Antibacterial flavanones and dihydrochalcones from Macaranga trichocarpa

Previously we had isolated two prenylated flavanones and two prenylated dihydrochalcones, macatrichocarpins A-D (1-4), from the acetone extract of the leaves of Macaranga trichocarpa. Re-examination of the fractions containing minor components resulted in the isolation of four more flavonoid derivatives, including two new prenylated dihydrochalcones, oxymacatrichocarpin C (5) and isomacatrichocarpin C (6). The structures of these compounds were determined by the analysis of UV, NMR, and mass spectral data. The eight isolated flavonoids were tested on eight pathogenic bacteria and found to be mostly moderate antibacterial agents, with the lowest MIC value of 26.5 μM achieved by the flavanone macatrichocarpin A (1) against Bacillus subtilis.