Trikentramides A–D, Indole Alkaloids from the Australian Sponge <i>Trikentrion flabelliforme</i>

Abstract

Chemical investigations of two specimens of <i>Trikentrion flabelliforme</i> collected from Australian waters have resulted in the identification of four new indole alkaloids, trikentramides A–D (<b>9</b>–<b>12</b>). The planar chemical structures for <b>9</b>–<b>12</b> were established following analysis of 1D/2D NMR and MS data. The relative configurations for <b>9</b>–<b>12</b> were determined following the comparison of ¹H NMR data with data previously reported for related natural products. The application of a quantum mechanical modeling method, density functional theory, confirmed the relative configurations and also validated the downfield carbon chemical shift observed for one of the quaternary carbons (C-5a) in the cyclopenta­[<i>g</i>]­indole series. The indole-2,3-dione motif present in trikentramides A–C is rare in nature, and this is the first report of these oxidized indole derivatives from a marine sponge