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Chagas disease and visceral leishmaniasis are two neglected tropical diseases responsible for numerous deaths around the world. For both, current treatments are largely inadequate, resulting in a continued need for new drug discovery. As both kinetoplastid parasites are incapable of de novo purine synthesis, they depend on purine salvage pathways that allow them to acquire and process purines from the host to meet their demands. Purine nucleoside analogues therefore constitute a logical source of potential antiparasitic agents. Earlier optimization efforts of the natural product tubercidin (7-deazaadenosine) involving modifications to the nucleobase 7-position and the ribofuranose 3'-position led to analogues with potent anti- Trypanosoma brucei and anti- Trypanosoma cruzi activities. In this work, we report the design and synthesis of pyrazolo[3,4- d ]pyrimidine nucleosides with 3'- and 7-modifications and assess their potential as anti- Trypanosoma cruzi and antileishmanial agents. One compound was selected for in vivo evaluation in an acute Chagas disease mouse model.

Swapping the substituents in positions 2 and 4 of the previously synthesized but yet undisclosed 5-cyano-4-(methylthio)-2-arylpyrimidin-6-ones 4 , ring closure, and further optimization led to the identification of the potent antitubercular 2-thio-substituted quinazolinone 26 . Structure-activity relationship (SAR) studies indicated a crucial role for both meta -nitro substituents for antitubercular activity, while the introduction of polar substituents on the quinazolinone core allowed reduction of bovine serum albumin (BSA) binding ( 63c , 63d ). While most of the tested quinazolinones exhibited no cytotoxicity against MRC-5, the most potent compound 26 was found to be mutagenic via the Ames test. This analogue exhibited moderate inhibitory potency against Mycobacterium tuberculosis thymidylate kinase, the target of the 3-cyanopyridones that lies at the basis of the current analogues, indicating that the whole-cell antimycobacterial activity of the present S -substituted thioquinazolinones is likely due to modulation of alternative or additional targets. Diminished antimycobacterial activity was observed against mutants affected in cofactor F 420 biosynthesis ( fbiC ), cofactor reduction ( fgd ), or deazaflavin-dependent nitroreductase activity ( rv3547 ), indicating that reductive activation of the 3,5-dinitrobenzyl analogues is key to antimycobacterial activity.

Trypanosoma cruzi is the causative pathogen of Chagas disease and the main culprit for cardiac-related mortality in Latin-America triggered by an infective agent. Incapable of synthesizing purines de novo, this parasite depends on acquisition and processing of host-derived purines, making purine (nucleoside) analogues a potential source of antitrypanosomal agents. In this respect, hitherto 7-deazaadenosine (tubercidin) analogues attracted most attention. Here, we investigated analogues with an additional nitrogen (N1) removed. Structure-activity relationship investigation showed that C7 modification afforded analogues with potent antitrypanosomal activity. Halogens and small, linear carbon-based substituents were preferred. Compound 11 proved most potent in vitro, showed full suppression of parasitemia in a mouse model of acute infection, and elicited 100% animal survival after oral dosing at 25 mg/kg b.i.d. for 5 and 15 days. Cyclophosphamide-induced immunosuppression led to recrudescence. Washout experiments demonstrated a lack of complete clearance of infected cell cultures, potentially explaining the in vivo results.

Chagas disease is the leading cause of cardiac-related mortality in Latin American countries where it is endemic. Trypanosoma cruzi, the disease-causing pathogen, is unable to synthesize purines de novo, necessitating salvage of preformed host purines. Therefore, purine and purine-nucleoside analogues might constitute an attractive source for identifying antitrypanosomal hits. In this study, structural elements of two purine-nucleoside analogues (i.e., cordycepin and a recently discovered 7-substituted 7-deazaadenosine) led to the identification of novel nucleoside analogues with potent in vitro activity. The structure-activity relationships of substituents at C-7 were investigated, ultimately leading to the selection of compound 5, with a C-7 para-chlorophenyl group, for in vivo evaluation. This derivative showed complete suppression of T. cruzi Y-strain blood parasitemia when orally administered twice daily for 5 days at 25 mg/kg and was able to protect infected mice from parasite-induced mortality. However, sterile cure by immunosuppression could not be demonstrated.

