title: Switching from S- to R-selectivity in the Candida antarctica lipase B-catalyzed ring-opening of omega-methylated lactones: tuning polymerizations by ring size.
abstract: 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=7) to large lactones (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%).
authors.affiliation: Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
authors.forename: Jeroen
authors.initials: J
authors.lastname: van Buijtenen
authors.forename: Bart A C
authors.initials: BA
authors.lastname: van As
authors.forename: Marloes
authors.initials: M
authors.lastname: Verbruggen
authors.forename: Luc
authors.initials: L
authors.lastname: Roumen
authors.forename: Jef A J M
authors.initials: JA
authors.lastname: Vekemans
authors.forename: Koen
authors.initials: K
authors.lastname: Pieterse
authors.forename: Peter A J
authors.initials: PA
authors.lastname: Hilbers
authors.forename: Lumbertus A
authors.initials: LA
authors.lastname: Hulshof
authors.forename: Anja R A
authors.initials: AR
authors.lastname: Palmans
authors.forename: E W
authors.initials: EW
authors.lastname: Meijer
mesh_terms: D001665:Binding Sites; D002384:Catalysis; D003198:Computer Simulation; D005656:Fungal Proteins / Q000737:chemistry; D007783:Lactones / Q000737:chemistry*; D008049:Lipase / Q000737:chemistry*; D008745:Methylation; D008958:Models, Molecular; D008968:Molecular Conformation; D011108:Polymers / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D005656:Fungal Proteins; D007783:Lactones; D011108:Polymers; D008049:Lipase; C431349:lipase B, Candida antarctica