The effect of decreasing the size of the ring present in deamino-oxytocin by one methylene group on its biological properties. The synthesis of 1-mercaptoacetic acid-oxytocin.

I-Mercaptoacetic acid-oxytocin, an analogue of deaminooxytocin in which the size of the disuhide ring is decreased from 20 to 19 members, has been synthesized and isolated in highly purified form by means of countercurrent distribution. The analogue possessed 4 units per mg of avian vasodepressor activity, 25 units per mg of oxytocic activity, 50 units per mg of milk-ejecting activity, 0.1 unit per mg of antidiuretic activity, and 0.01 unit per mg of pressor activity. The mixed disulfide of L-cysteine and mercaptoacetic acid has been synthesized, and its chromatographic behavior in the Beckman/Spinco amino acid analyzer has been shown to be the same as that of the mixed disulfide produced by acid hydrolysis of I-mercaptoacetic acid-oxytocin.