Enantioselective ring-opening polymerization

Lipase catalysis is often used for enantioselective production of chiral compounds. Lipase induced the enantioselective ring-opening polymerization of racemic lactones. In the lipase-catalyzed polymerization of racemic (3-BL, the enantioselec-tivity was low an enantioselective polymerization of (3-BL occurred by using thermophilic lipase to give (/ )-enriched PHB with 20-37% enantiomeric excess (ee). ... 

Optically active polyesters were synthesized by lipase CA-catalyzed ring-opening polymerization of racemic 4-methyl or ethyl-e-caprolactone. The (5 )-isomer was enantioselectively polymerized to produce the polyester with >95% ee. Quantitative reactivity of 4-substituted e-caprolactone using lipase CA as catalyst was analyzed. The polymerization rate decreased by a factor of 2 upon the introduction of a methyl substitutent at the 4-position. Furthermore, 4-ethyl-8-caprolactone polymerized five times slower than the 4-methyl-8-caprolactone. This reactivity difference is strongly related to the enantioselectivity. Interestingly, lipase CA displayed 5 -selectivity for 4-methyl or ethyl-8-caprolactone, and the enantioselectivity was changed to the (f )-enantiomer in the case of 4-propyl-8-caprolactone. 

Ring-opening polymerization of racemic a-methyl-/J-propiolactone using lipase PC catalyst proceeded enantioselectively to produce an optically active (S)-enriched polymer [68]. The highest ee value of the polymer was 0.50. NMR analysis of the product showed that the stereoselectivity during the propagation resulted from the catalyst enantiomorphic-site control. 

Ring-opening polymerization of a-methyl-substituted medium-size lactones, a-methyl-y-valerolactone and a-methyl-c-caprolactone, proceeded by using lipase CA catalyst in bulk [82]. As to (R)- and (S)-3-methyl-4-oxa-6-hexa-nolides (MOHELs), lipase PC induced the polymerization of both isomers. The apparent initial rate of the S-isomer was seven times larger than that of the R-isomer, indicating that the enantioselective polymerization of MOHEL took place through lipase catalysis [83]. 

Al-Azemi TF, Kondaveti L, Bisht KS (2002) Solventless enantioselective ring-opening polymerization of substituted-caprolactones by enzymatic catalysis. Macromolecules 35 3380-3386... 

Enantioselective Ring-Opening Polymerizations of Substituted Lactones Using Lipases... 

Lipase-catalyzed ring-opening polymerization of nine-membered lactone, 8-octanolide (OL), has been reported.165 Lipases CA and PC showed the high catalytic activity for the polymerization. Racemic fluorinated lactones with a ring size from 10 to 14 were enantioselectively polymerized by lipase CA catalyst to give optically active polyesters.166... 

Ligand Design in Enantioselective Ring-opening Polymerization of Lactide... 

Scheme 11.9 Enantioselective ring opening polymerization of methyl substituted 4-membered resulting in the formation of enantiomerically enriched (a) poly(S-2-methylpropionate) (S-30) and (b) poly(R-3-hydroxybutyrate) (R-32).

Figure 12.2 Enantioselective enzyme-catalyzed ring-opening polymerization of caprolactone from PHB-diol [10].

---