New flavonoids from the stem bark of Erythrina caffra Thunb.

Three new flavonoids 5,7-dihydroxy-2',4'-dimethoxy-5'-formylisoflavanone (erycaffra E) (1), 5,7-dihydroxy-3'-(2″-hydroxy-3″-methylbut-3-enyl)-5'-(3‴-hydroxy-3‴-methyl-trans-but-1-enyl)-4'-methoxyflavanone (erycaffra D) (2) and 5,7-dihydroxy-4'-methoxy-3',5'-di-(3″-hydroxy-3″-methyl-trans-but-1-enyl)flavanone (erycaffra F) (3) were isolated from the stem bark of Erythrina caffra along with four known compounds, namely 5,4'-dihydroxy-6-(3″-methylbut-2″-enyl)-5‴-hydroxyisopropyldihydrofurano[2‴,3‴:7,8]isoflavone (isosenegalensein) (4), 5,7-dihydroxy-4'-methoxy-3'-(3″-methylbut-2-enyl)-5'-(3‴-hydroxy-3‴-methylbut-1-enyl)flavanone (burttinone) (5), 5,4'-dihydroxy-5″-hydroxyisopropyldihydrofurano[2‴,3‴:7,6]isoflavone (erythrinin C) (6) and 5,4'-dihydroxy-6″-hydroxymethyl-6″-methylpyrano[2″,3″:6,7]isoflavone (erysubin B) (7). The structures were determined on the basis of spectroscopic data (1D, 2D NMR and MS) and by comparison with literature values.