Radiolabeled compounds and their use as radiotracers for quantitative imaging of phosphodiesterase (pde10a) in mammals

A compound represented by the formula (I):

• wherein:
• ring A is selected from the group consisting of
• (1) a benzene,
• (2) a pyrazole,
• (3) a thiazole,
• (4) a piperidine, and
• (5) a tetrahydropyridine,
• wherein said ring A may optionally be substituted by 1 to 4 substituents selected from the group consisting of halogens, an optionally substituted C1-4 alkyl, an optionally substituted C1-4 alkoxy, an optionally substituted C7-14 aralkyl, an optionally substituted C2-4 alkenyl, an optionally substituted C2-4 alkynyl and a cyclic group which may optionally be substituted (provided that a cyclic group represented by the formula
• (wherein p is 1 to 4) which may optionally be substituted, is excluded),
• R1 is an optionally substituted C1-4 alkoxy, wherein the optionally substituted C1-4 alkoxy is radiolabeled,
• R2 and R3 are each substituent,
• m is 0 to 2,
• n is 0 to 5;
• provided that
• 1-(2-fluorophenyl)-5-[11C]methoxy-3-(1-phenyl-1H-pyrazol-5-yl)pyridazin-4(1H)-one,
• 1-[4-(3,5-dimethylisoxazol-4-yl)-2-fluorophenyl]-5-11C-methoxy-3-(1-phenyl-1H-pyrazol-5-yl)pyridazin-4(1H)-one and
• 1-(2 fluoro-4-(morpholin-4-yl)phenyl)-5-11C-methoxy-3-(1-phenyl-1H-pyrazol-5-yl)-pyridazin-4(1H)-one
• are excluded;
• or a salt thereof.