of a ketone side product, ensuring that the reaction remains inert at all times. 
         [0139]    In some embodiments of the process where the carbonyl by-product is removed, the corresponding amino group donor can be added during the transamination reaction to replenish the amino group donor and/or maintain the pH of the reaction. Replenishing the amino group donor also shifts the equilibrium towards product formation, thereby increasing the conversion of substrate to product. Thus, in some embodiments wherein the amino group donor is IPM and the acetone product is removed in situ, the method can further comprise a step of adding IPM to the reaction solution to replenish the amino group donor lost during the acetone removal and to maintain the pH of the reaction (e.g., at about 8.5). 
         [0140]    Alternatively, in embodiments where an amino acid is used as amino group donor, the keto acid carbonyl by-product can be recycled back to the amino acid by reaction with ammonia and NADH using an appropriate amino acid dehydrogenase enzyme, thereby replenishing the amino group donor. 
         [0141]    In some embodiments, the process of the instant invention can further comprise extraction, isolation, purification, and/or crystallization of the compound of formula I, each of which can be carried out under a range of conditions. 
         [0142]    These and other aspects of the invention will be apparent from the teachings contained herein. 
       EXAMPLES 
       [0143]    Examples provided are intended to assist in a further understanding of the invention. Particular materials employed, species and conditions are intended to be illustrative of the invention and not limiting of the reasonable scope thereof. 
         [0144]    Certain starting materials and reagents are either commercially available or known in the chemical scientific or patent literature. Purification procedures include, for example, distillation, crystallization, and normal or reverse phase high performance liquid chromatography. 
         [0145]    The abbreviations used herein have the following tabulated meanings (see Table 2). Abbreviations not tabulated below have their meanings as commonly used unless specifically stated otherwise. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
             
               
                   
                 NaOH = 
                 Sodium hydroxide 
               
               
                   
                 AlCl 3  = 
                 Aluminum chloride 
               
               
                   
                 H 2 SO 4  = 
                 Sulfuric acid 
               
               
                   
                 IPA = 
                 Isopropyl alcohol 
               
               
                   
                 Na 2 CO 3  = 
                 Sodium carbonate 
               
               
                   
                 MgSO 4  = 
                 Magnesium sulfate 
               
               
                   
                 Me 3 SOI = 
                 Trimethyl sulfoxonium iodide 
               
               
                   
                 KOt-Bu (s)  = 
                 Potassium tert-butoxide 
               
               
                   
                 DMSO = 
                 Dimethyl sulfoxide 
               
               
                   
                 THF = 
                 Tetrahydrofuran 
               
               
                   
                 Na 2 SO 4  = 
                 Sodium sulfate 
               
               
                   
                 ZnBr 2  = 
                 Zinc bromide 
               
               
                   
                 NaHSO 3  = 
                 Sodium bisulfite 
               
               
                   
                 PhMe = 
                 Toluene 
               
               
                   
                 NaCl = 
                 Sodium chloride 
               
               
                   
                 iPrNH 2  = 
                 Isopropylamine 
               
               
                   
                 MeCN = 
                 Acetonitrile 
               
               
                   
                 PLP = 
                 Pyridoxal-phosphate 
               
               
                   
                 NaBH 4  = 
                 Sodium borohydride 
               
               
                   
                 EtOH = 
                 Ethanol 
               
               
                   
                 BF 3 •THF = 
                 Boron trifluoride tetrahydrofuran complex 
               
               
                   
                 MeOH = 
                 Methanol 
               
               
                   
                 NH 4 OH = 
                 Ammonium hydroxide 
               
               
                   
                 LCAP = 
                 Liquid chromatography area percent 
               
               
                   
                 MeLi = 
                 Methyllithium 
               
               
                   
                 DBU = 
                 1,8-Diazabicyclo[5.4.0]undec-7-ene 
               
               
                   
                 DIBAL = 
                 Diisobutylaluminium hydride 
               
               
                   
                 MsCl = 
                 Methanesulfonyl chloride 
               
               
                   
                 Et 3 N = 
                 Triethylamine 
               
               
                   
                 CH 2 Cl 2  = 
                 Dichloromethane 
               
               
                   
                 DMF = 
                 Dimethylformamide 
               
               
                   
                   
               
             
          
         
       
