6-Amino-3-methylpyrimidinones as Potent, Selective, and Orally Efficacious SHP2 Inhibitors.

Protein tyrosine phosphatase SHP2 is an oncoprotein associated with cancer as well as a potential immune modulator because of its role in the programmed cell death PD-L1/PD-1 pathway. In the preceding manuscript, we described the optimization of a fused, bicyclic screening hit for potency, selectivity, and physicochemical properties in order to further expand the chemical diversity of allosteric SHP2 inhibitors. In this manuscript, we describe the further expansion of our approach, morphing the fused, bicyclic system into a novel monocyclic pyrimidinone scaffold through our understanding of SAR and use of structure-based design. These studies led to the identification of SHP394 (1), an orally efficacious inhibitor of SHP2, with high lipophilic efficiency, improved potency, and enhanced pharmacokinetic properties. We also report other pyrimidinone analogues with favorable pharmacokinetic and potency profiles. Overall, this work improves upon our previously described allosteric inhibitors and exemplifies and extends the range of permissible chemical templates that inhibit SHP2 via the allosteric mechanism.

Dual Allosteric Inhibition of SHP2 Phosphatase.

SHP2 is a cytoplasmic protein tyrosine phosphatase encoded by the PTPN11 gene and is involved in cell proliferation, differentiation, and survival. Recently, we reported an allosteric mechanism of inhibition that stabilizes the auto-inhibited conformation of SHP2. SHP099 (1) was identified and characterized as a moderately potent, orally bioavailable, allosteric small molecule inhibitor, which binds to a tunnel-like pocket formed by the confluence of three domains of SHP2. In this report, we describe further screening strategies that enabled the identification of a second, distinct small molecule allosteric site. SHP244 (2) was identified as a weak inhibitor of SHP2 with modest thermal stabilization of the enzyme. X-ray crystallography revealed that 2 binds and stabilizes the inactive, closed conformation of SHP2, at a distinct, previously unexplored binding site-a cleft formed at the interface of the N-terminal SH2 and PTP domains. Derivatization of 2 using structure-based design resulted in an increase in SHP2 thermal stabilization, biochemical inhibition, and subsequent MAPK pathway modulation. Downregulation of DUSP6 mRNA, a downstream MAPK pathway marker, was observed in KYSE-520 cancer cells. Remarkably, simultaneous occupation of both allosteric sites by 1 and 2 was possible, as characterized by cooperative biochemical inhibition experiments and X-ray crystallography. Combining an allosteric site 1 inhibitor with an allosteric site 2 inhibitor led to enhanced pharmacological pathway inhibition in cells. This work illustrates a rare example of dual allosteric targeted protein inhibition, demonstrates screening methodology and tactics to identify allosteric inhibitors, and enables further interrogation of SHP2 in cancer and related pathologies.

1,4-Functionalization of 1,3-dienes with low-valent iron catalysts.

Iron-catalyzed or -mediated transformations of organic substrates have been important throughout the development of organic chemistry due to iron's abundance, low cost, and favorable toxicity profile. Highly reduced iron species, although difficult to isolate and characterize, have proven valuable as catalysts for a variety of C-C and C-heteroatom bond forming processes, as well as cyclization and cycloisomerization reactions. We have developed iminopyridine-ligated low-valent iron catalysts that facilitate selective 1,4-hydrovinylation, hydoboration, hydrosilylation, and polymerization of 1,3-dienes. The catalysts are generated in situ from iron(II) precursors in the presence of activated magnesium metal or trialkylaluminum reductants. The 1,4-addition processes provide access to valuable products such as 1,4-dienes, allylboronic esters, allylsilanes, and highly regioregular polyisoprene. In these transformations, addition is stereoselective, providing (E)-alkene isomers selectively, and (1,2)-addition products are generally not observed. Moreover, modification of steric bulk on the iminopyridine ligand can be used to change selectivity for (1,4)- versus (4,1)-addition to dienes with nonsymmetric substitution. Access to low-valent iron precursor complexes is limited, and we have developed a diaryliron(II) precursor that undergoes smooth reductive elimination in the presence of iminopyridine ligands to provide easy access to low-valent iron catalysts without the use of heterogeneous reductants, which complicate the isolation and study of low-valent iron complexes. We obtained crystal structures of our iron(II) catalyst precursor and an iminopyridine-ligated reduced iron species generated from it. Spectroscopic analysis suggests that although this species is formally iron(0), the redox-active iminopyridine ligands accept electron density from the metal and the complex is more properly formulated as iron(II) coordinated by two radical-anion ligands. We believe that a closely-related set of reaction manifolds is responsible for the 1,4-functionalization reactivity displayed by the iron(iminopyridine) complexes (see text). Kinetics experiments and deuterium-labeling studies provide evidence for the proposed catalytic cycle. The geometry of the double bond remaining after 1,4-addition is set by the requirement that the diene bind to the iron center in an s-cis geometry, and the regioselectivity of addition can be rationalized by the location of steric bulk on the iminopyridine ligand. The transformations presented in this Account utilize iron catalysts to provide access to valuable diene 1,4-addition products such as 1,4-dienes, allylboronate esters, and allylsilanes, as well as highly regioregular polyisoprene. The development of a stable diaryliron(II) precatalyst, structural characterization of an iminopyridine-ligated iron(0) complex, and mechanistic insights into the selective nature of this transformation provide a window into the reactivity profile of low-valent iron.

Condensed-phase, halogen-bonded CF3I and C2F5I adducts for perfluoroalkylation reactions.

A family of practical, liquid trifluoromethylation and pentafluoroethylation reagents is described. We show how halogen bonding can be used to obtain easily handled liquid reagents from gaseous CF3I and CF3CF2I. The synthetic utility of the new reagents is exemplified by a novel direct arene trifluoromethylation reaction as well as adaptations of other perfluoroalkylation reactions.

Ruthenium-catalyzed hydroxylation of unactivated tertiary C-H bonds.

The combination of catalytic RuCl(3) and pyridine with KBrO(3) as the stoichiometric oxidant is shown to efficiently promote the hydroxylation of unactivated tertiary C-H bonds. Substrates possessing different polar functional groups--ester, epoxide, sulfone, oxazolidinone, carbamate, and sulfamate--are found to engage in this reaction to give alcohol products in yields generally exceeding 50%. As judged based on efficiency, ease of operation, substrate scope, and selectivity toward tertiary C-H centers, the method appears competitive with other C-H hydroxylation processes.

Palladium-catalyzed silylation of aryl chlorides with hexamethyldisilane.

A method for the palladium-catalyzed silylation of aryl chlorides has been developed. The method affords desired product in good yield, is tolerant of a variety of functional groups, and provides access to a wide variety of aryltrimethylsilanes from commercially available aryl chlorides. Additionally, a one-pot procedure that converts aryl chlorides into aryl iodides has been developed.

Synthesis of a ketone analogue of biotin via the intramolecular Pauson-Khand reaction.

We report an improved synthesis of 5-(5-oxohexahydrocyclopenta[c]thiophen-1-yl)pentanoic acid (ketone biotin, 1) based on the intramolecular Pauson-Khand cyclization. The synthesis proceeds in eight steps and in 2.7% overall yield from cyclohexene.