Synthesis and antibacterial activity of new long-chain-alkyl bile acid-based amphiphiles

• Synthesis of some bile acid-derived cationic amphiphiles with a flexible long hydrocarbon tail.
• Antibacterial activity is interrelated with hydrocarbon tail and the number of charged groups.
• The hydrophobic tails play an important role in lowering the surface tension.

The efficient synthesis of some bile acid-derived cationic amphiphiles with a flexible long hydrocarbon tail was investigated. Firstly, the modification on the side-chain carboxyl of bile acids was carried out efficiently by one-pot amidation of bile acids and a long-chain aliphatic amine in the presence of HOBt and DCC to introduce a flexible long hydrocarbon tail. Then the hydrophilic concave side of bile acids with hydroxyl groups was further modified into cationic groups for strengthening hydrophilicity. This strategy offered a very straightforward and efficient method for access to the designed amphiphiles in good overall yields. The preliminary results showed that an increase both in the length of the hydrophobic tail and in the number of charged groups resulted in a decrease in the CMC of bile acid-derived cationic amphiphiles. And the bile acid-derived cationic amphiphiles with a flexible longer hydrocarbon tail and more positive charges had the highest antibacterial and antimicrobial activity.

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