D-manno epimer

The introduction of the a-keto acid function on the way to the ulosonic acids is a main problem of their syntheses. By analogy with the biosynthetic pathway, the aldol reaction between sugar aldehydes and a pyruvate equivalents seems to be the most simple and versatile. As it has been demonstrated by Comforth [74] in the first chemical synthesis, the reaction of arabinose and oxalacetic acid as pyruvate equivalent, followed by decarboxylation afforded KDO, albeit in low yield. This condensation has been optimized by use of Ni(II) catalyst for the decarboxylation [75], In this case, reaction of D-mannose and oxalacetic acid gave KDN (11) and its D-manno epimer 37 in 70% yield [75] (Scheme 12). 

Scheme 1) whereas the reaction with the D-man/io-hexodialdo-l,5-pyranose derivative 3 produced, in low yield, the cyanohydrin 4 having an L-glycero-D-manno configuration and the stereoisomeric epimer at C-5, rather than at C-6 [14J. With an atm toward the synthesis of d- and L-glycero-D-manno-heptoses, the reaction of 3 with other reagents (2-inethyl-furan, alkyl magnesium chlorides) was also explored, without any substantial improvement of either stereoselectivity or yield. 

It has been mentioned (p. 13) that D-manno-o-tolo-heptitol is identical with natural voleraitol. If -one desires a supply of voleraitol, probably the best procedure at the present time is its synthetic production from D-mannose even though the D-manno-D-synthetic method appears to be more practicable than the isolation of the alcohol in quantity from known natural sources. The use of barium cyanide or the equivalent mixture of a barium salt and sodium cyanide, in place of hydrocyanic acid appears to favor the yield of the desired heptonic acid. On the other hand, the possibility of starting with o-altrose, which is now no longer a particularly rare sugar, appears of interest because the desired heptose (D-altro-D-mormo-heptose) should be the major product in that series if the generalizations that have been presented hold for altrose. This speculation has been offered because it seems to the writer that many carbohydrates that are now only laboratory curiosities, can be made at costs that are not prohibitive for the use of them in exploratory researches, especially in the bacteriological, physiological and biochemical fields. 

An improved, three-step synthesis of iV-butyl-l-deoxynojiromycin from D-glucose has been described, involving an enzymic oxidation ofN-butylglucamine. A synthesis ofA/ -[ C]methyl-1-deoxynojirimycin and its manno epimer has been reported in a study of glycosidase inhibition. l,3,4-Trideoxy-3-fluoronojirimycin and its manno epimer have been characterized and stereochemically distinguished by mass-analyzed ion kinetic energy spectroscopy. ... 

The problem of epimer formation depends on the reaction time and reaction conditions as well as the components employed. Heyns investigated the ratio of the two possible epimers as well as the fraction of the corresponding Amadori product in the reaction of D-fructose with glycine. In this particular case, the product of kinetic control was the D-manno-configured 2-aminosugar, but the proportion of the more stable D-gluco epimer increased upon extended reaction times. The analysis of the products from the reaction of D-fructose with alanine and valine provided a similar picture [115]. 

Conventional reactions have been used to prepare 1-deoxy-nojiri-mycin (9) from D-glucose via a protected 5-azido-glucofuranose intermediate, together with minor amounts of the manno epimer (10). The manno-isomer was also synthesized, more satisfactorily, from D-mannose by an analogous sequence in this case, a concomitant... 

The individual 2-C-(hydroxymethyl) aldoses were obtained after a combined separation of the epimers via their phenylhydrazones followed by chemisorption chromatography on a cation-exchange resin in the Ba + form [50]. Then, on treatment with molybdic acid at increased temperature, 2-C-(hydroxymethyl)-D-mannose (16c) rearranged to D-g/wco-hept-2-ulose (15c) as expected. Under similar conditions, 2-C-(hydroxymethyl)-D-glucose (15 d) was transformed to D-manno-hept-2-ulose (16d). The analysis of the reaction equilibria by H NMR spectroscopy revealed the presence of small quantities of the respective starting branched-chain aldoses 15d (3.5%) and 16c (8%). The same equilibria were also obtained from the side of the model ketoses 15 c and 16 d. Thus, for example, the equilibrium of the sugars 15c and 16c at their total 2% concentration in a 0.2%... 

The furyl-tetrahydrofuran (68) and its C-4 epimer were synthesised from 3-deoxy-l,2-0-isopropylidene a-D-erythro-pento-1.5-dialdofuranose and its C-4 epimer, and these products were proposed as convenient chiral precursors of furanoterpenes. Some 2-amino-2-deoxy-3- -branched D-manno- and D-altro-... 

The addition of NH3 to the double bond does not. however, as was or nally supposed, proceed stereospecifically, but only stereoselectively. According to Sowden and Oftedahl, the D-manno and D-giuco epimers arise in the ratio of 6 1. The addition of NH3 to 3,4,5,6-tetra-0-acetyl-D-arabo-i,i-bis(ethanesulfonyl)-hexene-i yields, on the contrary, a preponderant amount of the D-gluco epimer. 

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