8 purine, alkaline hydrolysis

Oligonucleotides have also been separated by ion-exchange chromatography of yeast ribonucleic acid treated either with acid216 or with ribonuclease.209 Alkaline hydrolysis of the fission products obtained with the latter gives rise to pyrimidine nucleoside 3-phosphates and mixtures of purine nucleoside 2- and 3-phosphates. Bone phosphomonoesterase196 followed by alkaline hydrolysis gives pyrimidine nucleosides and purine... 

Alkaline hydrolysis splits the nucleotide into its phosphate and sugar-base residues. The sugar-base is known as a nucleoside. The nucleosides are named according to the type of base present. If a purine base is present it will end -osine, e.g. adenosine, while if a pyrimidine is present the name will end -idine, e.g. uridine. 

Remarkably, HCN-polymers are efficiently obtained at low temperatures suggesting a plausible cold origin-of-life scenario [63-65]. This latter hypothesis provides a mechanism to account for the concentration of HCN and a more stable environment for the newly formed nucleic acid components. Moreover, HCN is easily concentrated at its eutectic temperature (- 23.4 °C) [66,67] and the production of DAMN was found to be accelerated by lowering the temperature of the reaction medium. A large panel of purine derivatives, adenine 1, hypoxanthine 2, diaminopurine 3, xanthine 4 and guanine 5 was obtained after acidic and alkaline hydrolysis at high temperatures of the HCN-polymer produced in a frozen ammonium cyanide solution at - 78 °C for 27 years (Scheme 6 yields of products are reported... 

Alkaline hydrolysis of 2-cyano-l-hydroxyimidazole 3-oxide affords the 2-carboxamide with barium hydroxide the corresponding carboxylic add salt is formed." Selective reaction at each of the two different cyano groups of 1,2-disubstituted 4,5-dicyanoimidazole allows the synthesis of purine derivatives of unequivocal structure. ... 

The N-glycosidic bonds of nucleosides are usually highly stable in neutral and alkaline media and prone to acid hydrolysis. Purine derivative hydrolysis is then much faster than that of pyrimidine derivatives (Table 8.5.1). 

Mild acid hydrolysis of the deaminated purine nucleotides, xanthylic acid and inosinic acid, gives the purine bases (xanthine and hypo-xanthine, respectively) and a reducing sugar phosphate. The same hydrolytic products are obtained by use of a specific pancreatic enzyme. On the other hand, mild alkaline hydrolysis of a nucleotide, or treatment with the appropriate enzyme, liberates free phosphoric acid and a non-reducing compound of base and sugar, known as a nucleoside. (Hydrolysis of ribosenucleic acid with fairly dilute ammonia under pressure, during 3.5 hours at a bath temperature of 175 to 180 , gives an equimolecular mixture of four nucleosides). 

DNA exhibits rather different properties from RNA in its susceptibility to acid and alkaline hydrolysis. The extreme acid lability of the iV-gly-cosy 1-purine linkages in DNA allows the quantitative liberation of free purines by very mild acid treatment, leaving a high molecular weight residue (called apurinic acid or thymic acid) complete in pyrimidine, deoxy-ribose, and phosphate composition 169), DNA, however, is quite stable to alkaline action since the absence of a hydroxyl group on carbon 2 of deoxy-ribose precludes the possibility of labilization through a cyclic 2, 3 -phos-phate intermediate. 

Histidine is an essential amino acid in nutrition, and provides the iminazole ring necessary for synthesis of purines and nucleo-proteins. It forms neither glucose nor acetoacetic acid in the diabetic animal, though it is attacked by histidase, the enzyme present in vertebrate liver, which converts it into a compound that yields glutamate on alkaline hydrolysis. 

As far as the reactivity of the above-described Mannich bases is concerned, studies of prcxlucts 469 indicate a much better resistance to alkaline than to acid hydrolysis the nature of the nucleoside also plays a role, as the cytidine derivatives arc much more stable than the purine derivatives. Similar investigations have been madc into the deaminomethylation of Mannich bases of type 466. 

The reaction fails when the purine contains electron-donating substituents. Thus, 2-(methyl-sulfanyl)adenine does not hydrolyze to any significant extent in 6 M hydrochloric acid. On the other hand, 2-(methylsulfanyl)hypoxanthine is readily converted into xanthine (4) by acid hydrolysis. S -Carboxymethylpurines which arc conveniently prepared from sulfanylpurines in aqueous alkaline solution with chloroacetic acid are used as intermediates in the conversion of sulfanylpurines into hydroxypurines, c.g. the conversions 2 - 3 4, and 5- 6- 1. ... 

More vigorous oxidation of sulfanylpurines or intermediately formed sulfinic acids with potassium permanganate in alkaline solution affords sulfonic acids. The purinesulfmic acids are readily hydrolyzed to hydroxypurines. The purine-6-sulfinic acid gives hypoxanthine when treated with 0.1 M hydrochloric acid, whereas the corresponding sulfonic acid requires brief heating to effect hydrolysis. 

Desoxyribosenucleic acid is readily hydrolyzed by mineral acids but is more resistant to alkaline fission than is ribosenucleic acid. Owing to the nature of the constituent sugar, the purine nucleotides are even more unstable than those of ribosenucleic acid. Hence, by acid hydrolysis of thymus nucleic acid, only the two pyrimidine nucleotides" " can be isolated. 

A daring expedient to obtain the right starting material was the alkaline cleavage of a similarly substituted purine (0.5 N NaOH, room temp, 1 h) to give 6-chloro-5-formamido-4[(2,3-0-isopropylidene-D-ribofuranosyl)-amino]pyrimidine, from which the formyl group was removed by acid hydrolysis, followed by formation of the triazole ring with aqueous nitrous acid (optical purity was retained). ... 

The chemical reactivity of the DNA and RNA polyphosphordiester bonds is very different. First of all, DNA is not hydrolyzed in alkaline media. It is as stable as monomeric dialkylphosphates at pH 13 (see Sec. 8.5.3). When treated, however, with acid, DNA is not only hydrolyzed at the phosphodiester positions, but the A-glycosides are also destroyed. Purines react here faster than pyrimidines. Chemical hydrolysis of DNA is thus useless as an analytical tool because either the monomers are destroyed or no reaction at all occurs. RNA, on the other hand, is readily hydrolyzed by alkali. Simultaneous cleavage of intemu-cleotide bonds over the entire length of the polymer chain occurs (Scheme 8.3.1) (Fung and Yeung, 1995). 

A number of other enzymes which catalyze the hydrolysis of phosphoesters are of biological importance. These include cyclic purine phosphodiesterase (little is known about its active site chemistry at present, but more shall be said about its biological role shortly) and the phosphatases. Acid and alkaline phosphatase catalyze the hydrolysis of phosphomonoesters to the corresponding alcohol and inorganic phosphate. Their pH optimums are 5.0 and 8.0, respectively hence their names. Both form covalent enzyme-substrate intermediates ... 

---