Trimethylsilyl glycosidation

From a trimethylsilyl glycoside TMSOTf or TFA or BF3-Et20, CH3OCH2OCH3, 54-66% yield." ... 

Lee, Acree, and Shallenberger have in some cases carried out actual isolations of the anomeric trimethylsilyl per-O-trimethylsilyl glycosides by preparative gas chromatography and have then characterized the separated derivatives by optical rotation, elementary analysis, and NMR spectroscopy (30). These characterizations, which have been done for glucose, mannose, and galactose (see below) confirm the usefulness of the GLC technique. 

Silylation, for instance, providing 1-0-trimethylsilyl glycosides frOTi 1-0-unprotected sugars in an anomerically pure form, has been shown by Tietze and coworicers to be useful in phenyl glycoside and l,l -diacetal (see Section 1.2.5) synthesis with 0-silylated acceptors and trimethylsilyl triflate as catalyst. The diastereoselectivity was dependent on 0-protection. 

Distinction between the d and l forms of sugars is made by acid-catalysed formation of glycosides with chiral 2-butanol or 2-octanol the acetylated or trimethylsilylated glycosides with d and l sugars will be diastereomers and thus have different GLC retention times. 

Related methyl -D-glucopyranosiduronates were made from the acetylated 0-trimethylsilyl glycoside and aldehyde dialkylacetals in the presence of trimethylsilyl triflate. Following deacetylation the products were tested as enzyme substrates, compound (38) giving the free carboxylic acid with pig liver esterase and hydrolysing to release butanol with -D-glucuronidase, the latter illustrating the potential of such substances as releases of cytotoxic aldehydes. ... 

Trichloroacetonitrile reacts with glycosidic hydroxy groups of protected sugars to form glycosyl trichloroacetimidates (R. R. Schmidt, 1980, 1984,1985,1986 B. Wegmann, 1988). The imidate is substituted by alcohols in the presence of trimethylsilyl trifluoromethanesulfonate... 

Glycosyl-residue compositions were determined by GC-CIMS analysis of the per-O-trimethylsilylated methyl glycosides [23] separated on a fused-silicaDB-1 capillary column. The identity of each peak was confirmed by CIMS on a HP-5989 MS Engine (Hewlett-Packard). 

RG-n, Rhamnogalacturonan II Kdo, 3-deoxy-D-manno-octulosonic acid Dha, 3-deoxy-D-/yxo-heptulosaric acid aceric acid, 3-C- carboxy-5-deoxy-L-xylose TMS, per-0-trimethylsilylated methyl glycosides. 

The monosaccharide composition of all the samples was determined by GLC analysis of the trimethylsilyl methyl glycoside derivatives [1]. 

Similarly, per-O-trimethylsilylated mono- and P-linked disaccharides (lactose and cellobiose, not melibiose) could be converted into the corresponding a-glycosyl iodides, which upon SN2 displacement with CbT using TBACN mainly afforded P-cyano derivatives in good overall yields [191]. The cyanoglycosides were transformed into aminomethyl glycosides via reduction under mild conditions (Scheme 2.52). 

Kusumoto and coworkers have found that the treatment of hemiacetal 1 with trifluoro- or trichloroacetic anhydride 94 (1 equiv) and trimethylsilyl perchlorate (0.2 equiv) selectively provides the corresponding anomeric ester intermediate 91 [152], Hemiacetal acylation occurs even in the presence of the alcohol acceptor. With Lewis acid assistance, the glycosyl ester intermediate is displaced to provide disaccharide products in good yields. This transformation allowed the synthesis of disaccharides 98 (81%) and 99 (91%). In some cases, acetic anhydride has been used as the electrophilic activator of hemiacetal donors and the reaction with thiol acceptors yields S-linked glycosides [153,154],... 

Anhydroalditols can be easily generated by Lewis acid catalysed reduction of the corresponding aldoses or glycosides with triethylsilane (Fig. 2). The reaction requires protection of the hydroxyl groups, which can be performed temporarily by preliminary treatment with bis(trimethylsilyl)-trifluoroacetamide (BSTFA).1... 

C-Allyl glycosides can be prepared by the reaction of glycal epoxides with allyltributyltin in the presence of tributyltin triflate as a Lewis acid,281 and aldonitrones can be allylated with trimethylsilyl triflate as a catalyst (Equations (101) and (102)).282... 

Other glycosides which have been formed by direct substitution at 0-1 are tetrahydrop5uanyl (two diastereoisomers being obtained from each anomer) trityl and trimethylsilyl... 

The key intermediate 14, a stable tetrasubstituted tetrahydropyran derivative, was obtained from commercially available methyl o-glucopyranoside 12 via a three-step reaction sequence (Scheme 4). First the primary hydroxyl group was protected as thexyldimethylsilyl (TDS) ether, then the other OH groups were methylated under standard conditions to give 13. The latter glycoside was deoxy-genated at the anomeric position by treatment at room temperature with a Lewis acid (trimethylsilyl triflate) and a hydride donor (triethylsilane). This treatment also... 

We have found that the secret to a successful synthesis of the alkenyl glycosides 64 lies in obtaining the pure -acetate 65 [47]. Condensation of the acetate 65 with the appropriate alkenol,in the presence of a small amount (5-20 mol% depending on the scale) of trimethylsilyl triflate, gave the alkenyl glycosides 64 in excellent yield. Oxidation of the alkene 64 with dimethyldioxirane, followed by deacetylation, then gave the putative enzyme inhibitors 60. 

El and Cl are normally unsuitable for most flavonoid glycosides because of their polarity and thermolability. Preparation of permethylated or trimethylsilylated derivatives may overcome this problem. However, derivatization often produces mixtures of partially derivatized compounds and may involve rearrangements,and usually only weak molecular ion signals is observed when permethylated compounds are studied under El conditions. 

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