A compound of formula I: ** Formula ** or a pharmaceutically acceptable salt thereof； wherein A is a ring moiety selected from the group consisting of: (a) 4-7 membered carbocyclyl, (b) 4-7 membered heterocyclyl, (c) phenyl, and (d) heteroaryl ring of 5 to 6 members, wherein each of said 4 to 7 member carbocyclyl and 4 to 7 member heterocyclyl of said group A may optionally contain one or two olefinic bonds； and wherein one or two carbon atoms in the ring in each of said 4 to 7 membered carbocyclyl and 4 to 7 membered heterocyclic of said group A may be independently optionally replaced with one or two moieties independently selected from the group that It consists of -C (O) -, -C (S) - and -C (>； = NR4) -； B is phenyl or a 5-6 membered heteroaryl； K is CH, C (NH2) or N； each R1 is independently selected from the group consisting of -H, halo, -CF3, -CN, -NO2, -NR7R8, - NR7C (NR7R8) (>； = CR9), -CR7 (NR7R8) (>； = NR7), -NR7C (NR7R8) (>； = NR7), -NR7C (O) R9, -C (O) NR7R8, -C (O) R9, - C (O) C (O) R9, -C (O) OR10, -OC (O) R9, -OR10, -OC (O) OR10, -S (O) jR11, -S (O) (>； = NR7) R8, -alkyl (C1-C6), -alkenyl (C2-C6) ), -C2-C6-alkynyl, -C3-C10-cycloalkyl, -C5-C10-cycloalkenyl, -C6-C10-cycloalkyl, -C6-C10-cycloalkenyl, -C1-C9 -cycloalkenyl, -heterocycloalkenyl (C4-C9), -heterobicycloalkyl (C6-C9), - heterobicycloalkenyl (C6-C9), -aryl (C6-C10), and -heteroaryl (C1-C9)； and wherein each of the above moieties - (C1-C6) alkyl, - (C2-C6) alkenyl, - (C2-C6) alkynyl, - (C3-C10) cycloalkyl, (C5-C10) cycloalkenyl, - heterocycloalkyl (C2-C9), -heterocycloalkenyl (C4-C9), -aryl (C6-C10) and -heteroaryl (C1-C9) of said R1 is optionally substituted independently by one to three groups R12； each of R2 and R3 is independently selected from the group consisting of -H, -halo, -OR10, -alkyl (C1-C6), -alkenyl (C2-C6), -alkynyl (C2-C6), -cycloalkyl (C3-C10), -cycloalkenyl (C5-C10), -heterocycloalkyl (C2-C9), -heterocycloalkenyl (C4-C9), -aryl (C6-C10) and -heteroaryl (C1-C9)； and w
