Peptide derivatives

A compound of Formula (1):

• wherein
• R1 represents a group selected from the following formulae:
• wherein R8 represents an amino group, an aminomethyl group or
• (wherein R9 represents a hydrogen atom, an amino group, a hydroxy group, an acyl group or an alkoxycarbonyl group having an optionally substituted linear or branched C1-C6 alkyl as its alkyl moiety, R10 represents an amino group, one of X and Y represents ═CH— and the other represents ═N—);
• R2 represents a hydrogen atom or a linear or branched C1-C6 alkyl group;
• R3 represents:
• or
• —(CH2)m—R11
• wherein m represents an integer of 1 to 6, and R11 represents:
• (wherein R12 represents a hydrogen atom or a linear or branched C1-C3 alkyl group) or
• R4 represents a hydrogen atom or a linear or branched C1-C6 alkyl group;
• R5 represents a linear or branched C1-C6 alkyl group or —CH2—R13 (wherein R13 represents an optionally substituted aryl group or an optionally substituted heterocyclic group);
• R6 represents a hydrogen atom or a linear or branched C1-C6 alkyl group;
• and
• R7 represents an optionally substituted linear or branched C1-C6 alkyl group or —SO2—R14 (wherein R14 represents an optionally substituted linear or branched C1-C8 alkyl group)
• or a tautomer or enantiomer of the compound, or a hydrate or pharmaceutically acceptable salt thereof.