Modified Koenigs-Knorr

Most of the methods available for the synthesis of this class of compoimd have been referred to in the preceeding pages. These include the modified Koenigs-Knorr reaction (p. 406), the use of glycosyl halides with non-... 

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%... 

Ackermann, I. E., Banthorpe, D. V., Fordham, W. D., Kinder, J. P., Poots, I. Preparation of new terpenyl 3-D-glucopyranosides by a modified Koenigs-Knorr procedure. Liebigs Ann. Chem. 1989, 79-81. 

Basic studies concerning their total synthesis have been undertaken by S. Umeza-wa and co-workers All the 0-(amino-deoxy-a-D-glucopyranosyl)-2-deoxystrept-amines listed in Table 2 have been synthesized by a modified Koenigs-Knorr condensation or via the nitrosyl chloride method mentioned above. 

Paromamine, neamine, 4-0-(6-amino-6-deoxy- -D-glucopyranosyI)-2-deoxystreptamine, 5-0- (2-amino-2-deoxy-o-D-glucopyranosyl) -2-deoxy-streptamine, kasugamycin, and a,a-trehalosamine have been synthesized. A common feature in the structures of these antibiotics is the presence of an a-o-glycosidic linkage. In the total syntheses, modified Koenigs-Knorr reactions, or addition of nitrosyl chloride " to an enose, were successfully used. 

Validamycin has been synthesized by 4-0- -D-glucosylation of validoxylamine A (using a modified Koenigs Knorr procedure), and its... 

Another total synthesis of ribostamycin (363), a broad-spectrum antimicrobial antibiotic produced by Streptomyces ribosidificus, has been reported. The synthetic route involved the condensation of a suitably protected S-O- -d-ribofuranosyl-2-deoxystreptamine derivative with 3,4-di-0-acetyl-2,6-dideoxy-2-(2,4-dinitroanilino)-6-phthalimido-a-D-gIucopyranosyl bromide under modified Koenigs-Knorr conditions. A standard Koenigs-Knorr reaction has been used... 

Modified Koenigs-Knorr reactions have been used in the synthesis of the glycopeptides (4)—(7) from hydroxyamino-acids, and the synthesis of the bivalent lactosyl haptens (8)—(10) and the interactions of the haptens with anti-lactosyl antibodies have been reported. ... 

Because a substantial excess of the halide is used in the Koenigs-Knorr synthesis of cardenolides, it is usually difficult, if not impossible, to secure the acylated intermediate in crystalline form. Hence, Reichstein nd coworkers18 introduced a procedure whereby the whole of the products arising from the coupling reaction are saponified, employing a solution of potassium hydrogen carbonate in aqueous methanol. This modified transesterification procedure renders all extraneous carbohydrate materials water-soluble the methanol is removed by evaporation, leaving an aqueous solution from which the (deacylated) cardenolide may be obtained by... 

Disaccharides are prepared by coupling two monosaccharide units together. This may be done in several ways. An effective method is the Koenigs-Knorr synthesis, after Wilhelm Koenigs (Germany 1851-1906) and Edward Knorr (Germany d. 1901). This method couples a carbohydrate and an alcohol. P-d-Allopyranose pentaacetate (82) is prepared previously from d-allose (18) and, if reacted with HBr in acetic acid, the a-bromide (96) is formed (2,3,4,6-tetra-0-acetyl-a-d-allopyranosyl bromide). When this bromide reacts with ethanol in the presence of silver oxide (AgaO), the product is the P-anomer, ethyl 2,3,4,6-tetra-O-acetyl-a-d-allopyranoside (97). It is possible to modify the procedure to make disaccharides. If bromide 97 is reacted with tetraacetate 98 (derived from a-d-idose), reaction with silver oxide and then sodium methoxide leads to the disaccharide 99 (0-a-d-allopyranosyl-[1 6]-a-d-idosopyranose). 

The latter was characterized by 2D n.m.r, studies carried out on the peracetylated, reduced tetrasaccharlde. The a- and 6-L-fucose-contalnlng compounds g-D-Gal(l - 4)a- and 3-L-Fuc(l 4)ot-L-Puc (1 - 3)D-Glc have been made by Koenigs Knorr procedures modified to favour each isomer and the repeating unit of the polysaccharide from Shigella flexnerl variant 7 has been synthesized. It is... 

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