An Efficient Synthesis of Cytosporone B

Abstract

The fungal polyketide cytosporone B (Csn-B) displays diverse biological activities, and is an important small molecule probe for the studies on biological progress thus that its efficient synthesis attracts much attention. In this study, the commercial available 1-(3,5-dihydroxyphenyl)ethanone was used as starting material. After converting to benzyl ether, the product 1-(3,5-dibenzyloxyphenyl)ethanone was treated with sulfur powder and morpholine followed by hydrolysis in one pot to afford the key intermediate 3,5-dibenzyloxyphenylacetic acid via Willgerodt-Kindler reaction. Respectively, the 3,5-dibenzyloxyphenylacetic acid was converted to Csn-B or secocurvularin (67.3% overall yield) through esterification, Friedel-Crafts acylation reaction and deprotection procedures in 5 steps totally. Cytosporone A (Csn-A) was obtained in 65.3% yield through hydrolysis of Csn-B and cytosporone C (Csn-C) was provided in 64.0% yield via reduction-cyclization of Csn-B. Our synthetic approach to Csn-B and its derivatives has the advantages of short pathways, high yield, economical starting material, and is suitable for large-scale preparation.