Structure Determination of New Isomeric Naphtho[2,3-b]furan-4,9-diones from Tabebuia avellanedae by the selective-INEPT technique

Beside the known naphthoquinones, dehydro-α-lapachone ( 17 ) and lapachol ( 20 ), four new naphtho2,3-b]-furan-4,9-diones, i.e. the 2-acetyl-5-hydroxy. 2-acetyl-8-hydroxy. (?)-5-hydroxy-2-(1′-hydroxyethyl), and (±)-8-hydroxy-2-(1′-hydroxyethyl) derivatives 16, 15, 12 , and 13 , respectively, and the new compound benzob]furan-6-carboxaldehyde ( 8 ) have been isolated from a CHCl₃ extract of the inner stem bark of Tabebuia avellanedae LORENTZ ex GRISEB ., together with four known naphthofurandiones, a dihydroisocoumarin derivative, (?)–6-hydroxymellein, and five benzoic-acid and three benzaldehyde derivatives which have not been reported previously from this plant. Structure determination of the isomeric 5- and 8-hydroxynaphtho2,3?b]furan-4,9-diones was carried out unambiguously by a combination of selective-INEPT experiments and X-ray crystallographic analysis.