Synthesis of New Antibody Hypervariable Loop Mimetics Using a D-Pro-L-Apro Template

The aim of this work is to develop new approaches for the synthesis of protein epitope mimetics. These should be conformationally well defined molecules, that accurately mimick the stuctures and properties of exposed surface regions of peptides and proteins. Here we describe the synthesis and application of a dipeptide template, comprising L-4-aminoproline (Apro) and D-proline (D-Pro), to induce a stable b-hairpin conformation in a loop mimetic based upon the L3 complementarity determining region (CDR) of the anti-haemagglutinin antibody HC19. The loop mimetic comprises the cyclic peptide cyclo-(Leu-Trp-Tyr-Ser-Asn-His-Trp-Val-D-Pro-Apro-), which by NMR is shown to adopt a stable and well defined ß-hairpin conformation in DMSO solution. The observed conformation is essentially identical to that found for the L3 CDR in the crystal structure of the antibody Fab fragment.