Synthesis, surface tension properties and antibacterial activities of amphiphilic d-galactopyranose derivatives

Several amphiphilic d-galactopyranose derivatives were synthesized in which the glycosidic moiety was separated from the hydrophobic alkyl chain (along 8 or 12 carbon atoms) by a spacer arm (butyl, butynyl or benzyl) in order to increase their surfactant properties and to obtain new antibacterial compounds. The surface tensions of the products were analyzed by Critical Micelle Concentration (CMC) and γCMC measurements and the antimicrobial activities were assayed against 10 bacterial species by Minimum Inhibitory Concentration (MIC) determination in liquid broth. The introduction of an aliphatic spacer arm increased the amphiphilic properties of the compounds and the CMC values were 40–500 times lower than their analogs without spacer arm. In the same manner, the spacer arms significantly increased the antibacterial power of the compounds. The products 4d and 4e exhibiting a C12 alkyl chain and an aliphatic spacer arm (butyl and butynyl) were the best surfactants (CMC = 0.023 and 0.032 mmol/L, respectively) and presented also the best antibacterial activities (MIC = 15.62 and 3.91 μg/mL for Micrococcus luteus, respectively). But the antibacterial activity of the newly synthesized products seemed to depend more on the cell wall composition of the bacteria than only on the amphiphilic character of the compounds.