Nucleotides methylated derivatives

Yeast alanine tRNA (tRNA 3), the first nucleic acid to be completely sequenced (Fig. 27-11), contains 76 nucleotide residues, 10 of which have modified bases. Comparisons of tRNAs from various species have revealed many common denominators of structure (Fig. 27-12). Eight or more of the nucleotide residues have modified bases and sugars, many of which are methylated derivatives of the principal bases. Most tRNAs have a guanylate (pG) residue at the 5 end, and all have the trinucleotide sequence CCA(3 ) at the 3 end. When... 

A mutant of Escherichia coli B, resistant to 2,6-diaminopurine, was found to convert this base to 6-amino-2-methylamino-purine (XXVII) at a rate 60 to 90 % of that of normal cells. The methylated base was isolated from the culture medium, but the organism lacked the ability to incorporate 2,6-diaminopurine or its A-methyl derivative into the nucleotide fraction of the cell. This observation supports previous data which had indicated that resistance to this substance in Lactobacillus casei is due to the loss of an enzyme system responsible for the incorporation of the base into the nucleotide. ... 

Early reviews on the mass spectra of nucleotides, more particularly of mononucleotides, " covered trimethylsilyl and methyl derivatives of nucleotides. The silylation of nucleotides, for instance, takes place on the base, on the sugar hydroxyls, and on the free phosphate hydroxyls under mild (room temperature) and basic (pyridine) silylation conditions (BSTFA/TMCS). The fragmentation of derivatives obtained from both procedures has been well studied. Several typical fragments ([M — CHj]", [base -I- 2H], silylated and desilylated sugar, S-TMSOH, etc.), as well as a weak M+ ion have been recorded. The FD spectrum of an underivatized... 

A study on the quantitative analysis of blood nucleotides by LC-MS or GC- MS of their methylated derivatives has been reported again derivatiza-tion, preconcentration, and summary separation on an XAD column preceded the final identification by GC-MS. ... 

Methylation of guanine nucleosides or nucleotides with diazomethane or methyl sulfate yields 7-methylated derivatives (241, R = ribosyl). These zwitterionic derivatives are unstable in acid, neutral, and alkaline media. In alkali, (241) undergoes cleavage at the 8-9 bond, to give... 

Eight or more of the nucleotide residues have modified bases and sugars, many of which are methylated derivatives of the principal bases. Most tRNAs have a guanylate (pG) residue at the 5 end, and all have the trinucleotide sequence CCA(3 ) at the 3 end. When... 

The NMR results show that, in the case of 3 and 5 nucleotides, the binding of metal, or at least copper, does occur at Nj for adenine and guanine and at Ni for cytosine very little binding of copper occurs in thymine, the methyl derivative of uracil. NMR studies have also shown us that in the polymeric nucleic acids binding occurs generally in the same position as in these monomers. For example, in polyadenylic acid, the binding is also at Nj, and in polycytidylic acid it is at Ni. 

Nucleosides. Nucleotides, and Derivatives.- 2, 3 ,5 -Trl-0 -acetyl-adenosine and -guanosine, 4- -ethyl-thymidlne, N -methyl-2 -deoxyadenoslne, 5-raethoxymethyl-2 -deoxy-urldlne and its 0-D-threo-isomer, 5-fluoroarablnosylcytoslne, the 2 -deoxynucleo-side (17), cls-thymldine 3 ,5 -cyclic methyl phosphonate and the corresponding 3, 5 -cycllc N,N-dlmethylphosphoramldate,a cobalt(II) complex with 2 -deoxyinosine 5 -monophosphate,... 

Adenosine triphosphate is the specific nucleotide of this reaction. Active methionine is the methyl donor to various acceptors, e.g., nicotinamide, glycocyamine, adrenaline. Transmethylations are catalyzed by specific methylpherases The product of transmethylation is usually the iV-methyl derivative of the acceptor while active methionine is converted to (S-adenosylhomocysteine. Active methionine may undergo hydrolytic cleavage in yeast to yield 5 -methylthioadenosine and homoserine 96). The reaction may not be enzymic. This adenosine derivative had been isolated long before active methionine was known 96). Betaine and certain sul-fonium compounds structurally related to active methionine, e.g., dimethyl-/8-propiothetin [(CHs)2= S—CH —CHj—COOH] 97), can also act as methyl donors for homocysteine in liver suspensions 98). 

Uracil reacts with hydrazine to give pyrazol-3(2if)-one (944) and urea N-methyl- and dimethyl-hydrazine behave similarly to give the 2-methyl- and 1,2-dimethyl derivatives. The reactions of hydrazines with uridine and related nucleosides and nucleotides is well studied (67JCS(C)1528). The tautomerism and predominant form of uracil are discussed in Section 2.13.1.8.4. 

Reaction 12 of Figure 34—7 is the only reaction of pyrimidine nucleotide biosynthesis that requires a tetrahydrofo-late derivative. The methylene group of A A Tmethyl-ene-tetrahydrofolate is reduced to the methyl group that is transferred, and tetrahydrofolate is oxidized to dihydro-... 

Tipson devoted most of his years in Levene s laboratory accomplishing seminal work on the components of nucleic acids. To determine the ring forms of the ribose component of the ribonucleosides he applied Haworth s methylation technique and established the furanoid structure for the sugar in adenosine, guanosine, uridine, and thymidine. He showed that formation of a monotrityl ether is not a reliable proof for the presence of a primary alcohol group in a nucleoside, whereas a tosyl ester that is readily displaced by iodide affords clear evidence that the ester is at the 5-position of the pentofuranose. Acetonation of ribonucleosides was shown to give the 2, 3 -C -isopropyl-idene derivatives, which were to become extensively used in nucleoside and nucleotide chemistry, and were utilized by Tipson in the first chemical preparation of a ribonucleotide, inosinic acid. 

The 5 cap is formed by condensation of a molecule of GTP with the triphosphate at the 5 end of the transcript. The guanine is subsequently methylated at N-7, and additional methyl groups are often added at the 2 hydroxyls of the first and second nucleotides adjacent to the cap (Fig. 26-12). The methyl groups are derived from S-adenosylmethionine. All these reactions occur... 

Starting from the comparative study of the ionization constants of uracil itself as well as of its several methylated or ethylated derivatives (representing models of tautomeric forms), it may be seen (Table XVII) that uracil and uridine exist in aqueous solution in the diketo form 32. The pX values are not known for the model tautomers 27, 29, and 30, but these forms have been ruled out on the basis of UV studies. Recently the ionization constants of uracil, thymine, their derivatives and nucleotides were determined over the range 10-50°, and thermodynamic enthalpy, entropy, and free energy changes for protonation and depro-tonation of these compounds have been evaluated.93-95,332... 

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