Enzymatic reactions lipase-catalyzed enantioselective acylation

For example, Mikolajczyk and Kielbasinski [172-175] studied the acylation of phosphine boranes 259 using CAL (Chirazyme ) lipase from Candida Antarctica and Lipase AK from Pseudomonas fluorescencs (Scheme 84). The best enantios-electivity was attained in the lipase AK-catalyzed acylation of 259 in cyclohexane solution with vinyl butyrate as an acyl donor (99% ee) for unreacted hydroxypho-sphinate 259 and 43% ee for the acylated product 260. The E-values were on the level of 15. The enzymatic resolution of alkoxy (hydroxymethyl)phenyl-phosphine boranes (/ /S)-261 was achieved by trans-esterification with vinyl acetate in the presence of CALB, Amano AK, Amano PS, Amano AH, and LPL in various solvents. The best enantioselectivity of imreacted alcohol 261 and acylated product 262 was attained in cyclohexane (37% ee, conversion 50%). Kielbasinski [176] recently reported some additional data, including theoretical calculations and more accurate chemical correlation, which proved that the borane reduction of acyclic phosphine oxides proceeded with inversion of configuration at the phosphoms center. On this basis, the stereochemistry of the enzymatic reaction was ultimately determined (Scheme 85). 

For the synthesis of p-lactam antibiotics, the presence of asymmetrical carbon at the 3 and 4 positions is critical to prepare optically active -lactams [197]. Nagai et al. [198] developed enzymatic synthesis of optically active p-lactams by lipase-catalyzed kinetic resolution using the enantioselective hydrolysis of iV-acyloxymethyl p-lactams 108 in an organic solvent (isopropyl ether saturated with water) and the transesterification of N-hydroxymethyl P-lactam 109 in organic solvent (metiiylene chloride) in tiie presence of vinyl acetate as acyl donor (Fig. 37). The reaction yield of 35-50% and e.e. s of 93 to more than 99% were obtained depending on the specific substrate used in the reaction mixture, Lipase B from Pseudomonas fragi and lipase PS-30 from Pseudomonas sp. were used in the reaction mixture. 

Recently, 1-ethoxyvinyl acetate has been proposed as a novel and reliable acyl donor for the enzymatic resolution of alcohols (Scheme 24) in a lipase-catalyzed irreversible transesterification procedure [135]. A similar protocol has been utilized for the irreversible acetoacetylation of alcohols with diketene in the presence of lipases in organic solvents [136,137] and the reaction has been reported to proceed with high enantioselectivity [136], as shown in Scheme 25. 

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