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J Am Chem Soc ; 129(23): 7393-8, 2007 Jun 13.
Artigo em Inglês | MEDLINE | ID: mdl-17508749

RESUMO

Novozym 435-catalyzed ring-opening of a range of omega-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 or=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%).


Assuntos
Lactonas/química , Lipase/química , Sítios de Ligação , Catálise , Simulação por Computador , Proteínas Fúngicas/química , Metilação , Modelos Moleculares , Conformação Molecular , Polímeros/química , Estereoisomerismo
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