Generalized anomeric effect in action: synthesis and evaluation of stable reducing indolizidine glycomimetics as glycosidase inhibitors

Pseudoamide-Type Pyrrolidine and Pyrrolizidine Glycomimetics and Their Inhibitory Activities against Glycosidases

Coupling reaction of (2R,3R,4R,5R)-2,5-hydroxymethyl-3,4-dihydroxypyrrolidine (DMDP) with isothiocyanates afforded the corresponding thiourea adducts, which were transformed into isourea-type bicyclic oxapyrrolizidine glycomimetics by mercury(II) oxide-assisted intramolecular sulfur displacement. Cyclic carbamate and thiocarbamate analogues were also prepared by direct carbonylation or thiocarbonylation of DMDP. Evaluation of the glycosidase inhibitory properties demonstrated that remarkable specificities in enzyme inhibition can be achieved upon modifications on the pseudoaglyconic side chain and on the nature of the sp(2)-hybridized endocyclic ring nitrogen.

Synthesis and Evaluation of Isourea-Type Glycomimetics Related to the Indolizidine and Trehazolin Glycosidase Inhibitor Families

A practical synthesis of reducing isourea-derived azasugar glycomimetics related to the indolizidine and trehazolin glycosidase inhibitor families with different pK(a) values is disclosed. The polyhydroxylated bicyclic system was built from readily accessible hexofuranose derivatives through a synthetic scheme that involves the preparation of a 5-deoxy-5-carbodiimido adduct by triphenylphosphine-mediated tandem Staudinger--aza-Wittig-type coupling of azide and isothiocyanate precursors, intramolecular cyclization of a transient vic-hydroxycarbodiimide derivative, and nucleophilic addition of the endocyclic nitrogen atom of the generated 2-amino-2-oxazoline intermediate, with a pseudo-C-nucleoside structure, to the masked aldehyde group of the monosaccharide. The last step is pH-dependent so that the final compounds can pivot between the furanose and the 2-oxaindolizidine forms. Nevertheless, the indolizidine tautomer having the R configuration at the aminoacetalic center, fitting the anomeric effect, was the only species detected in solution at neutral or slightly acidic pH when starting from solutions at basic pH. Glycosidase inhibition tests (K(i) values down to 1.9 microM) showed a marked dependence of the selectivity and potency toward alpha- and beta-glucosidases upon the nature of the substituent at the exocyclic isourea nitrogen, shifting from alpha- to beta-selectivity when going from hydrophilic to hydrophobic substituents. Enzyme inhibition is also pH dependent, supporting a dominant role for the uncharged form of the polyhydroxyiminoindolizidine system in the inhibition of beta-glucosidases.

One-step synthesis of non-anomeric sugar isothiocyanates from sugar azides

Tandem Staudinger-aza-Wittig reaction of primary azidodeoxy sugars with triphenylphosphine-carbon disulfide affords the corresponding primary deoxyisothiocyanato sugars in high yield. No products arising from O --> N acyl migration or formation of dimeric carbodiimides were observed. Interestingly, a polymer-supported triarylphosphine can advantageously replace triphenylphosphine, thus limiting the purification step to a simple filtration process. The reaction also allows the preparation of 5-deoxy-5-isothiocyanato sugars, a hitherto unknown class of compounds, from the corresponding azide precursors. Secondary sugar azides bearing the azido group at an endocyclic carbon atom afforded much lower isothiocyanation yields under these reaction conditions.

Synthesis and evaluation of calystegine B2 analogues as glycosidase inhibitors

A practical synthesis of polyhydroxylated 6-oxa-nor-tropanes incorporating the essential structural features of calystegine B(2) from 5-deoxy-5-thioureido and 5-ureido-L-idofuranose precursors is presented. The methodology relies on the ability of pseudoamide-type nitrogen atoms (thiourea, urea, and carbamate) to undergo nucleophilic addition to the masked aldehyde group of the monosaccharide. The generated hemiaminal functionality may further undergo in situ intramolecular glycosidation to give the bicyclic aminoacetal compounds, the whole process being favored by the anomeric effect. A series of derivatives bearing different substituents at nitrogen has been prepared and screened against several glycosidases in comparison with xylonojirimycin-type piperidine analogues. Interestingly, strong and highly specific inhibition of bovine liver beta-glucosidase was observed for 6-oxacalystegine B(2) analogues incorporating aromatic pseudoaglyconic groups. On the basis of these data, a 1-azasugar inhibition mode is proposed for this family of glycomimetics.

Beta-D-glycosylamidines: potent, selective, and easily accessible 1-glycosidase inhibitors

Beta-D-glycosylamidines, in which a glycon is connected via an N-glycoside linkage with a substituted amidine (aglycon), were synthesized in two steps from the corresponding sugars and served as stable and potent beta-glycosidase inhibitors with high selectivity according to the glycon- and alpha, beta-specificities of the enzymes.