Galactopyranosyl bromide

Applications of the procedure are described next. The 2,2-diflu-orodaunosamine derivative 495 (a four-compound mixture F-2ax,H-3 23-24, JF-2eq,H-3 6 Hz) was prepared from 4-0-benzoyl-2,3,6-tride-oxy-2-fluoro-3-(trifluoroacetamido)-o -L-galactopyranosyl bromide (493) through dehydrobromination (to give the 2-fluoroglycal 494 fh-i 5, f.c-i... 

The disaccharide derivatives 196 and 197 of N-tosyl-L-serine, of interest for the study of D-galactose-binding lectins, were prepared by Kaifu and Osawa148 from 194 and 195, respectively, by protection of 0-4 and -6 with a benzylidene group, condensation of the acetal with tetra-O-acetyl-a-D-galactopyranosyl bromide (110) under Koenigs-Knorr conditions, and deprotection. 

Benzoyl-2,3,6-trideoxy-2-iluoro-3-(triiluoroacetamido)-a>L-galactopyranosyl bromide ... 

The allyl ester [22] can be selectively removed in the presence of Z- [22], Boc- [25,28], or Fmoc amino protection [24]. For example, Fmoc threonine allyl ester 24 was glycosylated with 2-azido-3,4,6-tri-0-acetyl-2-deoxy-a-D-galactopyranosyl bromide 25 [6] to give the conjugate 26 in high yield [24]. Separation of the a-anomer and transformation of its... 

To a solution of the glycosyl acceptor 23 (400 mg, 0.89 mmol) in dry dichioromethane (10 mL) was added activated powdered 4-A MS (400 mg), and the mixtnre was stirred for 1 h at room temperature, then cooled to —78°C. Silver inflate (1 g, 3.89 mmol) and tetramethylurea (316 pL, 2.56 mmol) were added successively to the reaction mixture at -78°C, and the stirring was continued for 30 min. A solution of 2,3,4-tri-0-acetyl-6-0-pivaloyl-ot-D-galactopyranosyl bromide 31 (1.2 g, 2.65 mmol) in 10 mL of dichioromethane was added to the reaction mixture. After stirring for 3 h at —78°C, the precipitate was filtered off, and washed with dichioromethane. The filtrate and washings were combined, and the solution was processed as usual. Purification by flash chromatography on silica gel with EtOAc-hexane (1 1) gave the title disaccharide 32 (540 mg, 74%) mp 69°C, [a]D -15.7° (c 1.05, CHClj). 

Cognate preparations. 2,3,4,6-Tetra-O-acetyl-a-D-galactopyranosyl bromide. 

Cognate preparation. Methyl 2,3,4,6-tetra-O-acetyl-fi-D-galactopyranoside. Use 13.5 g (0.033 mol) of 2,3,4,6-tetra-O-acetyl-a-D-galactopyranosyl bromide (Expt 5.109), 19 g of anhydrous calcium sulphate, 5.6 g of yellow mer-cury(n) oxide, 0.5 g of mercury(n) bromide, 90 ml of dry chloroform and 90 ml of dry methanol under the reaction conditions and subsequent isolation procedure described above 7.5 g (63%) of methyl 2,3,4,6-tetra-0-acetyl-/ -D-galactopyranoside, m.p. 96-97 °C, [oc]d° —28.0° (c2.5 in CHC13), is obtained after several recrystallisations from ethanol. 

The intermediate trisaccharide (270) on deprotection gave the blood-group H (type 1) trisaccharide (278), and (271) was also condensed with tetra-O-benzyl-galactopyranosyl bromide in the presence of silver carbonate — silver perchlorate or mercury (II) cyanide to give a tetrasaccharide derivative which was converted into the blood-group B (type 1) tetrasaccharide (279). The blood-group A (type 2) tetrasaccharide (280) was prepared from the a-anomer of the bromide (275) by Paulsen and co-workers [156] via an intermediate trisaccharide used for the preparation of the blood-group B (type 2) tetrasaccharide (see Sect. 6.1). 

Benzyl trifluoromethanesulfonate. Preparation of tri-O-acetyl-2-O-benzyl-a-D-galactopyranosyl bromide from 1,3,4,6-tetra-O-acetyl-a-D-galactopyranose, R. U. Lemieux and T. Kondo, Carbohydr. Res., 35 (1974) C4-C6. 

Treatment of pentaacetyl-D-galactopyranose with liquid hydrogen bromide at room temperature yielded 6-deoxy-6-bromo-2,3,4-triacetyl-a-D-galactopyranosyl bromide (LXXVIII). The action of silver carbonate and methanol produced methyl 6-deoxy-6-bromo- 8-D-galacto-pyranoside 2,3,4-triacetate (LXXIX). Simultaneous reduction and deacetylation in alcoholic sodium hydroxide with Raney nickel gave methyl 0-D-fucopyranoside, which with silver oxide and methyl iodide afforded methyl trimethyl-/ -D-fucopyranoside (LXXX), from which... 

Triacetyl-0-D-arabinopyranosyl bromide Triace tyl-fl-n-arabinopyranosyl bromide Triacetyl-a-ir-rhamnopyranoayl bromide Triacetyl-a-D-ribosyl bromide Triace tyl-a-n-ribosyl bromide Triacetyl-a-D-xylopyranosyl bromide Triacetyl-a-n-xylopyranosyl bromide Tetraacetyl-of-D-galactopyranosyl bromide Tetraacetyl-a-D-glucopyranosyl bromide Tetraacetyl- -D-glucopyranosyl fluoride 2,3 5,6-diisopropylidene-a-D-mannofuranosyl chloride Tetraacetyl-a-D-mannopyranosyl bromide Heptaacetyl-a-cellobiosyl bromide Heptaacetyl-a-gentiobiosyl bromide Heptaacetyl-a-lactosyl bromide Heptaacetyl-a-maltosyl bromide... 

Further reactions have been performed with 2,4-diethoxypyri-midine as the basic component and 2,3,4-tri-O-acetyl-L-arabino-pyranosyl bromide,7 2,3,4-tri-O-acetyl-a-D-xylopyranosyl bromide,7 2,3,4,6-tetra-O-acetyl-a-D-galactopyranosyl bromide,7 and 2,3,4-tri-O-acetyl-D-ribopyranosyl bromide8 as halogenoses the products... 

In a similar manner, tetraacetyl-D-galactopyranosyl bromide yielded 6-(/S-D-galactopyranosyl)-D-glucopyranose (XXV) which was shown to be probably identical with allolactose from breast milk. ... 

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