Xylose acetal, synthesis

The autotropic pathway for acetate synthesis among the acetogenic bacteria has been examined (67). Quantitative fermentation of one mole of glucose [50-99-7] yields three moles of acetic acid, while two moles of xylose [58-86-6] C H qO, yields five moles. The glucose reaction is... 

A corresponding equilibrium between the pyrrolidine form, the Schiff base, and the dimer exists in aqueous solutions of 4-amino-4,5-dideoxy-L-xylose. Its synthesis proceeds from D-arabinose to 5-O-p-tolylsulfonyl-D-arabinose diediyl dithioacetal, which is reduced to 5-deoxy-D-arabinose diethyl dithioacetal. This compound, in the form of its 2,3-0-isopropylidene acetal, is transformed into 5-deoxy-2,3-O-isopropylidene-D-arabinose diethyl acetal. p-Toluenesulfonyl-ation followed by treatment with sodium azide gives 4-azido-4,5-dideoxy-2,3-0-isopropylidene-L-xylose diethyl acetal, which is reduced in the presence of Raney nickel catalyst to 4-amino-4,5-dideoxy-2,3-0-isopropylidene-L-xylose diethyl acetal (104). 

The Oxidation of Some Carbohydrate Derivatives using Acetic Anhydride - Methyl Sulphoxide Mixtures and the Pfitzner-Moffat Reagent. Facile Synthesis of 3-Acetamido-3-deoxy-D-glucose and 3-Amino-3-deoxy-D-xylose, J. S. Brimacombe, J. G. H. Bryan, A. Husain, M. Stacey, and M. S. 

Andreesen JR, Schaupp A, Neurauter C, et al. 1973. Fermentation of glucose, fructose, and xylose by Clostridium thermoaceticum effect of metals on growth yield, enzymes, and synthesis of acetate from CO2. J Bacteriol 114 743-51. 

A more-direct method of preparation is oxidation of aldoses, and optimal yields are afforded by the action of cupric acetate in methanol or ethanol.417 This method is suitable for large-scale preparation of intermediates however, a pure product is obtained only by chromatographic separation from the unreacted sugar byproducts. The synthesis of D-eryt/wo-pentos-2-ulose and its D-threo isomer by oxidation of D-arabinose and D-xylose, respectively, with cupric acetate followed by anion-exchange chromatography has been reported.418 The only product obtained by oxidation of D-glucose with sodium 2-anthraquinonesulfonate in alkaline... 

This Cl homologation of osones proved to be valuable in the preparation of L-ascorbic acid analogues (16) as well as in the preparation of radiolabeled L-ascorbic acid (17-20), This synthesis was greatly improved when aldoses were discovered to be directly oxidized to osones with cupric acetate (Equation 1) (21), Subsequently, the conditions were modified so that D-xylose could be oxidized to D-xylosone in 50-55% yield with cupric acetate in methanol. The intermediacy of the imino ether was proved by the isolation of 7 when D-glucosone was treated with potassium cyanide (16), The initial cyanohydrin adduct (3a) easily undergoes cyclization to the imino ether intermediate (aqueous solution for 10 min at room temperature. Scheme 5). This feature will be compared with the conditions required for the lactonization of other intermediates. 

Synthesis from xylose The xylose derivative 47, obtained from 5,5-bis-benzyloxy-7-oxa-bicyclo[2.2.1]hept-2-ene (45), has been used in the synthesis of (-P)-castanospermine (1) (Scheme 6). Bromination of 45 occurred exclusively on the less hindered convex face of 45, followed by stereoselective migration of the endo OBn group of the acetal to give 46, which subsequently converted to 47. Mesylation of 47 followed by cyclization with ammoifia gave 48, whose protection, hydrolysis, acetylation and cyclization by an intramolecular Wittig-Homer condensation gave 49. Conversion of 49 into epoxide 50... 

A synthesis of 1,2-O-isopropylidene-a-D-ribofuranose from l,3,5-tri-C)-benzoyl-a-D-ribofuranose has been described. The kinetic products of isopropylidenation of D-galactose, D-allose, and D-talose have been shown to be the 4,6-linked isomers in 67, 81, and 93% yield respectively. A shorter synthesis of 1,2-0-iso-propylidene-a-D-galactofuranose by hydrolysis of the 1,2 5,6-di-O-isopropylidene ketal with 40% acetic acid is reported. The product was converted into 1,2-0-isopropylidene-jS-L-arabinofuranoside by sequential periodate oxidation and borohydride reduction. Treatment of l,2-f -isopropylidene-glycofuranoses with boron trifluoride etherate in benzene has been shown to lead to dimeric dianhydrides, e.g., the 3,5-di-O-benzoyl-xylose derivative (1) (Scheme 1). ... 

