Vosamidines A–C, Polycyclic 2-Aminoimidazole Alkaloids from a Marine Calcareous Sponge Vosmaeropsis wilsoni

Vosamidines A-C (1-3), three polycyclic 2-aminoimidazole alkaloids, were isolated from a marine calcareous sponge, Vosmaeropsis wilsoni. Their structures were determined by extensive analysis of spectroscopic and spectrometric data, along with ECD computational studies. Vosamidine A possesses a 6/5/5/5/6/15(6)(5)-fused ring system based on a unique pentacyclic core. Vosamidine B is an oxidized and ring rearranged derivative of 1. Vosamidine C possesses an unusual 5/5/6/5/5/8 hexacyclic ring system incorporating a thioether ring. Plausible biosynthetic pathways for 1-3 are proposed. Compounds 1 and 2 had modest inhibition in the oncogenic fusion protein kinase DNAJB1-PKAcα assay.