Prenylated flavonoids with PTP1B inhibitory activity from the root bark of Erythrina mildbraedii

Phytochemical study on an EtOAc-soluble extract of the root bark of Erythrina mildbraedii resulted in the isolation of six prenylated flavonoids 1 - 6. Based on physicochemical and spectroscopic analyses, their structures were determined to be new natural products licoflavanone-4'-O-methyl ether (1), 2',7-dihydroxy-4'-methoxy-5'(3-methylbut-2 -enyl)isoflavone (2), and (3R)-2',7-dihydroxy-3'-(3-methylbut-2-enyl)-2''',2'''-dimethylpyrano[5''',6''' : 4',5']isoflavan (3), along with three known compounds erythrinin B (4), abyssinin 11 (5), and parvisoflavone B (6). All the isolates, except for compound 4, inhibited PTP1B activity in vitro with IC50 values ranging from 5.3 to 42.6 mu M. This result further suggests that the prenyl group on the B ring of flavonoids plays an important role in suppressing the enzyme PTP1B.