A new indole alkaloid (1) was isolated from the tunicate Dendrodoa grossularia. The structure was determined by spectroscopic means, particularly extensive 1D and 2D NMR studies and chemical transformation. X- Ray crystallographic analysis of 2, obtained from 1 by treatment with Ac2O- pyridine, unambiguously provided the structure and the relative stereochemistry at C-5' of compound 2, and hence of 1.