Glucopyranose selective methylation

The full methylation of melezitose in 1926-1927 by Zempldn and Braun and by Miss Leitch yielded a hendecamethyl-melezitose, the acid hydrolysis of which produced two moles of 2,3,4,6-tetramethyl-D-glucopyranose and one mole of a trimethyl-D-fructose, to which a 1,3,4-trimethyl structure was assigned on evidence that cannot now be regarded as precise, though it seemed reasonable at the time. The selection of a faulty formula for this trimethyl-D-fructose, which must have been 1,4,6-trimethyl-D-fructose as will be shown later, led to much confusion during the following decade. 

The selectivity of alkylation of 1,6-anhydrohexopyranoses is lower than drat of acylations. The relative rate-constants for the three hydroxyl groups in 1,6-anhydro-jS-D-glucopyranose (6) during methyla-tion with dimethyl sulfate in 19% sodium hydroxide solution689 are k2 ks k4 = 2.5 1 1.8, so that the formation of pure monomethyl or dimethyl ethers of 6 by this method is of little preparative value (compare Refs. 224 and 671). l,6-Anhydro-/3-D-galactopyranose (12) affords mostly the 2,4-di-O-methyl derivative,690 and 2-acetamido-l,6-anhy-dro-2-deoxy-/3-D-galactopyranose is mainly methylated at 0-4 by the... 

Inverse-phase Transfer Catalysis (cf. Section 4.6.2) has been successfully applied to perform the quantitative and selective oxidation of 1-decene in an aqueous two-phase system [22]. The success of this oxidation is mainly due to the use of /3-cyclodextrin - a cyclic oligosaccharide composed of seven glucopyranose units - functionalized with hydrophilic or lipophilic groups. The best results have been obtained with a multicomponent catalytic system composed of PdS04, H9PV6Mo6O40, CuS04, and per(2,6-di-0-methyl)-/3-cyclodextrin (Eq. 7) [23]. 

Oscarson et al. [5] found that benzoylation of 1 is often very slow when conventional methods are used, but it is dramatically accelerated under micro-wave activation. Benzoylation of selected substrates, for example acetonated a-D-galactopyranose and benzylidene 4,6-protected a-D-glucopyranose, which are not stable in acidic conditions, was performed by Cleophax et al. [13] under the action of microwave irradiation in a monomode system with methyl benzoate for 4-15 min. 

The zinc chloride (ZnCli) catalysed glycosidation of ara-substituted phenols with 1,2-anhydro-3,4,6-tri-(9-methyl-a-D-glucopyranose gives predominantly the corresponding a-anomer [69]. Addition of TMG (1) enhances the (3-selectivity, even to practical completion under the conditions of potassium carbonate (K2CO3) and 18-Crown-6, in THF (Table 4.7). 

The synthesis of D-myo-inositol 1,4,5-trisphosphate (18) (InsP3) from methyl a-i)-glucopyranose (17), via a type 2 Perrier rearrangement, has been reported by Keddie et al. (Scheme 7). Biological evaluation of the synthetic InsPs showed that this compound evoked a selective Ca + release via activation of InsP receptors. 

Some factors influencing the selectivity of the acetylation of 1,6-anhydro- -D-glucopyranose have been discussed in a theoretical paper. The expected mixture of mono- and di-benzoates was formed when methyl P-D-arabinopyranoside was exposed to 1 or 2 molar equiv. of benzoyl chloride in pyridine at -40 C. The order of reactivity was concluded to be OH-2>OH-4>OH-3 for mono-and OH-2>OH-3>OH-4 for di-benzoylation. For the 2-deoxy-2-amino-a-D-glucose derivative 21,... 

The results of selective cleavage, methylation, and oxidation with chromic oxide have shown that the repeating unit of the polysaccharide chain of the lipopolysaccharide from Sh. dysenteriae is 2-acetamido-2-deoxy-j3-D-galactosyl-(1 -> 3)-a-D-galactopyranosyl-(l 6)-o -D-glucopyranose, to which is attached... 

O-Glycosidic styrylcarbene complexes 298-302 prepared from chromium methyl-carbenes 239-243 and ben2aldehyde in a trans-selective aldol condensation undergo a chromium-templated benzarmulation upon reaction with per-benzyl-protected ethynyl glucopyranose 303. Oxidative demetallation results in the formation of hydroquinoid C- and O-biphenyl disacdiarides 304-308 (Scheme 11.62) [117]. 

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