Synthesis and biological property of alpha-human atrial natriuretic peptide analogs with a constrained or stereochemically modified cyclic moiety

Conformationally restricted analogs of alpha-human atrial natriuretic peptide (alpha-hANP) containing L- or D-penicillamine, or D-cysteine in place of cysteine residues at positions 7 and 23 were synthesized by the liquid phase procedure. Their biological properties in the assays of receptor binding and cyclic guanosine monophosphate (cGMP) accumulation employing rat vascular smooth muscle cells (VSMC), vasorelaxant activity using rat isolated aorta were evaluated. We found that the constrained and/or stereochemically altered ring moiety generally did not influence the receptor binding activity, however, cGMP accumulation and vasorelaxant activities were quite sensitive to conformational perturbation. Furthermore, a lack of correlation between cGMP accumulation activity and vasorelaxant activity was observed. Dissociation between these activities was typical in the case of DPen7,23]-alpha-hANP(7-28), which showed quite weak vasorelaxant activity in spite of its full cGMP accumulation and receptor binding potencies. This result suggests that cGMP accumulation alone is not sufficient to promote ANP-induced vasorelaxation, and that the other second messenger(s) may mediate this activity.