Crystallographic studies on two bioisosteric analogues, N-acetyl-b-D-glucopyranosylamine and N-trifluoroacetyl-b-D-glucopyranosylamine, potent inhibitors of muscle glycogen phosphorylase

Structure-based inhibitor design has led to the discovery of a number of potent inhibitors of glycogen phosphorylase b GPb), N-acyl derivatives of b-D-glucopyranosylamine, that bind at the catalytic site of the enzyme. The first good inhibitor in this class of compounds, N-acetyl-b-D-glucopyranosylamine NAG)(Ki = 32 lM), has been previously characterized by biochemical, biological and crystallographic experiments at 2.3 A ? resolution. Bioisosteric replacement of the acetyl group by trifluoroacetyl group resulted in an inhibitor, N-trifluoroacetyl-b-D-glucopyranosylamine (NFAG), with a Ki = 75 lM. To elucidate the structural basis of its reduced potency, we determined the ligand structure in complex with GPb at 1.8 A ? resolution. To compare the binding mode of N-trifluoroacetyl derivative with that of the lead molecule, we also determined the structure of GPb–NAG complex at a higher resolution (1.9 A). NFAG can be accommodated in the catalytic site of T-state GPb at approximately the same position as that of NAG and stabilize the T-state conformation of the 280s loop by making several favourable contacts to Asn284 of this loop. The difference observed in the Ki values of the two analogues can be interpreted in terms of subtle conformational changes of protein residues and shifts of water molecules in the vicinity of the catalytic site, variations in van der Waals interaction, and desolvation effects

Optimization of imidazo[4,5-b]pyridine-based kinase inhibitors: identification of a dual FLT3/aurora kinase inhibitor as an orally bioavailable preclinical development candidate for the treatment of acute myeloid leukemia

Optimization of the imidazo[4,5-b]pyridine-based series of Aurora kinase inhibitors led to the identification of 6-chloro-7-(4-(4-chlorobenzyl)piperazin-1-yl)-2-(1,3-dimethyl-1H-pyrazol-4-yl)-3H-imidazo[4,5-b]pyridine (27e), a potent inhibitor of Aurora kinases (Aurora-A K-d = 7.5 nM, Aurora-B K-d = 48 nM), FLT3 kinase (K-d = 6.2 nM), and FLT3 mutants including FLT3-ITD (K-d = 38 nM) and FLT3(D835Y) (K-d = 14 nM). FLT3-ITD causes constitutive FLT3 kinase activation and is detected in 20-35% of adults and 15% of children with acute myeloid leukemia (AML), conferring a poor prognosis in both age groups. In an in vivo setting, 27e strongly inhibited the growth of a FLT3-ITD-positive AML human tumor xenograft (MV4-11) following oral administration, with in vivo biomarker modulation and plasma free drug exposures consistent with dual FLT3 and Aurora kinase inhibition. Compound 27e, an orally bioavailable dual FLT3 and Aurora kinase inhibitor, was selected as a preclinical development candidate for the treatment of human malignancies, in particular AML, in adults and children