D-Mannose configuration

CDP-6-deoxy-D-xy/o-hexos-4-ulose (7b) serves as a precursor in the biosynthesis of CDP-3,6-dideoxyhexoses28,168 having the d-ribo (paratose, 3,6-dideoxy- D-glucose ), o-xylo (abequose, 3,6-dideoxy- D-galactose ), and d-arabino (tyvelose, 3,6-dideoxy- D-mannose ) configurations. These monosaccharides are characteristic components of O-specific polysaccharides from Salmonella and Yersinia pseudotuberculosis. 

Because the configuration at C-2 is lost on enolization, the enediol intermediate can revert either to D-glucose or to D-mannose. Two stereoisomers that have multiple chirality centers but differ in configuration at only one of them are refened to as... 

Walden inversion on C2 has occurred in one of these sequences if in the first, then chitose, chitonic acid and isosaccharic acid have the configuration of D-mannose if in the second, i. e., in the deamination of 2-amino-D-gluconic acid, then chitaric acid and epi-isosaccharic acid are... 

D-mannose derivatives. Chitose and its oxidation products must then necessarily have a D-glucose configuration. The problem thus presented was solved by Levene and LaForge in 191554- 58 in the following manner. 

Attempts to decide whether D-glucosamine is 2-amino-D-glucose or 2-amino-D-mannose have provided a series of fascinating investigations8-13 the balance of evidence therefrom favoring the D-glucose configuration. 

A new NMR method for the determination of the anomeric configuration in mono- and disaccharides has been described.18 The protocol is based on the different cross-correlated relaxation between proton chemical shift anisotropy (CSA) and dipolar relaxation for the a and (3 anomers of sugars. Only the ot-anomers show the presence of CSA (HI or Hl )-proton dipole (H1-H2 or Hl -H2 ) in the longitudinal relaxation of the anomeric protons. The method is of special interest for cases in which vicinal coupling constants between HI and H2 in both anomers a and (3 are similar and small, such as D-mannose, and the non-ambiguous description of the anomeric configuration needs additional measurements. 

Another proof of the configuration of D-mannitol and also of D-manno-n-manno-octitol (XVI), which is likewise dependent on the experimental proof of the equivalent symmetry of D-mannitol is the following. D-Mannose has been converted, by successive cyanohydrin syntheses, first to a mannoheptose and then to a mannooctose which on reduction yielded a mannooctitol whose octaacetyl derivative is optically inactive. (It was not possible to examine the octitol itself because of its very low solubility in water.)87 The meso character of the octaacetate shows that the mannooctitol must possess a meso configuration, with a plane of symmetry between carbon atoms 4 and 5. To write its formula, the hydroxyl at carbon atom 7 is placed on the... 

Swainsonine is a trihydroxylated bicyclic indolizidine alkaloid with four chiral centres, whose relative stereochemistry was determined by X-ray crystallographic analysis and the absolute configuration was deduced on the basis of biosynthetic and asymmetric induction studies, and then confirmed by an enantiospecific synthesis from D-mannose [2a]. 

For the first time, DFT theory has been applied to a study of diastereofacial selectivity in 1,3-dipolar cycloadditions of nitrones to di-3,4-dimethylcyclobutene. ° The stereochemical outcome of the INAC reactions of nitrones (49) and (52) derived from 3-(9-allyl-D-hexoses is dependent only on the relative configuration at C(2,3), and thus 3-(9-allyl-D-glucose (48) and -o-altrose (threo configuration) afford oxepanes (50) selectively whereas 3-O-allyl-D-allose (51) and -D-mannose (erythro configuration) give tetrahydrofurans (53) and (54) selectively (Scheme 18). frani-2-Methylene-... 

Epimerization. In weakly alkaline solutions, glucose is in equilibrium with the ketohexose D-fructose and the aldohexose D-mannose, via an enediol intermediate (not shown). The only difference between glucose and mannose is the configuration at C-2. Pairs of sugars of this type are referred to as epi-mers, and their interconversion is called epimerization. 

The oxime of D-lyxose has not been prepared, but L-rhamnose oxime (XX) with ithe same spatial configuration about carbon atoms 2, 3 and 4 reacts in an open-chain form when submitted to mild acetylation, and gives only the nitrile this reactivity is confirmed when the oxime is submitted to mild propionylation, for only the hexapropionyl-aWe%do-L-rhamnose oxime is produced and that in high yield. As already mentioned, the oximes of D-mannose (XXI), and D-gala-L- reawno-heptose (XXII),having the same configuration as rhamnose about carbon atoms 2, 3 and 4, react in a similar manner. 

Measurements of the influence of boric acid on the rotation and conductivity of 8-D-mannose yielded the results shown in Table VII. For /3-D-mannose both the rotation and the increase in conductivity become greater and these phenomena run practically parallel. Thus, it is not surprising that we assumed at the time that /3-D-mannose should be allotted the frans-mannofuranose configuration, and its isomer, which... 

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