Synthesis and dopamine receptor modulating activity of lactam conformationally constrained analogues of Pro-Leu-Gly-NH2

Article abstract of DOI:10.1021/jm00054a010

A series of analogues of the potent analogue of Pro-Leu-Gly-NH₂ (PLG), 2- oxo-3(R)-[(2(S)-pyrrolidinylcarbonyl)amino]-1-pyrrolidineacetamide (2) were synthesized in which the (R)-γ-lactam residue of 2 was replaced with a (R)- β-lactam, (R)-aminosuccinimide, (R)-cycloseryl, (R)-δ-lactam, (R)-ε- lactam, or (S)-ε-lactam residue to give analogues 3-8, respectively. These substitutions were made so as to vary the ψ₂ torsion angle. The analogues were tested for their ability to enhance the binding of the dopamine receptor agonist ADTN to the dopamine receptor. Analogues 3-6 and 8 exhibited dose- response curves that were bell-shaped in nature with the maximum effect occurring at a concentration of 1 μM. Analogue 7 was inactive. Analogues 3 and 4 were found to be as effective as PLG, while analogues 5, 6, and 8 appeared to be more effective than PLG in terms of enhancing the binding of ADTN to dopamine receptors. The activity of analogues 3-6 and 8 with their ψ₂ angles in the vicinity of that observed in a type II β-turn is consistent with the hypothesis that this type of turn is the bioactive conformation of PLG.