PMID: 24304238

Authors:

Carbain B, Paterson DJ, Anscombe E, Campbell-Dexter A, Cano C, Echalier A, Endicott J, Golding BT, Haggerty K, Hardcastle IR, Jewsbury PJ, Newell DR, Noble M, Roche C, Wang LZ, Griffin RJ

Title:

8-Substituted O6-Cyclohexylmethylguanine CDK2 Inhibitors; Using Structure-Based Inhibitor Design to Optimise an Alternative Binding Mode.

Journal:

J Med Chem. 2013 Dec 4.

Abstract:

Evaluation of the effects of purine C-8 substitution within a series of CDK1/2-selective O6-cyclohexylmethylguanine derivatives, revealed that potency decreases initially with increasing size of the alkyl substituent. Structural analysis showed that C-8 substitution is poorly tolerated, and to avoid unacceptable steric interactions, these compounds adopt novel binding modes. Thus, 2-amino-6-cyclohexylmethoxy-8-isopropyl-9H-purine adopts a 'reverse' binding mode where the purine backbone has flipped 180 degrees . This provided a novel lead chemotype from which we have designed more potent CDK2 inhibitors using, in the first instance, quantum mechanical energy calculations. Introduction of an ortho-tolyl or ortho-chlorophenyl group at the purine C-8 position restored the potency of these 'reverse' binding mode inhibitors to that of the parent 2-amino-6-cyclohexylmethoxy-9H-purine. By contrast, the corresponding 8-(2-methyl-3-sulfamoylphenyl)-purine derivative exhibited sub-micromolar CDK2-inhibitory activity by virtue of engineered additional interactions with Asp86 and Lys89 in the reversed binding mode, as confirmed by X-ray crystallography.