Quinones and related compounds in higher plants. Part 16. Naphthoquinones from Radermachera sinica Hemsl. (Bignoniaceae)

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Abstract
Five new naphthoquinones, along with the known naphthoquinones lapachol (1), dehydro-α-lapachone (2), and dehydroiso-α-lapachone (3), have been isolated from the wood of Radermachera sinica Hemsl. The structures of these new quinones were established as 3-hydroxy-6-methoxydehydroiso-α-lapachone (4), 3-hydroxydehydroiso-α-lapachone (5), 3,6-dimethoxydehydroiso-α-lapachone (6), 3,5-dihydroxy-6-methoxydehydroiso-α-lapachone (7), and 2-isopropenylnaphtho[2,3-b]furan-4,9-quinone (8). These quinones were found to be mixtures of both enantiomers in various proportions, e.g., (3), 2R:2S, 4.5:1; (4), 2R,3R:2S,3S, 1:1; (5), 2R,3R:2S,3S, 4.2:1; (6), predominantly 2R,3R; and (7), predominantly 2S,3S.