Prenylflavonoids with antiallergic activity from the roots of Sophora flavescens Aiton

A methanol extract of the roots of Sophora flavescens Aiton, which is used as a crude drug Sophora Root ( Sophorae Radix ; " Kujin " in Japanese) and is listed in the Japanese Pharmacopoeia XIX, exerted antiallergic effects on ear passive cutaneous anaphylaxis (PCA) reactions in mice. From the extract, we isolated three previously undescribed prenylflavonoids, kujinfulavanonols A ( 1 ) and B ( 2 ) and kujinflavanone A ( 3 ), along with 34 known compounds ( 4 – 37 ). The absolute stereostructures of 1 – 3 were established by comparing experimental and predicted ECD data as well as through DP4+ analysis using the calculated 13 C NMR chemical shifts. Among the isolates, principal prenylflavonoide sophoraflavanone G ( 4 ) and matrine-type alkaloid oxymatrine ( 30 ) showed in vivo antiallergic activity at a dose of 50 mg/kg, p.o . To determine the mechanisms of this antiallergic effect, hyaluronidase inhibitory activity and antigen-induced degranulation inhibitory activity were examined in vitro . The results showed that i) sophoraflavanone G ( 4 , IC 50 = 34.1 μM), isoxanthohumol ( 12 , 49.1 μM), and kushenols X ( 14 , 22.9 μM) and I ( 15 , 40.1 μM) and ii) sophoraflavanone G ( 4 , IC 50 = 48.9 μM), leachianone A ( 5 , 28.9 μM), kushenol U ( 6 , 32.9 μM), (–)-kurarinone ( 7 , 90.5 μM), (2 S )-2′-methoxykurarinone ( 8 , 34.4 μM), and isoxanthohumol ( 12 , 58.5 μM), (2 R )-3β,7,4′-trihydroxy-5-methoxy-8-prenylflavanone ( 17 , 50.8 μM), and (2 R )-3α,7,4′-trihydroxy-5-methoxy-8-prenylflavanone ( 19 , 66.6 μM) were the active constituents.