In this study, we designed and synthesized heterobivalent ligands targeting heteromers consisting of the metabotropic glutamate 5 receptor (mGluR5) and the dopamine D 2 receptor (D 2 R). Bivalent ligand 22a with a linker consisting of 20 atoms showed 4-fold increase in affinity for cells coexpressing D 2 R and mGluR5 compared to cells solely expressing D 2 R. Likewise, the affinity of 22a for mGluR5 increased 2-fold in the coexpressing cells. Additionally, 22a exhibited a 5-fold higher mGluR5 affinity than its monovalent precursor 21a in cells coexpressing D 2 R and mGluR5. These results indicate that 22a is able to bridge binding sites on both receptors constituting the heterodimer. Likewise, cAMP assays revealed that 22a had a 4-fold higher potency in stable D 2 R and mGluR5 coexpressing cell lines than 1. Furthermore, molecular modeling reveals that 22a is able to simultaneously bind both receptors by passing between the TM5-TM6 interface and establishing six protein-ligand H-bonds.

In recent years, thymidylate kinase (TMPK), an enzyme indispensable for bacterial DNA biosynthesis, has been pursued for the development of new antibacterial agents including against Mycobacterium tuberculosis, the causative agent for the widespread infectious disease tuberculosis (TB). In response to a growing need for more effective anti-TB drugs, we have built upon our previous efforts toward the exploration of novel and potent Mycobacterium tuberculosis TMPK ( MtTMPK) inhibitors, and reported here the design of a novel series of non-nucleoside inhibitors of MtTMPK. The inhibitors display hitherto unexplored interactions in the active site of MtTMPK, offering new insights into structure-activity relationships. To investigate the discrepancy between enzyme inhibitory activity and the whole-cell activity, experiments with efflux pump inhibitors and efflux pump knockout mutants were performed. The minimum inhibitory concentrations of particular inhibitors increased significantly when determined for the efflux pump mmr knockout mutant, which partly explains the observed dissonance.

Blocking the 2-C-methyl-d-erythrithol-4-phosphate (MEP) pathway for isoprenoid biosynthesis offers interesting prospects for inhibiting Plasmodium or Mycobacterium spp. growth. Fosmidomycin (1) and its homologue FR900098 (2) potently inhibit 1-deoxy-d-xylulose-5-phosphate reductoisomerase (Dxr), a key enzyme in this pathway. Here we introduced aryl or aralkyl substituents at the β-position of the hydroxamate analogue of 2. While direct addition of a β-aryl moiety resulted in poor inhibition, longer linkers between the carbon backbone and the phenyl ring were generally associated with better binding to the enzymes. X-ray structures of the parasite Dxr-inhibitor complexes show that the "longer" compounds generate a substantially different flap structure, in which a key tryptophan residue is displaced, and the aromatic group of the ligand lies between the tryptophan and the hydroxamate's methyl group. Although the most promising new Dxr inhibitors lack activity against Escherichia coli and Mycobacterium smegmatis, they proved to be highly potent inhibitors of Plasmodium falciparum in vitro growth.

To explore the hitherto successful derivatization of the α-carbon of fosmidomycin, a series of new α-substituted analogues was prepared. This was done by introduction of a heteroatom (N or O) in α-position to the phosphonate and using the resultant OH and NH₂ groups as a handle for appending a variety of substituents by means of several functional groups such as ether, amide, urea, and 1,4-triazole. The synthesized molecules, as a racemic mixture, were assayed for their EcDXR inhibitory potency. Both the α-azido-analogue and the α-hydroxylated analogue proved most promising, and docking experiments were performed. Although several compounds showed high potency when assayed against Plasmodium falciparum K1 in human erythrocytes, a clear correlation between the enzyme inhibition constants and P. falciparum inhibition concentrations could not be found.

Three alpha-halogenated analogues of 3-(acetylhydroxyamino)propylphosphonic acid (FR900098) have been synthesized from diethyl but-3-enylphosphonate using a previously described method for the alpha-halogenation of alkylphosphonates. These analogues were evaluated for antimalarial potential in vitro against Plasmodium falciparum and in vivo in the P. berghei mouse model. All three analogues showed higher in vitro and/or in vivo potency than the reference compounds.

