Pyridine derivatives substituted by heterocyclic ring and phosphonoamino group, and anti-fungal agent containing same

A compound represented by the following formula (I) or a salt thereof:

• wherein
• R1 represents a hydrogen atom, a halogen atom, an amino group, R11—NH— wherein R11 represents a C1-6 alkyl group, a hydroxy C1-6 alkyl group, a C1-6 alkoxy C1-6 alkyl group or a C1-6alkoxycarbonyl C1-6 alkyl group, R12—(CO)—NH— wherein R12 represents a C1-6alkyl group or a C1-6 alkoxy C1-6 alkyl group, a C1-6 alkyl group, a hydroxy C1-6 alkyl group, a cyano C1-6 alkyl group, a C1-6 alkoxy group, or a C1-6 alkoxy C1-6 alkyl group or a partial structure represented by the formula:
• R2 represents a hydrogen atom, a C1-6 alkyl group, an amino group or a di C1-6 alkylamino group or a partial structure represented by the formula:
• one of X and Y is a nitrogen atom while the other is a nitrogen atom or an oxygen atom;
• ring A represents a substituted or unsubstituted benzene ring wherein the substitution is a halogen atom or 1 or 2 C1-6 alkyl groups;
• Z represents a single bond, a methylene group, an ethylene group, an oxygen atom, a sulfur atom, —CH2O—, —OCH2—, —NH—, —CH2NH—, —NHCH2—, —CH2S— or —SCH2—;
• R3 represents a pyridine ring which may have 1 or 2 substituents selected from the group consisting of a halogen atom, a cyano group, a C1-6 alkyl group, a C1-6 alkoxy group, a C1-6 alkoxycarbonyl group, a C3-8 cycloalkyl group, a C2-6 alkenyl group, and a C2-6 alkynyl group;
• and
• R4 represents a hydrogen atom or a halogen atom;
• provided that either R1 or R2 represents a partial structure represented by the formula: