Halichonic acid, a new rearranged bisabolene-type sesquiterpene from a marine sponge Halichondria sp

A new compound, halichonic acid (1), was isolated from a marine sponge Halichondria sp., together with (6R,7S)-7-amino-7,8-dihydro-α-bisabolene (2). The structure of 1 was elucidated by spectroscopic analysis and ECD spectrum calculation to be a rearranged bisabolene-type sesquiterpene having a 3-azabicyclo[3.3.1]nonene moiety. Compound 2 was cytotoxic against HeLa cells with an IC50 value of 50 μM, whereas 1 did not show cytotoxicity even at 50 μM. It is possible that 1 is biosynthesized from farnesyl pyrophosphate and glycine, with rearrangement.