Mária Petrušová

Stereospecific molybdic acid-catalyzed isomerization of 2-hexuloses to branched-chain aldoses

Abstract On treatment with a catalytic amount of molybdic acid in aqueous solution, the 2-ketohexoses d -fructose, l -sorbose and d -tagatose undergo a stereospecific intramolecular rearrangement to give the corresponding 2- C -(hydroxymethyl)aldoses, 2- C -(hydroxymethyl)- d- ribose ( d -hamamelose), 2- C -(hydroxymethyl)- l -lyxose, and 2- C -(hydroxymethyl)- d -xylose, respectively. At equilibrium, the ratio of 2-ketose to 2- C -(hydroxymethyl)aldose ranged from 14:1 (fructose) to 32:1 (sorbose). A similar treatment of d -psicose failed to yield a significant amount of the corresponding branched-chain aldose. The equilibria can be shifted with the addition of boric acid to the reaction mixture; under these conditions, ratios of 3:1 and 7:1 were obserwed for d -fructose and l -sorbose, respectively. A mechanistic study with d -(3- 13 C)fructose afforded d -(1- 13 C)hamamelose, thus confirming C-3C-4 bond cleavage with concomitant C-2C-3 transposition suggested from recent studies with d -(2- 13 C)fructose.

A nitro sugar derivative route to 2-thioepisophorose and 2-thiosophorose and their remarkable facile epimerization☆

The addition of 1-thio-D-glucose sodium salt to per-O-acetylated 1,2-dideoxy-1-nitro-D-arabino-hex-1-enitol, readily available from D-arabinose, afforded the corresponding 2-S-glycosylated 1-deoxy-1-nitro-D-mannitol and -D-glucitol peracetates. These, after deacetylation, were transformed by the Nef reaction to 2-thioepisophorose and 2-thiosophorose, respectively. The 2-thiodisaccharides easily epimerize in aqueous sodium bicarbonate at ambient temperature to a 1:4 equilibrium mixture. The predominant 2-thiosophorose was obtained crystalline. A 1H NMR study of the epimerization in deuterium oxide showed that the reaction involves an H-2 proton exchange mechanism.

Full acetals of β -d-glycopyranosylnitromethanes and a 1,2-dideoxy-1-nitroalk-1-enitol derived from common hexoses

Abstract Kinetically controlled O-isopropylidenation of common 2,6-anhydro-1-deoxy-1-nitroalditols (β- d -glycopyranosylnitromethanes) derived from d -glucose, d -galactose, and d -mannose with 2-methoxypropene in 1,2-dimethoxyethane catalyzed with 4-toluenesulfonic acid afforded high yields of 2,3;4,6-di-O-isopropylidene acetals. With d -mannose, the bisacetal was also obtained in quantitative yield by reaction with 2,2-dimethoxypropane. Mono-O-benzylidenation of the starting compounds with benzaldehyde dimethyl acetal followed by O-isopropylidenation led to 4,6-O-benzylidene-2,3-O-isopropylidene acetals having better solubilities in non-polar solvents than the di-O-isopropylidene acetals. Di-O-benzylidenation of β- d -mannopyranosylnitromethane gave both (endo-2,3):4,6- and (exo-2,3):4,6-di-O-benzylidene acetals. Transacetalation of 1-deoxy-1-nitro- d -mannitol with 2,2-dimethoxypropane followed by 2-O-acetylation and β-elimination of the acetoxy group afforded (E)-1,2-dideoxy-2,4:5,6-di-O-isopropylidene-1-nitro- d -arabino-hex-1 -enitol.

The first synthesis of a nitromethylene-linked C-(1→2)-disaccharide

Abstract The Michael addition of the 2,3:4,6-di- O -isopropylidene-β- d -mannopyranosyl-nitromethane nucleophile to 1,2-dideoxy-3,4:5,6-di- O -isopropylidene-1-nitro- d - arabino -hex-1-enitol affords a dinitro adduct that can be regioselectively reduced on the primary nitromethyl group to the oxime of the corresponding nitromethylene-linked C -(1→2)-disaccharide.

