Isolation and synthesis of TNF-alpha release inhibitors from Fijian kawa (Piper methysticum)

Two unique evidence that cancer incidence rates in Fiji were unusually low, compared with those of another Pacific islands and that green tea beverage is an acknowledged cancer preventive in Japan, allowed us to study a local beverage in Fiji, kawa (kava kava) or yangona (Piper methysticum) belonging to Piperaceae. We isolated five known kawapyrones (kavapyrones) (1-5) and a new additional kawapyrone, 7,8-epoxyyangonin (6), from kawa MeOH extract and subjected them to TNF-alpha (tumor necrosis factor-alpha) release assay from BALB/3T3 cells treated with okadaic acid, a tumor promoter. 5,6-Dehydrokawain (desmethoxyyangonin)(1) and yangonin (4) significantly inhibited TNF-alpha release with IC50 values of 17 microM and 40 microM; a potency as great as (-)-epigallocatechin gallate (EGCG) isolated from green tea extract. Among the experiments with 1-5, dihydrokawain (2) was unique in showing the strongest inhibitory activity against TNF-alpha release in mice, but the weakest activity in the cells. We synthesized 5,6-dehydrokawain (1) and yangonin (4) via three steps from the dianion of ethyl acetoacetate achieving a good yield and determined their conformations by high resolution NMR and x-ray crystallographic analysis.