DESIGN OF A HELICAL BACKBONE, CONFORMATION OF SEQUENTIAL TRIDECAPEPTIDE CONTAINING Z-DEHYDROPHENYLALANINE RESIDUES

Sequential peptides containing Z-dehydrophenylalanine (Delta(Z)Phe) re sidues, Boc-(L-Leu-Delta(Z)Phe)(n)-L-Leu-OMe (n=2-6), were synthesized , and their conformations in solution were investigated using H-1 NMR and CD spectroscopy. Tridecapeptide (n=6) was shown to adopt a helical conformation in CDCl3 by observation of successive NiH<->Ni+1H nuclea r Overhauser effects. Solvent accessibility of NH resonances For pepti de n=6 in CDCl3 indicated that all the NI-I groups except those belong ing to the N-terminal Leu-Delta(Z)Phe moiety participate in intramolec ular hydrogen bonding. Similar accessibility was observed for peptides n=2-5. Thus, peptides n=2-6 in CDCl3 show a (i+3)-->i intramolecular hydrogen bonding pattern characteristic of a 3(10)-helix. CD spectra o f peptides n=3-6 in chloroform showed exciton couplers around 280 nm w ith a negative peak at longer wavelengths, corresponding to a right-ha nded helical sense. Delta(Z)Phe residue was shown to be effective to d esign a 3(10)-helical-type backbone using sequential peptides of(X-Del ta(Z)Phe) unit.