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 an 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 NMR spectroscopy and mass spectrometry. This represents the first report of natural products from the sponge A. citrina. Unified assignment of the absolute configurations of the new compounds and known compounds was 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. Chiroptical methods, including molar rotations and application of van't Hoff's principle of optical superposition, were applied to solve the configurations of two new diterpenoid alkaloids isolated from Agelas citrina, a sponge endemic to the Bahamas.