Xanthine derivative and DPPIV inhibitor

A compound represented by the formula (I):

• wherein,
• R1 stands for a hydrogen atom, a substituted or unsubstituted C1-6 alkyl group, a substituted or unsubstituted C1-6 alkoxy C1-6 alkyl group, a substituted or unsubstituted C3-6 alkynyl group, a substituted or unsubstituted C2-7 cyanoalkyl group, a substituted or unsubstituted C6-12 aryl C1-6 alkyl group, a substituted or unsubstituted C1-12 aryloxy C1-6 alkyl group, or a group represented by the formula:
• wherein,
• a denotes 1;
• R5 and R6 both denote a hydrogen atom;
• and,
• R7 denotes a hydroxyl group, a substituted or unsubstituted C1-6 alkoxy group, a substituted or unsubstituted phenyl group, or a group represented by the formula —N(R3)R4,
• wherein, R3 and R4 are identical to or different from each other and individually denote a hydrogen atom, or a substituted or unsubstituted C1-6 alkyl group;
• R2 stands for a hydrogen atom, a substituted or unsubstituted C1-6 alkyl group, a substituted or unsubstituted C1-6 alkoxy C1-6 alkyl group, a substituted or unsubstituted 3 to 10-membered heterocyclic C1-6 alkyl group, a substituted or unsubstituted C6-12 aryl C1-6 alkyl group, a group represented by the formula:
• wherein,
• a denotes 1;
• R5 and R6 are identical to or different from each other and individually denote a hydrogen atom, C1-6 alkyl group, or phenyl group;
• and,
• R7 denotes a hydroxyl group, C1-6 alkyl group, C1-6 alkoxy group, a substituted or unsubstituted phenyl group, or a group represented by —N(R3)R4,
• wherein,
• R3 and R4 are identical to or different from each other and individually denote a hydrogen atom, C1-6 alkyl group, C3-7 cycloalkyl group, C3-6 alkynyl group, or C6-12 aryl group;
• or,
• R3 and R4 may be linked to each other to form a ring containing one or more heteroatoms,
• or a group represented by the formula:
• wherein Y denotes an oxygen atom, or a group represented by —NR8, wherein R8 denotes a hydrogen atom, or C1-6 alkyl group;
• and
• X stands for a phenyl group wherein position 2 may have a substituent selected from the group consisting of a hydrogen atom, hydroxyl group, fluorine atom, chlorine atom, methyl group, ethyl group, fluoromethyl group, ethenyl group, methoxy group, ethoxy group, acetyl group, cyano group, formyl group, and C2-7 aliphaticailcoxy carbonyl group, or a salt thereof.