A-amino e-caprolactam

Racemic a-amino amides and a-hydroxy amides have been hydrolyzed enantio-selectively by amidases. Both L-selective and o-selective amidases are known. For example, a purified L-selective amidase from Ochrobactrum anthropi combines a very broad substrate specificity with a high enantioselectivity on a-hydrogen and a,a-disubstituted a-amino acid amides, a-hydroxyacid amides, and a-N-hydroxya-mino acid amides [102]. A racemase (a-amino-e-caprolactam racemase, EC 5.1.1.15) converts the o-aminopeptidase-catalyzed hydrolysis of a-amino acid amides into a DKR (Figure 6.38) [103]. 

The regiochemical course reacting saturated ketones depended on the substitution pattern of the a-positions. In most cases, the intermediate oxime had an anti N-OH function with respect to the chain branched a-position. Consequently, the more substituted alkyl group preferentially migrates. This advantage was utilized for synthesizing the spiro a-amino-e-caprolactam (202 203, Scheme 38) [12c], the Mexican bean beetle azamacrolide allomone (205 206, Scheme 39) [44 a], in a key step of the chiral synthesis of benzomorphanes... 

Asano, Y. and Yamaguchi, S. (2005) Dynamic kinetic resolution of amino acid amide catalyzed by D-aminopeptidase and a-amino-e-caprolactam racemase. Journal of the American Chemical Society, 127 (21), 7696-7697. 

L-Alanine amide (S)-8 was converted to D-alanine (R)-9 in excellent yield and enantiomeric excess by incubation of the substrate with a-amino-e-caprolactam racemase from Achromohacter obae and D-aminopeptidase from Ochrobactrum anthropi (Scheme 2.5) [7]. 

If one enantiomer obtained by resolution is the desired one, the other recovered from the mother liquor of the resolution should be racemized to use for the next resolution. In general, whether the racemization method for unwanted enantiomer is known or not will be key to producing optically active compounds on an industrial scale. In most cases, optical resolution and racemization are non-divisable for the realization of a practical and economical process. For instance, nickel chloride complex of DL-a-amino-e-caprolactam has been successfully resolved. The complex, dissolved in ethanol, was heated and inoculated with enantiopure complex, then racemization and crystallization of the complex occurred at the same time. As a result,... 

Sakai, K., Sakurai, R., Yuzawa, A. and Hirayama, N. (2003) Practical continuous resolution of a-amino-E-caprolactam by diastereomeric salt formation using a single resolving agent with a solvent switch method, Tetrahedron Asymmetry 14, 3713-3718. 

Recently it was reported that an a-amino-e-caprolactam racemase from Achro-mobacter obae can racemise a-amino acid amides efficiently. In combination with a D-amino acid amidase from Ochrobactrum anthropi L-alanine amide could be converted into D-alanine. This tour de force demonstrates the power of the racemase [84]. If racemic amide is used as a starting material the application of this racemase in combination with a d- or L-amidase allows the preparation of 100% d- or L-amino acid, a dynamic kinetic resolution instead of DSM s kinetic resolution (Scheme 6.24). 

Scheme 6.24 a-Amino-e-caprolactam racemase enables a dynamic kinetic resolution. 

For some years Foray s enzymatic process for L-lysine (L-Lys, 41) was competitive compared with fermentation. This chemoenzymatic L-Lys production was established with a capacity of 5000-10000 t/y. The key intermediate is a-amino-e-caprolactam (ACL), produced from cyclohexanone in a modified Beckmann rearrangement. The enantiospecific hydrolysis forming L-Lys is based on two enzymes L-ACL-hydrolase opens the ring of ACL to L-Lys and in the presence of the ACL-racemase the d-ACL is racemized. Incubating d,l-ACL with cells of Cryptococcus laurentii having l-ACL lactamase activity together with cells of Achromobacter obae with ACL-racemase activity, L-Lys could be obtained in a yield of nearly 100% (Scheme 24) [102]. 

