Synthesis of a thio analogue of n-propyl kojibioside, a potential glucosidase inhibitor

Automated Solution-Phase Synthesis of S-Glycosides for the Production of Oligomannopyranoside Derivatives

Thioglycosides are more resistant to enzymatic hydrolysis than their O-linked counterparts, thereby becoming attractive targets for carbohydrate-based therapeutic development. We report the first development of methods for the site-selective incorporation of S-linkages into automated solution-phase oligosaccharide protocols. The protocols were shown to be compatible with the formation of S- or O-glycosides for the synthesis of mannopyranoside trimmers that incorporate both S- and O-linkages to allow the selective incorporation of an S-glycoside in various stages in an automated program.

Photoinitiated Thiol-ene Reactions of Enoses: A Powerful Tool for Stereoselective Synthesis of Glycomimetics with Challenging Glycosidic Linkages

Thioglycosides and C-glycosides represent pharmacologically useful classes of glycomimetics that possess a high degree of biological stability. One emerging tool for the stereoselective synthesis of thioglycosides is the photoinitiated addition of thiols to unsaturated sugars. Moreover, thiyl radical-mediated reactions of exo-glycals and 1-substituted endo-glycals offer facile routes to β-C-glycosidic structures. This Concept article summarizes the thiol-ene coupling strategies developed recently by our group and Somsák's group for the synthesis of several kinds of glycomimetics which are difficult to synthesize by conventional methods. One unusual characteristic of the thiol-ene reactions of endo-glycals is that heating inhibits, whereas cooling promotes the reaction. This unique temperature dependence as well as the effects of the enose structures and thiol configurations on the efficacy and stereoselectivity of the reactions are also discussed.

Promoter free allylation of trichloroacetimidates with allyltributylstannanes under thermal conditions to access the common 1,1'-diarylbutyl pharmacophore

1,1'-Diarylbutyl groups are a common pharmacophore found in many biologically active small molecules. To access these systems under mild conditions, the reaction of diarylmethyl trichloroacetimidates with allyltributylstannanes was explored. Simply heating allyltributylstannane with the trichloroacetimidate resulted in substitution of the imidate with an allyl group. Unlike other methods used to access these systems, no strong base, transition metal catalyst, Brønsted acid or Lewis acid promoter was required to affect the transformation. Conversions are best with electron rich benzylic trichloroacetimidate systems, where excellent yields are achieved just by refluxing the reactants together in nitromethane.

Synthesis of 1,1'-Diarylethanes and Related Systems by Displacement of Trichloroacetimidates with Trimethylaluminum

Benzylic trichloroacetimidates are readily displaced by trimethylaluminum under Lewis acid promoted conditions to provide the corresponding methyl substitution product. This method is a convenient way to access 1,1'-diarylethanes and related systems, which play a significant role in medicinal chemistry, with a number of systems owing their biological activity to this functionality. Most benzylic substrates undergo ready displacement, with electron deficient systems being the exception. The use of an enantiopure imidate showed significant racemization, implicating the formation of a cationic intermediate.

Synthesis of 2-Thiocarbohydrates and Their Binding to Concanavalin A

A convenient and general synthesis of 2-thiocarbohydrates via cerium ammonium nitrate oxidation of the thiocyanate ion is described. Radical addition to glycals proceeds with excellent regio- and good stereoselectivities in only one step, deprotection affords water-soluble 2-thio saccharides. Binding studies to Con A have been performed by isothermal titration calorimetry (ITC) and saturation transfer difference (STD) NMR spectroscopy. The 2-thiomannose derivative binds even stronger to Con A than the natural substrate, offering opportunities for new lectin or enzyme inhibitors.

Towards the synthesis of aryl glucuronides as potential heparanase probes. An interesting outcome in the glycosidation of glucuronic acid with 4-hydroxycinnamic acid

This work describes our preliminary efforts towards the development of aryl glucuronides as potential probes for heparanase. During the course of these initial investigations, attempted glycosidation of methyl 2,3,4-tri-O-acetyl-alpha-D-glucopyranosyluronate trichloroacetimidate with 4-hydroxycinnamic acid gave a complex mixture of four different components. These were identified as the 1-cinnamyl glucuronate ester 13, the cinnamyl linked disaccharide 14, the glucuronate trichloroacetamide 15, and the glucuronyl alpha-fluoride 16. This paper rationalises the formation of each of these products, and reports our efforts in trying to optimise the formation of the alpha-fluoride 16.

The synthesis of phosphorylated disaccharide components of the extracellular phosphomannan of Pichia (Hansenula) holstii NRRL Y-2448

Methods for the stereoselective synthesis of alpha-(1-->2)- and alpha-(1-->3)-linked 6(II)-O-phosphomannobiosides were developed. Two strategies were successfully employed: a D-mannosyl acceptor was coupled with a phosphorylated D-mannosyl trichloroacetimidate donor, or alternatively with a differentially 6-O-protected D-mannosyl trichloroacetimidate donor which, after glycosylation, was selectively deprotected and phosphorylated. Two target phosphomannobiosides intended for use in SAR studies of the antiangiogenic drug candidate PI-88, 2-O-(6-O-phospho-alpha-D-mannopyranosyl)-D-mannopyranose and methyl 3-O-(6-O-phospho-alpha-D-mannopyranosyl)-alpha-D-mannopyranoside, were synthesized. The former is a minor component of the side-chain repeating unit of the extracellular phosphomannan of Pichia (Hansenula) holstii NRRL Y-2448, whilst the latter represents a nonreducing end fragment of the phosphomannan.

Synthesis and solution conformational analysis of 2,3-anhydro-3-C-[(1R)-2,6-anhydro-1-deoxy-1-fluoro-D-glycero-D-gulo-heptitol-1-C-yl]-beta-D-gulo-furanose: first example of a monofluoromethylene-linked C-disaccharide

Condensation of 2,3,4,6-tetra-O-benzyl-beta-D-glucopyranosylcarbaldehyde with isolevoglucosenone induced by Et(2)AlI, followed by epoxidation, gave an aldol that was fluorinated into a monofluoromethylene C-glucopyranoside that was converted into the title C-disaccharide 1. Its conformational behavior in water has been studied by using a combination of NMR spectroscopy (J and NOE data) and molecular mechanics calculations.

Synthesis of 1,2- and 1,3-N-Linked Disaccharides of 5-Thio-alpha-D-mannopyranose as Potential Inhibitors of the Processing Mannosidase Class I and Mannosidase II Enzymes

The syntheses of S/N acetal heteroatom analogues of 1,2- and 1,3-linked mannopyranose disaccharides are described. The compounds are analogues of the Man-alpha-(1-->2)-Man and Man-alpha-(1-->3)-Man disaccharide components of oligosaccharides found in N-glycoproteins that are cleaved by trimming mannosidases during glycoprotein processing. Glycosylamine formation, without the necessity of hydroxyl group protection, proceeded through acid-catalyzed condensation reactions of 5-thio-D-mannose with either methyl 2-amino-2-deoxy- or 3-amino-3-deoxy-alpha-D-mannopyranoside to give methyl 2-amino-2-deoxy-2-N-(5-thio-alpha/beta-D-mannopyranosyl)-alpha-D-mannopyranoside (2) or methyl 3-amino-3-deoxy-3-N-(5-thio-alpha/beta-D-mannopyranosyl)-alpha-D-mannopyranoside (3), respectively. The superiority of mercuric chloride over acetic acid as a catalyst for this reaction is reported. Acetylation of the anomeric mixtures gave the heptaacetates from which the major beta'-isomers could be separated by chromatography and/or crystallization.