Compounds of formula (I) are CRTH2 ligands, useful in the treatment of, for example, asthma and COPD wherein: R1 is halogen or cyano; R2 is hydrogen or methyl; R3 and R4 are independently —OR6, C1-C6alkyl or C3-C6cycloalkyl, the latter two groups being optionally substituted by one or more halogen atoms; R5 is hydrogen or halogen; R6 is C1-C6 alkyl or C3-C6 cycloalkyl, either of which being optionally substituted by one or more halogen atoms; X is —CH2—, —S—, or —O—; one of Y and Y1 is hydrogen and the other is OR6, —C(═O)R7, NR8SO2R6 or a heterocyclic group selected from those referred to in the specification; and R6, R7 and R8 are as defined in the specification.