Cholic acid as template for multivalent peptide assembly.

Cholic acid, an amphiphilic steroid containing several selectively addressable functionalities, was exploited as a rigid template for multivalent peptide assembly. Thus, cholic acid-based templates suitable for chemoselective peptide ligation were synthesized, in which maleimide or bromoacetyl moieties were selectively introduced at the 3alpha, 7alpha, 12alpha-positions of cholic acid with varied length of linkers. Three peptides were chosen and tested for the chemoselective ligation. These include the HIV-1 peptide inhibitor DP178, the universal T-helper epitope derived from tetanus toxoid (830-844), and the minimum epitope sequence of the HIV-neutralizing antibody 2F5. It was found that the maleimide-functionalized templates are highly efficient for the ligation of all the peptides, while bromoacetyl templates led to low yield of ligation. Circular dichroism (CD) spectroscopic studies of the multivalent peptides (10a and 11a) containing three strands of peptide DP178 indicate that the template-assembled peptides form three alpha-helix bundles with significantly enhanced alpha-helix contents than the single peptide. The results suggest that cholic acid is a valuable template for constructing alpha-helix bundles that may be useful as mimics of conformational epitopes for vaccine development.