Glycosidation stereoselective

It was projected that compound 13 could be stereoselectively linked, through its free phenolic hydroxyl group, with the anomeric carbon of intermediate 12 under suitably acidic conditions (see Scheme 8). Gratifyingly, the action of boron trifluoride etherate on a mixture of 12 and 13 in CH2CI2 at -50 °C induces a completely stereoselective glycosidation reaction, providing the desired a-ano-mer 48 in an excellent yield of 95 % from 46. It is presumed that boron trifluoride initiates cleavage of the anomeric trichloroacetimi-... 

Scheme 4.81 SBox glycosides in the stereoselective glycoside synthesis [436].

The stereoselective glycosidation of the secoaglycon 1338 was achieved by reaction of the sodium salt of 1338 with the a-l,2-anhydrosugar 1339 to give the p-glucopyranoside 1340 in 48% yield. After the removal of the SEM protecting group with TBAF, the photocyclization of compound 1341 afforded the indolocarbazole... 

Y. Du and F. Kong, Stereoselective glycosidic coupling reactions of fully benzylated 1,2-anhydro sugars with W-tosyl-L-serine methyl-ester or iV-benzyloxycarbonyl-L-serine methyl-ester, J. Carbohydr. Chem., 14 (1995) 341-352. 

Scheme 4.22 Glycosyl transferases in stereoselective glycosidic bond synthesis.

Higashi, K, Nakayama, K, Soga, T, Shioya, E, Uoto, K, Kusama, T, Novel stereoselective glycosidation by the combined use of a trityl hahde and Lewis acid, Chem. Pharm. Bull, 38, 3280-3282, 1990. 

Fukase, K, Hasuoka, A, Kinoshita, I, Aoki, Y, Kusumoto, S, A stereoselective glycosidation using thioglycosides, activation by combination of A-bromosuccinimide and strong acid salts. Tetrahedron, 51, 4923-4932, 1995. 

Fukase, K, Kinoshita, I, Kanoh, T, Nakai, Y, Hasuoka, A, Kusumoto, S, A novel method for stereoselective glycosidation with thioglycosides promotion by hypervalent iodine reagents prepared from PhIO and various acids. Tetrahedron, 52, 3897-3904, 1996. 

Adinolfi, M, Barone, G, Guariniello, L, ladonisi. A, Efficient activation of armed glycosyl trichloroacetimidates with Sm(OTf)3 in the stereoselective glycosidation of saccharidic acceptors. Tetrahedron Lett., 41, 9005-9008, 2000. 

The two-stage activation procedure for oligosaccharide synthesis, which was developed by Nicolaou and applied to his synthesis of avermectin Bia [10]> was also employed in his total synthesis of efrotomycin [15] (Scheme 12.11). The chemo- and stereoselective glycosidation of the... 

Yu HN, Furukawa J, Dceda T, Wong CH (2004) Novel efficient routes to heparin monosaccharides and disaccharides achieved via regio- and stereoselective glycosidation. Org Lett 6 723-726... 

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