Metabolites from the purple heartwood of mimosoideae. Part 3. Acacia crombei C. T. White: structure and partial synthesis of crombenin, a natural spiropeltogynoid

Abstract

Crombenin, 4,4′,6,6′,7-pentahydroxyisochroman-3′-spirobenzofuran-3(2H)-one, the first spiropeltogynoid, is related to the concomitant crombeone (8-hydroxypeltogynone) from which it is derived via oxidation with alkaline hydrogen peroxide of the chalcone intermediate. The method of synthesis and i.r. spectroscopy define the stereochemistry as either 2(3′)R,4′R or 2(3′)S,4′S. Crombenin is accompanied by the first natural 5,6-dihydroxyphthalide.