1,2,3-Triazolylalkylribitol derivatives as nucleoside hydrolase inhibitors

1,5-disubstituted 1,2,3-triazolylated carbohydrates and nucleosides

In general, 1,5-disubstituted 1,2,3-triazolyl moiety is much less common in the synthesis and applications in comparison to its regioisomeric counterpart. Moreover, the synthesis of 1,5-disubstituted 1,2,3-triazoles are not so straightforward as is the case for copper catalyzed strategy of 1,4-disubstituted 1,2,3-triazoles. The preparation of 1,5-triazolylated carbohydrates and nucleosides are even more complex because of the difficulties in accessing the appropriate starting materials as well as the compatibility of reaction conditions with the various protecting groups. 1,5-Disubstitution regioisomeric triazoles of carbohydrates and nucleosides were traditionally obtained as minor products through straightforward heating of the mixture of azides and terminal alkynes. However, the separation of isomers was tedious or in some cases futile. On the other hand, regioselective synthesis using ruthenium catalysis triggered serious concern of residual metal content in therapeutically important ingredients. Therefore, serious efforts are being made by several groups to develop non-toxic metal based or completely metal-free synthesis of 1,5-disubstituted 1,2,3-triazoles. This article strives to summarize the pre-Click era as well as the post-2001 reports on the synthesis and potential applications of 1,5-disubstituted 1,2,3-triazoles in biological systems.

Insights into nucleoside hydrolase from Leishmania donovani inhibition: A new bioaffinity chromatography-based screening assay and docking studies

Leishmaniasis, a group of neglected infectious diseases, encompasses a serious health concern, particularly with visceral leishmaniasis exhibiting potentially fatal outcomes. Nucleoside hydrolase (NH) has a fundamental role in the purine salvage pathway, crucial for Leishmania donovani survival, and presents a promising target for developing new drugs for visceral leishmaniasis treatment. In this study, LdNH was immobilized into fused silica capillaries, resulting in immobilized enzyme reactors (IMERs). The LdNH-IMER activity was monitored on-flow in a multidimensional liquid chromatography system, with the IMER in the first dimension. A C18 analytical column in the second dimension furnished the rapid separation of the substrate (inosine) and product (hypoxanthine), enabling direct enzyme activity monitoring through product quantification. LdNH-IMER exhibited high stability and was characterized by determining the Michaelis-Menten constant. A known inhibitor (1-(β-d-Ribofuranosyl)-4-quinolone derivative) was used as a model to validate the established method in inhibitor recognition. Screening of three additional derivatives of 1-(β-d-Ribofuranosyl)-4-quinolone led to the discovery of novel inhibitors, with compound 2a exhibiting superior inhibitory activity (Ki = 23.37 ± 3.64 µmol/L) compared to the employed model inhibitor. Docking and Molecular Dynamics studies provided crucial insights into inhibitor interactions at the enzyme active site, offering valuable information for developing new LdNH inhibitors. Therefore, this study presents a novel screening assay and contributes to the development of potent LdNH inhibitors.

Structure, Oligomerization and Activity Modulation in N-Ribohydrolases

Enzymes catalyzing the hydrolysis of the N-glycosidic bond in nucleosides and other ribosides (N-ribohydrolases, NHs) with diverse substrate specificities are found in all kingdoms of life. While the overall NH fold is highly conserved, limited substitutions and insertions can account for differences in substrate selection, catalytic efficiency, and distinct structural features. The NH structural module is also employed in monomeric proteins devoid of enzymatic activity with different physiological roles. The homo-oligomeric quaternary structure of active NHs parallels the different catalytic strategies used by each isozyme, while providing a buttressing effect to maintain the active site geometry and allow the conformational changes required for catalysis. The unique features of the NH catalytic strategy and structure make these proteins attractive targets for diverse therapeutic goals in different diseases.

