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■ Asymmetric Dihydroxylation onto the α,β-Unsaturated Carboxylic Ester Derivatives of Camptothecin

Keiko Tagami,* Shuzo Takagi, Shigeki Sano, Motoo Shiro, and Yoshimitsu Nagao

*Faculty of Pharmaceutical Science, Mukogawa-Women's University, 11-68 Koushien Kyuban-Cho, Nishinomiya, Hyogo 663-8179, Japan

Abstract

Dihydroxyalkanoic ester derivatives (4a,b) and (5a,b) of 20S-camptothecin (1) were diastereoselectively synthesized by exploiting osmium-catalyzed asymmetric dihydroxylation based on the Sharpless procedure. The absolute configuration of the newly formed chiral centers, the 2’ and 3’ positions of the 20-alkanoyl side chain of 4a,b and 5a,b was determined by the chemical correlation with the known chiral dihydroxyalkanoic acids.