 The structures of Bay 60-7550 and PDP are very similar.The difference between these molecules is the exocyclic methyl group on Bay 60-7550, which replaces the nitrogen atom in PDP decreasing the possibility to form hydrogen bonds with the enzyme in an important site for substrate and inhibitor binding.The oxindole structure differs from the other inhibitors since it is more divergent from the purine ring system and has less hydrogen binding possibilities.