1,2,3,4-Tetrahydroisoquinolines, processes for their preparation, and their use as kappa-receptor agonists

A compound, or a solvate or salt thereof, of formula (I): in which: RCO is an acyl group in which the group R contains a substituted or unsubstituted carbocyclic aromatic or heterocyclic aromatic ring and R1 and R2 are independently hydrogen, C1-6 alkyl, C2-6 alkenyl, C3-6 cycloalkyl or C4-12 cycloalkylalkyl groups or together form a C2-8 branched or linear polymethylene or C2-6 alkenylene group optionally substituted with a hetero-atom; R3 is hydrogen, C1-6 alkyl, or phenyl, or R3 together with R1 forms a -(CH2)3- or -(CH2)4-, group; R4 and R5, which may be the same or different and may be attached to the same or different carbon atoms of the isoquinoline nucleus, are each hydrogen, halogen, hydroxy, C1-6 alkyl, aryl, or R4 together with R5 form a -(CH2)p- group, where p is an integer of from 1 to 5 and one or more of the -(CH2)- moieties is optionally substituted by a C1-6 alkyl group. R6 and R6a, which may be the same or different, are each hydrogen, C1-6 alkyl, -CH2OR6b, halogen, hydroxy, C1-6 alkoxy, C1-6 alkoxycarbonyl, thiol, C1-6 alkylthio, -O @R6c, -NHCOR6d, -NHSO2R6e, -CH2SO2NR6fR6g, in which each of R6b to R6g is independently hydrogen, C1-6 alkyl, aryl or aralkyl; with the proviso that R4, R5, R6 and R6a are not simultaneously hydrogen, is useful for the treatment of pain. a