Antimicrobial constituents of Thompson seedless raisins (Vitis vinifera) against selected oral pathogens

From Thompson seedless raisins, four antimicrobial compounds were isolated, namely, oleanolic acid (1), oleanolic aldehyde (2), 5-(hydroxymethyl)-2-furfural (5), and rutin (8), together with four known inactive compounds. In an attempt to increase the resultant antimicrobial activity of 1, six derivatives were prepared. The compounds isolated and the derivatives 1a-1f were evaluated for their antimicrobial activity against two oral pathogens, Streptococcus mutans and Porphyromonas gingivalis. The MIC values ranged between 3.9 and 500 μg/mL.