A- and -Glycosides

Originally, the iV-trifluoroacetyl (TFAc) derivative of sialic acid was introduced by Bovins and co-workers as a 2-bromide glycosyl donor, which was reacted with benzyl alcohol in the presence of sym-collidine to give a 1/2 mixture of a- and -glycosides in 30% yield [16]. In our laboratory, the 2-phenylsulfenyl derivative of A-TFAc sialic acid has been used for the synthesis of de-A-acetyl-6-sulfo-sialyl Lewis X [97]. However, Boons and co-workers were again first to describe the high potential of the A-TFAc sialyl donor [98]. 

Phenols and naphthols also react with unprotected a- and -glycosides, directly, in the presence of trimethylsilyl triflate catalyst under mild conditions (equation 66) . 

Thiophene analogs of daunomycin (172, 173) were prepared in multistep reactions. The synthesis is based on a strong base-induced cycloaddition of homophthalic anhydrides. In the final step, glycosidation yielded a mixture of a- and -glycosides from which the a-isomer was separated (87TL3971). 

Inaccuracies in the GROMOS rotational energies for glyco-sidic angles have been recently reported by Ott and Meyer, and torsion terms for the 95-angles (O-C-O-C) in a- and -glycosides proposed (equations 17 and 18). 

The reaction conditions applied are usually heating the amine with a slight excess of aldehyde and a considerable.excess of 2d-30hydrochloric acid at 100 °C for a few hours, but much milder ( physiological ) conditions can be used with good success. Diols, olefinic double bonds, enol ethers, and glycosidic bonds survive a Pictet-Spengler reaction very well, since phenol and indole systems are much more reactive than any of these acid sensitive functional groups (W.M. Whaley, 1951 J.E.D. Barton, 1965 A.R. Battersby, 1969). 

Maltose obtained by the hydrolysis of starch and cellobiose by the hydrolysis of cellulose are isomenc disaccharides In both maltose and cellobiose two d glucopyra nose units are joined by a glycosidic bond between C 1 of one unit and C 4 of the other The two are diastereomers differing only m the stereochemistry at the anomeric carbon of the glycoside bond maltose is an a glycoside cellobiose is a (3 glycoside... 

The stereochemistry and points of connection of glycosidic bonds are commonly designated by symbols such as a(l 4) for maltose and (3(1 4) for cellobiose a and (3 designate the stereochemistry at the anomeric position the numerals specify the ring car bons involved... 

Lactose is a disacchande constituting 2-6% of milk and is known as milk sugar It differs from maltose and cellobiose m that only one of its monosaccharide units is D glucose The other monosaccharide unit the one that contributes its anomeric carbon to the glycoside bond is d galactose Like cellobiose lactose is a (3 glycoside... 

Lactam (Section 20 15) A cyclic amide Lactone (Section 19 15) A cyclic ester Lactose (Section 25 14) Milk sugar a disacchande formed by a p glycosidic linkage between C 4 of glucose and C 1 of galactose... 

Froehde s reagent (gives characteristic colorations with certain alkaloids and glycosides) dissolve 0.01 g of sodium molybdate in 1 mL of concentrated H2SO4 use only a freshly prepared solution. 

Suciose [57-50-1] (P-D-fructofuianosyl-a-D-glucopyianoside), 0 2 22, fomiula weight 342.3, is a disaccharide composed of glucose and fmctose residues joined by an a,P-glycosidic bond (Fig. 1). 

Neosidomycin (63) and SF-2140 (64) are indole N-glycosides produced by S. hjgroscopicus A.ctinomadura respectively (195,196). A revised stmcture for (63) has appeared (197). Compound (64) contains an a-N-glycoside linkage. Both (63) and (64) show activity against gram-positive bacteria, yeast, fungi, and vimses. 

Nikkomycins. The nikkomycins (141—159), isolated from S. tendae are nucleoside-peptide antibiotics (1,4,244,245) as shown in Table 8. Nikkomycins X and Z are stmcturaHy identical to neopolyoxins A and C, respectively. Compound (141) is a competitive inhibitor of chitin synthetase. Two new nikkomycins, nikkomycin pseudo-Z and pseudo-J (158, 159), contain a C-glycosidic bond between C-5 of uracil and C-1 of... 

Fig. 1. Primary stmctures of some common polysaccharides, (a) Alpha-glycoside linkages characterize amylose, amylopectin, and glycogen (b) cellulose has...

BBr is a very useful reagent for cleaving ethers, esters, lactones, acetals, and glycosidic bonds it is used to deoxygenate sulfoxides and in the preparation of image-providing materials for photography (5). 

Dlgltoxin. Digitoxin is a cardiac glycoside obtained from Digitalis purpurea. Digitoxin is indicated in the treatment of atrial flutter, atrial fibrillation, and supraventricular tachycardia. Its electrophysiologic and adverse effects are similar to those described for digoxin (87). 

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