A novel intramolecular hydrogen bonding between a side-chain pyridine ring and an amide hydrogen of the peptide backbone in tripeptides containing the new amino acid, α,α-di(2-pyridyl)glycine

Four tripeptides (Z-AA1-2Dpy-AA3-OMe; AA1, AA3 = Gly, Aib) containing a novel amino acid, alpha, alpha-di(2-pyridyl)glycine (2Dpy), were synthesized by the modified Ugi reaction. NMR analysis clearly indicated that the 2Dpy-containing tripeptides except the peptide in which AA1, AA3 = Aib, adopt a unique conformation with two intramolecular hydrogen bonds between 2Dpy-NH and a pyridine nitrogen and between AA3-NH and another pyridine nitrogen. This conformation has so far not been reported. On the other hand, the peptide Z-Aib-2Dpy-Aib-OMe probably adopts a beta-turn structure which is stabilized by two intramolecular hydrogen bonds between 2Dpy-NH and a pyridine nitrogen and between AA3-NH and the C=O of the Z group.