     
       EXAMPLE 1 
       [0146]    The following Example 1 describes synthesis of the chiral lactam 7 using DKR transamination: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    
       
                 
         
             
             
         
       
       
                 
         
             
             
         
       
     
       1.1 Acylation 
       [0147]    
       
                 
         
             
             
         
       
     
         [0148]    A mixture of succinic anhydride 1 (110 g) and bromobenzene (695 mL) was cooled to 2-5° C. then added AlCl 3  (294 g). The slurry was allowed to warm to RT and then aged until the reaction was complete judged by HPLC. The reaction mixture was then transferred slowly into a cold HCl solution resulting in the formation of a white precipitate. The white slurry was filtered through a fitted funnel rinsing with H 2 O. To the off-white product was added MTBE and extracted with aq. NaOH. The aqueous layer was cooled in an ice bath. Concentrated HCl was added drop wise to adjust the solution pH to 1, resulting in the formation of a white slurry. The slurry was collected on a fritted funnel, rinsed with H 2 O, and dried under vacuum with a N 2  sweep at RT to give the target compound (265 g, 93% corrected yield) as a white powder. 
       1.2 Esterification 
       [0149]    
       
                 
         
             
             
         
       
     
         [0150]    A mixture of the acid 2 (205 g), IPA (4 L) and conc. H 2 SO 4  (2.13 mL/3.91 g) was heated to a gentle reflux until the reaction was complete judged by HPLC. The solution was then cooled to RT and concentrated to a volume of 350-400 mL. The residue was dissolved in MTBE (1.2 L), washed with aq. Na 2 CO 3  followed by water. After dried over MgSO 4 , the filtrate was solvent-switched into heptane. The slurry was then filtered, and the cake was washed with cold heptane. After drying under vacuum, the target compound (223.5 g, 93% corrected yield) was obtained as a white powder. 
       1.3 Epoxidation 
       [0151]    
       
                 
         
             
             
         
       
     
         [0152]    A mixture of Me 3 SOI (230 g) and DMSO (300 mL) was added KOt-Bu (113 g) followed by DMSO (300 mL). The mixture was aged for a further 1.5 hr. In a separate flask, ketone 3 (230 g) was dissolved in a mixture of THF (250 mL) and DMSO (150 mL), and the resulting solution was added drop wise to the ylide solution. The mixture was aged for 2 hr at RT, added hexanes (1 L), and then quenched by the addition of ice-water (600 mL). The layers were cut, and the organic layer was washed with water then with brine. The slightly cloudy yellow organic layer was dried over Na 2 SO 4  and filtered through a fritted funnel. Product solution assay was 176.1 g (76% assay yield). This solution was carried forward into the rearrangement step. 
       1.4 Epoxide Rearrangement and Bisulfite Formation 
       [0153]    
       
                 
         
             
             
         
       
     
         [0154]    A solution of crude epoxide 4 (assay 59.5 g) in hexanes was solvent switched into PhMe, and added ZnBr 2  (10.7 g). When the rearrangement was complete judged by HPLC, the slurry was filtered through a fritted funnel. The clear filtrate was washed with 10% aq. NaCl and then stirred with a solution of sodium bisulfite (NaHSO 3 , 24.7 g) in H 2 O (140 mL) vigorously at RT for 3 hr. The cloudy aqueous layer was separated and washed with heptanes. By  1 H-NMR assay, the aqueous solution contained 71.15 g bisulfite adduct 6 (30.4 wt % solution, 90% yield from crude epoxide 4). This solution was used directly in the subsequent transaminase step. 
       1.5 Transaminase DKR 
       [0155]    
       
                 
         
             
             
         
       
