Substituted pyridazine compound

A compound of formula (I) or a salt thereof:

• wherein
• Ar is a group represented by the following formula (i) or (ii):
• wherein * represents a bonding site to the pyridazine ring of formula (I);
• L is C1-6 alkylene or C3-8 cycloalkylene;
• R1 is H, C1-6 alkyl, C3-8 cycloalkyl, aryl, cyano, —OR7, —N(C1-6 alkyl)2, or heteroaryl optionally substituted with 1 to 4 C1-6 alkyls;
• R2 is H, C1-6 alkyl, C3-8 cycloalkyl, aryl, cyano, —OR7, —N(C1-6 alkyl) 2, —C(═O)O—C1-6 alkyl, —C(═O)NR8R9, or heteroaryl optionally substituted with 1 to 4 C1-6 alkyls;
• R3 is OH, —NHC(═O) R10 or —OC(═O)—C1-6 alkyl;
• R4 is halogen, —O—C1-6 alkyl or halogeno C1-6 alkyl;
• R5 is H, C3-8 cycloalkyl or halogeno C1-6 alkyl;
• R6 is H, halogen, —O—C1-6 alkyl or halogeno C1-6 alkyl;
• R7 is-C1-6 alkylene-O—C1-6 alkylene-aryl or halogeno C1-6 alkyl;
• R8 and R9 are the same or different, and each are H or C1-6 alkyl;
• or R8 and R9, together with a nitrogen atom to which R8 and R9 are bonded, form morpholine, piperazine or thiomorpholine, and the morpholine, piperazine or thiomorpholine is optionally substituted with C1-6 alkyl;
• and
• R10 is C1-6 alkyl, halogeno C1-6 alkyl or C3-8 cycloalkyl,
• provided that when Ar is a group represented by formula (i) with R5 being H, R4 is halogeno C1-6 alkyl, and one of R1 and R2 is a group other than H.