CYLINDRICINES H-K, NOVEL ALKALOIDS FROM THE ASCIDIAN CLAVELINA-CYLINDRICA

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 alpha,beta-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 H-1 n.m.r., C-13 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.