Synthesis, stereochemistry, and antimicrobial activity of 2,6-diaryl-3-(arylthio)piperidin-4-ones

A series of novel 2,6-diaryl-3-(arylthio)piperidin-4-ones have been synthesized by reaction of arylthioacetones, substituted aromatic aldehydes, and methylamine/ammonium acetate and their structures elucidated by H-1, C-13, and 2D NMR (H, H-COSY, C, H-COSY, HMBC, and NOESY) spectroscopy. The NMR data reveal that all these piperidones exist in chair conformation with the 2,6-diaryl groups equatorially oriented, while the arylthio group prefers to be in either an equatorial or axial orientation depending on whether the substituent in the 2,6-diaryl rings is present in 4- or 2-position, respectively. In the case of NH-2,6-diaryl-3-(arylthio)piperidin-4-ones with o-substituted 2,6-diaryl groups, the arylthio group prefers the axial orientation presumably in a bid to minimize the steric and/or electronic repulsion. The arylthiopiperidin-4-ones exhibit significant antibacterial activity against Staphylococcus aureus, Vibrio cholerae, Salmonella typhi, and Escherichia coli and antifungal activity against Candida albicans and Aspergillus niger.