Ten analogues derived from oxytocin, deamino-oxytocin and deamino-carba-oxytocin were prepared which contained a D-amino acid in the position 2 of the parent system. The following D-amino acids were introduced: tyrosine, phenylalanine, p-methylphenylalanine, p-ethylphenylalanine and O-ethyltyrosine. Combination of two structural features which alone lead to strong inhibitors (a suitable D-amino acid in position 2 and a penicillamine moiety in position 1) did not enhance the inhibitory effect.

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... mpounds containing D-tyrosine are weak agonists in the uterotonic assay; in case of 1-carba-analogues they can be converted into sulfoxides with low inhibitory activity. Analogues with D-phenylalanine substituted in the para-position are the most potent antagonists of the uterotonic effect of oxytocin (pA2 = 8.73) in vitro.