2.3.6- Tri-O-methyl

A methylation analysis of S14, performed in the authors laboratory,44 gave 2,3,4,6-tetra-O-methyl-D-galactose, 2,4,6-tri-O-methyl-D-galactose, and 2,3,6-tri-O-methyl-D-glucose in the proportions 1 1 1. Although these are the same components as previously reported, the proportions are different. In addition to these sugars, 2-deoxy-3-0-methyl-2-(methylamino)-D-glucose was also obtained. 

Some modifications to the cyclodextrin structure have also been found to improve their complexing ability. Casu and coworkers prepared 2,3,6-tri-O-methyl and 2,6-di-O-methyl derivatives of alpha and beta cyclodextrin. They observed that tri-O-methyl-alpha cyclodextrin shows an almost ten-fold increased stability of the complex with the guest, Methyl Orange, compared with the unmodified alpha cyclodextrin. A possible reason for this increase in stability is that the methyl groups are responsible for an extension of the hydrophobic cavity of the cyclodextrin. Other workers,however, observed a much smaller enhancement of stability of complexes on methylation of the cyclodextrin, and a decrease in stability has even been reportedfor the one host-two guests complex of tropaeolin with beta cyclodextrin. Thus, the effect of methylation on the stability of a complex varies with the guest species involved, and cannot be readily predicted. 

L-Gulose readily forms an anhydride, and in a study on alginic acid, methylated L-guloses were isolated as their anhydrides.88 Other anhydro sugars, such as 3,6-anhydro-L-galactose and its 2-methyl ether, may be found in algae (see, for example, Ref. 412), and, under certain circumstances, 2,3,6-tri-O-methyl-D-galactose may form an anhydride.571... 

PrObtom 22.42 The polysaccharide amylose, the water-soluble component of starch, is hydrolyzed to ( + )-maltose and D-(-t-)-glucose, Methylated and hydrolyzed, amylose gives mainly 2,3,6-tri-O-methyl-D-glucopyranose. Deduce the structure of amylose. 4... 

It has D-glucose units joined by a-glycosidic linkages [Problem 22.35(a)] to the C of the next unit. This is revealed by isolating maltose, an a-glycoside, and the 2,3,6-tri-O-methyl derivative. The C —OH forms the pyranoside ring. 

Oxidation of the carboxyl-reduced and acetylated Pneumococcus type 2 capsular polysaccharide revealed that only one L-rhamnose residue in the hexasaccharide repeating-unit, later demonstrated to have the structure 60, was oxidized and, consequently, /3-L-linked.156 Replacement of 2,3,6-tri-O-methyl-D-glucose in the methylation analysis of the original polysaccharide by 2,3,4,6-tetra-O-methyl-D-glucose in that of the oxidized polysaccharide established that this L-rhamnose residue is linked to 0-4 of a D-glucose residue. The analysis also showed that it was an L-rhamnose residue in the chain (and not the branching L-rhamnose residue) that was /3-linked. 

Cationic movements are given as percentages of the anionic movement (about 10 cm) of p-nitrobenzenesulfonic acid on the same strip with 2,3,6-tri-O-methyl-D-glucose as non-migrating marker. The electrolyte solution was a 0.1 M solution of the metal acetate in 0.2 M acetic acid. 

Methylation with dimethyl sulfate in basic solution followed by acid hydrolysis gives 2,3,4,6-tetra-O-methyl-D-glucopyranose and 2,3,6-tri-O-methyl-D-glucose. 

Peaks identified penta-O-methyl-mono-O-acetylmyoinositol derived from mono-linked myoinositol, 2,3,6-tri-O-methyl-1,4,5-tri-O-acetylglucitol derived from a 4-linked glucose, and 3,4,6-tri-O-methyI-l, 5,di-0-aeetyl-2-acetamido-2-N-methylglucitol derived from a terminal H-acetylglucosamine. The PMAA sample was chromatographed on a 1.5 m X 2 mm ID column packed with 3% OV-210 in a Finnigan automated GC/MS model 3300/6110. Temperature program 150° to 215°C at 6°C/min. 

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