Structure-based design and synthesis of antiparasitic pyrrolopyrimidines targeting pteridine reductase 1

The treatment of Human African Trypanosomiasis remains a major unmet health need in sub-Saharan Africa. Approaches involving new molecular targets are important and pteridine reductase 1 (PTR1), an enzyme that reduces dihydrobiopterin in Trypanosoma spp. has been identified as a candidate target and it has been shown previously that substituted pyrrolo[2,3-d]pyrimidines are inhibitors of PTR1 from T. brucei (J. Med. Chem. 2010, 53, 221-229). In this study, 61 new pyrrolo[2,3-d]pyrimidines have been prepared, designed with input from new crystal structures of 23 of these compounds complexed with PTR1, and evaluated in screens for enzyme inhibitory activity against PTR1 and in vitro antitrypanosomal activity. 8 compounds were sufficiently active in both screens to take forward to in vivo evaluation. Thus although evidence for trypanocidal activity in a stage I disease model in mice was obtained, the compounds were too toxic to mice for further development

6-Acetyl-7,7-dimethyl-5,6,7,8-tetrahydropterin is an activator of nitric oxide synthases

6-Acetyl-7,7-dimethyl-7,8-dihydropterin 3 has been shown to be able to substitute for the natural cofactor of nitric oxide synthases, tetrahydrobiopterin 1, in cells and tissues that contain active nitric oxide synthases (NOSs). In both macrophages, which produce iNOS, and endothelial cells, which produce eNOS, in which tetrahydrobiopterin biosynthesis has been blocked by inhibition of GTP cyclohydrolase 1, dihydropterin 3 restored production of nitric oxide by these cells. In tissues, 3 caused relaxation in preconstricted rat aortic rings, again in which tetrahydrobiopterin biosynthesis had been inhibited, an effect that was blocked by the NOS inhibitor, l-NAME. However, dihydropterin 3 was not itself an active cofactor in purified NOS (nNOS) preparations free of tetrahydrobiopterin suggesting that intracellular reduction to 6-acetyl-7,7-dimethyl-5,6,7,8-tetrahydropterin 4 is required for activity. Compound 4 was prepared by reduction of the corresponding 7,8-dihydropterin with sodium cyanoborohydride and has been shown to be a competent cofactor for nitric oxide production by nNOS. Together, the results show that the 7,7-dimethyl-7,8-dihydropterin is a novel structural framework for effective tetrahydrobiopterin analogues

Structure-Based Design of Pteridine Reductase Inhibitors Targeting African Sleeping Sickness and the Leishmaniases

Pteridine reductase (PTR1) is a target for drug development against Trypanosoma and Leishmania species, parasites that cause serious tropical diseases and for which therapies are inadequate. We adopted a structure-based approach to the design of novel PTR1 inhibitors based on three molecular scaffolds. A series of compounds, most newly synthesized, were identified as inhibitors with PTR1-species specific properties explained by structural differences between the T. brucei and L. major enzymes. The most potent inhibitors target T. brucei PTR1, and two compounds displayed antiparasite activity against the bloodstream form of the parasite. PTR1 contributes to antifolate drug resistance by providing a molecular bypass of dihydrofolate reductase (DHFR) inhibition. Therefore, combining PTR1 and DHFR inhibitors might improve therapeutic efficacy. We tested two new compounds with known DHFR inhibitors. A synergistic effect was observed for one particular combination highlighting the potential of such an approach for treatment of African sleeping sickness.</p

Diversity oriented syntheses of fused pyrimidines designed as potential antifolates

