Sclerin, a New Cytotoxic Cyclononapeptide from Annona scleroderma

A new cytotoxic cyclononapeptide, sclerin, cyclo(–Dab1–Ser2–Tyr3–Gly4–Thr5–Val6–Ala7– Ile8–Pro9–) (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.