Ma Jesús Diánez

Reaction of 2-amino-2-deoxy-d-glucose with aryl and acyl isothiocyanates, and aryl isocyanates: structure of the intermediate products

Abstract The structure of (4 R )-1-aryl-5-hydroxy-4-( d - arabino -tetritol-1-yl)imidazolidine-2-thiones ( 1–3 ), obtained by reaction of 2-amino-2-deoxy- d -glucose with aryl isothiocyanates, has been confirmed by 1 H- and 13 C-n.m.r. spectroscopy. Likewise, the structures of 2-(3-benzoylthioureido)-2-deoxy- d -glucopyranose and 2-deoxy-2-(3-phenylureido)- d -glucopyranose, prepared by reaction of 2-amino-2-deoxy- d -glucose with benzoyl isothiocyanate and phenyl isocyanate, respectively, were also established. An X-ray analysis of 1 –5 R (aryl = phenyl) has been carried out and its conformation in the solid state is one of the preponderant conformations in solution.

Regio- and stereoselective synthesis of 3- and 5-(C-glycosyl)-4-nitroisoxazolidines by nitrone–nitroalkene [3+2] cycloaddition reactions

Abstract Cycloaddition reactions of nitrones, including sugar nitrones, with nitroalkenes, including sugar nitroolefins, led with complete regioselectivity and stereospecificity to 4,5- trans -4-nitroisoxazolidines in 51–78% global yields. The endo/exo stereoselectivity depends on the type of sugar derivative used. As expected, the best π-diastereofacial selectivity was observed when both partners were sugar derivatives. Isomerisation of the first formed diastereomers by the action of silica gel was observed in some cases. Absolute configurations for two crystalline products were assigned by X-ray diffraction methods.

Branched-chain fluoro nitro d- and l-sugars from glucose

Abstract Mixed crystals of methyl 3-deoxy-3- C -methyl-3-nitro-α- d - and β- l -glucopyranosides (1:1), easily available from d -glucose by means of the Baer reaction, were completely characterised by X-ray diffraction analysis. These diastereomeric components, separation of which could be achieved through their 4,6- O -benzylidene derivatives, were selectively fluorinated at position 6 by treatment with DAST and stereoselectively transformed into phenyl 3-deoxy-3- C -methyl-3-nitro-1-thio-β- d -glucopyranoside and phenyl 3-deoxy-3- C -methyl-3-nitro-1-thio-β- l -glucopyranoside, respectively. Fluorination with DAST of each pure enantiomer afforded, depending on the conditions, the corresponding enantiomeric phenyl 3,6-dideoxy-6-fluoro-3- C -methyl-3-nitro-1-thio-β- d - and β- l -glucopyranosides or the respective rearranged 2,3,6-trideoxy-6-fluoro-3- C -methyl-3-nitro-2-phenylthio-α- d - and α- l -mannopyranosyl fluorides. This route constitutes a simple method for obtaining fair-to-good yields of 6-fluorinated branched-chain d - and l -sugar derivatives, potentially useful as glycosyl donors, starting from d -glucose.

Synthesis of alkyl glyco-pyranosides and -furanosides of 2-amino-2-deoxy-d-glucose. Crystal structure of 2-deoxy-2-[(4,4-dimethyl-2,6-dioxocyclohexylidenemethyl)amino]-α-d-glucopyranose

Abstract The reaction of 2-amino-2-deoxy- d -glucose hydrochloride with 5,5-dimethyl-2-phenylaminomethylene-1,3-cyclohexanedione in MeOH in the presence of Et3N afforded 2-deoxy-2-[(4,4-dimethyl-2,6-dioxocyclohexylidenemethyl)amino]- d -glucose (6) in yields > 75%. Glycosidation of 6 with different alcohols (MeOH, CH2CHCH2OH, BnOH) under the Fischer conditions afforded mixtures of the corresponding alkyl 2-deoxy-2-[(4,4-dimethyl-2,6-dioxocyclohexylidenemethyl)-amino]-α,β- d -glucopyranoside and -α- d -glucofuranoside. Removal of the N-protecting group gave high yields of the free aminodeoxyglyco-pyranosides and -furanosides. In addition to other known glycosides, allyl and benzyl 2-amino-2-deoxy-α- d -glucopyranoside and ethyl and allyl 2-amino-2-deoxy-α-β-glucofuranoside were obtained. An X-ray crystallographic study of 6 indicated that, in the solid state, it has the α- d configuration and that the pyranoside ring adopts the 4C1 conformation.

Higher glycosamino acid precursors: C7 and C8 aminodialdoses via regio- and stereoselective [3+2] cycloaddition of vinyl trimethylsilane to C-glycosyl nitrones

Abstract Protected C 7 and C 8 aminodialdoses were prepared stereoselectively from readily available C 5 and C 6 monosaccharide N -benzyl nitrones, by regio- and diastereoselective 1,3-dipolar cycloaddition reactions with vinyl trimethylsilane, followed by acetyl chloride-mediated cleavage of the 5-(trimethylsilyl)isoxazolidine formed. The cycloaddition reaction took place in moderate to good global yields (67–74%); estimation of diastereoselectivities from isolated yields showed total endo preference for the reaction of the d - galacto configured nitrone and high endo preference for the d - ribo analogue, but exo preference for the d - xylo configured substrate. Attack on the re face of the nitrone was predominant in all cases. The absolute configuration of one of the protected 3-(α- d - galacto -pentopyranos-5-yl)isoxazolidine products was assigned by X-ray crystallographic analysis, allowing correlation of the configuration at the new stereogenic centre in the corresponding aminodialdose. For non-crystalline isoxazolidines, configurations were assigned on the basis of NOESY experiments and/or chemical correlation. Combined yields of aminodialdoses coming from isoxazolidines having identical configuration at C(3) sometimes reached high values (up to 90%). These compounds are precursors of higher-chain glycosamino acids.