A compound of formula (I) or a pharmaceutically acceptable salt thereof: wherein R1, R2, R5 and R6 are independently selected from hydrogen, hydroxy, methyl, trifluoromethyl, hydroxymethyl, methoxy, trifluoromethoxy, methylamino and dimethylamino； R3 and R4 are independently selected from hydrogen, hydroxy, C1-C3 alkyl, fluoro- (C1-C3) -alkyl, hydroxy- (C1-C3) -alkyl, C1-C3 alkoxy, fluoro- (C1-C3) -alkoxy , hydroxy- (C1-C3) -alkoxy, -N (R11) -R12, -Alk-N (R11) -R12, -O-Alk-N (R11) -R12, -C (>； = O) OH, carboxy- (C1-C3) -alkyl, or -C (>； = O) -NH-R13； Alk is a C1-C6 straight or branched chain divalent alkylene radical； R7 and R8 are independently selected from hydrogen, hydroxy, or C1-C3 alkoxy； X is a straight chain divalent C1-C3 alkylene radical, optionally substituted on one or more carbons by R9 and / or R10； R9 and R10 are independently selected from methyl, hydroxy, or fluoro； R11 is hydrogen, C1-C3 alkyl, or fluoro- (C1-C3) -alkyl, and R12 is C1-C3 alkyl or hydroxy- (C1-C6) -alkyl, any of which may be optionally substituted in the alkyl portion by phenyl, C1-C3 alkoxy- (C1-C3) -alkyl, halo- (C1-C4) -alkyl, C3-C6 cycloalkyl, methylsulfonyl- (C1-C3) -alkyl or -N (R18) -R19； R13 is hydrogen, C1-C6 alkyl, fluoro- (C1-C3) -alkyl, or a radical of the formula -Alk-N (R14) -R15； R14 and R15 are independently selected from hydrogen, C1-C3 alkyl, or fluoro- (C1-C3) -alkyl； or R11 and R12, or R14 and R15, together with the nitrogen atom to which they are attached respectively, form an optionally substituted monocyclic 4- to 6-membered heterocyclic ring, having no more than three additional heteroatoms independently selected from oxygen, sulfur and nitrogen； W is selected from -C (>； = O) -N (-R16) -o -N (-R17) -C (>； = O) -； R16 or R17 is selected from hydrogen, C1-C3-alkyl, or fluoro- (C1-C3) -alkyl； R18 and R19 are selected from hydrogen, C1-C3-alkyl, or fluoro- (C1-C3) -alkyl, or R18 and R19 together with the nitrogen atom to which they are attached respectiv
