Discovery of Orally Bioavailable FGFR2/FGFR3 Dual Inhibitors via Structure-Guided Scaffold Repurposing Approach.

Fibroblast growth factor receptors (FGFRs) are transmembrane receptor tyrosine kinases that regulate multiple physiological processes. Aberrant activation of FGFR2 and FGFR3 has been linked to the pathogenesis of many tumor types, including cholangiocarcinoma and bladder cancer. Current therapies targeting the FGFR2/3 pathway exploiting small-molecule kinase inhibitors are associated with adverse events due to undesirable inhibition of FGFR1 and FGFR4. Isoform-specific FGFR2 and FGFR3 inhibitors that spare FGFR1 and FGFR4 could offer a favorable toxicity profile and improved therapeutic window to current treatments. Herein we disclose the discovery of dual FGFR2/FGFR3 inhibitors exploiting scaffold repurposing of a previously reported ALK2 tool compound. Structure-based drug design and structure-activity relationship studies were employed to identify selective and orally bioavailable inhibitors with equipotent activity toward wild-type kinases and a clinically observed gatekeeper mutant.

Discovery of Potent and Selective Inhibitors of Wild-Type and Gatekeeper Mutant Fibroblast Growth Factor Receptor (FGFR) 2/3.

Upregulation of the fibroblast growth factor receptor (FGFR) signaling pathway has been implicated in multiple cancer types, including cholangiocarcinoma and bladder cancer. Consequently, small molecule inhibition of FGFR has emerged as a promising therapy for patients suffering from these diseases. First-generation pan-FGFR inhibitors, while highly effective, suffer from several drawbacks. These include treatment-related hyperphosphatemia and significant loss of potency for the mutant kinases. Herein, we present the discovery and optimization of novel FGFR2/3 inhibitors that largely maintain potency for the common gatekeeper mutants and have excellent selectivity over FGFR1. A combination of meticulous structure-activity relationship (SAR) analysis, structure-based drug design, and medicinal chemistry rationale ultimately led to compound 29, a potent and selective FGFR2/3 inhibitor with excellent in vitro absorption, distribution, metabolism, excretion (ADME), and pharmacokinetics in rat. A pharmacodynamic study of a closely related compound established that maximum inhibition of downstream ERK phosphorylation could be achieved with no significant effect on serum phosphate levels relative to vehicle.

Discovery of Novel Pyrazolopyrimidines as Potent, Selective, and Orally Bioavailable Inhibitors of ALK2.

Activin receptor-like kinase 2 (ALK2) is a transmembrane kinase receptor that mediates the signaling of the members of the TGF-ß superfamily. The aberrant activation of ALK2 has been linked to the rare genetic disorder fibrodysplasia ossificans progressiva (FOP) and diffuse intrinsic pontine glioma (DIPG) that are associated with severely reduced life expectancy in pediatric patients. ALK2 has also been shown to play an essential role in iron metabolism by regulating hepcidin levels and affecting anemia of chronic disease. Thus, selective inhibition of ALK2 has emerged as a promising strategy for the treatment of multiple disorders. Herein, we report the discovery of a novel pyrazolopyrimidines series as highly potent, selective, and orally bioavailable inhibitors of ALK2. Structure-based drug design and systematic structure-activity relationship studies were employed to identify potent inhibitors displaying high selectivity against other ALK subtypes with good pharmacokinetic profiles.

Inhibition of ALK2 with bicyclic pyridyllactams.

Activin receptor-like kinase 2 (ALK2) has been implicated as a key target in multiple rare diseases. Herein, we describe the design of a novel bicyclic lactam series of potent and selective ALK2 inhibitors. This manuscript details an improvement in potency of two orders of magnitude from the initial bicyclic structure as well as a two-fold improvement in cellular potency from the original monocyclic inhibitor. Furthermore, we provide a detailed strategy for progressing this project in the future.

Rhodium(III)-Catalyzed Imidoyl C-H Activation for Annulations to Azolopyrimidines.

Azolopyrimidines are efficiently prepared by direct imidoyl C-H bond activation. Annulations of N-azolo imines with sulfoxonium ylides and diazoketones under redox-neutral conditions and alkynes under oxidizing conditions provide products with various arrangements of nitrogen atoms and carbon substituents. We have also probed the mechanism of this first example of Rh(III)-catalyzed direct imidoyl C-H activation by structural characterization of a catalytically competent rhodacycle obtained after C-H activation and by kinetic isotope effects.

X-ray Characterization and Structure-Based Optimization of Striatal-Enriched Protein Tyrosine Phosphatase Inhibitors.

Excessive activity of striatal-enriched protein tyrosine phosphatase (STEP) in the brain has been detected in numerous neuropsychiatric disorders including Alzheimer's disease. Notably, knockdown of STEP in an Alzheimer mouse model effected an increase in the phosphorylation levels of downstream STEP substrates and a significant reversal in the observed cognitive and memory deficits. These data point to the promising potential of STEP as a target for drug discovery in Alzheimer's treatment. We previously reported a substrate-based approach to the development of low molecular weight STEP inhibitors with Ki values as low as 7.8 µM. Herein, we disclose the first X-ray crystal structures of inhibitors bound to STEP and the surprising finding that they occupy noncoincident binding sites. Moreover, we utilize this structural information to optimize the inhibitor structure to achieve a Ki of 110 nM, with 15-60-fold selectivity across a series of phosphatases.

A Simple Primary Amine Catalyst for Enantioselective α-Hydroxylations and α-Fluorinations of Branched Aldehydes.

A new primary amine catalyst for the asymmetric α-hydroxylation and α-fluorination of α-branched aldehydes is described. The products of the title transformations are generated in excellent yields with high enantioselectivities. Both processes can be performed within short reaction times and on gram scale. The similarity in results obtained in both reactions, combined with computational evidence, implies a common basis for stereoinduction and the possibility of a general catalytic mechanism for α-functionalizations. Promising initial results in α-amination and α-chlorination reactions support this hypothesis.

Catalytic asymmetric synthesis of 8-oxabicyclooctanes by intermolecular [5+2] pyrylium cycloadditions.

Highly enantioselective intermolecular [5+2] cycloadditions of pyrylium ion intermediates with electron-rich alkenes are promoted by a dual catalyst system composed of an achiral thiourea and a chiral primary aminothiourea. The observed enantioselectivity is highly dependent on the substitution pattern of the 5π component, and the basis for this effect is analyzed using experimental and computational evidence. The resultant 8-oxabicyclo[3.2.1]octane derivatives possess a scaffold common in natural products and medicinally active compounds and are also versatile chiral building blocks for further manipulations. Several stereoselective complexity-generating transformations of the 8-oxabicyclooctane products are presented.

Dual catalysis in enantioselective oxidopyrylium-based [5 + 2] cycloadditions.

A new method for effecting catalytic enantioselective intramolecular [5 + 2] cycloadditions based on oxidopyrylium intermediates is reported. The dual catalyst system consists of a chiral primary aminothiourea and a second achiral thiourea. Experimental evidence points to a new type of cooperative catalysis with each species being necessary to generate a reactive pyrylium ion pair that undergoes subsequent cycloaddition with high enantioselectivity.

Solid phase synthesis of hydrogen bond surrogate derived alpha-helices: resolving the case of a difficult amide coupling.

Solid phase synthesis of HBS helices involving the Fukuyama-Mitsunobu reaction and triphosgene coupling is described.