Diversity oriented syntheses of some furo[2,3-d]pyrimidines and pyrrolo[2,3-d] pyrimidines related to folate, guanine, and diaminopyrimidine-containing drugs have been developed for the preparation of potential anti-infective and anticancer compounds. Amide couplings and Suzuki couplings on the basic heterocyclic templates were used, in the latter case yields being especially high using aromatic trifluoroborates as the coupling partner. A new ring synthesis of 6-aryl-substituted deazaguanines bearing 2-alkylthio groups has been developed using Michael addition of substituted nitrostyrenes. Diversity at C-2 has been introduced by oxidation and substitution with a range of amino nucleophiles. The chemical reactivity of these pyrrolopyrimidines with respect to both electrophilic substitution in ring synthesis and nucleophilic substitution for diversity is discussed. Several compounds were found to inhibit pteridine reductases from the protozoan parasites Trypanosoma brucei and Leishmania major at the micromolar level and to inhibit the growth of Trypanosma brucei brucei in cell culture at higher concentrations. From these results, significant structural features required for inhibition of this important drug target enzyme have been identified.</p

A wind tunnel study of dense gas dispersion in a neutral boundary layer over a rough surface

Measurements of the vertical entrainment velocity into two-dimensional dense gas plumes over fully rough surfaces were carried out as part of a co-operative research programme with wind tunnel facilities in the USA. This paper presents results obtained for neutral boundary layer conditions in the EnFlo wind tunnel at the University of Surrey; a companion paper treats the stable boundary layer case. Entrainment velocities, WE, were deduced from the streamwise development of the concentration field, non-dimensionalised with respect to the friction velocity in the undisturbed flow, u*, and correlated with the plume Richardson number, Ri*. Results for Richardson numbers in the range Ri*&lt;15 were found to be well fitted by the empirical expression: WE/u*=0.65/(1+0.2Ri*). Flow visualisation studies showed layered plume structures with a sharp upper interface at higher Richardson numbers and in this regime turbulent motion below the interface became progressively more intermittent as Ri* increased. Measured turbulence levels collapsed within such high Richardson number plumes and flow and dispersion were significantly affected by molecular processes. Up-welling above the source was observed when the emission speed exceeded the approach flow friction velocity, though there was no clear evidence that this affected plume behaviour away from the immediate vicinity of the source

Structure-Based Design of Pteridine Reductase Inhibitors Targeting African Sleeping Sickness and the Leishmaniases

Pteridine reductase (PTR1) is a target for drug development against <i>Trypanosoma</i> and <i>Leishmania</i> species, parasites that cause serious tropical diseases and for which therapies are inadequate. We adopted a structure-based approach to the design of novel PTR1 inhibitors based on three molecular scaffolds. A series of compounds, most newly synthesized, were identified as inhibitors with PTR1-species specific properties explained by structural differences between the <i>T. brucei</i> and <i>L. major</i> enzymes. The most potent inhibitors target <i>T. brucei</i> PTR1, and two compounds displayed antiparasite activity against the bloodstream form of the parasite. PTR1 contributes to antifolate drug resistance by providing a molecular bypass of dihydrofolate reductase (DHFR) inhibition. Therefore, combining PTR1 and DHFR inhibitors might improve therapeutic efficacy. We tested two new compounds with known DHFR inhibitors. A synergistic effect was observed for one particular combination highlighting the potential of such an approach for treatment of African sleeping sickness

Designing Anti-inflammatory Drugs from Parasitic Worms: A Synthetic Small Molecule Analogue of the Acanthocheilonema viteae Product ES-62 Prevents Development of Collagen-Induced Arthritis

In spite of increasing evidence that parasitic worms may protect humans from developing allergic and autoimmune diseases and the continuing identification of defined helminth-derived immunomodulatory molecules, to date no new anti-inflammatory drugs have been developed from these organisms. We have approached this matter in a novel manner by synthesizing a library of drug-like small molecules based upon phosphorylcholine, the active moiety of the anti-inflammatory Acanthocheilonema viteae product, ES-62, which as an immunogenic protein is unsuitable for use as a drug. Following preliminary in vitro screening for inhibitory effects on relevant macrophage cytokine responses, a sulfone-containing phosphorylcholine analogue (<b>11a</b>) was selected for testing in an in vivo model of inflammation, collagen-induced arthritis (CIA). Testing revealed that <b>11a</b> was as effective as ES-62 in protecting DBA/1 mice from developing CIA and mirrored its mechanism of action in downregulating the TLR/IL-1R transducer, MyD88. <b>11a</b> is thus a novel prototype for anti-inflammatory drug development