In an effort to increase the potency and selectivity of earlier identified substrate-based inhibitors of mitochondrial thymidine kinase 2 (TK-2), we now describe the synthesis of new thymidine analogues containing a 4- or 5-substituted 1,2,3-triazol-1-yl substituent at the 3'-position of the 2'-deoxyribofuranosyl ring. These analogues were prepared by Cu- and Ru-catalyzed cycloadditions of 3'-azido-3'-deoxythymidine and the appropriate alkynes, which produced the 1,4- and 1,5-triazoles, respectively. Selected analogues showed nanomolar inhibitory activity for TK-2, while virtually not affecting the TK-1 counterpart. Enzyme kinetics indicated a competitive and uncompetitive inhibition profile against thymidine and the cosubstrate ATP, respectively. This behavior is rationalized by suggesting that the inhibitors occupy the substrate-binding site in a TK-2-ATP complex that maintains the enzyme's active site in a closed conformation through the stabilization of a small lid domain.

Recently, thymidine monophosphate kinase (TMPK) emerged as an attractive target for developing inhibitors of Mycobacterium tuberculosis growth. The elucidation of the X-ray structure of TMPK of M. tuberculosis (TMPKmt), as well as the structure of an earlier serendipitously discovered dimeric thymidine inhibitor, laid the foundation for the design of potent and selective TMPKmt inhibitors reported here. Several hits identified within a series of 3'-C-branched thiourea-substituted beta-thymidine derivatives inspired us to construct a set of 5'-thiourea-substituted alpha-thymidine derivatives characterized by a similar relative orientation of the thymine and arylthiourea moieties. alpha-Thymidine derivative 15, featuring a (3-trifluoromethyl-4-chlorophenyl)thiourea moiety, has a Ki of 0.6 microM and a selectivity index of 600 versus human TMPK. Moreover, it represents the first TMPK inhibitor showing good inhibitory activity on growing M. bovis (MIC99 = 20 microg/mL) and M. tuberculosis (MIC50 = 6.25 microg/mL) strains.

"Click chemistry" was explored to synthesize two series of 2-(1,2,3-triazolyl)adenosine derivatives (1-14). Binding affinity at the human A(1), A(2A), and A(3)ARs (adenosine receptors) and relative efficacy at the A(3)AR were determined. Some triazol-1-yl analogues showed A(3)AR affinity in the low nanomolar range, a high ratio of A(3)/A(2A) selectivity, and a moderate-to-high A(3)/A(1) ratio. The 1,2,3-triazol-4-yl regiomers typically showed decreased A(3)AR affinity. Sterically demanding groups at the adenine C2 position tended to reduce relative A(3)AR efficacy. Thus, several 5'-OH derivatives appeared to be selective A(3)AR antagonists, i.e., 10, with 260-fold binding selectivity in comparison to the A(1)AR and displaying a characteristic docking mode in an A(3)AR model. The corresponding 5'-ethyluronamide analogues generally showed increased A(3)AR affinity and behaved as full agonists, i.e., 17, with 910-fold A(3)/A(1) selectivity. Thus, N(6)-substituted 2-(1,2,3-triazolyl)adenosine analogues constitute a novel class of highly potent and selective nucleoside-based A(3)AR antagonists, partial agonists, and agonists.

An alternative approach to overcome the inherent lack of specificity of conventional agonist therapy can be the reengineering of the GPCRs and their agonists. A reengineered receptor (neoceptor) could be selectively activated by a modified agonist, but not by the endogenous agonist. Assisted by rhodopsin-based molecular modeling, we pinpointed mutations of the A(3) adenosine receptor (AR) for selective affinity enhancement following complementary modifications of adenosine. Ribose modifications examined included, at 3': amino, aminomethyl, azido, guanidino, ureido; and at 5': uronamido, azidodeoxy. N(6)-Variations included 3-iodobenzyl, 5-chloro-2-methyloxybenzyl, and methyl. An N(6)-3-iodobenzyl-3'-ureido adenosine derivative 10 activated phospholipase C in COS-7 cells (EC(50) = 0.18 microM) or phospholipase D in chick primary cardiomyocytes, both mediated by a mutant (H272E), but not the wild-type, A(3)AR. The affinity enhancements for 10 and the corresponding 3'-acetamidomethyl analogue 6 were >100-fold and >20-fold, respectively. 10 concentration-dependently protected cardiomyocytes transfected with the neoceptor against hypoxia. Unlike 10, adenosine activated the wild-type A(3)AR (EC(50) of 1.0 microM), but had no effect on the H272E mutant A(3)AR (100 microM). Compound 10 was inactive at human A(1), A(2A), and A(2B)ARs. The orthogonal pair comprising an engineered receptor and a modified agonist should be useful for elucidating signaling pathways and could be therapeutically applied to diseases following organ-targeted delivery of the neoceptor gene.

