Web Release Date: May 18,
Switching from S- to R-Selectivity in the Candida antarctica
Lipase B-Catalyzed Ring-Opening of 
-Methylated Lactones:
Tuning Polymerizations by Ring Size
and
Contribution from the Laboratory of Macromolecular and Organic Chemistry, Department of Chemical Engineering and the Biomodeling and Bioinformatics Group, Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
Received February 21, 2007
Abstract:
Novozym 435-catalyzed ring-opening of a range of -methylated lactones demonstrates
fascinating differences in rate of reaction and enantioselectivity. A switch from S- to R-selectivity was
observed upon going from small (ring sizes 
7) to large lactones (ring sizes 
8). This was attributed to
the transition from a cisoid to a transoid conformational preference of the ester bond on going from small
to large lactones. The S-selectivity of the ring-opening of the small, cisoid lactones was low to moderate,
while the R-selectivity of the ring-opening of the large transoid lactones was surprisingly high. The
S-selectivity of the ring-opening of the small, cisoid lactones combined with the established R-selectivity of
the transesterification of (aliphatic) secondary alcohols prevented polymerization from taking place. Ring-opening of the large, transoid lactones was R-selective with high enantioselectivity. As a result, these lactones
could be polymerized, without exception, by straightforward kinetic resolution polymerization, yielding the
enantiopure R-polyester with excellent enantiomeric excess (>99%).
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