title: Solvent effect observed in nucleophilic substitution of 4'-(benzoyloxy)cordycepin with AlMe(3): stereochemical evidence for S(N)i mechanism.
abstract: Nucleophilic substitution between the 4'-benzoyloxy derivative of cordycepin (3'-deoxyadenosine) and AlMe(3) proceeds mostly with retention of configuration at the 4'-position: the 4'-benzoyloxy substrate having the beta-d-configuration (8a) gave the 4'-methylated beta-d-nucleoside (9a) with a high diastereomeric excess, while the substrate 8b having the opposite 4'-configuration gave the corresponding alpha-l-isomer (9b) with a comparatively lower stereoselectivity. The S(N)i mechanism is proposed for this reaction (from 8 to 9). The polarity of the solvent has a significant influence on the stereoselectivity, especially for the formation of 9b.
authors.affiliation: School of Pharmaceutical Sciences, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Kubota
authors.forename: Mayumi
authors.initials: M
authors.lastname: Kunikata
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Haraguchi
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Tanaka