Thermorubin. 1. Structure Studies

The structure of thermorubin, thought previously to be 5,7-dihydroxy-3,6-dimethoxy-2-[l’,3'-dihydroxy-2'-methoxycarbonyl-9'-xanthon-4'-yl)methyl] anthracene, is shown by physical and chemical evidence to be incorrect. A new structure, namely, 12-hydroxy-10,11-dimethoxy-3-methoxycarbonyl-8-carboxymethyl-9-[1'-oxo-3'-hydroxy-3'-(2'-hydroxyphenyl)-prop-2'-enyl]-1 H-2-oxanaphthacen-1-one, has been determined largely by an X-ray diffraction analysis, and this accounts for all of the previously observed chemical degradation results. The structure of trimethylthermorubin, obtained by simple methylation of thermorubin, is also elucidated.