Novel alkyl substituted piperidine derivatives and their use as monoamine neurotransmitter re-uptake inhibitors

A piperidine derivative of the Formula I:

• any of its isomers or any mixture of its isomers,
• or a pharmaceutically acceptable salt thereof,
• wherein
• Ra represents hydrogen or alkyl;
• which alkyl is optionally substituted with one or more substituents independently selected from the group consisting of:
• halo, trifluoromethyl, trifluoromethoxy, cyano, hydroxy, amino, nitro, alkoxy, cycloalkoxy, alkyl, cycloalkyl, cycloalkylalkyl, alkenyl and alkynyl;
• X represents —O—, —S— or —NRc—;
• wherein Rc represents hydrogen, alkyl, —C(═O)Rd or —SO2Rd;
• wherein Rd represents hydrogen or alkyl;
• Rb represents an aryl group,
• which aryl group is optionally substituted with one or more substituents independently selected from the group consisting of:
• halo, trifluoromethyl, trifluoromethoxy, cyano, hydroxy, amino, nitro, alkoxy, cycloalkoxy, alkyl, cycloalkyl, cycloalkylalkyl, alkenyl and alkynyl;
• each of R2, R2′, R3, R3′, R5, R5′, R6 and R6′ independently of each other represents hydrogen or alkyl;
• with the proviso that at least one of R2, R2′, R3, R3′, R5, R5′, R6 and R6′ represents alkyl;
• and with the proviso that the compound is not
• 4-(4-hydroxy-phenoxy)-2,2,6,6-tetramethyl-piperidine or
• 4-(4-methoxy-phenoxy)-2,2,6,6-tetramethyl-piperidine.