Françoise Barbalat-Rey

α-Deoxy-α-hydroxyamino sugar phosphonates and the corresponding nitroxide free-radicals☆

Abstract Treatment of sugar aldonitrones with dialkyl phosphites gave sugar α-deoxy-α-( N -hydroxy- N -methylamino)phosphonates, often highly stereoselectively. Repeated nucleophilic addition to a nitrone followed by oxidation of the resulting hydroxylamine allows the “first generation” nitrone, 1,2- O -isopropylidene-α- d - xylo -pentodialdo-1,4-furanose 5-( N -methyloxime), to be converted into the “third generation” cyclic nitrone, [(4 R )-4-diethoxyphosphoryl-5 H ,6 H -1,3-oxazino][6,5- c ](1,2- O -isopropylidene-α- d - xylo -tetrofuranose) N -oxide. The configurational and conformational assignments for all the new compounds prepared were based on short and long-range H,H, H,P, and P,C couplings, and new empirical rules regarding long-range H,P couplings are proposed. The sugar α-deoxy-α-hydroxyamino-phosphonates spontaneously oxidised in the air to give the corresponding nitroxide free-radicals, which afforded good e.s.r. spectra that allowed epimers at the α-carbon atom to be discriminated.

New types of spin-labelled sugar and nucleoside analogs: Pyrrolidine, morpholine and piperidine N-Oxyls

Abstract Analogs of blocked furanose ( 20 ) or pyranose sugars (i.e. 15 ) and of nucleosides (i.e. 23 ) in which the ring oxygen has been replaced with a -N(OH)-bridge have been prepared in generally good yields by a general reductive cyclization procedure preserving the configuration of the preexistant asymetric centers and proceedings stereoselectively (in more favorable cases stereospecifically) when creating a new asymetric center. The title compounds oxidized to nitroxide free radicals affording usable ESR spectra.

1,2-O-Isopropylide`ne-pentodialdofuranoses

Abstract 1,2- O -Isopropylidenepentodialdofuranoses having ribo , lyxo , and arabino configurations, as well as analogs having one (C-3) or two (C-3 and C-4) hybrid sp 2 carbon atoms were synthesized. The orientation of these compounds at the C-4 C-5 bond is practically independent of the modifications of the substitution at C-3. It seems to be directed by orbital factors favoring a conformer having a carbonyl group and an O-C-4 bond nearly eclipsed.

Some Novel Types of Nitrosugars

Abstract The stereochemistry of the reaction of the conjugate base of nitromethane with aldehydosugars was shown to depend on the reaction conditions and the structure of the glycosyl group. Some reactions of a novel type of synthetic intermediates in carbohydrate chemistry, the gem-bromonitroenoses are described.

Dérivés C-glycosyliques : Partie XI. Étude de la chloration d'oximes d'aldéhydo-sucres☆

Abstract The chlorination of oximes of aldehydo sugars takes place via an S E 2′ mechanism and gives the corresponding gem -chloronitroso derivatives which are in equilibrium with their dimers. The study of the monomer formation from the dimer by n.m.r. spectroscopy at various temperatures indicates a positive difference of standard entropy. The gem -chloronitroso derivatives obtained isomerize into hydroximoyl chlorides.

Sucres insaturés fluorés

Abstract Treatment of 1,2:5,6-di- O -isopropylidene-α- d - ribo - and xylo -hexofuranos-3-uloses with (difluoromethylene)triphenylphosphorane and (chlorofluoromethylene)-triphenylphosphorane gave unsaturated, ramified halogeno sugars in good yield. Treatment of the chlorofluoromethylene derivatives with lithium aluminum hydride gave stereospecifically the corresponding fluoromethylene derivatives with inversion of configuration at the double bond. The configuration was determined by 1 h- and 19 F-n.m.r. spectrometry.

Synthetic usefulness of the sugar cyclopentylidene ketals

ABSTRACT Cyclopentylidene ketals, moderately more acid-labile than their isopropylidene analogs, offer an alternative to the latter blocking groups. They have been shown to resist a large variety of reaction conditions commonly encountered in carbohydrate chemistry.

Équilibres conformationnels de glucides au niveau de liaisons σ SP2-SP3: Partie V. Dérivés 2,3,-O-isopropylidène de pyranosides hybrides sp2 en C-4. Comparaison avec leurs analogues saturés☆☆☆

The conformation in solution of derivatives of methyl hexopyranosides has been studied by n.m.r. The esters of methyl 2,3-O-isopropylidene-α-D-manno- and -talopyranosides as well as their 4-deoxy-4-C-methyl analog having a manno configuration exist mainly in a flattened (4,0F) chair conformation (4C1). The presence in the talo epimer of the 4-deoxy-4-C-methyl analog of the bulky methyl group on the endo side of the bicyclic system results in a skew form (3S1). The methyl 4-deoxy-2,3-O-isopropylidene-4-C-methylene-α-D-lyxo-hexopyranosides monosubstituted at C-4′ adopt, in solution, a conformation close to 3S1, whichever their configuration (cis or trans) at the double bond, as indicated by their allylic coupling constants.

4'-AZA-3',5'-dihomothymidine and derivatives

Abstract A series of 3′-branched 4′-azanucleoside analogues have been prepared. These compounds comprise three asymmetric atoms, two carbons and one nitrogen. They constitute nucleoside analogues imparted with a “flickering configuration”, the nitrogen inversion replacing a D-L epimerization of their natural congeners. The 1′,3′-cis and 1′,3′-trans isomers have been separated and their configuration established by 1H NMR and the X-ray diffraction structure of one crystalline example. The configurations of the frozen invertomers were assessed by low temperature 1H NMR experiments assisted by molecular mechanics simulations. None of these compounds exhibited any significant in vitro antiviral activity.

Conformational study of a sugar nitroxyl free radical

Abstract Ethyl2,3-dideoxy-2-isopropylamino-α- d - arabino -hexopyranoside N -oxyl and its 2′- d analogue have been studied by variable-temperature e.s.r. spectroscopy. At low temperature, two frozen conformers ( 5 , a H-2 = 15.5 G; and 6 , a H-2 = 1.8 G) were found. Semi-empirical quantum mechanics and molecular mechanics, using specially developed parameters by hydroxylamines and nitroxyls, helped to assign an almost eclipsed geometry (ONC-2C-1 ∼ 10°) to 5 and a compromise between a staggered and the nearest eclipsed conformation (ONC-2C-1 ∼ 80°) to 6 .