A series of fosmidomycin analogues featuring restricted conformational mobility has been synthesized and evaluated as inhibitors of 1-deoxy-D-xylulose 5-phosphate (DOXP) reductoisomerase and as growth inhibitors of P. falciparum. The enantiomerically pure trans-cyclopropyl N-acetyl analogue 3b showed comparable inhibitory activity as fosmidomycin toward E. coli DOXP reductoisomerase and proved equally active when tested in vitro for P. falciparum growth inhibition. Conversely, the alpha-phenyl cis-cyclopropyl analogue 4 showed virtually no inhibition of the enzyme.

Thymidine monophosphate kinase of Mycobacterium tuberculosis (TMPKmt) represents an attractive target for selectively blocking bacterial DNA synthesis. Hereby, we report on the discovery of a novel class of bicyclic nucleosides (10 and 11) and one dinucleoside (12), belonging to the most selective inhibitors of TMPKmt discovered so far.

A three-dimensional model of the human A(2A) adenosine receptor (AR) and its docked ligands was built by homology to rhodopsin and validated with site-directed mutagenesis and the synthesis of chemically complementary agonists. Different binding modes of A(2A)AR antagonists and agonists were compared by using the FlexiDock automated docking procedure, with manual adjustment. Putative binding regions for the 9H-purine ring in agonist NECA 3 and the 1H-[1,2,4]triazolo[1,5-c]quinazoline ring in antagonist CGS15943 1 overlapped, and the exocyclic amino groups of each were H-bonded to the side chain of N(6.55). For bound agonist, H-bonds formed between the ribose 3'- and 5'-substituents and the hydrophilic amino acids T(3.36), S(7.42), and H(7.43), and the terminal methyl group of the 5'-uronamide interacted with the hydrophobic side chain of F(6.44). Formation of the agonist complex destabilized the ground-state structure of the A(2A)AR, which was stabilized through a network of H-bonding and hydrophobic interactions in the transmembrane helical domain (TM) regions, facilitating a conformational change upon activation. Both flexibility of the ribose moiety, required for the movement of TM6, and its H-bonding to the receptor were important for agonism. Two sets of interhelical H-bonds involved residues conserved among ARs but not in rhodopsin: (1) E13(1.39) and H278(7.43) and (2) D52(2.50), with the highly conserved amino acids N280(7.45) and S281(7.46), and N284(7.49) with S91(3.39). Most of the amino acid residues lining the putative binding site(s) were conserved among the four AR subtypes. The A(2A)AR/3 complex showed a preference for an intermediate conformation about the glycosidic bond, unlike in the A(3)AR/3 complex, which featured an anti-conformation. Hydrophilic amino acids of TMs 3 and 7 (ribose-binding region) were replaced with anionic residues for enhanced binding to amine-derivatized agonists. We identified new neoceptor (T88D)-neoligand pairs that were consistent with the model.

Thymidine monophosphate kinase (TMPK) of Mycobacterium tuberculosis (TMPKmt) represents an attractive target for blocking the bacterial DNA synthesis. In an attempt to find high-affinity inhibitors of TMPKmt, a cavity in the enzyme at the 3'-position was explored via the introduction of various substituents at the 3'-position of the thymidine monophosphate (dTMP) scaffold. Various 3'-C-branched chain substituted nucleotides in the 2'-deoxyribo (3-6) and ribo series (7, 8) were synthesized from one key intermediate (23). 2'-Deoxy analogues proved to be potent inhibitors of TMPKmt: 3'-CH(2)NH(2) (4), 3'-CH(2)N(3) (3), and 3'-CH(2)F (5) nucleotides exhibit the highest affinities within this series, with K(i) values of 10.5, 12, and 15 microM, respectively. These results show that TMPKmt tolerates the introduction of sterically demanding substituents at the 3'-position. Ribo analogues experience a significant affinity decrease, which is probably due to steric hindrance of Tyr103 in close vicinity of the 2'-position. Although the 5'-O-phosphorylated compounds have somewhat higher affinities for the enzyme, the parent nucleosides generally exhibit affinities for TMPKmt in the same order of magnitude and display a superior selectivity profile versus human TMPK. This series of inhibitors holds promise for the development of a new class of antituberculosis agents.

