Antifungal Diterpene Alkaloids from the Caribbean Sponge Agelas citrina: Unified Configurational Assignments of Agelasidines and Agelasines

Three new diterpene alkaloids - the hypotaurocyamines, (-)-agelasidines E and F (5-6), and the adeninium salt, agelasine N (9) - were isolated from the Caribbean sponge Agelas citrina along with six known natural products agelasines B-E (7, 10-12), 2-oxo-agelasine B (8), and (-)-agelasidine C (3). The chemical structures of 5, 6 and 9 were elucidated by analysis of NMR spectra and mass spectrometry. This represents the first report of natural products from the sponge A. citrina. Unified assignment of absolute configurations of the new compounds and known compounds were achieved by chemical correlation, quantitative measurements of molar rotations, and comparative analysis by van't Hoff's principle of optical superposition. (-)-Agelasidine C (3) exhibited potent antifungal and modest cytotoxic activity against human chronic lymphocytic leukemia (CLL) cells.