Structural analysis of a novel antimutagenic compound, 4-Hydroxypanduratin A, and the antimutagenic activity of flavonoids in a Thai spice, fingerroot (Boesenbergia pandurata Schult.) against mutagenic heterocyclic amines.

Six compounds were isolated from fresh rhizomes of fingerroot (Boesenbergia pandurata Schult.) as strong antimutagens toward 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) in Salmonella typhimurium TA98. These compounds were 2',4',6'-trihydroxychalcone (pinocembrin chalcone; 1), 2',4'-dihydroxy-6'-methoxychalcone (cardamonin; 2), 5,7-dihydroxyflavanone (pinocembrin; 3), 5-hydroxy-7-methoxyflavanone (pinostrobin; 4), (2,4,6-trihydroxyphenyl)-[3'-methyl-2'-(3' '-methylbut-2' '-enyl)-6'-phenylcyclohex-3'-enyl]methanone (5), and (2,6-dihydroxy-4-methoxyphenyl)-[3'-methyl-2'-(3' '-methylbut-2' '-enyl)-6'-phenylcyclohex-3'-enyl]methanone (panduratin A; 6). Compound 5 was a novel compound (tentatively termed 4-hydroxypanduratin A), and 1 was not previously reported in this plant, whereas 2-4 and 6 were known compounds. The antimutagenic IC(50) values of compounds 1-6 were 5.2 +/- 0.4, 5.9 +/- 0.7, 6.9 +/- 0.8, 5.3 +/- 1.0, 12.7 +/- 0.7, and 12.1 +/- 0.8 microM in the preincubation mixture, respectively. They also similarly inhibited the mutagenicity of 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). All of them strongly inhibited the N-hydroxylation of Trp-P-2. Thus, the antimutagenic effect of compounds 1-6 was mainly due to the inhibition of the first step of enzymatic activation of heterocyclic amines.