N-Glycosidic

Glycosides are a large and very important class of carbohydrate derivatives character ized by the replacement of the anomeric hydroxyl group by some other substituent Gly cosides are termed O glycosides N glycosides S glycosides and so on according to the atom attached to the anomeric carbon... 

Adenosine (an N glycoside also known as a nucleoside adenosine is one of the fundamental molecules of biochemistry)... 

The most important derivatives of pyrimidines and purines are nucleosides Nucleosides are N glycosides m which a pyrimidine or purine nitrogen is bonded to the anomeric carbon of a carbohydrate The nucleosides listed m Table 28 2 are the mam building blocks of nucleic acids In RNA the carbohydrate component is d ribofuranose m DNA It IS 2 deoxy d ribofuranose... 

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. 

Glykosid. n. glycoside, glucoside. (Preferably, glycoside is the general term, glucoside denotes a glucose derivative.)... 

Steric hindrance by the base restricts rotation about the P-N-glycosidic bond of nucleosides and nu-... 

Posttranslational modification of preformed polynucleotides can generate additional bases such as pseudouridine, in which D-ribose is linked to C-5 of uracil by a carbon-to-carbon bond rather than by a P-N-glycosidic bond. The nucleotide pseudouridylic acid T arises by rearrangement of UMP of a preformed tRNA. Similarly, methylation by S-adenosylmethionine of a UMP of preformed tRNA forms TMP (thymidine monophosphate), which contains ribose rather than de-oxyribose. 

The depurination of DNA, which happens spontaneously owing to the thermal lability of the purine N-glycosidic bond, occurs at a rate of 5000-10,000/cell/d at 37 °C. Specific enzymes recognize a depurinated site and replace the appropriate purine directly, without interruption of the phosphodiester backbone. 

Hemiacetal hydroxyl groups of carbohydrate molecules also may be coupled to amine-containing molecules to form N-glycosidic linkages, such as those in nucleic acids and oligonucleotides. 

Figure 1.39 The formation of an N-glycosidic bond links the base unit of nucleic acids to the associated ribose derivative.

Figure 1.42 The three pyrimidine bases common to nucleic acid construction. Cytosine and thymine are found in DNA, while in RNA, uracil residues replace thymine. The associated sugar groups are bound in N-glycosidic linkages to the N-l nitrogen.

In the carbohydrate chemistry arena, the Tsuji-Trost reaction has been applied to construct N-glycosidic bonds [53]. In the presence of Pd2(dba>3, the reaction of 2,3-unsaturated hexopyranoside 68 and imidazole afforded N-glycopyranoside 69 regiospecifically at the anomeric center with retention of configuration. In terms of the stereochemistry, the oxidative addition of allylic substrate 68 to Pd(0) formed the jc-allyl complex with inversion of configuration, then nucleophilic attack by imidazole proceeded with another inversion of the configuration. Therefore, the overall stereochemical outcome is retention of configuration. 

Some N-glycosides have been synthesized as nucleoside analogues by Vilarrasa and co-workers <1996TL901>, the result is shown in Scheme 8. The starting compound, [l,2,4]triazolo[5,l-c][l,2,4]triazine-4(l//)-one 54, was reacted with tri-0-benzoyl-/3-diribofuranosyl bromide under two different reaction conditions. In the presence of silver triflate at low temperature, the zwitterionic 2-substituted compound 55 was obtained, whereas under reflux conditions in acetonitrile the neutral 1-substituted compound 56 was formed. 

Scheme 5.69 Synthesis of N-glycosides from 1,2-anhydro sugars.

In 1939, Dr. Yoshiyuki Inoue became the Professor of the laboratory when Professor B. Suzuki moved to the University of Tokyo. In March, 1940, Onodera joined Professor Inoue s group, and continued his work in carbohydrate chemistry. In August, 1949, he received his Ph. D. degree from Kyoto University. The title of his thesis was Biochemical Studies on Starch, Amino-Containing Sugars, and N-Glycosides (written in Japanese). 

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