Chemical constituents of the Combretaceae. Part II. Substituted phenanthrenes and 9,10-dihydrophenanthrenes and a substituted bibenzyl from the heartwood of Combretum molle

Four new compounds have been isolated from the heartwood of Combretum molle and have been shown both by chemical and spectroscopic methods and by synthesis to be 4,7-dihydroxy-2,3,6-trimethoxyphenanthrene, 4,6,7-trihydroxy-2,3-dimethoxy- and 2,6-dihydroxy-3,4,7-trimethoxy-9,10-dihydrophenanthrene, and 3,4′-dihydroxy-4,5-dimethoxybibenzyl. The relevance of the latter compound to the biogenesis of the phenanthrenes and 9,10-dihydrophenanthrenes is discussed. The phenol (C′) from Combretum apiculatum has now been unambiguously established by total synthesis to be 6,7-dihydroxy-2,3,4-trimethoxyphenanthrene.