A new class of antimicrobial biosurfactants: quaternary ammonium sophorolipids

New synthetic pathways are proposed for the production of a broad range of innovative sophorolipid amines and sophorolipid quaternary ammonium salts starting from microbially produced sophorolipids. The selective formation of an intermediate sophorolipid aldehyde proved to be a key synthetic step of the new derivatives. The sophorolipid quaternary ammonium salts were evaluated for their antimicrobial activity against Gram-negative and Gram-positive test strains. Minimum inhibitory concentration (MIC) values were determined for the active compounds. Derivatives with an octadecyl group on the nitrogen atom proved to be more active than the antibiotic gentamicin sulfate against all tested Gram-positive strains. The results show great promise for modified sophorolipids in the medical sector.