Koenigs-Knorr conditions

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. 

The protected amino sugar glycoside was treated with "acetobromorhamnose" under Koenigs—Knorr conditions and an excellent yield of the corresponding 3 0-a-L-rhamnosyl derivative... 

Alternate synthesis of the 2— 4-linked disaccharide J,. Upon glycosidation of 18 with the methyl ester-ketopyranosy 1 bromide under the modified Koenigs-Knorr conditions given for the synthesis of above, a 7 1 mixture of the B and o >-, 2— 4-linked disaccharide derivatives 19 and 20 was obtained in 27%... 

Glycosyl fluorides are too unreactive to be activated under standard Koenigs-Knorr conditions, and, for this reason, their use as glycosyl donors was explored relatively late, after the development of glycosyl bromides. They were introduced in 1981 [103], and glycosyl fluorides are currently among the most frequently used donors. 

In addition, thioglycosylations using halide-assisted conditions (O Scheme 8) [75] and Koenigs-Knorr conditions (O Scheme 9) [76], the latter both with stannyl sulfides and free thiols, have been described. 

Koenigs-Knorr conditions. More recent work Indicates, however, that the silver triflate method of Hanes-sian may well have eclipsed earlier procedures. Thus the coupling of with the 4-deoxydaunosamine derivative 110(1.1 equiv) under the agency of CF3S03Ag provides the corresponding a-glycoslde in 70% yleld. Similarly, reaction of 111 (a-Cl anomer)... 

Many of the methods of activation using Koenigs-Knorr conditions require heterogeneous promoters and long reaction times at room temperature. In addition, the expense and toxicity of silver and mercury makes these methods impractical for large-scale syntheses. Consequently much research has focused on the development of glycosyl donors that could be activated at low temperature, under mild conditions, and without the need for heavy metal promoters. 

The two anomers (40) and (4I ) O-f a glycophospholipid have been synthesized, using halide-ion catalyzed glycosylation for construction of the 2-glucosidic l nk e and Koenigs-Knorr conditions for the... 

Pyrimidine nucleosides of N-acetylneurauninic acid have been prepared, with / -anomers predominating tinder Koenigs-Knorr conditions. ... 

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