STRUCTURE-BIOLOGICAL ACTIVITY RELATIONSHIP OF FLAVONOIDS FROM Boesenbergia rotunda (L.) Mansf. AND Kaempferia parviflora Wall. ex Baker.

Two flavanones (20 and 43) and five flavones (44-48) were isolated from the CH2Cl2 extracts of Boesenbergia rotunda and Kaempferia parviflora. Twenty-eight flavonoid derivatives (28-29, 33-34 and 49-72) were synthesized, among them seven were identified as new compounds. All collected flavonoids were examined on anti-bacterial, anti-tyrosinase and melanogenesis activities. Among twenty-two tested compounds, 6,8-dibromo-5,7-dihydroxyflavone (33) and 6,8-diiodo-5,7-dihydroxyflavone (34) exhibited the highest activity against all bacteria with MIC of 31.25-62.5 µM. They were bacteriostatic agent for Propionibacterium acnes and Staphylococcus aureus, and bactericidal agent for Streptococcus sobrinus, Streptococcus mutans and Salmonella typhi. The combination of 33 and 34 with commonly used antibiotic including chloramphenicol, tetracycline, streptomycin and ampicillin exhibited synergistic effect. Seventeen tested compounds did not show anti-tyrosinase activity (IC50 >100 µM). For melanogenesis activity, the methoxy group on A-ring played an important role in melanogenesis-stimulating activities. 5,7-dimethoxyflavone (49), 5-methoxy-7-ethoxyflavone (53), 5-methoxy-7-butoxyflavone (54) and 5,7,2´,3´,4´-pentamethoxyflavone (65) showed more than two-fold higher activity than theophylline although the concentration of compounds were ten-folds less. In addition, 5,7,3´,4´,5´-pentamethoxyflavone (67) showed strong activity at low concentration. At 3.125 µM, 67 still exhibited activity more than two-fold that of positive control.