Naturally occurring quinones. Part X. The quinonoid constituents of Tabebuia avellanedae(Bignoniaceae)

Two groups of quinones have been isolated from the heartwood of T. avellanedae, namely the naphthaquinones menaquinone-1, lapachol and its methyl ether, deoxylapachol, β-lapachone, α-lapachone, and dehydro-α-lapachone and the anthraquinones 1-hydroxy-, 1-methoxy-, 2-methyl-, 2-hydroxymethyl-, and 2-acetoxymethyl-anthraquinone, anthraquinone-2-aldehyde and 2-carboxylic acid, 2-hydroxy-3-methylanthraquinone and its 4-dihydrolapachenolyl ether, tabebuin. Lapachenole, quercetin, and o- and p-hydroxybenzoic acids were also isolated. The unusual coexistence of these two groups of quinones suggests that they are biogenetically related, the anthraquinones being derived from naphthalenic precursors by cyclisation. Deoxylapachol was cyclised in vitro to 2-methylanthraquinone.