Stella Manta

The σ-hole phenomenon of halogen atoms forms the structural basis of the strong inhibitory potency of C5 halogen substituted glucopyranosyl nucleosides towards glycogen phosphorylase b.

C5 halogen substituted glucopyranosyl nucleosides (1‐(β‐D‐glucopyranosyl)‐5‐X‐uracil; X=Cl, Br, I) have been discovered as some of the most potent active site inhibitors of glycogen phosphorylase (GP), with respective Ki values of 1.02, 3.27, and 1.94 μM. The ability of the halogen atom to form intermolecular electrostatic interactions through the σ‐hole phenomenon rather than through steric effects alone forms the structural basis of their improved inhibitory potential relative to the unsubstituted 1‐(β‐D‐glucopyranosyl)uracil (Ki=12.39 μM), as revealed by X‐ray crystallography and modeling calculations exploiting quantum mechanics methods. Good agreement was obtained between kinetics results and relative binding affinities calculated by QM/MM‐PBSA methodology for various substitutions at C5. Ex vivo experiments demonstrated that the most potent derivative (X=Cl) toward purified GP has no cytotoxicity and moderate inhibitory potency at the cellular level. In accordance, ADMET property predictions were performed, and suggest decreased polar surface areas as a potential means of improving activity in the cell.

Antiviral Unsaturated Nucleosides

In the search for effective, selective and nontoxic antiviral agents, a variety of nucleoside analogues have been synthesized, with different functionalities in the carbohydrate moiety. Unsaturated nucleoside analogues are recognized as an important class of biologically active compounds and appear to be prominent drugs in the management of several viral infections, including HSV, HIV, HBV, HCV and HCMV infections. Currently, unsaturated nucleoside mimetics, such as stavudine, abacavir and entecavir have been approved for the treatment of viral infections, while elvucitabine and � -L-2� - F-d4C are in clinical trials. The purpose of this review is to give an update of the recent developments on unsaturated nu- cleoside and nucleoside analogues, in both cyclic and acyclic forms, which possess promising therapeutic potential, mainly antiviral. It covers analogues with ring sizes from three to six and provides useful data, in the aim to enhance chemical reactivity or to study the fixation of the sugar conformation.

The binding of C5-alkynyl and alkylfurano[2,3-d]pyrimidine glucopyranonucleosides to glycogen phosphorylase b: Synthesis, biochemical and biological assessment.

C5-alkynyl and alkylfurano[2,3-d]pyrimidine glucopyranonucleosides have been synthesized and studied as inhibitors of glycogen phosphorylase b (GPb). Kinetic experiments have shown that most of these compounds were low micromolar inhibitors of the enzyme. The best inhibitor was 1-(β-D-glucopyranosyl)-5-ethynyluracil (K(i)=4.7 μM). Crystallographic analysis of these compounds in complex with GPb revealed that inhibitors with a long C5-alkynyl group exploited interactions with β-pocket of the active site and induced significant conformational changes of the 280s loop compared to GPb in complex with compounds with a short C5-alkynyl group. The results highlight the importance in the length of the aliphatic groups used to enhance inhibitory potency for the exploitation of the hydrophobic β-pocket. The best of the inhibitors had also a moderate effect on glycogenolysis in the cellular lever with an IC(50) value of 291.4 μM.

Dissipation, metabolism and sorption of pesticides used in fruit-packaging plants: Towards an optimized depuration of their pesticide-contaminated agro-industrial effluents.

Wastewaters from the fruit-packaging industry constitute a serious point source contamination with pesticides. In the absence of effective depuration methods, they are discharged in municipal wastewater treatment plants or spread to land. Modified biobeds could be an applicable solution for their treatment. We studied the dissipation of thiabendazole (TBZ), imazalil (IMZ), ortho-phenylphenol (OPP), diphenylamine (DPA) and ethoxyquin (EQ), used by the fruit-packaging industry, in anaerobically digested sewage sludge, liquid aerobic sewage sludge and in various organic substrates (biobeds packing materials) composed of soil, straw and spend mushroom substrate (SMS) in various volumetric ratios. Pesticide sorption was also determined. TBZ and IMZ showed higher persistence especially in the anaerobically digested sewage sludge (DT50=32.3-257.6d), in contrast to OPP and DPA which were rapidly dissipated especially in liquid aerobic sewage sludge (DT50=1.3-9.3d). EQ was rapidly oxidized mainly to quinone imine (QI) which did not persist and dimethyl ethoxyquinoline (EQNL, minor metabolite) which persisted for longer. Sterilization of liquid aerobic sewage sludge inhibited pesticide decay verifying the microbial nature of pesticide dissipation. Organic substrates rich in SMS showed the highest dissipation capacity with TBZ and IMZ DT50s of ca. 28 d compared to DT50s of >50 d in the other substrates. TBZ and IMZ showed the highest sorption affinity, whereas OPP and DPA were weakly sorbed. Our findings suggest that current disposal practices could not guarantee an efficient depuration of effluents from the fruit-packaging industry, whereas SMS-rich biobed organic substrates show efficient depuration of effluents from the fruit-packaging industry via accelerated dissipation even of recalcitrant fungicides.

