Synthesis of coumarin-based 1,3,4-oxadiazol-2ylthio-N-phenyl/benzothiazolyl acetamides as antimicrobial and antituberculosis agents

In an attempt to find new agents to fight against microbial infections, a series of coumarin-based 1,3,4-oxadiazol-2ylthio-N-phenyl/benzothiazolyl acetamides was synthesized starting from coumarin-3-carboxylic acid ethyl ester obtained through Knoevenagel and Pinner reaction. In vitro antimicrobial activity against several bacteria (S. aureus, B. cereus, E. coli, P. aeruginosa, K. pneumoniae, S. typhi, P. vulgaris, S. flexneri), fungi (A. niger, A. fumigatus, A. clavatus, C. albicans) and antimycobacterial activity against Mycobacterium tuberculosis H37Rv strain was assessed. This study shows to what extent the presence of various electron withdrawing/donating substituents on the phenyl or benzothiazole ring affects the activity profiles of the newer molecules. The relationship between activity profiles (MICs, 3.12-25 mu g/mL) and the lipophilic character (LogP) of the prepared products is also discussed and the MIC values of the active conjugates seem to correlate to some extent with the lipophilicity profiles. Two (5e and 6c) of the final analogues displayed promising antimycobacterial activity at 12.5 mu g/mL of MIC, half fold potent to the standard drug pyrazinamide (6.25 mu g/mL). Compounds were characterized by IR, H-1 NMR, C-13 NMR spectroscopy and elemental analysis.