Substituted diketopiperazines and their pharmaceutical use as oxytocin antagonists

Substituted diketopiperazine compounds of formula (1) wherein R1 is 2-indanyl, R2 is 1-methylpropyl, R3 is 2-methyl-1,3-oxazol-4-yl and R4 and R5 together with the nitrogen atom to which they are attached represents morpholino, process for their preparation, pharmaceutical compositions containing them and their use in medicine as oxytocin antagonists are disclosed. These compounds are suitable for treating or preventing diseases or conditions mediated through the action of oxytocin, wherein said diseases are selected from: pre-term labour, dysmenorrhea, endometriosis, benign prostatic hyperplasia, sexual dysfunction, premature ejaculation, obesity, congestive heart failure, arterial hypertension, liver cirrhosis, nephritic or ocular hypertension, obsessive-compulsive disorder and neurospsychiatric disorders.