Progress toward the total synthesis of rhodexin A

ORGN 747

Michael E. Jung, jung@chem.ucla.edu, Dongwon Yoo, dongwon@chem.ucla.edu, and Hiufung V. Chu, hchu@chem.ucla.edu. 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.