3′‐Axial CH2OH Substitution on Glucopyranose does not Increase Glycogen Phosphorylase Inhibitory Potency. QM/MM‐PBSA Calculations Suggest Why

Glycogen phosphorylase is a molecular target for the design of potential hypoglycemic agents. Structure‐based design pinpointed that the 3′‐position of glucopyranose equipped with a suitable group has the potential to form interactions with enzyme’s cofactor, pyridoxal 5′‐phosphate (PLP), thus enhancing the inhibitory potency. Hence, we have investigated the binding of two ligands, 1‐(β‐d‐glucopyranosyl)5‐fluorouracil (GlcFU) and its 3′‐CH2OH glucopyranose derivative. Both ligands were found to be low micromolar inhibitors with Ki values of 7.9 and 27.1 μm, respectively. X‐ray crystallography revealed that the 3′‐CH2OH glucopyranose substituent is indeed involved in additional molecular interactions with the PLP γ‐phosphate compared with GlcFU. However, it is 3.4 times less potent. To elucidate this discovery, docking followed by postdocking Quantum Mechanics/Molecular Mechanics – Poisson–Boltzmann Surface Area (QM/MM‐PBSA) binding affinity calculations were performed. While the docking predictions failed to reflect the kinetic results, the QM/MM‐PBSA revealed that the desolvation energy cost for binding of the 3′‐CH2OH‐substituted glucopyranose derivative out‐weigh the enthalpy gains from the extra contacts formed. The benefits of performing postdocking calculations employing a more accurate solvation model and the QM/MM‐PBSA methodology in lead optimization are therefore highlighted, specifically when the role of a highly polar/charged binding interface is significant.

Dideoxy fluoro-ketopyranosyl nucleosides as potent antiviral agents: Synthesis and biological evaluation of 2,3- and 3,4-dideoxy-3-fluoro-4-and -2-keto-β-D-glucopyranosyl derivatives of N4-benzoyl cytosine

Abstract The synthesis of the dideoxy fluoro ketopyranonucleoside analogues, 1-(2,3-dideoxy-3-fluoro-6-O-trityl-β-d-glycero-hexopyranosyl-4-ulose)-N 4-benzoyl cytosine (7a), 1-(3,4-dideoxy-3-fluoro-6-O-trityl-β-d-glycero-hexopyranosyl-2-ulose)-N 4-benzoyl cytosine (13a) and their detritylated analogues 8a and 14a, respectively, is described. Condensation of peracetylated 3-deoxy-3-fluoro-d-glucopyranose (1) with silylated N 4-benzoyl cytosine, followed by selective deprotection and isopropylidenation afforded compound 2. Routine deoxygenation at position 2′, followed by a deprotection-selective reprotection sequence afforded the partially tritylated dideoxy nucleoside of cytosine 6, which upon oxidation of the free hydroxyl group at the 4′-position, furnished the desired tritylated 2,3-dideoxy-3-fluoro ketonucleoside 7a in equilibrium with its hydrated form 7b. Compound 2 was the starting material for the synthesis of the dideoxy fluoro ketopyranonucleoside 13a. Similarly, several subsequent protection and deprotection steps as well as routine deoxygenation at position 4′, followed by oxidation of the free hydroxyl group at the 2′-position of the partially tritylated dideoxy nucleoside 12, yielded the desired carbonyl compound 13a in equilibrium with its hydrated form 13b. Finally, trityl removal from 7a/b and 13a/b provided the unprotected 2,3-dideoxy-3-fluoro-4-keto and 3,4-dideoxy-3-fluoro-2-ketopyranonucleoside analogues 8a and 14a, in equilibrium with their gem-diol forms 8b and 14b. None of the compounds showed inhibitory activity against a wide variety of DNA and RNA viruses at subtoxic concentrations, except 7a/b that was highly efficient against rotavirus infection. Nucleoside 7a/b also exhibited cytostatic activity against cells of various cancers. BrdU-cell cycle analysis revealed that the mechanism of cytostatic activity may be related to a delay in G1/S phase and initiation of programmed cell death.

