Methylated deoxyhexoses

The carbohydrates found in the glycolipids of acid-fast bacteria are either very common sugars, such as D-arabinose, D-glucose, D-mannose, or a, trehalose, or are rare 0-methylated deoxyhexoses. Table I gives a survey of the carbohydrates found in the glycolipids considered in the present article. 

Not much has been added to the biochemistry of STRs in the recent years. Therefore, we will only briefly treat the biosynthetic pathway here. Biosynthesis of the aminocyclitol (streptidine) and 6-deoxyhexose (streptose) moieties are well understood, with some remaining gaps in the enzymology. Much less is known about the residual biosynthetic phases, the formation of A-methyl-L-glucosamine, the condensation of subunits, and the late modification steps potentially coupled with export. ... 

As expected, the spectrum of the 6-deoxyhexose (23) contains no peaks of the E series however, the B series appears (m/e 176, 131), the peaks of the F, G, H, and J series have the same intensities and positions as with permethylated methyl hexosides, and the peaks of fragments involving C-5 and C-6 are shifted 30 mass units to lower m/e values compared with the peaks of permethylated methyl hexosides (Di, m/e 119 C2, m/e 129, and so on). 

Detailed investigation of the mass spectra of permethylated methyl glycosides of the pentose,1617 27 hexose,13-16 6-deoxyhexose,16 and 2-amino-2-deoxyhexose30 series, using compounds specifically labeled with trideuterio-methyl groupings in all of the positions, served as a basis for elucidating... 

This interesting transformation from a readily available 6-deoxyhexose forms the basis for the synthesis231 of 6-deoxy-2,3-di-0-methyl-D-allose (mycinose),168 one of the carbohydrate moieties of the antibiotic chalco-mycin. The synthesis merely involves the protection of the C-5 hydroxyl group in (41) by benzylation, followed by partial hydrolysis with acid, methylation of the product at the C-2 and C-3 hydroxyl groups, and debenzylation. 

Halogen atoms have been placed at C-6 of substituted 6-deoxy-hexoses by a variety of interesting ways, and the products provide potential routes to 6-deoxyhexoses. Helferich and coworkers 4 reported a low yield of methyl 6-chloro-6-deoxy-a-D-glucoside which they prepared by reaction of the (suitably protected) corresponding 6-trityl ether with phosphorus pentachloride. Sinclair 44 has provided a convenient procedure for the preparation of the 6-chloro derivative in yields of 30-35% by allowing methyl a-D-glucopyranoside to react with sulfur monochloride, SjClj, in N,/V-dimethylformamide. A much better yield (73%) of the 6-bromo derivative was reported1 in the reaction of methyl 2,3,4-tri-O-benzoyl-6-O-trityl-a-D-altroside with phosphorus tribromide and bromine. 

The u-deoxy sugars studied (6-deoxy and 5-deoxy) have intense peaks for the dithioacetal fragment, and also break down to Fragments A, B, and C. < -Deoxyhexose dithioacetals cannot be differentiated from 5-deoxy-hexose dithioacetals. The deoxy function is, apparently, too far removed from the bonds most susceptible to cleavage to have a significant effect. Mass spectrometry can also be useful in the characterization of terminal branched-chain deoxy sugars. The spectrum of 6-deoxy-5-C-methyl-D-xylo-hexose diethyl dithioacetal 1 contains prominent peaks due to Fragments A, B, and C. Apparently, substitution beyond C-4 does not affect... 

Deoxygenation at C-2, C-3, and C-4 of 6-deoxyhexoses and substitution of one of the remaining OH-groups by amino, di-V-methyl, O-methyl, and C-methyl groups creates significant structural diversity. In secondary metabolites, such as the polyketide antibiotics, 2,6-dideoxy- and 2,3,6-trideoxy-hexoses, contribute to the antibiotic and antitumor activity. 

Although D-fucose is not found as a constituent of polysaccharides, 3-methyl-D-fucose is the constituent sugar of the glycosides of the digitalis group, such as emicymarin and isoemicymarin. Researches to characterize this sugar have been responsible for considerable activity in the preparation of the monomethyl-6-deoxyhexoses.68... 

Early on in the analysis of LPS from members of the Rhizobiales, it was shown that there was (a) significant variability in the OPS even among strains of the same species (Carlson, 1984 Carlson et al., 1978), and (b) that major glycosyl residues commonly found in these OPSs consisted of deoxyhexoses as well as methylated glycosyl residues (Carlson, 1984 Carlson et al., 1978). It was also shown that... 

METHYL ETHERS OF PENTOSES AND 6-DEOXYHEXOSES Table I Continued)... 

Mycoside A.—This compound haa been obtained as a nearly colorless solid, melting at 105°, [a] -37° (CHCl,) C, 72.2 H, 11.3 OCH, 8.6 N, 0 P, 0%. The ultraviolet absorption spectrum shows maxima at 222, 274, and 278 m/i (in hexane). Mycoside A contains three different 0-methylated 6-deoxyhexoses, which have been identified as 2-0-methyl-fucose, 2-0-methylrhamnose, and 2,4-di-0-methylrhamnose. The lipid moiety of mycoside A is a di- or tri-mycocerosate of an aromatic alcohol. 

Among the other sugars detected in the soil, only the 6-deoxyhexoses have been quantitatively determined. In Delaware soils, rhamnose and fucose, determined by quantitative paper-chromatography, amounted to 20% of the sugars. Under the conditions of furfural formation from pentoses, the 6-deoxyhexoses yield 5-methyl-2-furaldehyde this has been determined by the differential solubilities of the phloroglucides in alcohol. The proportion of 6-deoxyhexoses in some cases exceeded that of pentoses. 

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