Synthesis and biological activity profiles of atrial natriuretic factor (ANF) analogs

Several analogs of the atrial natriuretic factor (ANF) were synthesized by the solid-phase method using the acetamidomethyl (Acm) group for sulfhydryl protection. The compounds were tested in a receptor binding assay using bovine adrenal zona glomerulosa cell membranes and in the rat diuresis/natriuresis assay. Substitution of tyrosine in position 116 of ANF(101–126) and of the analog [3-Mpr¹⁰⁵]ANF(105–126)(3-Mpr = 3-mercaptopropionic acid) did not alter the biological activity profiles and, therefore, these two analogs in radioiodinated form will be useful for enzymatic degradation and clearance studies. Replacement of 3-mercaptopropionic acid with 2-mercaptopropionic acid in [3-Mpr¹⁰⁵]ANF(105–126) resulted in an analog with very low potency in both assay systems, presumably as a consequence of the steric bulk and/or local conformational restriction produced by the methyl group attached to the α-carbon in position 105. The analog [3-Mpr¹⁰⁵, Nva¹⁰⁹]ANF(105–126)(Nva = norvaline) showed very low affinity in the receptor binding assay but displayed considerable diuretic/natriuretic activity. The obtained biological activity profiles suggest that in comparison with other ANF peptides the des-amino ANF(105–126) analogs may have a somewhat longer half-life in vivo or, alternatively, may indicate a more complex situation of ANF receptor or binding site heterogeneity.