Synthesis, Antiviral and Cytostatic Evaluation of Unsaturated Exomethylene and Keto D-Lyxopyranonucleoside Analogues

This report describes the synthesis of unsaturated exomethylene lyxopyranonucleoside analogues as potential biologically active agents. Commercially available 1,2,3,4‐tetra‐O‐acetyl‐α‐D‐lyxopyranose 1 was condensed with silylated thymine and uracil, respectively, deacetylated and acetalated to afford 1‐(2,3‐O‐isopropylidene‐α‐D‐lyxopyranosyl)thymine 4a and 1‐(2,3‐O‐isopropylidene‐α‐D‐lyxopyranosyl)uracil 4b. The new derivatives 1‐(2,3,4‐trideoxy‐4‐methylene‐α‐pent‐2‐enopyranosyl)thymine 8a and 1‐(2,3,4‐trideoxy‐4‐methylene‐α‐pent‐2‐enopyranosyl)uracil 8b were prepared via two different key intermediates, 7a, b and 13a, b in order to elucidate the influence of 2′,3′‐unsaturation and to clarify the difference between the keto and exomethylene group on the biological activity of the target molecules. Compounds 7a, b, 8a, b, and 13a, b were evaluated for their antiviral and cytostatic activity using several virus strains and cell lines. Whereas no marked antiviral activity was noticed, 13a and 13b showed a cytostatic activity that ranged between 7 and 23 μM for 13a and 26 and 38 μM for 13b against murine leukemia L1210, human lymphocyte Molt4/C8 and CEM cells, and human breast carcinoma MCF7 cells.

Study of the interaction among Notch pathway receptors, correlation with stemness, as well as their interaction with CD44, dipeptidyl peptidase-IV, hepatocyte growth factor receptor and the SETMAR transferase, in colon cancer stem cells

Abstract Context: The Notch signaling pathway is one of the most important pathways during normal development and implicated in self-renewal of adult stem cells and differentiation of progenitor cells. Abnormal expression of Notch receptors has been associated with many epithelial metaplastic and neoplastic lesions. Objective-materials and methods: In this particular study, it was determined the relative gene expression of Notch receptors after knockdown experiments in colon cancer stem cells (CSCs) and the gene expression changes in stemness transcription factors (Oct4, Sox2, Nanog), as well in dipeptidylpeptidase-4, CD44 antigen, Met proto-oncogene and in Metnase transposase. Results: In control CSCs Notch-2 had the higher expression, followed by Notch-1, Notch-3. Notch-4 demonstrated the lower gene expression among the receptors. The suppression of Notch-1 led to increased expression of Oct4 and Sox2, but in decreased gene expression of cMET, Setmar and CD44. The CD26 expression remained unchanged. The knockdown of Notch-2 led to decreased expression of all transcription factors. Notch-3 down regulation caused increased Oct4 gene expression, but decreased levels for the rest of the genes. Finally, the suppression of Notch-4 had the same effect as in receptor Notch-3. Discussion and conclusion: The above experimental data suggest the possible interaction between the four different receptors of Notch signaling pathway. The expression of CD26, cMET and N-methyltransferase Setmar was also changed. Finally, the stemness phenotype was changed in a different way each time, according to the receptor that was down regulated. All Notch receptors and particularly Notch-2 seem to play an important role in cancer stem cells.

Branched-chain C-cyano pyranonucleosides: Synthesis of 3'-C-cyano & 3'-C-cyano-3'-deoxy pyrimidine pyranonucleosides as novel cytotoxic agents

Abstract This report describes the total and facile synthesis of 3′-C-cyano & 3′-C-cyano-3′-deoxy pyrimidine pyranonucleosides. Reaction of 3-keto glucoside 1 with sodium cyanide gave the desired precursor 3-C-cyano-1,2:5,6-di-O-isopropylidene-α-D-glucofuranose (2). Hydrolysis followed by acetylation led to the 1,2,3,4,6-penta-O-acetyl-3-C-cyano-D-glucopyranose (4). Compound 4 was condensed with silylated 5-fluorouracil, uracil, thymine and N 4-benzoylcytosine, respectively and deacetylated to afford the target 1-(3′-C-cyano-β-D-glucopyranosyl)nucleosides 6a–d. Routine deoxygenation at position 3′ of cyanohydrin 2, followed by hydrolysis and acetylation led to the 3-C-cyano-3-deoxy-1,2,4,6-tetra-O-acetyl-D-allopyranose (10). Coupling of sugar 10 with silylated pyrimidines and subsequent deacetylation yielded the target 1-(3′-C-cyano-3′-deoxy-β-D-allopyranosyl)nucleosides 12a–d. The new analogues were evaluated for their antiviral and cytostatic activities. It was found that 6a was endowed with a pronounced anti-proliferative activity that was only 2- to 8-fold less potent than that shown for the parental base 5-fluorouracil. None of the compounds showed activity against a broad panel of DNA and RNA viruses.

A Facile, One‐Step Conversion of 6‐O‐Trityl and 6‐O‐TBDMS Monosaccharides into the Corresponding Formate Esters

A convenient method has been developed for a facile and high‐yield conversion of 6‐O‐tert‐butyldimethylsilyl and 6‐O‐trityl protected monosaccharides to their formate esters, which may serve as useful intermediates for the replacement of the primary hydroxyl group of sugars by other functional groups.