Behaviour of the Primary Nitro Group Under Denitration Conditions

ABSTRACT Treatment of per-O-acetylated or acetalated glycosylnitromethanes derived from the common hexoses and pentoses with tributyltin hydride and a catalytic amount of a radical initiator [1,1′-azobis(cyclohexanecarbonitrile)] in refluxing benzene easily afforded the corresponding glycosylmethanal oximes in 84-97% yields. Per-O-acetylated C-β-glycopyranosylmethanal oximes were employed for synthesis of versatile C-β-glycopyranosyl cyanides of the β-D-gluco, β-D-manno, β-D-galacto, β-D-xylo, and β-L-rhamno configurations.

A straightforward route to N-acetyl-d-glucosamine-derived C-β-D-Glycosyl synthons

Abstract A practical synthesis of formaldehyde, nitroethene, and nitroethane C -glycosylated with a 2-acetamido-2-deoxy-β- d -glucopyranosyl group is described. Synthesis follows the nitromethane route and involves an unusual, intramolecularly catalyzed β-elimination of acetic acid and pH-controlled ozonolysis of nitronate salts.

Crystal and molecular structures of β-cellobiosylnitromethane and of β-maltosylnitromethane heptaacetate

The structures of the title compounds have been determined by X-ray crystallography, using direct methods, and have been refined to conventional final residual factors of R = 0.063 and R = 0.046, respectively.

Base-catalyzed β-elimination of 2,3-di-O-methyl-d-glyceraldehyde

Abstract 2,3-Di- O -methyl- d -glyceraldehyde undergoes base-catalyzed β-elimination with formation of 2-methoxypropenal in two steps by the ElcB mechanism. The first step is a rapid, reversible, general base-catalyzed reaction giving an anionic intermediate of 2,3-di- O -methyl- d -glyceraldehyde. The second, slower step involves liberation of methoxide ion from the intermediate to give 2-methoxypropenal as the end-product. Reversibility of the first step was proved by incorporation of deuterium at C-2 of the starting compound. The order of the reaction decreases with increasing concentration of catalyst. A kinetic equation reflecting this fact was derived to determine the equilibrium constant of the first, reversible step and the rate constant of the second step. The mechanism of the reaction was elucidated on the basis of the kinetic rate-constants, deuterium solvent isotope-effect, and the activation parameters.

Conversions of Nitroalkyl to Carbonyl Groups in Carbohydrates

Since the development of the Sowden methodology in the middle of the twentieth century, several other efficient and complementary methods for the transformation of sugar nitromethyl groups to aldehyde functionalities in their free, hemiacetal, or otherwise derivatized forms have been developed. Hydrogen peroxide oxidation as well as ozonolysis of 1-deoxyalditol-1-nitronates in aqueous solution provide free aldoses, thus presenting alternatives to the well-known Nef reaction. When applied to 2,5- or 2,6-anhydro-1-deoxy-1-nitroalditols, also known also as glycosylnitromethanes, the Nef reaction fails, and the hydrogen peroxide oxidation overoxidizes the expected products to 2,5- or 2,6-anhydroaldonic acids. On the other hand, the ozonolysis of such compounds under pH-controlled conditions results in up to 85% of the interesting glycosylformaldehydes. The Nef reaction carried out in anhydrous low alcohols, however, has revealed a new conversion of glycosylnitromethanes to glycosylmethanal dialkyl acetals, even more interesting C-glycoside synthons. A similar acid-catalyzed methanolysis of 1-deoxyalditol-1-nitronates leads to methyl furanosides. Finally, a treatment of per-O-substituted glycosylnitromethanes with tributyltin hydride in boiling benzene causes their radical reduction under a nearly quantitative formation of glycosylmethanal oximes.

Acid-catalyzed hydrolysis of 2-methoxypropenal

Abstract 2-Methoxypropenal in acid media undergoes general acid-catalyzed hydrolysis with formation of 2-oxopropanal. The kinetics of this reaction were studied, the rate constants established, and a reaction mechanism is suggested. Hydrolysis of 2-methoxypropenal is governed by a mechanism of the vinyl ether type, and the presence of the aldehyde group causes a decrease in the reaction rate. The analogy of the acid-catalyzed hydrolysis of 2-methoxypropenal to that of a vinyl ether was shown by the solvent isotope-effect, kD/kH = 0.41, and the value of the Bronsted exponent, α = 0.60. The activation parameters found and quantum-chemical calculations of charge distribution in 2-methoxypropenal and other model compounds were also utilized to explain the mechanism of the acid-catalyzed hydrolysis of the title compound.