1,721,270 research outputs found
Thiazolylketoses: a new class of versatile intermediates for glycoside synthesis
No full textAn account is provided on the very recent work carried out in the author's laboratory dealing with the preparation of thiazolylketose acetates and their use as effective glycosyl donors in reactions with oxygen, carbon, nitrogen and phosphorus nucleophiles. These reagents are formed by addition of 2-lithiothiazole to sugar lactones followed by acetylation of the resulting thiazolylketoses. Coupling reactions, promoted by TMSOTf in CH2Cl2, are described with primary and secondary sugar alcohols, trimethylsilyl azide, triethyl phosphite and various C-nucleophiles. Suitable transformations of the resulting glycosides are carried out owing to the ready conversion of the thiazole ring into the formyl group followed by reduction to alcohol and/or oxidation to carboxylic acid. Thus, anomeric glycosyl amino acids, ketosyl and ulosonyl disaccharides and phosphonates have been prepared. Special applications include the synthesis of O-glycosyl calix[4]arene derivatives (calix-sugars) and a cyclic ketotrisaccharide. The triethylsilane reduction of thiazolylketose acetates leads to thiazolyl C-glycosides that once subjected to the thiazole-to-formyl conversion afford formyl C-glycosides. These anomeric sugar aldehydes are convenient starting reagents for the synthesis of various C-glycosides and C-glycoconjugates, such as (1→6)-disaccharides and oligosaccharides, glycosyl aminoacids (glycine, serine, asparagine), and a galactocerebroside. Formyl C-glycosides participate in the azomethine ylide 1,3-dipolar cycloaddition reaction to C60 fullerene to give sugar fullerenes. The cover illustration shows some products of these reactions and a view of Palazzo dei Diamanti (Palace of Diamonds), a beautiful and unique building in the architectural context of Ferrara, constructed in the first half of 1500. The facade of the Palace is decorated with more than eight thousand five-hundred diamond shaped small blocks of marble
Thiazole as leaving group. Thermal elimination from thiazolylketoses
No full textHeating thiazolylketofuranoses and -ketopyranoses in refluxing toluene results in the elimination of thiazole and formation of the corresponding sugar lactones in nearly quantitative yield. The same reaction does not occur with 1-O-acetyl and 1-O-trimethylsilyl derivatives. Also model furyl- and thienylketofuranoses and various thiazolyl alcohols proved to be stable under the above thermolysis conditions. A possible mechanism of the observed thermolysis of thiazolylketoses involves the thiazolium 2-ylide as the actual leaving group
Transformation of linear oligoketosides into macrocyclic neoglycoconjugates
No full textThe macrocyclization of linear D-galacto-2-heptulopyranose-containing oligoketosides has been carried out by intramolecular glycosidation and ring-closing metathesis. The aglycon fragment of the cyclic neglycoconjugates thus formed was an alkylidene or a polyether chain. One of the oligoketoside–crown ethers showed a moderate asymmetric induction in the Cram model phenyl acetate–acrylate addition
Synthesis of [60]fulleropyrrolidine glycoconjugates using 1,3-dipolar cycloaddition with C-glycosyl azomethine ylides
No full textHeating a mixture of [60]fullerene, N-methylglycine (sarcosine), and a sugar aldehyde in refluxing toluene resulted in the formation of a complex mixture of products from which the fulleropyrrolidine monocycloadduct was isolated in 14, 10, and 12% yield for formyl C-galactopyranoside, formyl C-glucopyranoside, and formyl C-mannofuranoside, respectively. © 2002 Elsevier Science Ltd. All rights reserved
A novel stereoselective synthesis of N-acetyl-α-neuraminosyl-galactose di-saccharide derivatives, using anomeric S-glycosyl xanthates
No full text--
A new synthetic approach to mycobacterial cell wall alpha-(1 -> 5)-D-arabinofuranosyl C-oligosaccharides
No full textThree designed arabinofuranose building blocks allowed the diastereoselective synthesis of a C-disaccharide and a
C-trisaccharide by Wittig olefination. The latter compound represents the first example of all-carbon linked arabinofuranotriose
analogue
Chemical synthesis of 3-deoxy-D-glycero-D-galacto-2-nonulosonic acid (KDN) from D-mannose. Testing a Wittig-Michael type route to 3-deoxy-2-ulosonic acids
No full text--
Addressing the scope of the azide-nitrile cycloaddition in glycoconjugate chemistry. The assembly of C-glycoclusters on a calix[4]arene scaffold through tetrazole spacers
No full textNew glycoclusters constituted of ribosylmethyl, galactosylmethyl, and glucosylmethyl fragments assembled on a calix[4]arene platform by means of propoxytetrazole spacers have been prepared by coupling the corresponding sugar azides with p-toluenesulfonyl cyanide, and then reacting 1-glycosylmethyl-5-sulfonyl-tetrazole derivatives thus formed with a calix[4]arene tetrol
Discussion Addendum for: Diastereoselective homologation of D-(R)-glyceraldehyde acetonide using 2-(trimethylsilyl)thiazole: 2-O-benzyl-3,4-isopropylidene-D-erythrose
No full textOver the last several decades, numerous heterocycles have emerged as useful tools (precursors, reagents, chiral auxiliaries) in new methodologies for organic synthesis.2 In that context, the five-membered heterocycle 1,3-thiazole attained considerable popularity by virtue of its stability under a wide range of reaction conditions, as well as its facile conversion into the formyl group by a very efficient three-step one-pot procedure. The widespread use of the thiazole ring as masked formyl group led to the formulation of a general synthetic strategy that we have referred to as the “Thiazole-Aldehyde Synthesis”
- …