Tetroses and Pentoses - 4-0- -Butyldimethylsilyl-2,3-0-isopropylidene-L-threose (1) has been prepared in seven efficient steps from o-xylose. 3,4-0-Isopropylidene-D-eythrulose (4) has been synthesized from the known tetritol derivative 2 by primary protection as the silyl ether 3, followed by Dess-Martin oxidation and desilylation. Compound 2 was derived from D-isoascorbic acid (see Vol. 22, p. 178, refs. 9,10). In a similar reaction sequence, the enantiomer 5 has been obtained from L-ascorbic acid. The dehomologation of several di-0-isopropylidenehexofuranoses e.g., 6- 7) has been carried out in two steps without intermediate purification, by successive treatment with periodic acid in ethyl acetate, followed by sodium borohydride in ethanol. Selective reduction of 3-deoxy-D-g/jcero-pentos-2-ulose (8) to 3-deoxy-D-g/> cero-pent-2-ose (9) has been achieved enzymically with aldose reductase and NADPH." 4-Isopropyl-2-oxazolin-5-one (10) is a masked formaldehyde equivalent that is easily converted to an anion and demasked by mild acid hydrolysis. One of the three examples of its use in the synthesis of monosaccharides is shown in Scheme 1. ... 

Chloroacetyl groups (see Vol. 4, p. 38) have been used as temporary protecting groups in the synthesis of a number of o-xylose derivatives, including 1,2,3-tri-0-acetyl-p-D-xylopyranose and 1,2-di-O-acetyl-a- and -P-D-xylofuranose. The hydroxy-groups of nucleosides have been protected as crotonic and other substituted acrylic esters, which can be readily removed with hydrazine under mild conditions. The claim that acetylation of D-ribose with hot acetic anhydride in the presence of barium carbonate gives only 1,2,3,5-tetra-O-acetyl-P-D-ribofuran-ose has been refuted, since n.m.r. spectroscopy has shown D-ribo-furanose and -pyranose tetra-acetates are formed. ... 

A method of more general application depends on the reduction of iodo derivatives in which the iodine has replaced the hydroxyl of a primary alcoholic group. These are easily obtained by treatment of the tosyl derivatives with sodium iodide in acetone solution (sealed tube) or in refluxing acetonyl-acetone 228) or acetic anhydride 229). The reduction is often carried out by catalytic methods. The 5-deoxy-n-xylose is synthesized from D-xylose by this method, and by application of the cyanohydrin synthesis 6-deoxy-n-gulose is prepared 230). 

The Lewis acid-controlled addition of allyltrimethylsilane to various L-xylose derived acetals 16 afford chelation or non-chelation products 17 or 18. In two cases in which 16 R=Ph or C Yi -p-OMe was used in the presence of Bp3.0Et2, the tetrahydrofuran derivative 19 was obtained. The synthesis of compounds 16 are effected by way of periodate oxidation of appropriate alkylidene D-glucitols. 

Methyl 4,6-O-methylene-o-D-mannopyranoside was the only product isolated from the LiBr-catalised transacetalation of the unprotected methyl glycoside with dimethojqmiethane. Cyclopentylidene derivatives of pentoses have been prepared in moderate yields by treatment of the free sugars with cyclopentanone in the presence of copper (II) sulphate and sulphuric acid. D-Xylose formed the diacetal (11) (also used in Scheme 3 below), whereas from D-ribose the 2,3-monoacetal (12) was obtained. A novel, selective synthesis of (5)-configurated 4,6-pyruvate acetals of methyl D-hexopyranosides is illustrated in Scheme 1. It relies on transacetalation from the dimethyl acetal of 3,4-dimethoxybenzophenone to give, after acetylation, preferentially the intermediate (13) with an axial aryl substituent which, on oxidation, suffers rapid degradation to a carboxylic acid group. ... 

The synthesis and some reactions of 4,5-epithio-2,3-di-0-methanesulphonyl-L-xylose dimethyl acetal (41) are summarised in Scheme 9, and Scheme 10 shows the preparation of 3-0-acetyl-5,6-epithio-l,2-0-isopropylidene-a-L-galactofuranose (43) from the D-altrose compound (42) - itself available in ten steps from D-glucose - and its conversion to 5-thio-L-fucose (44), an inhibitor of a-fucosidases. ... 

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