Methylation sugars

Two branched-chain sugars, methyl 3-azido-4,6-0-benzylidene-2,3,-dideoxy-3-C-(fluoromethyl)-a-D-flraZ)/ o-hexopyranoside and methyl 2-azido-4,6-0-benzylidene-2,3-dideoxy-2-C-(fluoromethyl)-) -D-r/to-hexo-pyranoside have been prepared through the usual displacement reactions. 

Reduction of the nitro group of 545-547 in the presence of Raney nickel catalyst respectively afforded the corresponding 4-amino-pento-, -hexo-, and -hepto-pyranosides 548-550. Methyl 4-amino-2,3,4,6-tetradeoxy-a- and -/3-DL-en/t/iro-hexopyranoside (549), characterized as the A -benzoyl derivative, was identical in its H-n.m.r.-speetral data with the analogous derivative of the natural, antibiotic sugar tolyposamine. On the other hand, reductive demethyl-ation of 549 with formaldehyde-Raney nickel (under 3.5 kg/cm2 pressure of hydrogen) was effected, to yield another antibiotic sugar, methyl DL-forosaminide (551). 

The other two known examples of intramolecular H-bonds within a monosaccharide unit in the crystalline state occur in two thio-sugars, methyl-l-thio and methyl-1,5-dithio-a-D-ribopyranoside (40) (illustrated in Figure 3). As far as we know, these are the first examples of syn-diaxial O-H O bonding in a cyclic carbohydrate in the solid state. It is not certain now, whether any particular significance should be associated with the fact that these are thio sugars. 

Dashed frames identical sugar methyl resonances... 

Silanes Sugars Methyl silicone phases STAP Apiezon L butanediol succinate carbowax 4000, Hyprose SP80 mannitol methyl silicone phases... 

For targets with more than one stereogenic centre, only one need be borrowed from the chiral pool, provided diastereoselective reactions can be used to introduce the others with control over relative stereochemistry. Because the first chiral centre has defined absolute configuration, any diastereoselective reaction that controls the relative stereochemistry of a new chiral centre also defines its absolute configuration. In this synthesis of the rare amino sugar methyl mycaminoside, only one chiral centre comes directly from the chiral.pool—the rest are introduced diastereoselectively. 

Sugar methylation is the last step during REB biosynthesis (Scheme 20.2). A rebM-disrupted mutant of Lech, aerocolonigenes accumulated 4 -0-demethyl-REB (17),... 

In their extensive studies of branched-chain sugars. Overend and coworkers have examined the reaction of several tertiary p-tol-uenesulfonic esters with lithium aluminum hydride in ether, as a method of obtaining branched-chain deoxy sugars. Methyl 3,4-0-isopropylidene-2-C-methyl-2-0-p-tolylsulfonyl-/8-L-arabinopyrano-side (3, R = CHs, R = OTs) afforded methyl 2-deoxy-3,4-0-isopropyli-dene-2-C-methyl-j8-L-erythro-pentopyranoside (3, R = CH3, R = H) in 50 % yield. Extension of this method to the 2-C-(phenylethynyl) and... 

Under certain conditions halodesoxy derivatives prepared from trityl ethers may be converted to anhydro sugars. Methyl a-D-glucopyrano-side 3,6-anhydride (XLVII) was prepared in this manner. The corresponding /3-isomer had been described by Fischer and Zach. ... 

The acetylated neolactose methyl 1,2-orthoacetate was isolated in crystalline form when the original methanol solution was evaporated in air to a sirup and triturated with ethanol. After several recrystallizations the compound (XIV) had m. p. 121-122 and [a]n -t-25.3 . It showed the reactions and properties which characterize the sugar methyl orthoacetates, including stability of the orthoacetate group toward alkaline hydrolysis. When the new compound was treated with an anhydrous 0.1 V solution of hydrogen chloride in chloroform, it was converted into the crystalline heptaacetyl-a-neolactosyl chloride. Alkaline hydrolysis also indicated the presence of six acetyl groups, whereas dilute acid removed seven. 

In the presence of a sufficient quantity of water, the first product may suffer hydrolysis into the partly deacetylated sugar, methyl acetate and methyl alcohol. Of course, the reagent may contain enough water for a direct hydrolysis, the rate of which, however, will be slower in such aqueous alcoholic medium, than in pure aqueous hydrochloric acid. ... 

Cane sugar Methyl alcohol Ethyl alcohol Benzene Ether... 

Relative Retentions op Isomeric Sugar Methyl Ethers - ... 

The structure of gentamicin A (34) was elucidated by Maehr and SchaflFner. Methanolysis of gentamicin A afforded paromamine and a new sugar, methyl gentosaminide, which was identified, by n.m.r.-spectral... 

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