Chagas disease, caused by the parasitic protozoan Trypanosoma cruzi , affects over 8 million people worldwide. Current antiparasitic treatments for Chagas disease are ineffective in treating advanced, chronic stages of the disease, and are noted for their toxicity. Like most parasitic protozoa, T. cruzi is unable to synthesize purines de novo , and relies on the salvage of preformed purines from the host. Hypoxanthine–guanine phosphoribosyltransferases (HGPRTs) are enzymes that are critical for the salvage of preformed purines, catalyzing the formation of inosine monophosphate (IMP) and guanosine monophosphate (GMP) from the nucleobases hypoxanthine and guanine, respectively. Due to the central role of HGPRTs in purine salvage, these enzymes are promising targets for the development of new treatment methods for Chagas disease. In this study, we characterized two gene products in the T. cruzi CL Brener strain that encodes enzymes with functionally identical HGPRT activities in vitro : TcA (TcCLB.509693.70) and TcC (TcCLB.506457.30). The TcC isozyme was kinetically characterized to reveal mechanistic details on catalysis, including identification of the rate-limiting step(s) of catalysis. Furthermore, we identified and characterized inhibitors of T. cruzi HGPRTs originally developed as transition-state analogue inhibitors (TSAIs) of Plasmodium falciparum hypoxanthine–guanine–xanthine phosphoribosyltransferase ( Pf HGXPRT), where the most potent compound bound to T. cruzi HGPRT with low nanomolar affinity. Our results validated the repurposing of TSAIs to serve as selective inhibitors for orthologous molecular targets, where primary and secondary structures as well as putatively common chemical mechanisms are conserved.

De-protected arabino N-glycosyl sulfamides, sulfonamides and sulfamates were found to mutarotate and convert from the furanose to the thermodynamically more stable pyranose form in aqueous solution. The presence of a strongly electron withdrawing group in the alkyl chain stopped mutarotation and furanose/pyranose equilibration, allowing the isolation of the first unprotected furanose N-glycosyl sulfonamide.

Plasmodium falciparum hypoxanthine−guanine−xanthine phosphoribosyltransferase (Pf HGXPRT) is essential for purine salvage of hypoxanthine into parasite purine nucleotides. Transition state analogue inhibitors of Pf HGXPRT are characterized by kinetic analysis, thermodynamic parameters, and X-ray crystal structures. Compound 1, 9-deazaguanine linked to an acyclic ribocation phosphonate mimic, shows a kinetic K i of 0.5 nM. Isothermal titration calorimetry (ITC) experiments of 1 binding to Pf HGXPRT reveal enthalpically driven binding with negative cooperativity for the binding of two inhibitor molecules in the tetrameric enzyme. Crystal structures of 1 bound to Pf HGXPRT define the hydrogen bond and ionic contacts to complement binding thermodynamics. Dynamics of ribosyl transfer from 5-phospho-α-D-ribosyl 1-pyrophosphate (PRPP) to hypoxanthine were examined by 18 O isotope exchange at the bridging phosphoryl oxygen of PRPP pyrophosphate. Rotational constraints or short transition state lifetimes prevent torsional rotation and positional isotope exchange of bridging to nonbridging oxygen in the α-pyrophosphoryl group. Thermodynamic analysis of the transition state analogue and magnesium pyrophosphate binding reveal random and cooperative binding to Pf HGXPRT, unlike the obligatory ordered reaction kinetics reported earlier for substrate kinetics.

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Organic azides are readily reduced to the corresponding amines by treatment with sodium iodide in the presence of acidic ion exchange resin. The process, optimal when performed at 40 °C and 200 mbar pressure on a rotatory evaporator, is extremely efficient, clean, and tolerant of a variety of functional groups.