Gnetins: Resveratrol oligomers from Gnetum species

Gnetum leyboldii and G. schwackeanum (Gnetaceae) are lianas of Amazonia. The former contains in its wood the gnetins A, B, C, D and E for which the structures of rel-(1R,5R,6R,7R)-6-(4-hydroxyphenyl)-7-(3,5-dihydroxyphenyl)-2-(E) — (4-hydroxystyryl) — 4,8-dioxobicyclo | 3.2.1 | oct-2-ene; 1-hydroxy-5-(4-hydroxyphenyl)-6-(3,5-dihydroxyphenyl)-3-(E)-(4-hydroxystyryl)-7-oxobicyclo |2.2.2| oct-2-ene; rel-(2S, 3S)-4-hydroxy-2-(4-hydroxyphenyl)-3-(3,5-dihydroxyphenyl)-6-(E)-(4-hydroxystyryl)-2,3-dihydrobenzofuran; rel-(2S,3S)-4-hydroxy-2-(2,4-dihydroxyphenyl)-3-(3,5-dihydroxyphenyl)-6-(E)-(4-hydroxystyryl)-2,3-dihydrobenzofuran; and rel-(2S,3S)-4-hydroxy-2-(4-hydroxyphenyl)-3-[6-re/-(2s,3s)-4-hydroxy-2-(4-hydroxyphenyl)-3-(3,5-dihydroxyphenyl)-2,3-dihydrobenzofuranyl]-6-(E)-(4-hydroxystyryl)-2,3-dihydrobenzofuran were proposed, respectively. The fruits of G. schwackeanum contain the gnetins C and E.