Large scale resolution of amino acids is an area where immobilized enzyme technology has triumphed. L-Phe and L-Met are now continuously produced on a 20 ton/month scale via immobilized aminocyclase hydrolysis of their racemic N-acetyl precursors.43 Similarly L-Ly has been obtained by yeast hydrolysis of (+)-a-amino-e-caprolactam.44 The value of mild and specific enzyme procedures when dealing with sensitive molecules is demonstrated by the conversion of 23 to 24.45... 

Enantiopure a-amino-e-caprolactam is used not only as a synthetic intermediate... 

MeOH was the best solvent for the first enantioseparation to give the (S) (.S ) H2O salt with 93% diastereomeric purity (30% yield). An equimolar mixture of (R)-enriched (40%) a-amino-e-caprolactam and N-tosyl-(S)-phenylalanine, which was recovered upon concentrating the mother hquor, was crystallized from 89% aqueous 2-PrOH/H2O (89/11) to give the (P)-(S) salt with a high resolution efficiency (41% yield, 93% diastereomeric purity). The processes could be repeated with high reproducibility (the first enantioseparation 29-31% yield, 91-93% diastereomeric purity the second enantioseparation 41-42% yield, 91-94% diastereomeric purity). The diastereomeric purity of the crude salts could be easily improved by recrystallization once from MeOH and 2-PrOH/H2O (89/11), respectively, to afford fhe pure salts with a diastereomeric purity of more than 99%. Treatment of the salts with 35% HCl in EtOH, followed by recrystallization gave a-amino-e-caprolactam-HCl with enantiomeric excess of more than 99.9%. 

L-Eysine via asymmetric transformation of a-amino-e-caprolactam, A.N. Collins,... 

D-a-Amino-e-caprolactam Complex of L-substrate L-a-Amino-e-caprolactam [177]... 

L-Lysine, an essential amino acid, is used in very large quantities to supplement human foods and animal feeds. Traditionally, L-Lysine is produced by fermentation processes. An alternative route developed by Toray Ind. involves the chemical synthesis of D/L-a-amino-s-caprolactam followed by the selective hydrolysis of the L-a-amino-s-caprolactam catalyzed by intracellular lactamase in Cryptococcus laurentii, to give L-Lysine. The process can be improved by adding a second micro-organism, Achromobacter obae, containing a-amino-E-caprolactam racemase.Thus, quantitative yields of L-lysine are obtained. 

Synthesis of (S)- and (/ )-a-amino acids using nitrile hydratase (NHase) from Rhodococcus opacus, a-amino-e-caprolactam racemase (ACL) from Achromobacter obae, and different amidases (amidase 1, o-amino-peptidase from Ochrobactrum anthropi amidase 2, i-amino acid amidase from Brevundimonas diminuta) [111, 112]. / =CH3, CH CH, CH3CH(CH3), CH3CH(CH3)CH2. 

Fukumura, T., "Conversion of d- and DL-a-amino-e-caprolactam into L-lysine using both yeast cells and bacterial cells." Agric. Biol. Chem., 41,1327-1330 (1977). 

Ahmed, S. A., Esaki, N., Tanaka, H., and Soda, K., "Properties of a-amino-e-caprolactam racemase from Achromobacter oboe. "Agric. Biol. Chem., 47,1887-1893 (1983). 

Yamaguchi, S., Komeda, H., and Asano, Y., "New enzymatic method of chiral amino add synthesis by dynamic kinetic resolution of amino acid amides use of stereoselective amino acid amidases in the presence of a-amino-e-caprolactam racemase." Appl. Environ. Microbiol, 73,5370-5373 (2007). 

Okazaki, S., Suzuki, A., Mizushima, T, Kawano, T., Komeda, H., Asano, Y., and Yamane, T., "The novel structure of a pyridoxal 5 -phosphate-dependent fold-type I racemase, a-amino-e-caprolactam racemase from Achromobacter oboe." Biochemistry, 48,941-950 (2009). 

Payoungkiattikun, W., Okazaki, S., Nakano, S., Ina, A., H-Kittikun, A., and Asano, Y, "In silica identification for a-amino-e-caprolactam racemases by using information of the structure and function relationship." Appl Biochem. Biotechnol, 176,1303-1314 (2015). 

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