Glycosyl selenoacetates: versatile building blocks for the preparation of stereoselective selenoglycosides and selenium linked disaccharides

A selenoureido-iminoglycolipid transported by zeolitic-imidazolate framework nanoparticles: a novel antioxidant therapeutic approach

A selenium-containing metal-organic framework with remarkable antioxidant capacity and ROS-scavenging activity was constructed by a controlled de novo encapsulation approach of a glycoconjugate mimetic, specifically a sp2-iminoglycolipid bearing a selenoureido fragment (DSeU), within a zeolitic-imidazolate framework exoskeleton. Biocompatible and homogeneous nanosized particles of ∼70 nm (DSeU@ZIF8) were obtained, which could be efficiently internalized in cells, overcoming the poor solubility in biological media and limited bioavailability of glycolipids. The ZIF-particle served as nanocarrier for the intracellular delivery of the selenocompound to cells, promoted by the acidic pH inside endosomes/lysosomes. As demonstrated by in vitro studies, the designed DSeU@ZIF8 nanoparticles displayed a high antioxidant activity at low doses; lower intracellular ROS levels were observed upon the uptake of DSeU@ZIF8 by human endothelial cells. Even more interesting was the finding that these DSeU@ZIF8 particles were able to reverse to a certain level the oxidative stress induced in cells by pre-treatment with an oxidizing agent. This possibility of modulating the oxidative stress in living cells may have important implications in the treatment of diverse pathological complications that are generally accompanied with elevated ROS levels.

Organoselenium Compounds: Chemistry and Applications in Organic Synthesis

Selenium, originally described as a toxin, turns out to be a crucial trace element for life that appears as selenocysteine and its dimer, selenocystine. From the point of view of drug developments, selenium-containing drugs are isosteres of sulfur and oxygen with the advantage that the presence of the selenium atom confers antioxidant properties and high lipophilicity, which would increase cell membrane permeation leading to better oral bioavailability. In this article, we have focused on the relevant features of the selenium atom, above all, the corresponding synthetic approaches to access a variety of organoselenium molecules along with the proposed reaction mechanisms. The preparation and biological properties of selenosugars, including selenoglycosides, selenonucleosides, selenopeptides, and other selenium-containing compounds will be treated. We have attempted to condense the most important aspects and interesting examples of the chemistry of selenium into a single article.

Synthesis of fluoro- and seleno-containing D-lactose and D-galactose analogues

Synthetic deoxy-fluoro-carbohydrate derivatives and seleno-sugars are useful tools in protein-carbohydrate interaction studies using nuclear magnetic resonance spectroscopy because of the presence of the ¹⁹F and ⁷⁷Se reporter nuclei. Seven saccharides containing both these atoms have been synthesized, three monosaccharides, methyl 6-deoxy-6-fluoro-1-seleno-β-D-galactopyranoside (1) and methyl 2-deoxy-2-fluoro-1-seleno-α/β-D-galactopyranoside (2α and 2β), and four disaccharides, methyl 4-O-(β-D-galactopyranosyl)-2-deoxy-2-fluoro-1-seleno-β-D-glucopyranoside (3), methyl 4-Se-(β-D-galactopyranosyl)-2-deoxy-2-fluoro-4-seleno-β-D-glucopyranoside (4), and methyl 4-Se-(2-deoxy-2-fluoro-α/β-D-galactopyranosyl)-4-seleno-β-D-glucopyranoside (5α and 5β), the three latter compounds with an interglycosidic selenium atom. Selenoglycosides 1 and 3 were obtained from the corresponding bromo sugar by treatment with dimethyl selenide and a reducing agent, while compounds 2α/2β, 4, and 5α/5β were synthesized by the coupling of a D-galactosyl selenolate, obtained in situ from the corresponding isoselenouronium salt, with either methyl iodide or a 4-O-trifluoromethanesulfonyl D-galactosyl moiety. While benzyl ether protecting groups were found to be incompatible with the selenide linkage during deprotection, a change to acetyl esters afforded 4 in a 17% overall yield and over 9 steps from peracetylated D-galactosyl bromide. The synthesis of 5 was performed similarly, but the 2-fluoro substituent led to reduced stereoselectivity in the formation of the isoselenouronium salt (α/β ∼ 1 : 2.3). However, the β-anomer of the uronium salt could be obtained almost pure (∼98%) by precipitation from the reaction mixture. The following displacement reaction occurred without anomerisation, affording, after deacetylation, pure 5β.

Synthesis of sp2-Iminosugar Selenoglycolipids as Multitarget Drug Candidates with Antiproliferative, Leishmanicidal and Anti-Inflammatory Properties

sp²-Iminosugar glycolipids (sp²-IGLs) represent a consolidated family of glycoconjugate mimetics encompassing a monosaccharide-like glycone moiety with a pseudoamide-type nitrogen replacing the endocyclic oxygen atom of carbohydrates and an axially-oriented lipid chain anchored at the pseudoanomeric position. The combination of these structural features makes them promising candidates for the treatment of a variety of conditions, spanning from cancer and inflammatory disorders to parasite infections. The exacerbated anomeric effect associated to the putative sp²-hybridized N-atom imparts chemical and enzymatic stability to sp²-IGLs and warrants total α-anomeric stereoselectivity in the key glycoconjugation step. A variety of O-, N-, C- and S-pseudoglycosides, differing in glycone configurational patterns and lipid nature, have been previously prepared and evaluated. Here we expand the chemical space of sp²-IGLs by reporting the synthesis of α-d-gluco-configured analogs with a bicyclic (5N,6O-oxomethylidene)nojirimycin (ONJ) core incorporating selenium at the glycosidic position. Structure-activity relationship studies in three different scenarios, namely cancer, Leishmaniasis and inflammation, convey that the therapeutic potential of the sp²-IGLs is highly dependent, not only on the length of the lipid chain (linear aliphatic C₁₂ vs. C₈), but also on the nature of the glycosidic atom (nitrogen vs. sulfur vs. selenium). The ensemble of results highlights the α-dodecylseleno-ONJ-glycoside as a promising multitarget drug candidate.

On-water synthesis of glycosyl selenocyanate derivatives and their application in the metal free organocatalytic preparation of nonglycosidic selenium linked pseudodisaccharide derivatives

Glycosyl selenocyanate derivatives were prepared in very good yield by the treatment of glycosyl halide or triflate derivatives with potassium selenocyanate in water. A variety of selenium linked pseudodisaccharide derivatives were prepared in excellent yield using glycosyl selenocyanates as stable building blocks in the presence of hydrazine hydrate under metal-free organocatalytic reaction conditions.

Switchable synthesis of glycosyl selenides or diselenides with direct use of selenium as the selenating agent

Chemoselective synthesis of either diglycosyl selenides or diselenides. Elementary selenium as the selenating agent.