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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

DL-threo-and DL-erythro-Cn-dihydrosphingosines (n=12, 14, and 16) were separated from the corresponding 2-amino-1, 3-alkanediols by repeated recrystallization of the N, O, O-triacetyl and N-acetyl derivatives. Ceramides having DL-threo-and DL-erythro-Cn-dihydrosphingosines were prepared by reactions of the bases with N-acyloxysuccinimides in tetrahydrofuran. CLC-MS analysis of O, O-di-TMS derivatives of the ceramides was carried out to find differences between threo and erythro isomers in mass spectra. One characteristic difference was observed in the relative intensity (RI) at m/e=M-103; i.e., the relative intensities of threo compounds (RI 40•`80%) were stronger than those of erythro isomers (RI 6•`14%). The ratios, RI(M-103)/RI(M-15), were 3.7•`6.8 and 0.8•`1.3 for threo and erythro compounds, respectively. These observations demonstrate the possibility of determining erythro and threo isomers by mass spectrometry.

This method uses pig eyes filled with cooked chestnuts serving as pseudonuclei with the goal of teaching dividing techniques of phacoemulsification and aspiration. The pseudonuclei simulate the various degrees of human lens nuclear sclerosis. The chestnuts are trimmed to lens size. After lens extraction through a self-sealing straight incision from the pig eyes, the chestnuts are inserted in the capsular bag through the incision, which is then sutured. These preparatory procedures were initially performed by experienced surgeons but after practicing phacoemulsification technique several times, inexperienced surgeons were able to complete the entire procedure, allowing them to practice phaco chop, divide and conquer, and nondividing phacoemulsification.

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OH], and different organic solvents ( ) in order to clarify the second order rate constants for (R)-(1) and (S)-(1), and the enantioselectivity which are affected by solvent 309Correspondence to: Hirofumi Hirata, Department of Bioscience and Technology, School of Engineering, Hokkaido Tokai University, 5-1 Minamisawa, Minami-ku, Sapporo 005-8601, JAPAN E-mail: hirata@db.htokai.ac.jp Accepted February 26, 2007 (received for review December 7, 2006 Journal of Oleo Science Copyright ©2007 by Japan Oil Chemists ' Society J. Oleo Sci. 56,(6) 309-317 (2007) Abstract: Lipase-catalyzed acetylation of 2-alkanol with vinyl acetate has been studied kinetically using Burkholderia cepacia lipase (BCL), enantiomerically pure (R)-and (S)-2-alkanols and different organic solvents. The rate equation was derived by the steady state method for the simplified mechanism. The second order rate constants (k R and k S ) for (R)-and (S)-2-alkanols were evaluated from the slopes of the double reciprocal plots, v -1 vs. [2-alkanol] -1 , where v is the initial rate of the reaction. The log k R value increased with the solvent hydrophobicity log P, where P is a partition coefficient of a given solvent between octanol and water. The log k S value also increased with log P except the bulky solvents such as 1,4-dioxane and cyclohexane, in which the rates were faster than those expected from the log k S vs. log P plot. The slope of log k S vs. log P plot was larger than that for (R)-2-alkanol. Thus, log E (E=k R /k S : enantioselectivity) decreased with log P except the bulky solvents. The rate constants and the enantioselectivity were different depending on the structure (carbon number CN) of 2-alkanol. The log E vs. CN plot was minimized at CN=8 and 10 and the log k S vs. CN plot maximized at CN=8 and 10. In contrast the log k R vs. CN plot showed a different feature from the log E vs. CN plot. These facts suggest that dependence of E on CN is more strongly affected by the reactivity of (S)-2-alkanol than that of (R) isomer in this acetylation. Kinetic Studies on Lipase-Catalyzed Acetylation of 2-Alkanol with Vinyl Acetate in Organic Solvent