The synthesis and structure-activity relationship of N(6)-cyclopentyl-3'-substituted-xylofuranosyladenosine analogues with respect to various adenosine receptors were explored in order to identify selective and potent antagonists and inverse agonists for the adenosine A(1) receptor. In particular, the effects of removal of the 5'-OH group and introduction of selected substituents at the 3'-NH(2) position of 9-(3-amino-3-deoxy-beta-D-xylofuranosyl)-N(6)-cyclopentyladenine were probed. A solid phase-assisted synthetic approach was used to optimize the 3'-amide functionality. In view of the general concern of the presence of a 5'-OH moiety with regard to cellular toxicity, the present study describes 5'-deoxy compounds with reasonable affinity for the human adenosine A(1) receptor. Interestingly, this study shows that optimization of the 3'-"up" amide substituent can substantially compensate for the drop in affinity for the adenosine A(1) receptor, which is generally observed upon removal of the 5'-OH group. The fact that for several 3'-amido-substituted (5'-deoxy)-N(6)-cyclopentyladenosine derivatives, guanosine 5'-triphosphate-induced shifts in K(i) values were significantly lower than 1 implies that these analogues behave as inverse agonists. This is further supported by their 1,3-dipropyl-8-cyclopentylxanthine-like capacity to increase forskolin-induced adenosine cyclic 3',5'-phosphate production.

Adenosine A(3) receptors are of interest in the treatment of cardiac ischemia, inflammation, and neurodegenerative diseases. In an effort to create a unique receptor mutant that would be activated by tailor-made synthetic ligands, we mutated the human A(3) receptor at the site of a critical His residue in TM7, previously proposed to be involved in ligand recognition through interaction with the ribose moiety. The H272E mutant receptor displayed reduced affinity for most of the uncharged A(3) receptor agonists and antagonists examined. For example, the nonselective agonist 1a was 19-fold less potent at the mutant receptor than at the wild-type receptor. The introduction of an amino group on the ribose moiety of adenosine resulted in either equipotency or enhanced binding affinity at the H272E mutant relative to wild-type A(3) receptors, depending on the position of the amino group. 3'-Amino-3'-deoxyadenosine proved to be 7-fold more potent at the H272E mutant receptor than at the wild-type receptor, while the corresponding 2'- and 5'-amino analogues did not display significantly enhanced affinities. An 3'-amino-N(6)-iodobenzyl analogue showed only a small enhancement at the mutant (K(i) = 320 nM) vs wild-type receptors. The 3'-amino group was intended for a direct electrostatic interaction with the negatively charged ribose-binding region of the mutant receptor, yet molecular modeling did not support this notion. This design approach is an example of engineering the structure of mutant receptors to recognize synthetic ligands for which they are selectively matched on the basis of molecular complementarity between the mutant receptor and the ligand. We have termed such engineered receptors "neoceptors", since the ligand recognition profile of such mutant receptors need not correspond to the profile of the parent, native receptor.

The biological activity of synthetic ceramide analogues, having modified sphingoid and N-acyl chains, as well as fluorine substituents in the allylic position, was investigated in hippocampal neurons. Their influence on axonal growth was compared to that of C(6)-N-acyl analogues of natural ceramides. D-erythro-Ceramides with a phenyl group in the sphingoid moiety and a short N-acyl chain were able to reverse the inhibitory effect of fumonisin B(1) (FB(1)), but not of D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), on accelerated axonal growth in hippocampal neurons. Moreover, we demonstrated that a ceramide analogue with an aromatic ring in the sphingoid moiety is recognized as a substrate by glucosylceramide synthase, which suggests that the observed biological effects are mediated by activation of the ceramide analogue via glucosylation. Introduction of a methyl, pentyl, fluoro, or methoxy substituent in the para position of the phenyl ring in the sphingoid moiety yielded partly active compounds. Likewise, substitution of the benzene ring for a thienyl group did not abolish the ability to reverse the inhibition of accelerated axonal growth by FB(1). Both D-erythro- and L-threo-ceramide analogues, having an allylic fluorine substituent, partly reversed the FB(1) inhibition.

