Enhancement of O-GlcNAcylation on Mitochondrial Proteins with 2-(4-Methoxyphenyl)Ethyl-2-Acetamido-2-Deoxy-β-d-Pyranoside, Contributes to the Mitochondrial Network, Cellular Bioenergetics and Stress Response in Neuronal Cells under Ischemic-like Conditions

O-GlcNAcylation is a nutrient-driven post-translational modification known as a metabolic sensor that links metabolism to cellular function. Recent evidences indicate that the activation of O-GlcNAc pathway is a potential pro-survival pathway and that acute enhancement of this response is conducive to the survival of cells and tissues. 2-(4-methoxyphenyl)ethyl-2-acetamido-2-deoxy-β-d-pyranoside (SalA-4g), is a salidroside analogue synthesized in our laboratory by chemical structure-modification, with a phenyl ring containing a para-methoxy group and a sugar ring consisting of N-acetylglucosamine. We have previously shown that SalA-4g elevates levels of protein O-GlcNAc and improves neuronal tolerance to ischemia. However, the specific target of SalA-4g regulating O-GlcNAcylation remains unknown. To address these questions, in this study, we have focused on mitochondrial network homeostasis mediated by O-GlcNAcylation in SalA-4g’s neuroprotection in primary cortical neurons under ischemic-like conditions. O-GlcNAc-modified mitochondria induced by SalA-4g demonstrated stronger neuroprotection under oxygen glucose deprivation and reoxygenation stress, including the improvement of mitochondrial homeostasis and bioenergy, and inhibition of mitochondrial apoptosis pathway. Blocking mitochondrial protein O-GlcNAcylation with OSMI-1 disrupted mitochondrial network homeostasis and antagonized the protective effects of SalA-4g. Collectively, these data demonstrate that mitochondrial homeostasis mediated by mitochondrial protein O-GlcNAcylation is critically involved in SalA-4g neuroprotection.

Selenium-Containing Polysaccharides—Structural Diversity, Biosynthesis, Chemical Modifications and Biological Activity

Selenosugars are a group of sugar derivatives of great structural diversity (e.g., molar masses, selenium oxidation state, and selenium binding), obtained as a result of biosynthesis, chemical modification of natural compounds, or chemical synthesis. Seleno-monosaccharides and disaccharides are known to be non-toxic products of the natural metabolism of selenium compounds in mammals. In the case of the selenium-containing polysaccharides of natural origin, their formation is also postulated as a form of detoxification of excess selenium in microorganisms, mushroom, and plants. The valency of selenium in selenium-containing polysaccharides can be: 0 (encapsulated nano-selenium), IV (selenites of polysaccharides), or II (selenoglycosides or selenium built into the sugar ring to replace oxygen). The great interest in Se-polysaccharides results from the expected synergy between selenium and polysaccharides. Several plant- and mushroom-derived polysaccharides are potent macromolecules with antitumor, immunomodulatory, antioxidant, and other biological properties. Selenium, a trace element of fundamental importance to human health, has been shown to possess several analogous functions. The mechanism by which selenium exerts anticancer and immunomodulatory activity differs from that of polysaccharide fractions, but a similar pharmacological effect suggests a possible synergy of these two agents. Various functions of Se-polysaccharides have been explored, including antitumor, immune-enhancement, antioxidant, antidiabetic, anti-inflammatory, hepatoprotective, and neuroprotective activities. Due to being non-toxic or much less toxic than inorganic selenium compounds, Se-polysaccharides are potential dietary supplements that could be used, e.g., in chemoprevention.

HIV reverse transcriptase pre-steady-state kinetic analysis of chain terminators and translocation inhibitors reveals interactions between magnesium and nucleotide 3’-OH

Deoxythymidine triphosphate analogs with various 3’ groups (-OH (dTTP), -H, -N3, -NH2, -F, -O- CH3, and no group (2′,3′-didehydro-2′,3′-dideoxythymidine triphosphate (d4TTP)), and those retaining the 3’-OH but with 4’ additions (4’-C-methyl, 4’-C-ethyl) or sugar ring modifications (D-carba dTTP) were evaluated using pre-steady-state kinetics in low (0.5 mM) and high (6 mM) Mg2+ with HIV reverse transcriptase (RT). All analogs showed diminished incorporation compared to dTTP ranging from about 2-fold (3’-H, -N3, and d4TTP with 6 mM Mg2+) to >10-fold (3’-NH2 and 3’-F with 0.5 mM Mg2+). The exception was 3’-O-CH3 dTTP which was incorporate profoundly more slowly than other analogs. The incorporation rate (k) using 5 µM dTTP and 0.5 mM (free) Mg2+ was modestly slower (1.6-fold) than with 6 mM Mg2+, while analogs with 3’ modifications were incorporated more slowly (2.8-5.1-fold) in 0.5 mM Mg2+. In contrast, 4’-C-methyl and D-carb, which retain the 3’-OH, were not significantly affected by Mg2+. Consistent with the above results, analogs with 3’ modifications were better inhibitors with 6 mM vs. 0.5 mM Mg2+, in primer extension reactions on a long template. Equilibrium dissociation constant (Kd) and kpol determinations for dTTP and analogs lacking a 3’-OH indicated that low Mg2+ caused a several-fold greater reduction in kpol with the analogs but had little effect on Kd. Overall, results emphasize the importance of as yet undefined interactions between Mg2+ and the 3’-OH and indicate that inhibitors with 3’-OH groups may have an advantage in a physiological setting where the concentration of free Mg2+ is low.

