Arginine-vasotocin, a synthetic analogue of the posterior pituitary hormones containing the ring of oxytocin and the side chain of vasopressin.

Several analogues of the posterior pituitary hormones, oxytocin I and the vasopressin# II and III, have been synthesized in this laboratory (l-5) in an attempt to detect possible correlations between chemical structures and biological properties in this group of compounds. Among these analogues is oxypressin IV (l), a cyclic octapeptide amide which contains a cyclic pentapeptide amide portion identical with the one existing in the vasopressins, linked to the tripeptide amide side chain that is present in oxytocin. It may be recalled that oxypressin possesses very low pressor activity, although it contains the ring structure that is present in the vasopressins. This may be attributable (2) to the absence of a strongly basic amino acid in the side chain, such as is present in the vasopressins. It was therefore of interest to synthesize and determine the biological properties of a compound which, like oxypressin, would also be a combination of the two moieties existing in osytocin and vasopressin but, unlike oxypressin and histidinevasopressin, would have a strongly basic amino acid in the side chain.