Cholic Acid-Derived Facial Surfactants with Long Side-Chain Quaternary Ammonium: Synthesis and Antimicrobial Activity Study

Four cholic acid cationic surfactants containing a flexible long aliphatic chain were synthesized efficiently. A long aliphatic chain was introduced first on the side-chain carboxyl of cholic acid by one-pot condensation reaction of cholic acid and C12–C18 amines using DCC (Dicyclohexylcarbodiimide) and HOBt (N-hydroxybenzotrizole) as condensation agents for the formation of an amide framework. Then reduction of the amide and quaternization gave a cationic group for strengthening hydrophilicity. This strategy offered a very straightforward and efficient method for access to the designed surfactants in good overall yields. Preliminary results show that an increase both in the length of the hydrophobic tail and in the number of charged groups lowered the CMC of cholic acid-derived cationic surfactants. Cholic acid-based cationic surfactants containing a flexible longer aliphatic chain and a quaternary ammonium had the highest antimicrobial activity.