Cytosine, isolation

Fig. 15 Observed photoprocesses taking place upon UV and IR irradiations of 5-methyl (X = CH3) and 5-fluoro (X = F) cytosines isolated in solid argon. AO, AH and 10 designate the amino-oxo, amino-hydroxo and imino-oxo tautomers of the compounds. Reprinted with permission from L. Lapinski, I. Reva, H. Rostkowska, R. Fausto and M. J. Nowak, J. Phys. Chem. B, 2014, 118, 2831. Copyright (2014). American Chemical Society.

Documented effects An infusion of the herb is used as an expectorant to treat chronic bronchitis and residual pneumonia. The preparation Cytiton, which contains the alkaloid cytosine isolated from the seeds, in is used to stimulate respiratory function and improve blood circulation. The preparation is used to treat asphyxia in newborns and when a person stops breathing during surgical procedures or from trauma (Khalmatov et al. 1984). The alkaloid pachycarpine, isolated from this plant, is used to treat peripheral vessel spasms and to induce labor when necessary (Akopov 1990). 

Since Kossel and Stendel had also shown that cytosine (isolated with sulfuric acid), on treatment with nitrous acid, gave a substance having the properties of uracil, Wheeler and Johnson (also) concluded that cytosine was most likely an aminooxypyrimidine and considered the possibilities. They decided that there were seven possibilities (ignoring tautomers) for cytosine (Figure 14.3) based on the formation of uracil (Equation 14.1). 

Fosfadecin (186) and fosfocytocin (187) are adenine and cytosine nucleotide antibiotics isolated from the culture filtrates of Pseudomonas viridiflava PK-5 and P. fluorescens PK-52, respectively (283). Hydrolysis produces fosfoxacin which is also isolated from the culture filtrates. Compounds (186) and (187) inhibit gram-positive and gram-negative bacteria. 

Cytosine was isolated from hydrolysis of calf thymus in 1894 and by 1903 its structure was known and it had been synthesized from 2-ethylthiopyrimidin-4(3H)-one. The acid hydrolysis of ribonucleic acid gives nucleotides, among which are two cytidylic acids, 2 -and 3 -phosphates of cytidine further hydrolysis gives cytidine itself, i.e. the 1-/3-D-ribofuranoside of cytosine, and thence cytosine. The deoxyribonucleic acids likewise yield deoxyribonucleotides, including cytosine deoxyribose-5 -phosphate, from which the phosphate may be removed to give cytosine deoxyriboside and thence cytosine. 

Hydroxymethylcytosine (967) was isolated only in 1952 from the T-even bacteriophages of Escherichia coli, in which it occurs instead of cytosine in the 2-deoxyribonucleic acid (65MI21304). Of several syntheses described, the most convenient is probably that beginning with ethyl 4-amino-2-methylthiopyrimidine-5-carboxylate which is reduced by LAH to 4-amino-2-methylthiopyrimidin-5-ylmethanol followed by hydrolysis to 5-hydroxymethyl-cytosine (967) (B-68MI21302, B-68MI21306). 

Three more antibiotics, all discovered about 1953, are also derivatives of cytosine. Amicetin, bamicetin and plicacetin may all be isolated from Streptomyces plicatus and all have some activity against some acid-fast and Gram-positive bacteria as well as some other microbial systems (69MI21301). Structural work in this area is fascinating (62JOC2991). 

As is well-known, nucleic acids consist of a polymeric chain of monotonously reiterating molecules of phosphoric acid and a sugar. In ribonucleic acid, the sugar component is represented by n-ribose, in deoxyribonucleic acid by D-2-deoxyribose. To this chain pyrimidine and purine derivatives are bound at the sugar moieties, these derivatives being conventionally, even if inaccurately, termed as pyrimidine and purine bases. The bases in question are uracil (in ribonucleic acids) or thymine (in deoxyribonucleic acids), cytosine, adenine, guanine, in some cases 5-methylcytosine and 5-hydroxymethylcyto-sine. In addition to these, a number of the so-called odd bases occurring in small amounts in some ribonucleic acid fractions have been isolated. 

Samples of DNA isolated from different tissues of the same species have the same proportions of heterocyclic bases, but samples from different species often have greatly different proportions of bases. Human DNA, for example, contains about 30% each of adenine and thymine and about 20% each of guanine and cytosine. The bacterium Clostridium perfringens, however, contains about 37% each of adenine and thymine and only 13% each of guanine and cytosine. Note that in both examples the bases occur in pairs. Adenine and thymine are present in equal amounts, as are cytosine and guanine. Why ... 

Thus, thymine-tyrosine, thymine-aliphatic amino acid and cytosine-tyrosine links have been identified in isolated calf thymus chromatin subjected to 7-irradiation, or treated with metal ions and H2O2 (Dizdaroglu, 1991 Nackerdien et al., 1991). 

The data in Table 2.1 suggest that the O-benzylated adduct cannot be isolated since it is less stable than reactants. The N3-benzylated adduct should be generated faster, but it should also decompose under mild conditions into free reactants, because the activation free energy in aqueous solution for the decomposition into free QM and methylcytosine is only 21.4 kcal/mol.14 In other words, these data suggested that the QM-N3-cytosine conjugate could act as QM-carrier, few years before the experimental data related to the stability of QM-conjugates became available.4... 

