TRH-like peptide derivatives as inhibitors of the TRH-degrading ectoenzyme

A compound of the formula I:

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• wherein:
• R1 is an optionally substituted 4-, 5- or 6-membered heterocyclic ring having one or more heteroatoms, in which at least one carbon atom of the ring is substituted with O or S;
• X1 is —CO— or —CS— or —CH2CO— or CH(R4) wherein R4 is H or optionally substituted alkyl or —COOH or —COOR11 wherein R11 is optionally substituted alkyl;
• X2 and X3 (which may be the same or different) are —CO— or —CS—;
• Z is —CH2— or —S— or —O— or —NH—;
• Q is O or S;
• R2 is H or optionally substituted alkyl or an optionally substituted carbocyclic ring;
• R3 is H or optionally substituted alkyl or an optionally substituted mono- or polycyclic ring, optionally having one or more heteroatoms in the ring(s) and optionally being a fused ring;
• or R2 and R3 together form an optionally substituted mono- or polycyclic ring optionally having one or more heteroatoms in the ring(s) and optionally being a fused ring;
• R5 and R6 (which may be the same or different) are H, or lower alkyl;
• R7 and R8 (which may be the same or different) are H, or optionally substituted lower alkyl;
• R9 and R10 (which may be the same or different) are H, or optionally substituted alkyl, or an optionally substituted carbocyclic ring;
• Y is —(CH2)n— where n is 0, 1, 2 or 3 provided that when R2 and R3 form part of the ring n is 0;
• provided that when R1 is:
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• and X1, X2 and X3 are —CO—
• and R5, R6, R7, R8, R9, R10 are H
• and Z is —CH2—
• and Q is O
• and Y is —(CH2)n— where n is 0,
• then R2and R3 are not both H;
• and pharmaceutically acceptable salts thereof.