Synthesis, surface active and antimicrobial properties of new alkyl 2,6-dideoxy-L-arabino-hexopyranosides

Abstract

Synthesis of alkyl 2,6-dideoxy-l-arabino-hexopyranosides was accomplished by the reaction of 1,5-anhydro-2,6-dideoxy-l-arabino-hex-1-enitol with fatty alcohols in dichloromethane, catalyzed by triphenylphosphine hydrobromide. Reaction with octanol and dodecanol gave the corresponding α-glycosides in 50% and 42% yield, the β-glycosides in 20% and 21% yield and the α-anomer of the Ferrier product in 10% and 9% yield, respectively. Deacetylation of the α-/β-glycosides with sodium methoxide in methanol afforded the amphiphilic l-arabino-hexopyranosides in 94-99% yield. The surface tension at the air-water interface of the octyl l-glycosides and of the dodecyl α-l-glycoside aqueous solutions at 35°C was measured with a du Noüy ring tensiometer and surface properties such as critical micelle concentration (CMC), relative surface excess, molecular area at the interface and Gibbs micellization free energy were evaluated. The stereochemistry of the hexopyranoside ring in unimers and aggregates is correlated to the hydrophobicity and packing efficiency on the air-water interface. The antibacterial and antifungal activities of the surface-active glycosides were evaluated using the paper disk diffusion method. The dodecyl α-l-arabino-hexopyranoside was quite active over Bacillus cereus and Bacillus subtilis, while low activity was found for this glycoside over Enterococcus faecalis and Listeria monocytogenes. The octyl glycosides tested showed low activity over almost all the above-mentioned bacteria, and also over the fungus Candida albicans. No inhibition of Salmonella enteritidis and of the filamentous fungus Aspergillus niger was detected for any of the compounds tested.