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 Delta G(not equal) 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-thiazo-lidine-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. (C) 2018 Elsevier B.V. All rights reserved.