Lipase catalyzed acetylation with vinyl

KINETIC RESOLUTION OF A SECONDARY ALCOHOL (4-TRIMETHYLSILYL-3-BUTYN-2-0L) BY LIPASE-CATALYZED ACETYLATION WITH VINYL ACETATE... 

Multiarm heteroblock star-type copolymers of poly(lactic acid) (PLA) and poly(e-CL), poly(LA-co-e-CL) were prepared via a chemoenzymatic route [90]. Firstly, ROP of e-CL was initiated regioselectively from 6-OH site of ethyl glucopyrano-side (EGP) (see also above) using porcine pancreatic lipase as catalyst followed by termination of the EGP-PCL-OH terminus by lipase-catalyzed acetylated using vinyl acetate. Subsequently, Sn-catalyzed ROP of lactide was initiated from 2-, 3- and 4-OH groups of EGP to give a copolymer consisting of one poly(e-CL) arm with M = 1300 and three PLA arms so that the M of the final product was 11500 (Scheme 4.25). 

Kinetic resoiution of 4-trimethyl iiyi-3-bu1yn-2-ol by lipase AK-catalyzed acetylation with vinyl acetate. 

The first enzymatic desymmetrizations of prochiral phosphine oxides was recently reported by Kielbasinski et al.88 Thus, the prochiral bis(methoxycarbonylmethyl)-phenylphosphine oxide 93 was subjected to the PLE-mediated hydrolysis in buffer affording the chiral monoacetate (RJ-94 in 72% ee and 92% chemical yield. In turn, the prochiral bis(hydroxymethyl)phenylphosphine oxide 95 was desymmetrized using either lipase-catalyzed acetylation of 95 with vinyl acetate as acyl donor in organic solvent or hydrolysis of 97 in phosphate buffer and solvent affording the chiral monoacetate 96 with up to 79% ee and 76% chemical yield. 

Less commonly used are transesterifications. For example, fluorinated benzoic esters can be treated with alcoholatcs to form the corresponding esters. Alternatively, lipase-catalyzed acetylation of fluorophenols with vinyl acetate has been reported. ... 

Examples of kinetic resolutions with lipases are numerous [9], Impressive enantioselectivities are often obtainable with secondary alcohols, e.g., in acetylations with vinyl acetate, or in hydrolysis of the racemic ester. Likewise, the corresponding amines can be resolved, e.g. by enantioselective acetylation with EtOAc as both acyl donor and solvent. This has been demonstrated by Gotor and coworkers using Novozym 435 [50]. The reaction (Scheme 13.3) follows Kazlauskas selectivity. In fact an impressive range of CALB (Novozym 435) catalyzed transformations on nitrogenated compounds have been collected in a recent review article [51]. 

Compound 168 is a key intermediate for the synthesis of prostaglandin or prostacyclin compounds. Scheme 5-50 shows its preparation via a retro Diels-Alder reaction and subsequent treatment. Using enzyme-catalyzed acetylation, Liu et al.80 succeeded in the asymmetric synthesis of enantiomerically pure (+)/ (—)-156 and (—)-168 from the meso-Aio 164. When treated with vinyl acetate, meso-diol 164 can be selectively acetylated to give (+)-165 in the presence of Candida cyclindracea lipase (CCL). The yield for the reaction is 81%, and the enantiomeric excess of the product is 98.3%. 

A broad spectrum of racemic 2-hydroxy acids 65 were resolved via lipase-catalyzed enantioselective acetylation to their corresponding 2-acetoxy acids 66 using vinyl acetate as acyl donor in methyl Art-butyl ether as organic solvent. The unreacted enantiomer (R)-65 was recovered with ee values up to >99%.80... 

With vinyl acetate as the acyl donor, a lipase from Candida cylindracea (CCL) catalyzed the acetylation of a series of ( )-i 2j -flavan-4-ols, such as (77), to give (—)-(27( ,47( )-4-acetoxyflavans (78) and (+)-(2d, 4d )-flavan-... 

Enzymes other than CAL B have also been reported to operate under the biphasic conditions. CAL A and CAL B or a lipase from Mucor miehei were tested for the kinetic resolution of glycidol using vinyl acetate or vinyl butyrate. The enzymes were used either suspended in the free ILs or immobilized, when the reactions were carried out in [EMIM][NTf2] [71]. CALAwas inactive, butthe other two enzymes showed activity, albeit at 10-20% of that in the absence of COj whether they were free or immobilized. In general, the supported enzymes showed superior performance [71]. Chymotripsin, a specific protease for aromatic amino acids, was found to catalyze the hydrolysis or transesterification of the ethyl ester of N-acetyl-phenylalanine with propanol in scC02-[RMIM][PF5] (R = butyl or octyl) with or without added water [Eq. (15)]. 

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