According to the invention there is provided a compound of formula (I) wherein: A represents C(&boxH；N&mdash；W-D) or S； B represents S or C(&mdash；NH&mdash；W-D)； when: A represents C(&boxH；N&mdash；W-D) and B represents S then the bond between B and the NH atom is a single bond； or A represents S and B represents C(&mdash；NH&mdash；W-D) then the bond between B and the NH atom is a double bond； X represents -Q-[CRxRy]n&mdash；； W represents &mdash；[CRxRy]m&mdash； or &mdash；C(O)&mdash；[CRxRy]p&mdash；； Q represents a bond, &mdash；N(Ra)&mdash；, &mdash；S&mdash；, or &mdash；O&mdash；； A1 to A5 respectively represent C(R1), C(R2), C(R3), C(R4) and C(R5), or, alternatively, up to two of A1 to A5 may independently represent N； D represents phenyl, pyridyl or pyrimidinyl optionally substituted by one or more R6 groups, which compounds are useful in the treatment of cancer.
