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  • To guide our attempts at achieving AKT

    2024-02-19

    To guide our attempts at achieving AKT potency and selectivity against p70S6K and other kinases from (p70 S6K IC: 0.004 μM) and , we took advantage of exploiting the subtle sequence differences in the active sites of the AGC family kinases, we utilized the information around crystal structure of AKT1 at the hinge region with analogs of –. During this Hit optimization, through several scaffold morphing steps we have discovered chiral DHP as potent and selective AKT inhibitor. A crystal structure of in complex with AKT1 confirmed the presence of key hydrogen bonds from the amine group of the ligand and to Glu-234 of the protein back bone that is necessary for the AKT1 biological activity. Among the hydrogen bond donors we explored in this region -ethyl pyrrolidine provided the best potency and improved metabolic stability profile. In addition, the dramatic improvement of cell potency with enantiomer of the lactam could be rationalized by chiral methyl group nicely accommodating the lipophilic pocket near the hinge binder region, whereas the enantiomer had sterically hindered effect with protein backbone with loss biological activity. To characterize the kinase selectivity of and its analogs, we profiled their ability to inhibit a panel of ∼100 in vitro expressed human protein kinases assays and many of them with IC50 values listed in . In general, the DHP war head demonstrated high AKT selectivity in enzyme and low activity against ROCK2 and many other kinases (90 Kinases had <80% inhibition at 1 μM, >1000-fold selectivity over ROCK2). The key difference between AKT1 and ROCK2 in the ATP binding site is the gate keeper pocket where there is a favorable hydrogen bond interaction from the carbonyl moiety of the hinge binder with Thr-211 hydroxyl group of AKT1, however in ROCK2 the gatekeeper residue is Val-153. A summary of this structure based drug design, which led to the discovery of potent and selective carbonyl containing chiral dihydropyridopyrimidinone hinge binder as AKT inhibitors, is shown in . While and related analogs had attractive cell potency, a major challenge in optimization of this series was a struggle with poor physicochemical properties. Lipophilic Micafungin (LogP/D = 4.84) suffered from relatively high plasma protein binding, poor aqueous solubility (0.035 mg/mL at pH = 7.4) and hERG activity. While the addition of lipophilicity improved potency, clearance and solubility further deteriorated. Alternately, if polar functional groups were simply appended to the periphery of the hinge binder, then potency was compromised and passive permeability decreased. Thus, the focus of further work was to determine whether analogs could be generated with better solubility and permeability while maintaining the kinase selectivity. With this goal in mind, our medicinal chemistry strategy was therefore to investigate the liphophillic P-loop pocket of lead compound where the fluorinated aryl ring occupies. We reasoned that if we could reduce the molecular weight and co-planarity of on the aryl-heteroaryl junction, then we might improve physicochemical characteristics and in vivo ADME properties. With the aim of deconstructing the aryl ring, we made the rational design decision of introducing smaller hydrophobic trifluoromethyl substitutions at the imidazole represented by compound . Replacement of the aryl ring with an aliphatic substitutions lowered logP by >2 units and led to increased aqueous solubility, lack of hERG binding and decreased unbound intrinsic clearance (). Although compound and analogs was sufficiently potent in enzyme with >10-fold selectivity for many of the AGC kinase family member, cell potency remained less attractive. We hypothesized that reducing the ring size followed by significant changes to planarity at the P-loop pocket resulted in a dramatic loss of cell activity. On the basis of structural guidance, our attention was directed towards identifying a similarly sized saturated aliphatic ring at the P-loop pocket that might mimic the aryl ring and spatially suitable enough for accommodating the hydrophobic pocket. With this goal in mind we rationalized that symmetrical 4-pyran could be an appropriate saturated ring that could fit well without significantly increased hydrophobicity. Replacing the trifluromethyl substitution with six-membered 4-pyran as compound that resulted in 10-fold boost in both cell and enzyme potency.