New 5,6,7,8-Tetrahydropyrido[4',3':4,5]thieno[2,3-d]pyrimidin-4(3H)-one Derivatives as Sigma Ligands

A compound of the formula:

• or a corresponding salt, co-crystal or prodrug thereof, or a corresponding solvate thereof, wherein
• R1 is an aryl optionally substituted with one or more R1a substituents;
• each of R1a is independently a halogen atom;
• a branched or unbranched C1-6 alkyl;
• —CN;
• an —OR′ where R′ is hydrogen or an unsubstituted C1-6 alkyl;
• or an optionally substituted heterocyclyl group containing one or more heteroatoms selected from N, O or S;
• R2 is a branched or unbranched C1-6 alkyl;
• or a C1-6 haloalkyl;
• R3 is a hydrogen;
• or a branched or unbranched C1-6 alkyl;
• with the proviso that when R1 is an unsubstituted phenyl, then R3 is not methyl;
• and
• with the proviso that when R3 is a hydrogen, then R1 is not a phenyl group substituted with a pyrazole.