Deoxynucleoside hydrolysis

The assignment of the 2-deoxy-D-er yhydroxymethyl)cytosine deoxynucleoside rested, at first, on the fact that purine nucleosides of T6 nucleic acid liberated, on weak acid hydrolysis, a deoxypentose having the same R value as the deoxypentose of thymus deoxyribonucleic acid.37 In addition, the glucose-free nucleotide of 5-(hy-droxymethyl)cytosine39 gave a positive Dische test76 for deoxypentose. 

More difficulty was encountered with the pyrimidine deoxynucleosides. It was tacitly assumed that the sugar radical in thymidine and deoxy-cytidine, by analogy with the ribonucleosides, is attached to position Nl. The first significant experiment111 to shed some light upon the validity of this assumption was based upon the methylation studies of Levene and Tipson.108 Deoxyribonucleic acid from thymus was methylated with dimethyl sulfate plus alkali, and the product was degraded by strong-acid hydrolysis. One of the products obtained was 3-methylthymine (XI).111 A... 

Parallel kinetic resolution (PKR), a concept that has been introduced for reactions where starting from a racemic mixture can allow the preparation of two different compounds at the same reaction rate [31], has been appHed for the separation of a mixture of P-D/L-deoxynucleosides. A practical synthesis of P-t-3 - and P-L-5 -0-levuHnyl-2 -deoxynucleosides has been described for the first time [32] through enzymatic acylation and/or hydrolysis processes. It is remarkable that the different behavior exhibited by PSL in the acylation of D- and L-nucleosides allows the parallel kinetic resolution of D/L nucleoside racemic mixtures. Scheme 10.12 shows a PKR of a 1 1 mixture of D and L nucleosides via an acylation reaction for furnishing easily separable compounds. This methodology would have tremendous potential for both research and industrial applications in the nucleic acid field. 

Major and modified deoxynucleosides were isolated fi om the enzymatic hydrolysis of DNA by Kuo t a . (K37). The chromatographic system uses a two-buffer step gradient with a reversed-phase C-18 column. This method has good sensitivity, selectivity, precision, and accuracy for the determination of all six deoxynucleosides without the use of drastic hydrolysis conditions or difficult sample preparation procedures. In addition, Nazar al. (N3) and Salas and Sellinger (SI) have described liquid chromatographic methods for DNA and RNA hydrolysates. 

The chain-elongation reaction catalyzed by DNA polymerases is a nucleophilic attack by the 3 -hydroxyl group of the primer on the innermost phosphorus atom of the deoxynucleoside triphosphate (Figure 5.22). A phosphodiester bridge forms with the concomitant release of pyrophosphate. The subsequent hydrolysis of pyrophosphate by pyrophosphatase,... 

Scheme 6 illustrates the use of these protecting groups in the phosphorylation of 2 -deoxynucleosides by Michelson and Todd. 5 -0-Trityl-thymidine (110) was phosphorylated with dibenzyl phosphorochloridate (44) to (111), which, after treatment with 80% acetic acid, afforded thymidine 3-(benzyl phosphate) (112). Catalytic hydrogenolysis of (112) gave thymidine 3 -phosphate. Acetylation of (110) yielded the 3 -acetate (114) which, on detritylation to (115), followed by phosphorylation, catalytic reduction, and deacetylation, gave thymidine 5 -phosphate (116), identical with the thymidylic acid obtained by enzymic hydrolysis of 2 -deoxyribonueleic acid. A rather similar sequence was applied to the preparation of the 2 -deoxycytidine analogs of (113) and (116). 

Triethylammonium salts of aryl H-phosphonates have been coupled to the 3 -OH of deoxynucleosides using pivaloyl chloride as condensing agent subsequent hydrolysis by aqueous pyridine gives nucleoside H-phosphonate building blocks... 

N. and deoxynucleosides can be synthesized via a Salvage pathway (see). TTiey are also produced by hydrolysis of nucleic acids and nucleotides. Nucleoside phosphorylases and deoxynucleoside phosphorylases catalyse the reversible, phosphate-dependent cleavage of N. and deoxyribonucleosides, forming ribose 1-phosphate or deoxyribose 1-phosphate and the free base. N. and deoxyribonucleosides can be converted into their corresponding nucleotides by the action of specific kinases. 

The selective deacetylation of methyl 2,3-di-0-acetyl-a-D-threoside by use of porcine liver esterase afforded the 3-0-acetate exclusively. The P-anomer gave a mixture of the 2- and 3-monoacetates without any trace of fully deacetylated product. Hydrolysis of a series of 1,2-isopropylidene-a-D-hexofuranose 5,6-diacetates 29 by the same enzyme gave initially the 5-acetates 30, which quickly isomerized to the 6-acetates 31. Selective secondary acylation of 2-deoxynucleosides was achieved with Amano PS lipase and oxime esters in pyridine at 60 and... 

---