Head group-modified sophorolipids: Synthesis of new cationic, zwitterionic, and anionic surfactants

Amino acid-glycolipid conjugates were prepared using carbodimide-mediated coupling methods. The amino acid units were multifunctional and possessed a para-aminobenzoic acid linker. The glycolipid used was a stearic sophoroside. The aim of preparing these modified sophorolipids was to increase their water solubility as well as to introduce sites at the polar head groups that permitted further chemical derivatization. After acidolytic or hydrogenolytic deprotection of the amino acid N-terminus or side chain, water-soluble compounds were obtained that displayed good surfactant properties. Critical micelle concentration values were clustered in the range of high 10(-6) to low 10(-5) M, and minimum surface tension values were below 40 mN m(-1). Two of the compounds represented more complicated structural classes, namely, gemini and bolaform surfactants.