Tau imaging probe

A compound represented by formula (I′):

• wherein
• A is a cyclic group represented by a formula:
• ring A is unsubstituted, or substituted with R6 (the R6 is one or more substituents selected independently from halogen, OH, COOH, SO3H, NO2, SH, NRaRb, lower alkyl (the alkyl group each independently may be optionally substituted with one or more substituents selected from halogen and hydroxy), and —O-lower alkyl (the alkyl group each independently may be optionally substituted with one or more substituents selected from a p-toluenesulfonyloxy group, a methanesulfonyloxy group, a chloromethanesulfonyloxy group, a trifluoromethanesulfonyloxy group, a 2-tetrahydropyranyloxy group, an acetoxy group, a halogen atom, a hydroxy group, and a hydroxy lower alkyl group protected with a protecting group for hydroxy)),
• R1 is a halogen atom, a —C(═O)-lower alkyl group (the alkyl group each independently may be optionally substituted with one or more substituents selected from NRaRb, halogen and hydroxy), a lower alkyl group (the alkyl group each independently may be optionally substituted with one or more substituents selected from halogen atom and hydroxy), a —O-lower alkyl group (the alkyl group each independently may be optionally substituted with one or more substituents selected from a p-toluenesulfonyloxy group, a methanesulfonyloxy group, a chloromethanesulfonyloxy group, a trifluoromethanesulfonyloxy group, a 2-tetrahydropyranyloxy group, an acetoxy group, a halogen atom, a hydroxy group, and a hydroxy lower alkyl group that is protected with a protecting group for hydroxy), or a group represented by a formula:
• wherein
• R4 and R5 each independently represents a hydrogen atom, a lower alkyl group (the alkyl group each independently may be optionally substituted with one or more substituents selected from a p-toluenesulfonyloxy group, a methanesulfonyloxy group, a chloromethanesulfonyloxy group, a trifluoromethanesulfonyloxy group, a 2-tetrahydropyranyloxy group, an acetoxy group, a halogen atom, a hydroxy group, and a hydroxy lower alkyl group that is protected with a protecting group for hydroxy) or a cycloalkyl group, or R4, R5 and the nitrogen atom to which they are attached are taken together to form a 3- to 8-membered nitrogen-containing aliphatic ring (one or more carbon atoms constituting the nitrogen-containing aliphatic ring each independently may be optionally replaced by a nitrogen atom, a sulfur atom or an oxygen atom, and when a carbon atom is replaced by a nitrogen atom, the nitrogen atom may be optionally substituted with lower alkyl), or
• R4 and the nitrogen atom to which it is attached are taken together with ring A to form a 8- to 16-membered nitrogen-containing fused bicyclic ring (one or more carbon atoms constituting the nitrogen-containing fused bicyclic ring each independently may be optionally replaced by a nitrogen atom, a sulfur atom or an oxygen atom, and when a carbon atom is replaced by a nitrogen atom, the nitrogen atom may be optionally substituted with one or two lower alkyl groups), and R5 represents a hydrogen atom, a lower alkyl group, or a cycloalkyl group,
• R2 or R3 each independently represents a halogen atom, OH, COOH, SO3H, NO2, SH, NRaRb, a —O-lower alkyl group (the alkyl group each independently may be optionally substituted with one or more substituents selected from a p-toluenesulfonyloxy group, a methanesulfonyloxy group, a chloromethanesulfonyloxy group, a trifluoromethanesulfonyloxy group, a 2-tetrahydropyranyloxy group, an acetoxy group, a halogen atom, a hydroxy group, and a hydroxy lower alkyl group that is protected with a protecting group for hydroxy),
• Ra and Rb each independently represents a hydrogen atom or a lower alkyl group (the alkyl group each independently may be optionally substituted with one or more substituents selected from halogen and hydroxy),
• m is an integer of 0 to 2, and
• n is an integer of 0 to 2,
• with the proviso that regardless of the above-mentioned definitions of R1, R2, R3, and R6, at least one of the R1, R2, R3, and R6 represents a group represented by formula:
• or the R1 represents a group represented by formula:
• wherein,
• R5 is the same as defined above, and
• the Q substituent represents a protecting group for hydroxy group that has a resistance against a nucleophilic substitution by fluorine anion and may be removed under acidic or alkali condition, and the R substituent represents a functional group that works as a leaving group against a nucleophilic substitution by fluorine anion, and
• each line that the above dotted line intersects with means a bond to the other structural moiety of the above general formula I′,
• or a pharmaceutically acceptable salt or solvate thereof.

