Stereoisomeric effect on antimicrobial activity of a series of quaternary ammonium salts

Two homologous series of diastereoisomeric racemic +/- cis and +/- trans-N,N-dimethyl-N-alkyl-2-benzoyloxycyclohexylmethylammonium bromides with the number of carbon atoms in the alkyl chain from six to twenty (m = 6,8...20) were synthesised. Their structures have been elucidated by IR, UV and in some cases also with H-1 and C-13 NMR spectrometry. The title compounds were assayed for their antimicrobial activity on microorganisms S. aureus, E. coli and C. albicans. The highest antimicrobial activity was observed against S. aureus (log 1/MIC = 5.5 mol(-1) dm(3)) and the lowest against E, coli (log 1/MIC = 4.5 mol(-1) dm(3)). The +/- cis and +/- trans stereoisomers of all eight couples of diastereoisomeric compounds show differences in their physico-chemical characteristics (including partition coefficient and lipophilicity) which is also reflected in the different antimicrobial activity of these diastereoisomers. (C) 1998 Elsevier Science S.A.