Alditols 0-alkylation

The reaction of 1-amino-1-deoxyketoses, and their N-alkyl and N-aryl derivatives, with alkyl or aryl isothiocyanates (Huber et al, 1960) was studied in more detail, and new 4-(alditol-l-yl)-l-alkyl(aryl)-3-alkyl(aryl)-l,3-dihydro-2H-imidazole-2-thiones were obtained. These compounds were used as starting materials for the synthesis of OL-histidines, DL-histidine-2-thiol, and other imidazole derivatives of biological interest. 

Among them are found the naturally occurring 1-deoxynojirimycin (DNJ) and 1-deoxymannojirimycin (DMJ) [96]. Practical syntheses of DNJ and DMJ start from L-gulono-1,4-lactone (20b) and o-mannono-1,4-lactone (74), respectively [97]. Key intermediates are 2,6-dibromo-2,6-dideoxy-D-alditol derivatives 75a and 75b obtained by 2,6-dibromination of the starting lactones, followed by reduction with NaBH4 [98, 99]. Then a five-step sequence involving selective partial protection, introduction of an amine functionality, and intramolecular N-alkylation, lead to DNJ and DMJ, respectively (Scheme 22). 

Lithium chloride, preferably dissolved in absolute ethanol, has also been used306 419 420 for preparing alkyl chlorides. Dissolved in absolute ethanol-acetone (1 1, by vol.), it has recently414 found application with alditol sulfonates. Its action on l,4 3,6-dianhydro-2,5-di-0-mesyl-L-iditol, l,4 3,6-dianhydro-2,5-di-0-mesyl-D-mannitol, and l,4 3,6-dian-hydro-2,5-di-0-mesyl- (and -2,5-di-O-tosyl-) sorbitol resembles the action of sodium iodide on these compounds, i.e., the first displays no appreciable reaction, the second gives the 2,5-dichloro-2,5-dideoxy derivative, and the last two afford the respective monochloromonodeoxy-mono-O-sulfonyl derivatives. Treatment of l,4 3,6-dianhydro-2,5-di-0-mesyl-sorbitol during 48 hours at 180-90° gives some of a dianhydro-mono-chloromonodeoxy-sorbitoleen. 

M. McNeil, Elimination of internal glycosyl residues during chemical ionization-mass spectrometry of per-O-alkylated oligosaccharide-alditols, Carbohydr. Res., 123 (1983) 31-40. 

Plasma-desorption mass spectrometry is another technique that has been applied successfully to the detection of readily removable fatty acyl substituents in intact glycolipids and their acylated derivatives. The specific location of the fatty acyl substituents in the ring of the glycosyl residues, as in LOS antigens, is determined by methylation under nonbasic conditions (see Section II.lb), followed successively by O-deacylation, ethylation of the exposed hydroxyl groups, and GC-MS analysis of partially alkylated alditol acetates21 ethyl groups denote the sites of previous O-acylation. 

Adsorption surface, SFC, solvent Interactions, 1>>9 Air monitors. Industrial chromatography, 200 Alditol acetates, chromatogram, 32f Alkyl groups, bonded, HPLC development, 82,83 Amides, enantiomeric, separation, >l3,>l>lf Amine compounds, RPLC, 8>l Amino acids HPLC, 86,87f Ion exchange, 81 ligand exchange, >>... 

An interesting approach towards KDO, KDN and Neu5Ac as well, utilized a protected cyanohydrine 80 as a versatile acylanion equivalent of alkyl glyoxylate. Its reaction with appropriate halogeno alditol, as it is depicted in Scheme 20, provided the alkylated product 81 in good yield [91]. Conversion of 81 into desired KDO derivative 83 was achieved via a-ketoacid 82, resulted from hydrolysis of cyano group with NHjaq. 

Unlike neutral polysaccharides undermethylated acidic polysaccharides cannot be realkylated directly. The Hakomori procedure leads to esterification of uronic acid residues that on further treatment with base will undergo extensive p-elimination. Therefore the methylated acidic polymer should be carboxyl-reduced with LiAFH4 prior to realkylation. This is illustrated by our work (O Neill et al., 1986a) on the extracellular polysaccharide produced by Alcaligenes (ATCC 31555). After a single methylation an excess of branch points was observed which indicated incomplete methylation of position 2 of (l- 3)-linked glucose residues. To confirm this, the methylated polysaccharide was carboxyl-reduced, ethylated, and the alkylated alditol acetates analyzed by GLC-MS. The... 

The structures of these complex oligosaccharides were established using methylation, partial acid hydrolysis, and subsequent separation of the alkylated oligosaccharide alditols by HPLC, which were characterized by a combination of FAB-MS, EI-MS, and H-NMR. 

The methods of Valent et al. (1980) and McNeil et al. (1982b) have been applied to the rigorous characterization of a nonasaccharide derived from the enzymic degradation of sycamore cell wall xyloglucan. Following partial acid hydrolysis and workup, 16 alkylated oligosaccharide-alditols were isolated by reverse-phase HPLC, but only 12 were sufficiently pure to be unambiguously characterized. 

Anhydro-alditols - The preparations of polyesters based on l,4 3,6-di-anhydro-D-glucitol and -o-mannitol with succinyl-, glutaryl- and adipoyl-dichlor-ides have been reported. Also reported have been the syntheses of poly(1 6)-2,5-anhydro-D-glucitol and its 3,4-di-0-alkylated derivatives by Lewis acid induced polymerization of 3,4-di-0-alkyl-l,2 5,6-dianhydro-D-mannitol base induced polymerization of l,2 5,6-dianhydro-3,4-di-0-methyl- or 3,4-di-O-iso-propylidene-D-mannitol base induced polymerization of l,2 5,6-dianhydro-3,4-di-O-pentyl- or di-O-decyl-o-mannitol and base induced polymerization of l,2 5,6-dianhydro-3,4-di-0-methyl-L-iditol. The solubilities of these 3,4-di-O-alkylated and deprotected polymers in aqueous and organic media were studied. Further, it has been reported that 2,5-anhydro-3,4-di-0-methyl-D-glucitol linked 1,6 to silica gel was useful for the optical resolution of amines and amino acid salts. ... 

Further 2-(alditol-l-yl)-l-alkyl-4,5,6,7-tetrahydroindol- l-ones have been obtained from 2-alkylamino-2-deoxy-hexoses and -heptoses with 5,5-dimethyl-l, 3-cyclohexadione (c.f. Vol.l7, p.113)." ... 

A GC/MS method, commonly called linkage analysis or methylation analysis, has also proven to be a successful approach to determining interresidue linkage and branch points [14]. It involves complete alkylation of all free hydroxyl groups. The fully methylated oligosaccharides are hydrolyzed into monomers, which are further reduced and acetylated to provide partially methylated alditol acetates (PAMAs). Acetylation takes place at those positions that were newly exposed by hydrolysis and reduction. The GC retention times and fragmentation patterns can reveal the mode of attachment in the native sugar. 

Deoxy-2-thioureido-sugars, e.g. 53 (R=Bz or CO2EO could be synthesized by direct condensation of amino-sugars with benzoyl or ethoxycarbonyl isothiocyanate, whereas similar reactions with aryl or alkyl isothiocyanates led to alditol-1-yl substituted heterocycles, e.g. 54 by way of 53 (R=Ph or Me). These monocyclic products further cyclize in dilute acetic acid to give 55... 

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