Laboratory Synthesis of Nucleosides and Nucleotides

The chapter begins with a discussion of the structure of nucleosides and nucleotides. Then the structure of the nucleic acids, DNA and RNA. the polymers formed from nucleotide monomers, is presented. The function of these polymers in the replication, transcription, and translation of genetic information is briefly addressed. Next, the organic chemistry involved in determining the sequence of DNA is presented. Finally, the synthesis of small DNA molecules in the laboratory is discussed. 

The synthesis and chemistry of heterocyclic analogues of purine nucleosides and nucleotides have been comprehensively reviewed, as have the synthesis and properties of various disaccharide nucleosides.5 Other reviews have discussed the importance of nucleoside analogues in chemotherapy and in other potential therapeutic applications such as immunomodulation or the regulation of gene expression, recent developments in the synthesis of nucleoside analogues with anti-HIV activity, and the synthesis of 2, 3 -dideoxynucleosides, with or widiout substituents at C-2 or C-3, by methods which involve condensations of modified sugars with heterocyclic bases. In a review on progress in free radical chemistry in his laboratories. Barton has discussed applications to the synthesis of C-nucleosides, chain-extended nucleosides and nucleoside phosphonates. ... 

For the past decade this laboratory has devoted much of its attention to an examination of various facets of purine metabolism in human erythrocytes. These cells do not have the complete pathway for the novo synthesis of purines and do not make nucleic acids. On the other hand, they have an active nucleotide metabolism and contain the salvage enzymes, hypoxan-thine-guanine phosphoribosyl transferase (HGPRTase), adenine phosphoribosyl transferase (APRTase) and adenosine kinase. In view of the fact that the activities of certain enzymes of purine metabolism are quite high (e.g., purine nucleoside phos-phorylase occurs at a level of about 15 umolar units/ml of erythrocytes) and the total mass of erythrocytes in the adult human being is in excess of two liters, it appears that these cells play an important and perhaps not yet fully appreciated role in the whole body economy of purines in man. Therefore, we believe that the human erythrocyte provides a very useful model system for the examination of purine metabolism in man as well as for investigations of the action of certain purine and purine nucleoside antimetabolites, many of which are important in medicine. 

The synthesis of nucleotide triphosphates required for polynucleotide chain building is a complex process which will not be considered in full detail here. The biosynthetic routes for purine and pyrimidine nucleosides are somewhat different and commence with 5 phosphoribosyl-l-pyrophos-phate and carbamyl phosphate, respectively. These two materials undergo successive enzyme-catalysed reactions, linking at times with compounds encountered in other biochemical cycles, and utilising ATP in several stages. Polynucleotides can be synthesised by purely chemical means in the laboratory (Chapter 10.4). 

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