Potent Uncompetitive Inhibitors of Nicotinamide N-Methyltransferase (NNMT) as In Vivo Chemical Probes.

NNMT uses SAM as a cofactor to catalyze the methylation of nicotinamide, producing 1-methylnicotinamide. Recent studies have shown that NNMT upregulation in cancer-associated fibroblasts (CAFs) is required to maintain the CAF phenotype in high-grade serous carcinoma. These observations suggest that NNMT should be evaluated as a therapeutic target, especially in cancer. Although several small-molecule inhibitors of NNMT have been identified, there remains a need for highly potent and selective inhibitors with excellent in vivo activity and ADME properties that can be used as reliable chemical probes. We have identified azaindoline carboxamide 38 as a selective and potent NNMT inhibitor with favorable PK/PD and safety profiles as well as excellent oral bioavailability and pharmaceutical properties. Our mechanistic studies indicate that 38 binds uncompetitively with SAM but competitively with nicotinamide consistent with its binding in the nicotinamide binding site and likely forming a positive interaction with SAM.

Stereoelectronic Features of a Complex Ketene Dimerization Reaction.

The amidation reaction of a tetrahydroisoquinolin-1-one-4-carboxylic acid is a key step in the multi-kilogram-scale preparation of the antimalarial drug SJ733, now in phase 2 clinical trials. In the course of investigating THIQ carboxamidations, we found that propanephosphonic acid anhydride (T3P) is an effective reagent, although the yield and byproducts vary with the nature and quantity of the base. As a control, the T3P reaction of a 3-(2-thienyl) THIQ was performed in the absence of the amine, and the products were characterized: among them are three dimeric allenes and two dimeric lactones. A nucleophile-promoted ketene dimerization process subject to subtle steric and stereoelectronic effects accounts for their formation. Two novel monomeric products, a decarboxylated isoquinolone and a purple, fused aryl ketone, were also isolated, and mechanisms for their formation from the ketene intermediate are proposed.

Evaluation of 1,1-cyclopropylidene as a thioether isostere in the 4-thio-thienopyrimidine (TTP) series of antimalarials.

The 4-(heteroarylthio)thieno[2,3-d]pyrimidine (TTP) series of antimalarials, represented by 1 and 17, potently inhibit proliferation of the 3D7 strain of P. falciparum (EC50 70-100 nM), but suffer from oxidative metabolism. The 1,1-cyclopropylidene isosteres 6 and 16 were designed to obviate this drawback. They were prepared by a short route that features a combined Peterson methylenation / cyclopropanation transformation of, e. g., ketone 7. Isosteres 6 and 16 possess significantly attenuated antimalarial potency relative to parents 1 and 17. This outcome can be rationalized based on the increased out-of-plane steric demands of the latter two. In support of this hypothesis, the relatively flat ketone 7 retains some of the potency of 1, even though it appears to be a comparatively inferior mimic with respect to electronics and bond lengths and angles. We also demonstrate crystallographically and computationally an apparent increase in the strength of the intramolecular sulfur hole interaction of 1 upon protonation.

Computational assessment of thioether isosteres.

Replacement of the sulfur atom in biologically active diaryl and heteroaryl thioethers (Ar-S-Ar', HAr-S-Ar, and HAr-S-HAr') with any of several one-atom or two-atom linkers can be expected to reduce the susceptibility of the analogue to metabolic oxidation, a well-documented problem for thioethers intended for medicinal chemistry applications. Ab initio calculations indicate how well various proposed thioether isosteric groups, including some new and unusual ones, may perform structurally and electronically in replacing the bridging sulfur atom. Four of these are calculationally evaluated as proposed substructures in Axitinib analogues. The predicted binding behavior of the latter within two different previously crystallographically characterized protein-Axitinib binding sites (VEGFR2 kinase and ABL1 T315I gatekeeper mutant kinase), and an assessment of their suitability and anticipated shortcomings, are presented.