Structure-Function Relationship of PTH(1-11) Analogues Containing Combinations of Aib and (alpha-Me)Val

The N-terminal 1-34 segment of parathyroid hormone (PTH) is fully active in vitro and in vivo and it elicits all the biological responses characteristic of the native intact PTH. Recent studies reported potent helical analogues of the PTH(1-11) with helicity-enhancing substitutions. The present work describes the synthesis, biological activity and conformational studies of analogues obtained from the most active non-natural PTH(1-11) peptide H-Aib-Val-Aib-Glu-Ile-Gln-Leu-Nle-His-Gln-Har-NH2; specifically, the replacement of Val in position 2 with D-Val, L-(aMe)-Val and N-Isopropyl-Gly were studied. The synthesized analogues were characterized functionally by in-cell assays and their structures were determined by CD and NMR spectroscopy. To clarify the relationship between structure and activity, the structural data were used to generate a pharmacophoric model, obtained overlapping all the analogues. This model underlines the fundamental functional role of the side chain of Val2, and, at the same time, reveals that the introduction of conformationally constrained Ca-tetrasubstituted a-amino acids in the peptides increases their helical content, but does not necessarily ensure significant biological activity.