A compound of formula or a pharmaceutically acceptable salt or a pharmaceutically acceptable stereoisomer thereof, wherein, X represents N; Y represents NR 1 or CHR 1; Z represents CR 2 R 3; R 1 represents hydrogen or alkyl; R 2 and R 3 independently represent substituted or unsubstituted alkyl, wherein the substituent is independently selected from cycloalkyl and heterocyclyl; alternatively, R 2 and R 3 may be taken together with the carbon atoms to which they are attached to form an optionally substituted 3-7 membered ring containing 0-3 hetero atoms or groups; wherein the optional substituent is R 4 and the heteroatoms are independently selected from N, O, NH and CO in any stable combination; alternatively, R 1 and R 2 may be taken together with the carbon or nitrogen atom to which they are attached to form unsubstituted 5-membered fused ring; R 4 at each occurrence is selected from substituted or unsubstituted alkyl, - COOR 5,-COR 5, -CONR 5 R 5, -SO 2 R 5, -COCH 2 OR 5, -CO(CH 2) 2 COOR 5, - COCH 2 NR 5 R 5 and substituted or unsubstituted cycloalkyl; R 5 at each occurrence is selected from hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl and substituted or unsubstituted heterocyclyl; and 'n' is selected from an integer 0 or 1. or a pharmaceutically acceptable salt or a pharmaceutically acceptable stereoisomer thereof, wherein, X represents N; Y represents NR 1 or CHR 1; Z represents CR 2 R 3; R 1 represents hydrogen or alkyl; R 2 and R 3 independently represent substituted or unsubstituted alkyl, wherein the substituent is independently selected from cycloalkyl and heterocyclyl; alternatively, R 2 and R 3 may be taken together with the carbon atoms to which they are attached to form an optionally substituted 3-7 membered ring containing 0-3 hetero atoms or groups; wherein the optional substituent is R 4 and the heteroatoms are independently selected from N, O, NH and CO in any stable combination; alternatively, R 1 and R 2 may be taken together with the carbon or nitrogen atom to which they are attached to form unsubstituted 5-membered fused ring; R 4 at each occurrence is selected from substituted or unsubstituted alkyl, - COOR 5,-COR 5, -CONR 5 R 5, -SO 2 R 5, -COCH 2 OR 5, -CO(CH 2) 2 COOR 5, - COCH 2 NR 5 R 5 and substituted or unsubstituted cycloalkyl; R 5 at each occurrence is selected from hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl and substituted or unsubstituted heterocyclyl; and 'n' is selected from an integer 0 or 1. X represents N; Y represents NR 1 or CHR 1; Z represents CR 2 R 3; R 1 represents hydrogen or alkyl; R 2 and R 3 independently represent substituted or unsubstituted alkyl, wherein the substituent is independently selected from cycloalkyl and heterocyclyl; alternatively, R 2 and R 3 may be taken together with the carbon atoms to which they are attached to form an optionally substituted 3-7 membered ring containing 0-3 hetero atoms or groups; wherein the optional substituent is R 4 and the heteroatoms are independently selected from N, O, NH and CO in any stable combination; alternatively, R 1 and R 2 may be taken together with the carbon or nitrogen atom to which they are attached to form unsubstituted 5-membered fused ring; R 4 at each occurrence is selected from substituted or unsubstituted alkyl, - COOR 5,-COR 5, -CONR 5 R 5, -SO 2 R 5, -COCH 2 OR 5, -CO(CH 2) 2 COOR 5, - COCH 2 NR 5 R 5 and substituted or unsubstituted cycloalkyl; R 5 at each occurrence is selected from hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl and substituted or unsubstituted heterocyclyl; and 'n' is selected from an integer 0 or 1.