Kinetic Studies on the Optical Resolution of 2-Alkanol by Pseudomonas cepaciaLipase Catalyzed Transesterification with Vinyl Acetate in Organic Solvent.

Abstract

Vinyl acetate (VA) is a potential and practical acetylating reagent for the optical resolution of enantiomers in the racemate by lipase (triacylglycerol hydrolase, EC 3.1.1.3) catalyzed transesterification in organic solvent: VA irreversibly reacts with the active serine (Ser) residue in lipase to give the acetyl-enzyme intermediate [Enz-Ac] because vinyl alcohol is immediately converted to acetaldehyde by keto-enol tautomerization. This irreversibility is considered to accelerate the reaction rate. Such a reaction is called "irreversible transesterification" (1) and applied to the optical resolution of numerous secondary alcohols (1-5). On the other hand, the analyses of optical resolution data are complicated for lipase catalyzed transesterification with VA. It is reported that the enantioselectivity [E: the enantiomeric ratio for the homocompetitive reaction (6-9), i.e., as the reaction is irreversible] at low conversion is greater than that at high conversion (>50%) for Pseudomonas fluorescens lipase (PFL) catalyzed transesterification with racemic b-methyl-(2-643

Kinetic Resolution of Optically Pure 3-Alkanol by Pseudomonas cepacia Lipase-Catalyzed Transesterification with Vinyl Acetate in Organic Solvent

“…The E value sharply decreased with c in the range of above 0.55 (Fig. 1B) in PCL-catalyzed transesterification between VA and 2-alkanol in various organic solvents (14). In contrast, we observed that the optical resolution data fit Eq.…”

“…Table 4 shows that 1,2-dichloroethane, acetonitrile and acetone gave higher E than the other solvents. A similsr tendency has been reported in PCL-catalyzed transesterification between TB and secondary alcohol (18)(19)(20)(21) and also in the reaction between VA and 2-alkanol (14). Thus, we selected 1,2-dichloroethane and acetonitrile as the reaction solvents and also used hexane as a standard solvent in the following studies.…”

“…Furtheremore it has been reported that the optical resolution data did not fit the previously resolution format (5,(10)(11)(12)based on the observation: the E value increases with c in the range of below 0.5 in Pseudomonas cepacia lipase (PCL)-catalyzed transesterification with racemic sulcatol, ( )-6-methyl-5-hepten-2-ol, in chlorinated solvents (13). In the previous papers on PCL-catalyzed transesterification with 2-alkanol, we reported that the E value showed the maxima at around 0.5 of c in all systems studied (14) and that the reaction of enantiomerically enriched substrate was a powerful strategy for kinetic resolution of chiral compounds with high optical purity (15). So far, no information is available about quantitative analyses of the optical resolution data in kinetic resolution of chiral compounds with OH group at C-3.…”

“…In contrast, we observed that the optical resolution data fit Eq. (1) with E=23 and K=0.02 in the transesterification between triacetylglycerol (TA) and (RS)-83-OH in 1,2-dichloroethane at 30 as for the reversible reaction of TA with (RS)-2-octanol in 1,2-dichloroethane (E=18 and K=0.01 at 30 ) (14).…”

“…where c R and c S are the extents of conversion of (R) and (S) isomers in the racemate (14). Then we invetigated the analysis of optical resolution data by Eqs.…”