Basic Synthesis of Fluorinated Carbohydrates

Because of the high C - F bond energy, glycosyl fluorides are stable in comparison to the other glycosyl halides, and this character has attracted much attention. They have been prepared in many different ways. One of them, rather classical, is through addition of the elements of HF (for example, HF in benzene ), BrF, or IF to per-O-acylated glycals.  

Glycosyl fluorides may be prepared by displacement of per-O-acyl or suitably protected 2-0-acyl 1-halides (Cl or Br) with fluoride [AgF (Refs. 28 and 29), KHF2 (Ref 30) or AgBF4 (Ref 31)]. -o-Glucopyranosyl [ F]fluo- 

Glycosyl fluorides have also been prepared by treatment of per-O-acyl or partially 0-acylated sugars with hydrogen fluoride [liquid HF (for example, see Refs. 38 and 39) or HF in acetic acid or dichloromethane], as exemplified by 2,3,4-tri-O-benzyl-a-D-xylopyranosyl (18), a-D-glucopyranosyl (19), tetra-O-pivaloyl-a-D-glucopyranosyl (20), and 2,3,5-tri-O-acetyl-D-xylofur-anosyl fluorides (21) (see Table 1). Frequently, HF treatment - leads to 

Treatment of inulin or D-fructose with liquid HF (neat or diluted with liquid SOj) gave a mixture of six di-D-fructose dianhydrides, including 23, 25, 27, and )3-D-fructofuranosyl ) -D-fructopyranose 2,l 3,2 -dianhydride 

Treatment of an extracellular polysaccharide of Rhizobium japonicum (an important factor for nitrogen-fixing symbiosis between bacteria and soybeans) with liquid HF (—40°, 30 min) gave mono- and oligo-saccharides involving 0- -D-glucopyranosyl-( 1 - 3)-C -(4-0-acetyl-a-D-galactopyrano-syluronic acid)-(l— 3)-D-mannose and its 1-fluoride. 

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