A separation method of racemic compounds represented by formula (I):

• wherein
• A represents a cyclic group represented by formula:
• ring A is unsubstituted, or substituted with R6 (the R6 is one or more substituents selected independently from halogen, OH, COOH, SO3H, NO2, SH, NRaRb, lower alkyl (the alkyl group each independently may be optionally substituted with one or more substituents selected from halogen and hydroxy) and —O-lower alkyl (the alkyl group each independently may be optionally substituted with one or more substituents selected from halogen and hydroxy)),
• R1 is a halogen atom, a —C(═O)-lower alkyl group (the alkyl group each independently may be optionally substituted with one or more substituents selected from NRaRb, halogen and hydroxy), a lower alkyl group (the alkyl group each independently may be optionally substituted with one or more substituents selected from halogen and hydroxy), a —O-lower alkyl group (the alkyl group each independently may be optionally substituted with one or more substituents selected from halogen and hydroxy), or a group represented by a formula:
• wherein
• R4 and R5 each independently represent a hydrogen atom, a lower alkyl group (the alkyl group each independently may be optionally substituted with one or more substituents selected from halogen and hydroxy) or a cycloalkyl group, or R4, R5 and the nitrogen atom to which they are attached are taken together to form a 3- to 8-membered nitrogen-containing aliphatic ring (one or more carbon atoms constituting the nitrogen-containing aliphatic ring each independently may be optionally replaced by a nitrogen atom, a sulfur atom or an oxygen atom, and when a carbon atom is replaced by a nitrogen atom, the nitrogen atom may be optionally substituted with lower alkyl), or
• R4 and the nitrogen atom to which it is attached are taken together with ring A to form a 8- to 16-membered nitrogen-containing fused bicyclic ring (one or more carbon atoms constituting the nitrogen-containing fused bicyclic ring each independently may be optionally replaced by a nitrogen atom, a sulfur atom or an oxygen atom, and when a carbon atom is replaced by a nitrogen atom, the nitrogen atom may be optionally substituted with one or two lower alkyl groups), and R5 represents a hydrogen atom, a lower alkyl group (the alkyl group each independently may be optionally substituted with one or more substituents selected from halogen and hydroxy), or a cycloalkyl group,
• R2 or R3 each independently represents a halogen atom, OH, COOH, SO3H, NO2, SH, NRaRb, a lower alkyl group (the alkyl group each independently may be optionally substituted with one or more substituents selected from halogen and hydroxy) or a —O-lower alkyl group (the alkyl group each independently may be optionally substituted with one or more substituents selected from halogen and hydroxy),
• Ra and Rb each independently represents a hydrogen atom or a lower alkyl group (the alkyl group each independently may be optionally substituted with one or more substituents selected from halogen and hydroxy),
• m is an integer of 0 to 4, and
• n is an integer of 0 to 2,
• with the proviso that regardless of the above-mentioned definitions of R1, R2, R3, and R6, at least one of the R1, R2, R3, and R6 represents a group represented by formula:
• wherein
• R9 represents each independently a lower alkyl group (the alkyl group each independently may be optionally substituted with one or more substituents selected from halogen and hydroxy),
• o is an integer of 0 to 1,
• p is an integer of 0 to 1,
• q is an integer of 0 to 2, and
• each line that the above dotted line intersects with means a bond to the other structural moiety of the above general formula (I),
• separating the optical active compound as one enantiomer by using an optical active column.