Sclerin, a New Cytotoxic Cyclononapeptide from Annona scleroderma

A new cytotoxic cyclononapeptide, sclerin, cyclo(⁻Dab¹⁻Ser²⁻Tyr³⁻Gly⁴⁻Thr⁵⁻Val⁶⁻Ala⁷⁻ Ile⁸⁻Pro⁸⁻) (1), was isolated from the methanol extract of the seeds of Annona scleroderma, together with the known metabolite, cyclosenegalin A, cyclo(⁻Pro¹⁻Gly²⁻Leu³⁻Ser⁴⁻Ala⁵⁻Val⁶⁻Thr⁷⁻) (2). The planar structures for the two compounds were established by comprehensive analysis of NMR and ESI-HRMS data, and the absolute stereochemistry was stablished by Marfey's method. Compound 1 showed moderate cytotoxic activity against the human prostate carcinoma cell line DU-145 at µM concentration.