A series of D-erythro- and L-threo-ceramide analogues was synthesized and investigated for their ability to reverse the inhibitory effects of fumonisin B(1) (FB(1)) on axonal growth in hippocampal neurons. The analogues contained either a C(7) side chain or a phenyl group substituted for the C(13) residue present in naturally occurring ceramides, while the N-acyl chain length was reduced from C(16)-C(24) to C(2)-C(8). D-erythro-Ceramide 18a with a C(7) side chain and an N-acetyl residue and D-erythro-ceramide 20c with an aromatic side chain and an N-hexanoyl residue were most active in reversing the inhibitory effects of FB(1) on axonal growth, although the mechanism remains unclear.

The present study explores the C-3' site of the 3-deoxy-3-xylofuranosyl ring of nucleoside analogues with an adenine or N6-cyclopentyladenine (CPA) base moiety and evaluates the effect on adenosine receptor affinity. Two series of sugar-modified adenosines, i.e., 3'-amido-3'-deoxyadenosines and 3'-amidated 3'-deoxyxylofuranosyladenines, were synthesized and tested for their affinity at A1 and A2a receptors in rat brain cortex and rat striatum, respectively. The modest affinity found in the "xylo series" prompted us to synthesize the corresponding N6-cyclopentyl derivatives, which proved to be well accommodated by the A1 receptors with potencies in the lower nanomolar range. This represents a new perspective in the purinergic field. The absence of a GTP-induced shift, i.e., the ratio between the affinities measured in the presence and absence of 1 mM GTP indicates an antagonistic behavior of this new class of CPA analogues.

In continuation of a project aimed at the structure-based design of drugs against sleeping sickness, analogs of 2'-deoxy-2'-(3-methoxybenzamido)adenosine (1) were synthesized and tested to establish structure-activity relationships for inhibiting glycosomal glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Compound 1 was recently designed using the NAD:GAPDH complexes of the human enzyme and that of Trypanosoma brucei, the causative agent of sleeping sickness. In an effort to exploit an extra hydrophobic domain due to Val 207 of the parasite enzyme, several new 2'-amido-2'-deoxyadenosines were synthesized. Some of them displayed an interesting improvement in inhibitory activity compared to 1. Carbocyclic or acyclic analogs showed marked loss of activity, illustrating the importance of the typical (C-2'-endo) puckering of the ribose moiety. We also describe the synthesis of a pair of compounds that combine the beneficial effects of a 2- and 8-substituted adenine moiety on potency with the beneficial effect of a 2'-amido moiety on selectivity. Unfortunately, in both cases, IC50 values demonstrate the incompatibility of these combined modifications. Finally, introduction of a hydrophobic 5'-amido group on 5'-deoxyadenosine enhances the inhibition of the protozoan enzyme significantly, although the gain in selectivity is mediocre.

Within the framework of a project aimed at rational design of drugs against diseases caused by trypanosomes and related hemoflagellate parasites, selective inhibitors of trypanosomal glycolysis were designed, synthesized, and tested. The design was based upon the crystallographically determined structures of the NAD:glyceraldehyde-3-phosphate dehydrogenase complexes of humans and Trypanosoma brucei, the causative agent of sleeping sickness. After one design cycle, using the adenosine part of the NAD cofactor as a lead, the following encouraging results were obtained: (1) a 2-methyl substitution, targeted at a small pocket near Val 36, improves inhibition of the parasite enzyme 12.5-fold; (2) an 8-(thien-2-yl) substitution, aimed at Leu 112 of the parasite enzyme, where the equivalent residue in the mammalian enzyme is Val 100, results in a 167-fold better inhibition of the trypanosomal enzyme, while the inhibition of the human enzyme is improved only 13-fold; (3) exploitation of a "selectivity cleft" created by a unique backbone conformation in the trypanosomal enzyme near the adenosine ribose yields a considerable improvement in selectivity: 2'-deoxy-2'-(3-methoxybenzamido)adenosine inhibits the human enzyme only marginally but enhances inhibition of the parasite enzyme 45-fold when compared with adenosine. The designed inhibitors are not only better inhibitors of T. brucei GAPDH but also of the enzyme from Leishmania mexicana.