Structure and synthesis of some complex pyranoisoflavonoids from the bark of Dalbergia nitidula Welw. ex Bak.

Abstract

Exhaustive examination of the flavonoid content of the bark of Dalbergia nitidula revealed, amongst other substances a mixture of eight novel and complex (3S)-isoflavans [leiocin, leiocinol, nitidulin, nitidulan, heminitidulan] and (6aS,11aS)-pterocarpans [nitiducarpin, hemileiocarpin, nitiducol]. These insoflavonoids all possess the equivalent of prenyl or geranyl side-chains, which, with one exception, are cyclized to stereochemically related 2H-pyran moeities during biogenesis. Structures determined by physical means were substantiated for the isoflavans by a single synthesis.