Synthesis of α- and β-Glycosyl Isothiocyanates via Oxazoline Intermediates

One step stereoselective synthesis of oxazoline-fused saccharides and their conversion into the corresponding 1,2-cis glycosylamines bearing various protected groups

Herein we disclosed a straightforward synthesis of oxazoline-fused saccharides (oxazolinoses) from peracetylated saccharides and benzonitriles under acidic conditions with stoichiometric amounts of water. The density functional theory (DFT) calculations have revealed the origin of the stereoselectivity and the key role of water in promoting the departure of the acetyl group at C-2. The resulting oxazolinoses can be concisely converted into the corresponding 1,2-cis glycosylamines bearing various protected groups, allowing the access to schisandrin derivatives.

On the anomeric preference of the isothiocyanato group

Anomeric effect of the isothiocyanato group has been quantified for the first time in xylopyranose triacetates; both anomers being synthesized.

Evidence of robust participation by an equatorial 4-O group in glycosylation on a 2-azido-2-deoxy-glucopyranosyl donor

An isolated bridging intermediate as evidence of equatorial 4-O group participation in glycosylation.

Synthesis of rhamnosylated arginine glycopeptides and determination of the glycosidic linkage in bacterial elongation factor P

We describe the synthesis and incorporation of α- and β-configured rhamnosyl arginine cassettes into Pseudomonas aeruginosa elongation factor P-derived glycopeptides. These were used to unequivocally determine the native anomeric configuration of the rhamnose moiety in EF-P.

A new class of N-linked protein glycosylation – arginine rhamnosylation – has recently been discovered as a critical modification for the function of bacterial elongation factor P (EF-P). Herein, we describe the synthesis of suitably protected α- and β-rhamnosylated arginine amino acid “cassettes” that can be directly installed into rhamnosylated peptides. Preparation of a proteolytic fragment of Pseudomonas aeruginosa EF-P bearing both α- and β-rhamnosylated arginine enabled the unequivocal determination of the native glycosidic linkage to be α through 2D NMR and nano-UHPLC-tandem mass spectrometry studies.

Synthesis of D-fructose-derived spirocyclic 2-substituted-2-oxazoline ribosides

The TMSOTf-mediated synthesis of β-configured spirocyclic 2-substituted-2-oxazoline ribosides was achieved using a “Ritter-like” reaction in toluene through nucleophilic addition of electron-rich nitriles to the oxacarbenium ion intermediate of 1,2;3,4-di-O-isopropylidene-β-D-psicofuranose derivatives with concomitant intramolecular trapping of the C2 hydroxymethyl group on the electrophilic nitrilium carbon. These carbohydrate-derived spirooxazolines are stable and were obtained in good yield with high stereoselectivity due to the conformational rigidity imparted by the 3,4-isopropylidene group.

Synthesis and hydrolytic properties of water-soluble poly(carbonate–hydroxyurethane)s from trimethylolpropane

Water-soluble poly(carbonate–hydroxyurethane)s with sodium carboxylate side chains synthesized from trimethylolpropaneviaphosgene derivative- and isocyanate-free routes are rapidly degradable to their small components in weak alkaline aqueous environments.

Recent developments in glycosyl urea synthesis

The area of sugar urea derivatives has received considerable attention in recent years because of the unique structural properties and activities that these compounds display. The urea-linkage at the anomeric center is a robust alternative to the naturally occurring O- and N-glycosidic linkages of oligosaccharides and glycoconjugates, and the natural products that have been identified to contain these structures show remarkable biological activity. While methods for installing the β-urea-linkage at the anomeric center have been around for decades, the first synthesis of α-urea glycosides has been much more recent. In either case, the selective synthesis of glycosyl ureas can be quite challenging, and a mixture of α- and β-isomers will often result. This paper will provide a comprehensive review of the synthetic approaches to α- and β-urea glycosides and examine the structure and activity of the natural products and their analogues that have been identified to contain them.

Antioxidant activities of thiosemicarbazones from substituted benzaldehydes and N-(tetra-O-acetyl-β-D-galactopyranosyl)thiosemicarbazide

Reaction of N-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)thiosemicarbazide and different substituted benzaldehydes gave some new substituted benzaldehyde N-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)thiosemicarbazones. The reaction was performed using conventional and microwave-assisted heating methods. The structures of thiosemicarbazones were confirmed by spectroscopic (IR, (1)H NMR, (13)C NMR and ESI-MS) method. The antioxidant activity of these thiosemicarbazones was evaluated in vitro and in vivo, and it's shown that some of these compounds had significant antioxidant activity. Amongst the compounds screened for antioxidant activity, thiosemicarbazones 4a, 4b and 4c showed good antioxidant activity on DPPH. The compounds 4g, 4i, 4l caused significant elevation of SOD activity and 4e, 4g, 4i, 4l had higher catalase activity, and only compounds 4c and 4f expressed the GSH-Px activity.