ABSTRACT
The preparation of carbohydrate mimics in which the endocyclic oxygen has been replaced by a guanidine-type nitrogen atom is reported. The synthetic strategy involves the furanose --> piperidine rearrangement of 5-deoxy-5-guanidino-L-idose precursors. The reaction proceeds through elimination of water to give 3-oxopiperidines, which were isolated as the corresponding hydrates. Biological evaluation of the new glycomimetics evidenced a strong influence of the nature of the substituents at the nitrogen atoms on the glycosidase inhibitory properties.
Subject(s)
Guanidine/chemical synthesis , Guanidine/pharmacology , Imino Sugars/chemical synthesis , Imino Sugars/pharmacology , Drug Evaluation, Preclinical , Magnetic Resonance Spectroscopy , Spectrometry, Mass, Fast Atom BombardmentABSTRACT
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.
Subject(s)
Disaccharides/chemical synthesis , Enzyme Inhibitors/chemical synthesis , Glycoside Hydrolases/antagonists & inhibitors , Indolizines/chemical synthesis , Urea/chemistry , Animals , Carbohydrate Sequence , Disaccharides/chemistry , Disaccharides/pharmacology , Enzyme Inhibitors/chemistry , Enzyme Inhibitors/pharmacology , Indolizines/chemistry , Indolizines/pharmacology , Molecular Mimicry , Spectrum AnalysisABSTRACT
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.
Subject(s)
Carbohydrates/chemical synthesis , Isothiocyanates/chemical synthesis , Azides/chemistry , Carbodiimides/chemistry , Organophosphorus Compounds/chemistryABSTRACT
Bicyclic azasugar glycomimetics related to castanospermine and trehazolin have been prepared from sugar carbodiimides via aminooxazoline intermediates; preliminary enzyme inhibition tests showed a marked dependence of the selectivity and potency towards alpha and beta-glucosidases upon the nature of the exocyclic substituent.