Structural explanation for the tunable substrate specificity of an E. coli nucleoside hydrolase: insights from molecular dynamics simulations

Parasitic protozoa rely on nucleoside hydrolases that play key roles in the purine salvage pathway by catalyzing the hydrolytic cleavage of the N-glycosidic bond that connects nucleobases to ribose sugars. Cytidine-uridine nucleoside hydrolase (CU-NH) is generally specific toward pyrimidine nucleosides; however, previous work has shown that replacing two active site residues with Tyr, specifically the Thr223Tyr and Gln227Tyr mutations, allows CU-NH to process inosine. The current study uses molecular dynamics (MD) simulations to gain atomic-level insight into the activity of wild-type and mutant E. coli CU-NH toward inosine. By examining systems that differ in the identity and protonation states of active site catalytic residues, key enzyme-substrate interactions that dictate the substrate specificity of CU-NH are identified. Regardless of the wild-type or mutant CU-NH considered, our calculations suggest that inosine binding is facilitated by interactions of the ribose moiety with active site residues and Ca²⁺, and π-interactions between two His residues (His82 and His239) and the nucleobase. However, the lack of observed activity toward inosine for wild-type CU-NH is explained by no residue being correctly aligned to stabilize the departing nucleobase. In contrast, a hydrogen-bonding network between hypoxanthine and a newly identified general acid (Asp15) is present when the two Tyr mutations are engineered into the active site. Investigation of the single CU-NH mutants reveals that this hydrogen-bonding network is only maintained when both Tyr mutations are present due to a π-interaction between the residues. These results rationalize previous experiments that show the single Tyr mutants are unable to efficiently hydrolyze inosine and explain how the Tyr residues work synergistically in the double mutant to stabilize the nucleobase leaving group during hydrolysis. Overall, our simulations provide a structural explanation for the substrate specificity of nucleoside hydrolases, which may be used to rationally develop new treatments for kinetoplastid diseases.

Antifungal activity of 1'-homo-N-1,2,3-triazol-bicyclic carbonucleosides: A novel type of compound afforded by azide-enolate (3+2) cycloaddition

The first report of 1'-homo-N-1,2,3-triazol-bicyclic carbonucleosides (7a and 7b) is described herein. Azide-enolate (3+2) cycloaddition afforded the synthesis of this novel type of compound. Antifungal activity was evaluated in vitro against four filamentous fungi (Aspergillus fumigatus, Trichosporon cutaneum, Rhizopus oryzae and Mucor hiemalis) as well as nine species of Candida spp. as yeast specimens. These pre-clinical studies suggest that compounds 7a and 7b are promising candidates for complementary biological studies due to their good activity against Candida spp.

N-Arylmethyl substituted iminoribitol derivatives as inhibitors of a purine specific nucleoside hydrolase

A key enzyme within the purine salvage pathway of parasites, nucleoside hydrolase, is proposed as a good target for new antiparasitic drugs. We have developed N-arylmethyl-iminoribitol derivatives as a novel class of inhibitors against a purine specific nucleoside hydrolase from Trypanosoma vivax. Several of our inhibitors exhibited low nanomolar activity, with 1,4-dideoxy-1,4-imino-N-(8-quinolinyl)methyl-d-ribitol (UAMC-00115, K(i) 10.8nM), N-(9-deaza-adenin-9-yl)methyl-1,4-dideoxy-1,4-imino-d-ribitol (K(i) 4.1nM), and N-(9-deazahypoxanthin-9-yl)methyl-1,4-dideoxy-1,4-imino-d-ribitol (K(i) 4.4nM) being the three most active compounds. Docking studies of the most active inhibitors revealed several important interactions with the enzyme. Among these interactions are aromatic stacking of the nucleobase mimic with two Trp-residues, and hydrogen bonds between the hydroxyl groups of the inhibitors and amino acid residues in the active site. During the course of these docking studies we also identified a strong interaction between the Asp40 residue from the enzyme and the inhibitor. This is an interaction which has not previously been considered as being important.