FIELD: chemistry.SUBSTANCE: invention relates to organic chemistry, particularly to a heterocyclic compound of formula I or a pharmaceutically acceptable salt thereof, where W represents CR3； X and Z are CH or N； R1 selected from chlorine, phenyl, heteroaryl (selected from furan, pyridine, pyrimidine, isoxazole, imidazole and pyrazole), heterocyclyl (selected from pyrrolidine, piperidine, morpholine, piperazine, azetidine, 6-azaspiro[3.4]octane, 2-oxa-6-azaspiro[3.4]octane, 2-oxa-6-azaspiro[3.3]heptane, thiomorpholine-1,1-dioxide, 7-oxa-2-azaspiro[3.5]nonane, 6-oxa-2-azaspiro[3.4]octane, 2-oxa-7-azaspiro[4.4]nonane, 2-oxa-6-azaspiro[3.5]nonane and dihydropyran), (3-6C)cycloalkyl, NR7R8, OR9, S(O)pR9 (where p = 0), N(R10)SO2R9 or N(R10)SOR9； and where R1 is optionally substituted with 1–2 substituents selected from fluorine, cyano, hydroxy, (1-4C)alkyl, (1-4C)alkoxy, S(O)qCH3 (where q = 2) and piperidine, and where any (1-4C)alkyl, (1-4C)alkoxy or heterocyclyl part present in the substituent group in R1, is optionally further substituted with 1-2 substituents selected from fluorine, hydroxy, (1-4C)alkyl, NRaRb, ORa and C(O)ORa, where each of Ra and Rb is independently selected from H or (1-4C)alkyl； R3 represents hydrogen, (1-4C)alkyl or (3-6C)cycloalkyl； R4 represents hydrogen or (1-3C)alkyl； Ar has the formula,where (i) all of A1, A2 and A3 represent CH or (ii) one of A1 and A2 represents N and others represent CH； R5 is selected from hydrogen, cyano, (1-3C)alkyl, (1-3C)alkoxy, (1-3C)fluoroalkoxy and halogen and where any alkyl or alkoxy parts present in the substituent group R5, are optionally further substituted with hydroxy or methoxy； R6 is selected from halogen or cyano or R6 represents a group of formula -L1-L2-R17, where L1 is absent, L2 is absent or is selected from O, SO2, C(O) or C(O)N(R20), where each of R20 and R21 is independently selected from hydrogen or (1-2C)alkyl, and R17 is (1-6C)alkyl, heteroaryl (selected from imidazole, pyrazole, isoxazole, tr
