Thioureas and their cyclized derivatives: Synthesis, conformational analysis and antimicrobial evaluation

Several single enantiomer thioureas have been synthesized and have been converted to their cyclic derivatives: 2-imino-thiazolidin-4-ones. The conformations of the thioureas have been determined in solution and in the solid state. In solution; an interconversion between the E,Z and Z,E conformations has been observed with ΔG^≠ values of around 50 kJ/mol whereas in the solid state they were shown to possess a Z,Z conformation. The thiazolidin-4-ones have been found to be present only in the anti-conformation. All compounds were screened for antimicrobial activity against 4 bacteria. For three of the compounds with the highest antimicrobial activity, the antimicrobial evaluation was expanded using more reference strains and clinical isolates. Among the compounds studied the 5-benzylidene-thiazolidine-4-ones 15RR, 15SS and the thiourea 5RR carrying a benzylpyrrolidine scaffold showed better antibacterial activities than the others. The fungicidal activities of all compounds were found to be better than those of the bactericidal activities.