Tripeptides having an antidepressive and prolactin-releasing action

DETAILED DESCRIPTION What we claim is: 1.
A tripeptide of the formula ##SPC2## wherein X is alkyl having 3 to 8 carbon atoms, cycloalkyl having 5 to 7 carbon atoms, or aralkyl having 1 or 2 carbon atoms in the alkyl portion thereof.
2.
A tripeptide as in claim 1 wherein X is n-propyl.
3.
A tripeptide as in claim 1 wherein X is isobutyl.
4.
A tripeptide as in claim 1 wherein X is n-pentyl.
5.
A tripeptide as in claim 1 wherein X is .
beta.
-phenylethyl.
6.
A tripeptide as in claim 1 wherein X is n-hexyl.
7.
A tripeptide as in claim 1 wherein X is cyclohexyl.




Description:
It is already known that the tripeptide Glu-his-pro-NH.
sub.
2 (TRH) does not only aid the liberation of thyreotropic hormone but also the release of prolactin (German Offenlegungsschrift No.
2,253,274) and furthermore has an anti-depressive action (U.
S.
Pat.
No.
3,737,549).
However, the TRH which has been hitherto examined, especially with regard to the three actions mentioned, has the disadvantage of the strong thyreotropin -releasing effect when used as an anti-depressive drug and as a lactation-promoting factor.
It has now been found, surprisingly, that by a relatively small substitution in the TRH molecule, compounds may be prepared in which the TRH effect is insignificant, but the prolactin-releasing and anti-depressive action remains nearly unchanged.
With these compounds there is no risk of hyperthyreosis.
The present invention relates to tripeptides of the general formula I ##SPC1## wherein X is alkyl having 2 to 8 carbon atoms, a cycloalkyl radical having 5 to 7 carbon atoms or an aralkyl radical having 1 or 2 carbon atoms in the alkyl portion.
The invention further relates to a process for preparing these peptides, wherein either A.
Z-Histidine-azide is reacted with a proline derivative of the general formula II ##EQU1## wherein X has the above meaning and Z is the benzylcarboxy radical, the N radical Z is subsequently removed by hydrogenation and the compound formed is reacted with a pyroglutamic acid active ester or B