Progress toward the total synthesis of rhodexin A

ORGN 747

Michael E. Jung,, Dongwon Yoo,, and Hiufung V. Chu, Department of Chemistry and Biochemistry, University of California, Los Angeles (UCLA), 607 Charles E. Young Drive East, Box 951569, Los Angeles, CA 90095-1569
Rhodexin A, the L-rhamnoside of sarmentogenin, is a cardiac glycoside that was isolated in 1951 from the leaves and roots of the evergreen Rhodea japonica. Rhodexin A is active against human leukemia K562 cells (IC50 19 nM). Like all cardiac glycosides, rhodexin A differs from most common steroids in that its AB and CD rings are cis rather than trans fused, and it possesses a tertiary hydroxyl group at C14 and a β-butenolide substituent at C17. A highly regio and stereoselective inverse-electron-demand Diels-Alder reaction was used to construct the BCD ring system of the steroid. The progress toward the total synthesis as well as the formation of the A ring and β-butenolide will be discussed.