Avermectin derivatives

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

• wherein —X----Y— represents —CH═CH—, —CH2—C(═O)—, —CH2—CH2—, or —CH2—CH(R13)—;
• ---- between R1 and a carbon atom at the 4″-position represents a single or double bond;
• ---- between R2 and a carbon atom at the 5-position represents a single or double bond, with the provisos that
• 1) when —X----Y— represents —CH═CH— and ---- between R1 and a carbon atom at the 4″-position represents a double bond;
• R1 represents (R11)(R12)C wherein R11 represents a lower alkyl group (optionally substituted with from 1 to 3 members selected from the group consisting of a hydroxyl group, a halogen atom, an amino group, a hydroxyamino group, a mono(lower alkyl)amino group, a mono(lower alkoxy)amino group, an alkanoylamino group, an azide group, a heterocyclic group, a lower alkanoyloxy group, a heterocyclic carbonyloxy group where the heterocyclic moiety may be substituted with a halogen atom or a lower alkoxycarbonyl group, and a heterocyclic oxy group);
• a formyl group;
• a lower alkoxycarbonyl group, the alkyl moiety of which is optionally substituted with a heterocyclic group;
• —CH═N—OR3 wherein R3 represents a hydrogen atom or a lower alkyl group;
• a lower alkenyloxycarbonyl group;
• —CH═N—NH—CONH2;
• a cyano group;
• —COR4 wherein R4 represents a hydroxyl group or N(R5)(R6) wherein R5 and R6 form a nitrogen-containing heterocyclic group together with the adjacent nitrogen atom;
• a vinyl group substituted with a lower alkenyloxycarbonyl group;
• —CO—S—CH2—CH2—NH—CO—Rx wherein Rx represents a lower alkyl group;
• or —CH═CH—COOH;
• and R12 represents a hydrogen atom, except that when R11 represents a cyano group, R12 represents a hydrogen atom or a lower alkyl group;
• when ---- between R2 and a carbon atom at the 5-position represents a single bond, R2 represents a hydroxyl group, a lower alkoxyl group, or a tri(lower alkyl)silyloxy group;
• and when ---- between R2 and a carbon atom at the 5-position represents a double bond, R2 forms a carbonyl group or a hydroxime group together with the carbon atom at the 5-position;
• 2) when —X----Y— represents —CH2—C(═O)—, ---- between R1 and a carbon atom at the 4″-position represents a double bond;
• R1 represents (R11a)R12a)C wherein R11a represents a lower alkoxycarbonyl group, the alkyl moiety of which is optionally may be substituted with a heterocyclic group, or —COOCH2CH═CH2;
• and R12a represents a hydrogen atom;
• ---- between R2 and a carbon atom at the 5-position represents a single bond;
• and R2 represents a hydroxyl group, a lower alkoxy group, or a tri(lower alkyl)silyloxy group;
• 3) when —X----Y— represents —CH2—CH2—,
• R1 represents (R11b)(R12b)C wherein R11b represents a cyano group, a carboxyl group, or a lower alkenyloxycarbonyl group;
• and R12b represents a hydrogen atom;
• or when ---- between R1 and a carbon atom at the 4″-position represents a single bond, R1 represents a carboxymethyl group or a cyanomethyl group;
• ---- between R2 and a carbon atom at the 5-position represents a single bond;
• and R2 represents a hydroxyl group, a lower alkoxy group, or a tri(lower alkyl)silyloxy group;
• 4) when —X----Y— represents —CH2—CH(R13)—, and ---- between R1 and a carbon atom at the 4″-position represents a double bond;
• R1 represents (R11c)(R12c)C wherein R11c represents a cyano group, a carboxyl group, a lower alkoxycarbonyl group or a lower alkenyloxycarbonyl group;
• and R12c represents a hydrogen atom;
• R13 represents a hydroxyl group or a lower alkylcarbonyloxy group;
• ---- between R2 and a carbon atom at the 5-position represents a single bond;
• and R2 represents a hydroxyl group, a lower alkoxy group or a tri(lower alkyl)silyloxy group.