Enantioselectivity, lipase-catalyzed polymer

Lipase catalysis is often used for the enantioselective production of chiral compounds indeed, lipase has been known to induce an enantioselective ROP of racemic lactones. In the lipase-catalyzed polymerization of racemic j8-butyrolactone (/3-BL), the enantioselectivity was low rather, an enantioselective polymerization of /3-BL occurred by employing a thermophilic lipase to yield the (R)-enriched polymer with 20-37% enantiomeric excess (e.e.) [101]. The enantioselectivity was greatly improved by copolymerization with seven- or 13-membered nonsubstituted lactones, using the lipase CA catalyst, whereby the e.e.-value reached almost 70% for the copolymerization of /3-BL with DDL [102]. It should be noted that, in the case of the lipase CA catalyst, the (S)-isomer was reacted preferentially to produce the (S)-enriched, optically active copolymer. The lipase CA-catalyzed copolymerization of i5-CL (six-membered) with DDL proceeded enantioselectively, to yield the (R)-enriched optically active polyester with an e.e.-value of 76%. 

PPF catalyzed an enantioselective polymerization of bis(2,2,2-trichloroethyl) tra 5-3,4-epoxyadipate with 1,4-butanediol in diethyl ether to give a highly optically active polyester (Scheme 9). °° The molar ratio of the diester to the diol was adjusted to 2 1 to produce the (-) polymer with enantiomeric purity of >96%. The polymerization of racemic bis(2-chloroethyl) 2,5-dibromoadipate with excess of 1,6-hexanediol using lipase A catalyst produced optically active trimer and pentamer. The polycondensation of 1,4-cyclohexanedimethanol with fumarate esters using PPL catalyst afforded moderate diastereoselectivity for the cis/trans monocondensate and markedly increased diastereoselectivity for the dicondensate product. 

Fluorinated lactones in the ring-size from 10 to 14 were enantioselectively polyunerized using lipase catalyst (173). The lipase CA-catalyzed polymerization of lO-fluorodecan-9-olide (10-membered) produced the optically active polymer with positive rotation. Interestingly, the corresponding oxyacid gave an optically inactive polyester. 

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