Cylindricines H-K, Novel Alkaloids From the Ascidian Clavelina cylindrica

Abstract

Three novel reduced pyrrolo [2,1-j] quinolines (cylindricines H, I and K) and one novel pyrido [2,1-j] quinoline ( cylindricine J) have been isolated from two further Tasmanian collections of the ascidian Clavelina cylindrica. These alkaloids are all related in structure to cylindricines A-G which have been obtained previously from the same ascidian. Cylindricines H-J are the first acetoxycylindricines obtained. Furthermore cylindricines I and J are isothiocyanates, the first such compounds identified from an ascidian, while cylindricine H is a thiocyanate which, together with cylindricines F and G, are the only ascidian thiocyanates known. Cylindricine K is an α,β -unsaturated ketone with the carbonyl group in the 8-position rather than the more usual 4-position as found in cylindricines A-G. Identification of the new alkaloids was by ¹H n.m.r., ¹³C n.m.r., XHCORR, COSY and Fourier-transform i.r . Spectroscopy as well as high resolution e.i. mass spectrometry. Molecular modelling was used to assign relative stereochemistry. The geographical variation of the cylindricines is also reviewed.