Biaryl amino acid templates in place of D-Pro-L-Pro in cyclic beta-hairpin cationic antimicrobial peptidomimetics.

The turn-forming D-Pro-L-Pro template has been frequently used to promote regular beta-hairpin conformations in cyclic protein epitope mimetics. Here the use of three isomeric biaryl templates has been studied as alternatives to D-Pro-L-Pro in the preparation of beta-hairpin peptidomimetics. The o,o'- o,m'- and m,m'-isomers of carboxymethyl- and aminomethyl-substituted biaryl templates have been incorporated into novel macrocyclic mimics of the naturally occurring cationic antimicrobial peptide protegrin I. The presence of the o-carboxymethyl-o'-aminomethyl-biaryl template within the macrocyclic peptide resulted in the appearance of slowly interconverting atropisomers. Although none of the resulting mimetics adopted stable beta-hairpin structures in aqueous solution, they all nevertheless retained a significant antimicrobial activity against Gram positive and Gram negative bacteria. These mimetics provide interesting starting points for an optimization program in the search for potent and novel antimicrobial compounds.