Antimicrobial Activity of N-Methyl 4-Piperidone-Derived Monoketone Curcuminoids Against Cariogenic Bacteria

Background/Objectives: Dental caries and candidiasis are major health problems worldwide. Dental caries is caused by cariogenic bacteria, especially those belonging to the Streptococcus genus, whereas candidiasis is caused by Candida species. In this study, the antimicrobial activity of a series of synthetic N-methyl-4-piperidone-derived monoketone curcuminoids (MKCs) against Candida albicans, C. krusei, and a representative panel of cariogenic bacteria was assessed. Methods: Fifteen MKCs were synthesized using an environmentally friendly base-catalyzed Claisen–Schmidt condensation between an aromatic aldehyde (R-PhCHO) and N-methyl-4-piperidone ethanol using NaOH as the catalyst. These compounds were evaluated for their antibacterial activity against a representative panel of cariogenic bacteria, along with their antifungal activity against Candida krusei and C. albicans. The antimicrobial activity was determined based on the Minimum Inhibitory Concentration (MIC) values. Results: Most of the compounds were obtained in about 2 h in yields ranging from 40 to 70%. None of the compounds displayed antifungal activity, even at 100 μg/mL, the highest tested concentration. Similarly, none of the compounds were active against Enterococcus faecalis. On the other hand, compounds 1 (R = H), 10 (R = 3,4,5-OMe), and 13 (R = 3-F) displayed moderate activity against Streptococcus mutans (13), S. salivarus (1), L. paracasei (1 and 10), S. mitis (1, 10, and 13), S. sanguinis (1, 10, and 13), and S. sobrinus (13), with MIC values of 250 μg/mL and 500 μg/mL. The presence of the N-methyl-4-piperidone ring was found to boost the antibacterial activity as compared to the corresponding acetone-derived MKCs. Moreover, the antibacterial activity of compounds 10 and 13 was associated with the presence and position of the fluor atom and the methoxy groups at the aromatic ring. Conclusions: This study contributed to a better understanding of the antimicrobial activity of MKCs, whose data in the literature are still scarce.