Synthesis of α-O- and α-S-glycosphingolipids related to Sphingomonous cell wall antigens using anomerisation

An experimental and theoretical study on stereocontrolled glycosylations by a “one-pot” procedure

Herein we describe a “one-pot” strategy to install the stereoselectivity of both α- and β-glycosides by changing reaction conditions.

Synthesis and biological evaluation of S-simplexides and other analogues of simplexide

Simplexides are natural glycolipids isolated from the marine sponge Plakortis simplex, and contain alkyl 4-O-(α-D-glucopyranosyl)-β-D-galactopyranoside. Simplexides can release of cytokines (IL-6) and chemokines (CXCL-8) from human monocytes and cause the expansion of natural killer T-cells (iNKTs) in vitro, with iNKTs contributing to the sustenance of immune homeostasis. Herein, the stereoselective syntheses of S-glycosidic analogues, i.e. S-simplexides, are described. The routes included Lewis acid promoted anomerisation of glycosyl thiols and thioglycolipids, as well as anomeric S-alkylation. Synthesis of O-glycosidic analogues are included. Heptadecanyl O- and S-glycosides as well as the 17-tritriacontyl 4-O-(α-D-glucopyranosyl)-β-D-galactopyranoside, a component of the natural simplexide isolate, all induced IL-6 and CXCL-8 production at both 10 and 30 μg/mL concentrations from PBMCs whereas the two S-simplexides were inactive. It is speculated that the lack of activity for the S-disaccharide analogue could be due to inhibition of cellular α-glucosidase, preventing degradation of the simplex disaccharide to a simpler galactopyranoside, whereas lack of activity for the S-galactolipid analogue could be due to increased conformational flexibility of S-glycosides. On the other hand, simpler unbranched O- and S-glycolipid analogues were active. Natural simplexide, and a synthetic simplexide, the 18-pentatriacontanyl 4-O-(α-D-glucopyranosyl)-β-D-galactopyranoside, were more potent than the new compounds tested.

Lewis acid promoted anomerisation of alkyl O- and S-xylo-, arabino- and fucopyranosides

Pentopyranoside and 6-deoxyhexopyranosides, such as those from d-xylose, l-arabinose and l-fucose are components of natural products, oligosaccharides or polysaccharides. Lewis acid promoted anomerisation of some of their alkyl O- and S-glycopyranosides is reported here. SnCl₄ was more successful than TiCl₄, with the latter giving the glycosyl chloride by-product in some cases, and both were superior to BF₃OEt₂. Kinetics study using ¹H NMR spectroscopy showed an order of reactivity: O-xylopyranoside > O-arabinopyranoside > O-fucopyranoside. Benzoylated glycosides were more reactive than acetylated glycosides. The reactivity of S-glycosides was greater than that of O-glycosides for both arabinose and fucose derivatives; the reactivity of O- and S-xylopyranosides was similar. The highest stereoselectivities were observed for fucopyranosides. The β-d-xylopyranoside and α-l-arabinopyranoside reactants are conformationally more flexible than β-l-fucopyranosides.

The 1,2,3-triazole ring as a bioisostere in medicinal chemistry

1,2,3-Triazole is a well-known scaffold that has a widespread occurrence in different compounds characterized by several bioactivities, such as antimicrobial, antiviral, and antitumor effects. Moreover, the structural features of 1,2,3-triazole enable it to mimic different functional groups, justifying its wide use as a bioisostere for the synthesis of new active molecules. Here, we provide an overview of the 1,2,3-triazole ring as a bioisostere for the design of drug analogs, highlighting relevant recent examples.

Synthesis of Chrysogeside B from Halotolerant Fungus Penicillium and Its Antimicrobial Activities Evaluation

Chrysogeside B, a natural cerebroside, was efficiently synthesized from commercial feedstocks. The bioassays showed that compounds 4, 5 and 6 exhibited enhanced biological activities compared Chrysogeside B. Further studies revealed that free hydroxyl groups and glycosidic bond have significant impact on the antimicrobial activities. The synthesis of Chrysogeside B and analogues designed to allow identification of the features of this glycolipid required for recognition by tested bacteria and Hela cells is described.

Mycothiol synthesis by an anomerization reaction through endocyclic cleavage

Mycothiol is found in Gram-positive bacteria, where it helps in maintaining a reducing intracellular environment and it plays an important role in protecting the cell from toxic chemicals. The inhibition of the mycothiol biosynthesis is considered as a treatment for tuberculosis. Mycothiol contains an α-aminoglycoside, which is difficult to prepare stereoselectively by a conventional glycosylation reaction. In this study, mycothiol was synthesized by an anomerization reaction from an easily prepared β-aminoglycoside through endocyclic cleavage.

Design, Synthesis, and Immunological Evaluation of Benzyloxyalkyl-Substituted 1,2,3-Triazolyl α-GalCer Analogues

Replacement of the amide moiety in the structure of α-GalCer with a 1,2,3-triazole linker is known to elicit a response skewed toward Th2 immunity, and glycolipids containing an aromatic ring in the terminus of their acyl or phytosphingosine structural component exhibit an enhanced Th1 immune response. In the current study, synthesis and immunological screening of a focused library of benzyloxyalkyl-substituted 1,2,3-triazolyl α-GalCer analogues are reported. The novel α-GalCer analogues activate invariant natural killer T (iNKT) cells via CD1d mediated presentation, which was confirmed by in vitro tests performed on iNKT hybridomas incubated with CD1d proteins. When tested on isolated murine splenocytes, the T1204B and T1206B compounds stimulated higher levels of both IFN-γ and IL-4 cytokine expression in vitro compared to that of α-GalCer.