✍ Scribed by Michael Ludewig; Joachim Thiem
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The 2-azidofucosyl donor 4 was synthesised via a azidonitratisation and stereoselectively α-linked to the benzyl fucoside acceptor 5 by methyl triflate catalysis. The Since lung-specific lectins are identified as the responsible factor for the adhesion of disseminated tumor cells, [1] we have investigated several aspects of enhancing the blocking capacity of fucose by employing approaches such as oligomerisation, [2] clustering [3] and derivatisation. [4] This paper reports the preparation of a thiomethyl 2-azidofucosyl donor and its application to the synthesis of 2-amino-and 2acetamido-α-fucopyranose containing disaccharides.
Aminosugars such as N-acetylglucosamine, N-acetylneuraminic acid and N-acetylgalactosamine are widely spread in nature and belong to the group of sugars that are often required by the metabolism of higher organisms. Other glycosamines are rather seldom, often carry the amino group at a different position and occur mainly in plants and bacteria. They are known to act as potent inhibitors of enzymes and are sometimes part of antibiotic or other biologically active glycosides. Fucosamines are found in microorganisms as well, [5] [6] were isolated from them [7] and synthesised chemically. [8] By providing an easy and selective method for the synthesis of 2-amino-fucosides their potential in lectin inhibition can be investigated.
Starting from 3,4-di-O-acetyl-1,5-anhydro-2,6-dideoxy-lyxo-hex-1-enitol (3,4-di-O-acetyl--fucal, 1), [9] the azido group was introduced employing the azidonitratisation method of Lemieux et al. [10] The resulting anomeric mixture of nitrates 2 was not isolated but directly converted into the corresponding acetates 3 by heating the crude product with acetic acid and sodium acetate. Chromatography gave 51% of the anomeric mixture 3, and no trace of the talo-configured epimer could be detected. The conversion into the thioglycoside was performed with trimethylsilyl methylsulfide (TMSSMe) and trimethylsilyl triflate (TMSOTf) in nearly quantitative yields to give the product 4 as an anomeric mixture.
Attempts to activate the thioglycoside with halonium ions met with problems. The use of N-iodosuccinimide (NIS) as well as CuBr 2 /Bu 4 NBr together with a glycosyl acceptor did not lead to the formation of a new glycoside; the latter did not even form the corresponding bromide pre-
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Syntheses have been described of the 2-acetamido-2-deoxy derivatives of 5-thio-Dglucose [1-3], 5-thio-I>mannose [4], and 5-thio-D-allose [5]. We now describe the synthesis of another member of this series, 2-acetamido-2-deoxy-5-thio-I)-altrose. Treatment of oxirane 1 [6] with sodium azide and ammon