Glycosides pyrimidine 2-deoxy

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... 

Most nucleosides contain D-ribose or 2-deoxy-D-ribose linked to N-1 of a pyrimidine or to N-9 of a purine by a P-glycosidic bond whose syn conformers predominate. 

This enzyme [EC 3.2.2.17], also known as deoxyribodi-pyrimidine endonucleosidase, catalyzes the hydrolysis of the A -glycosidic bond between the 5 -pyrimidine residue in cyclobutadipyrimidine (in the DNA) and the corresponding deoxy-D-ribose residue. 

The DNA sugar is 2-deoxy-D-ribose. The four heterocyclic bases in DNA are cytosine, thymine, adenine, and guanine. The first two bases are pyrimidines, and the latter two are purines. In nucleosides, the bases are attached to the anomeric carbon (C-1) of the sugar as p-N-glycosides. In nucleotides, the hydroxyl group (-OH) at C-3 or C-5 of the sugar is present as a phosphate ester. 

Within the structure of the nucleic acids, a pyrimidine or purine is linked to the sugar (2-deoxy-D-ribose or D-ribose) to give a nucleoside. The nucleosides are referred to as deoxyribonucleosides if they contain deoxyribose, and ribonucleosides if they contain ribosc. The purine nucleosides have a (3-glycosidic linkage from N-9 of the base to C-l of the sugar. In pyrimidine nucleosides, the linkage is from N-l of the base to C-l of the sugar. 

Gougerotin (= l-[4-Deoxy-4-(sarcosyl-D-seryl) amino-(3-I)-gluco-pyranuramide] cytosine)] (pyrimidine glycoside)... 

The term nucleoside was once restricted to pyrimidine and purine A-glycosides of D-ribofnranose and 2-deoxy-D-ribofuranose, becanse these are the substances present in nncleic acids. The term is nsed more liberally now with respect to the carbohydrate portion, bnt is still nsnally limited to pyrimidine and pnrine snbstitnents at the anomeric carbon. Uridine is a representative pyrimidine nncleoside it bears a D-ribofuranose gronp at N-1. Adenosine is a representative purine nncleoside its carbohydrate unit is attached at N-9. 

The monosaccharide component of DNA is 2-deoxy-D-ribose (the 2-deoxy refers to the absence of a hydroxyl group at the 2 position), whereas that of RNA is D-ribose. The glycosidic bond is between C-1 (the anomeric carbon) of ribose or 2-deoxyribose and N-1 of a pyrimidine base or N-9 of a purine base. Figure 20.2 shows the structural formula for uridine, a nucleoside derived from ribose and uracil. 

Deoxy-p-D-rhreo-pentofuranosyl nucleoside derivatives of type 38 could be obtained by condensation of silylated heterocycles with the a-(phenylthio)glycoside, induced by NBS. With pyrimidines, good p-selectivity was found, whereas with purines longer reaction times were... 

Deoxy-6,2 -methano-pyrimidine nucleosides are accessible by a sequence including Peterson olefination and intramolecular glycosidation, as outlined in Scheme 3 (for an earlier route, see Vol. 19, p. 198-9). Intermediate (19) can be transformed into the uridine, cytidine and 4-thiouridine systems. 8... 

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