Other degradation products of the cytosine moiety were isolated and characterized. These include 5-hydroxy-2 -deoxycytidine (5-OHdCyd) (22) and 5-hydroxy-2 -deoxyuridine (5-OHdUrd) (23) that are produced from dehydration reactions of 5,6-dihydroxy-5,6-dihydro-2 -deoxycytidine (20) and 5,6-dihydroxy-5,6-dihydro-2 -deoxyuridine (21), respectively. MQ-photosen-sitized oxidation of dCyd also results in the formation of six minor nucleoside photoproducts, which include the two trans diastereomers of AT-(2-de-oxy-/j-D-eryf/iro-pentofuranosyl)-l-carbamoyl-4 5-dihydroxy-imidazolidin-2-one, h/1-(2-deoxy-J8-D-crythro-pentofuranosyl)-N4-ureidocarboxylic acid and the a and [5 anomers of N-(2-deoxy-D-eryfhro-pentosyl)-biuret [32, 53]. In contrast, formation of the latter compounds predominates in OH radical-mediated oxidation of the pyrimidine ring of dCyd, which involves preferential addition of OH radicals at C-5 followed by intramolecular cyclization of 6-hydroperoxy-5-hydroxy-5,6-dihydro-2 -deoxycytidine and subsequent generation of the 4,6-endoperoxides [53]. 

The components of nucleic acids have been the subject of continuous DFT stud-ies61 S5,67 69. Jasien and Fitzgerald calculated dipole moments and polarizabilities for a series of molecules of biological interest including nucleic acid bases (adenine, thymine, cytosine, and guanine) and their pairs (adenine-thymine and cytosine-guanine)61. A good correlation between DFT(HL), experimental, and MP2 results was obtained for dipole moments and polarizabilities. More detailed analyses of DFT(SVWN) and DFT(B88/P86) results, which included vibrational frequencies, were reported for isolated bases and their... 

Solomon JJ, Segal A. 1985. Direct alkylation of calf thymus DNA by acrylonitrile. Isolation of cyanoethyl adducts of guanine and thymine and carboxyethyl adducts of adenine and cytosine. Environ Health Perspect 62 227- 230. 

The equilibrium between the amino and imino forms of cytosine has also been studied by Cieplak et al.9 Their results agree with those of Colominas et al. In this study, the related 2-oxopyridine and 2-oxopyrimidine molecules were also treated. In both these molecules the amine group of cytosine is not present, and in oxopyridine only one ring nitrogen is present. This enabled the keto-imino tautomerism to be studied in isolation. In both cases the imino form dominates in the gas phase, but the keto form is stabilised by solvation, and dominates in solution, in agreement with experiment. 

Also for cytosine, red shifts are detected in the NH2 stretching and bending modes. Ring stretchings and deformations, involving the CO vibration, suffer little changes with respect to the isolated base (see Fig. 16). In the overall, the computed frequency shifts are in agreement with the... 

Cytosine (Cyt) and 2 -deoxycytine (dCyd) hydroxyhydroperoxides generated by either OH radical or one-electron oxidation have been shown to be highly unstable, so far preventing their isolation and characterization by spectroscopic measurements such as NMR and MS. However, information is available on the chemical transformation of the 5- and 6-hydroperoxides as inferred from the isolation and identification of the main radical oxidation products of Cyt and dCyd. 

The most important pyrimidine derivatives are those upon which biological organisms depend. Cytosine 1018 and uracil 1019 are found in ribonucleic acid (RNA) in the form of their ribonucleotides, cytidine 1020 and uridine 1021, while in deoxyribonucleic acid (DNA), cytosine and thymine 1022 are found in the form of their 2 -deoxyribonucleotides, 2 -deoxycytidine 1023 and thymidine 1024. 5-Methylcytosine 1025 is also found to a small extent (c. 5%) in human DNA in the form of its 2 -deoxyriboside 1026, and 5-(hydroxymethyl)cytosine-2 -deoxyriboside 1027 has also been detected in smaller amounts <2005CBI1>. Many variants of cytosine and uracil can be found in RNA including orotic acid 1028 in the form of its ribonucleotide orotidine 1029. Other pyrimidine derivatives to have been isolated from various biological sources include 2 -deoxyuridine 1030, alloxan 1031, and toxopyrimidine (pyramine) 1032 (Figure 2). 

The behavior of cytosine and cytidylic acid during photolysis are quite different existing reports about the behavior of cytosine are contradictory. It should be noted that neither the cytosine hydrate nor the dimer has been isolated from photolyzed solutions nor identified by comparison with known substances. Early work7 reports that photolysis of cytosine in solution resulted in a decrease in absorption at 270 nm, and an increase at 240 nm. This transformation was partly reversible at room temperature,7 but the reversal was prevented by the presence of 0.1M NaCl. The quantum yield for disappearance of cytosine was about 1 to 2 x 10-3. 

---