     
         [0156]    To a cylindrical Labfors reactor was charged pyridoxal-5-phosphate (1.4 g, 5.66 mmol), 452 ml 0.2 M borate buffer pH 10.5 containing 1M iPrNH 2 , 52 g transaminase (SEQ ID NO: 180), and 75 ml DMSO, and the resulting mixture was warmed to 45° C. The pH was controlled at pH 10.5 using 8 M aq iPrNH 2 . To this was added dropwise a mixture of 17.16 wt % aq solution of ester bi-sulfite 6 (147.2 g, 353 mmol) and 219 ml DMSO under N 2  atmosphere. When the reaction was complete judged by HPLC, the reaction mixture was cooled and extracted with 1 volume of 3:2 IPA:IPAc. The aq/rag layer was extracted again with 1 volume of 3:7 IPA:IPAc. The organic layer was washed with brine at pH&gt;9. Assay yield in solution was 78 g (87%); 99.3% ee. After dried over MgSO 4 , and filtered through a fritted funnel, the crude solution was concentrated under vacuum flushing with IPAc to remove IPA. The resulting slurry was concentrated to a final volume of ˜200 mL, cool to below 0° C., and filtered to collect the solid. The cake was washed with ice-cold IPAc and dried at RT under vacuum to give the desired product (84% corrected yield, 99.3 LCAP) as a white powder. 
       Alternative Substrates 
       [0157]    While the DKR transaminase reaction described above was performed using the bisulfite adduct of ester aldehyde 5, it was also determined that aldehyde 5 itself is a good substrate for DKR transamination using the process as described above. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0158]    When screening two transaminases, SEQ ID NO: 18 and SEQ ID NO: 180, using either the ester aldehyde 5 of its bisulfite adduct 6, the enantiomeric excess of each reaction was found to be 99% or greater. 
       1.6. Reduction of Amide 
       [0159]    
       
                 
         
             
             
         
       
     
         [0160]    The lactam 7 can be reduced to form the piperidine 8 as described below: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0161]    A mixture of lactam 7 (10.25 g at 97.5 wt %) in THF (100 mL) was cooled to &lt;10° C., and added NaBH 4  (4.47 g). EtOH (6.89 mL) was then added slowly over 20 min. The slurry was aged for an additional 1 hr at 2° C. after which BF 3 ·THF (13.03 mL) was added over 1 hr. The slurry was slowly warmed to RT and aged until complete conversion judged by HPLC. The reaction was then cooled to &lt;5° C. then slowly quenched with MeOH (7.96 mL), added HCl (9.69 mL), then the reaction was heated to 45° C. until decomplexation of product-borane complex was complete, as indicated by LC assay. The reaction was cooled, diluted with IPAc (75 mL) and water (80 mL), and then pH was adjusted with aqueous NH 4 OH to pH 8. The organic layer was separated, added 75 mL water, then pH adjusted to 10.5 with 50 wt % NaOH. The layers were separated and the organic layer was washed with brine. After solvent-switched to IPAc, LC Assay yield was 9.1g; 95.9%. 
       EXAMPLE 2 
       [0162]    The DKR transaminase reaction described in Example 1 can be performed using related substates, yielding similar products. For example, the following schemes can also be used to generate the key intermediate described as part of the present invention. 
         [0000]    
       
                 
         
             
             
         
       
       
                 
         
             
             
         
       
     
         [0000]    
       
                 
         
             
             
         
       
     
       EXAMPLE 3 
       [0163]    Different transaminases were tested in the reaction as described in Example 1 (section 1.5), using the ester aldehyde 5 as the substrate to form the lactam 7 by DKR transamination. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0164]    Pryridoxal-5-phosphate (1 mg; 4.05 μmol) was dissolved in water 0.2M borate buffer pH 10.5 (400 μl ) containing isopropylamine hydrochloride (50 mg, 0.523 mmol). The respective transaminase (2 mg), 0.663 mmol) was added and slowly dissolved. Then a solution of ester aldehyde 5 (2 mg, 6.39 μmol) in DMSO (100 p1) was added and the reactions aged at 45° C. As control, ester adehyde 5 (2 mg, 6.39 μmol) was incubated in water 0.2M borate buffer pH 10.5 (400 pl) and DMSO (100 μl) with and without the isopropylamine hydrochloride (50 mg, 0.523 mmol). 
         [0165]    The enantiomeric excess was determined for the transaminases tested in this reaction, the results shown in the table below: 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Transaminase Sequence 
                 % e.e. 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 SEQ ID NO: 18 
                 99 
               
               
                 2 
                 SEQ ID NO: 207 
                 75 
               
               
                 3 
                 SEQ ID NO: 208 
                 59 
               
               
                 4 
                 SEQ ID NO: 209 
                 66 
               
               
                 5 
                 SEQ ID NO: 210 
                 44 
               
               
                 6 
                 SEQ ID NO: 211 
                 45