Pyranoid Spirosugars as Enzyme Inhibitors

Background: Pyranoid spirofused sugar derivatives represent a class of compounds with a significant impact in the literature. Under the structural point of view, the rigidity inferred by the spirofused entity has made these compound object of interest mainly as enzymatic inhibitors, in particular of carbohydrate processing enzymes among which glycogen phosphorylase and sodium glucose co-transporter 2, important target enzymes for diverse pathological states. Most of the developed compounds present the spirofused entity at the C1 position of the sugar moiety, nevertheless spirofused entities can also be found at other sugar ring positions. The main spirofused entities encountered are spiroacetals/thioacetals, spiro-hydantoin and derivatives, spiro-isoxazolines, spiro-aminals, spiro-lactams, spiro-oxathiazole and spiro-oxazinanone, but also other are present. Objectives: The present review focuses on the most explored synthetic strategies for the preparation of this class of compounds, classified according to the position and structure of the spirofused moiety on the pyranoid scaffold. Moreover, the structures are correlated to their main biological activities or to their role as chiral auxiliaries. Conclusion: It is clear from the review that, among the different derivatives, the spirofused structures at position C1 of the pyranoid scaffold are the most represented and possess the most relevant enzymatic inhibitor activities. Nevertheless, great efforts have been devoted to the introduction of the spirofused entity also in the other positions, mainly for the preparation of biologically active compounds but also for the synthesis of chiral auxiliaries useful in asymmetric reactions; examples of such auxiliaries are the spirofused chiral 1,3-oxazolidin-2-ones and 1,3-oxazolidine-2-thiones.

Crystallographic snapshots of UDP-glucuronic acid 4-epimerase ligand binding, rotation, and reduction

UDP-glucuronic acid is converted to UDP-galacturonic acid en route to a variety of sugar-containing metabolites. This reaction is performed by a NAD+-dependent epimerase belonging to the short-chain dehydrogenase/reductase family. We present several high-resolution crystal structures of the UDP-glucuronic acid epimerase from Bacillus cereus. The geometry of the substrate-NAD+ interactions is finely arranged to promote hydride transfer. The exquisite complementarity between glucuronic acid and its binding site is highlighted by the observation that the unligated cavity is occupied by a cluster of ordered waters whose positions overlap the polar groups of the sugar substrate. Co-crystallization experiments led to a structure where substrate- and product-bound enzymes coexist within the same crystal. This equilibrium structure reveals the basis for a “swing and flip” rotation of the pro-chiral 4-keto-hexose-uronic acid intermediate that results from glucuronic acid oxidation, placing the C4′ atom in position for receiving a hydride ion on the opposite side of the sugar ring. The product-bound active site is almost identical to that of the substrate-bound structure and satisfies all hydrogen-bonding requirements of the ligand. The structure of the apoenzyme together with the kinetic isotope effect and mutagenesis experiments further outlines a few flexible loops that exist in discrete conformations, imparting structural malleability required for ligand rotation while avoiding leakage of the catalytic intermediate and/or side reactions. These data highlight the double nature of the enzymatic mechanism: the active site features a high degree of precision in substrate recognition combined with the flexibility required for intermediate rotation.

Crystal structure of 4,6-dimethyl-2-[(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)sulfanyl]pyrimidine

In the title compound, C20H26N2O9S, the S atom is attached equatorially to the sugar ring. The C—S bond lengths are unequal, with S—Cs = 1.8018 (13) Å and S—Cp = 1.7662 (13) Å (s = sugar and p = pyrimidyl). In the crystal, a system of three weak hydrogen bonds, sharing an oxygen acceptor, links the molecules to form chains propagating parallel to the b-axis direction.

Towards hydrophobic carminic acid derivatives and their incorporation in polyacrylates

Carminic acid, a natural hydrophilic dye extensively used in the food and cosmetic industries, is converted in hydrophobic dyes by acetylation or pivaloylation. These derivatives are successfully used as biocolourants for rubber objects. In this paper, spectroscopic properties of the carminic acid derivatives in dimethyl sulfoxide and in polybutylacrylate are studied by means of photoluminescence and time-resolved photoluminescence decays, revealing a hypsochromic effect due to the presence of bulky substituents as the acetyl or pivaloyl groups. Molecular mechanics and density functional theory calculations confirm the disruption of planarity between the sugar ring and the anthraquinoid system determined by the esterification.

Crystal structure of racemic 2-[(β-arabinopyranosyl)sulfanyl]-4,6-diphenylpyridine-3-carbonitrile

In the racemic title compound, C23H20N2O4S, the sulfur atom is attached equatorially to the sugar ring with unequal S—C bonds,viz.: S—Cs= 1.808 (2) and S—Cp= 1.770 (2) Å (s = sugar, p = pyridyl). The dihedral angles between the pyridine ring and its attached phenyl groups are 42.24 (8) and 6.37 (14)°. In the crystal, a system of classical O—H...O and O—H...(O,O) hydrogen bonds links the molecules to form tube-like assemblies propagating parallel to thec-axis direction. Weak C—H...N interactions are also observed.