Heterocyclic compounds as CRTH2 receptor antagonists

A compound of formula I:

• or a pharmaceutically acceptable salt thereof, wherein:
• A is N and B, C, and D are independently selected from CH and C(R1);
• m is an integer from 1 to 4;
• n is an integer from 0 to 4;
• R1 is halogen;
• R2 and R3 are hydrogen;
• R4 is selected from H, C1-6 alkyl;
• Ar is aryl optionally substituted with one or more halogen atoms;
• X is —C(Ra)(Rb)—, wherein Ra and Rb are H;
• Y is —S(O)2—.