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A series of quaternary diammonium salts derivatives of 1,4:3,6-dianhydro-<span style="font-variant: small-caps;">l</span>-iditol were synthesized, using isommanide (1,4:3,6-dianhydro-<span style="font-variant: small-caps;">d</span>-mannitol) as a starting material. Both aromatic (pyridine, 4-(<i>N</i>,<i>N</i>-dimethylamino)pyridine (DMAP), (3-carboxamide)pyridine; <i>N</i>-methylimidazole) and aliphatic (trimethylamine, <i>N</i>,<i>N</i>-dimethylhexylamine, <i>N</i>,<i>N</i>-dimethyloctylamine, <i>N</i>,<i>N</i>-dimethyldecylamine) amines were used, giving eight gemini quaternary ammonium salts (QAS). All salts were tested for their antimicrobial activity against yeasts, <i>Candida albicans</i> and <i>Candida glabrata</i>, as well as bacterial <i>Staphylococcus aureus</i> and <i>Escherichia coli</i> reference strains. Moreover, antibacterial activity against 20 isolates of <i>S. aureus</i> collected from patients with skin and soft tissue infections (<i>n</i> = 8) and strains derived from subclinical bovine mastitis milk samples (<i>n</i> = 12) were evaluated. Two QAS with octyl and decyl residues exhibited antimicrobial activity, whereas those with two decyl residues proved to be the most active against the tested pathogens, with MIC of 16–32, 32, and 8 µg/mL for yeast, <i>E. coli,</i> and <i>S. aureus</i> reference and clinical strains, respectively. Only QAS with decyl residues proved to be cytotoxic in MTT assay against human keratinocytes (HaCaT), IC₅₀ 12.8 ± 1.2 μg/mL. Ames test was used to assess the mutagenic potential of QAS, and none of them showed mutagenic activity in the concentration range 4–2000 µg/plate.