Retrodihydrochalcones in Sorghum species: Key intermediates in the biosynthesis of 3-deoxyanthocyanidins?

Two new open chain flavonoids were isolated from the butanediol/ethanol extract of Sorghum bicolor (L.) Moench leaf sheaths by fractionation and purification processes. This work led to the structural characterization of the 3-(2,4,6-trihydroxyphenyl)-1-(4-hydroxyphenyl)-propan-1-one (or 2,4,4 ',6-tetrahydroxydihydrochalcone) 1, and 3-(2,6-dihydrox-4-methoxyphenyl)-1-(4-hydroxyphenyl)-propan-1-one (or 2,4 ',6-trihydroxy-4-methoxydihydro-chalcone) 2. The structures of these flavonoids were determined by extensive spectroscopic analyses, including UV, ESIMS, HRESIMS, 1D and 2D NMR. The chemical properties of 1 were similar to those earlier described in literature for apiforol, never fully characterized. These results led us to re-question the real structure of this flavan-4-ol, which is often described to be present in Sorghum and has even been considered as a key intermediate in the formation of Sorghum 3-deoxyanthocyanidins. (C) 2011 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.