Nucleosides, Methylated

Sequence analysis of the 5 -ends of viral and nuclear mRNA molecules reveals that these are frequently capped , with an unusual structure in which 7-methylguanosine is joined by a (5 - 5 ) triphosphate link to a 2 -0-methyl nucleoside moiety which is the first residue in the (3 ->5 )-linked polynucleotide chain.166-168 The presence of this cap structure is required for ribosomal binding and translation to take place,167- 168 and 7-methylguanosine-5 -phosphate inhibits translation by preventing formation of the ribosome-mRNA complex.169... 

Search for the structures of methyl nucleosides in tRNA and suggest spectral characteristics that distinguish these minor bases from their corresponding parent (major) bases. 

To make the required methylated RNA sequences available for our folding studies we synthesized the methylated nucleosides as 2 -0-(triisopropylsilyl)oxy-methyl (TOM)-phosphoramidites and applied the building blocks to RNA synthesis and purification procedures [36, 46]. 

Nucleosides are metabolites of ribonucleic acid (RNA). As a result of excessive turnover of RNA, which occurs in such pathological conditions as cancer, inflammation, and AIDS, nucleosides are excreted into urine in increased amounts. Normal nucleosides (adenosine, guanosine, cytidine, uridine) either undergo further degradation into uric acid, p-alanine, or p-aminoisobutyrate or are reutilized. On the other hand, modified nucleosides, especially methylated nucleosides, are excreted unchanged in urine. Therefore, it seems that elevated levels of modified nucleosides could be an indicator of the presence of cancer and used as a diagnostic tool in cancer prognosis [23]. 

In addition to the variety of modifications found on the heterocyclic base discussed above, many nucleosides are also methylated at the 2 -hydroxyl of the ribose moiety and make up approximately 8 % of existing tRNA modifications. One interesting example of the 2 - 0-ribose modification was studied in S. cerevisiae, where the yeast tRNA molecules corresponding to His, Pro, and Gly(G-C-C) contain a 2 -0-methylated nucleoside at position 4 in the acceptor stem. A methylated cytosine is found in tRNA ° and tRNA, and the modified Am nucleoside is found in tRNA . Modifications in a duplex region of tRNA are very rare, yet modification at this position ( 4) is conserved in eukaryotes. A yeast knock-out strain of the gene trmlS was produced, and it was determined by HPLC and primer extension analysis that tRNAs purified from this organism did not exhibit the 2 - 0-methyl modification at position 4. 

All transfer RNAs (tRNAs) contain a number of modified nucleobases and typically 2 -D-methylated nucleosides. DNA also contains a more limited number of such species. Some of these modifications, for example, N-7 methylation of guanosine, diminish the metal-binding ability of the bases. A few functional groups, such as the exocyclic S in 4-thiouridine and 2-thiocytidine and the exocyclic substituent in 5-carboxymethylaminomethyluridine, enhance the ambivalent nature of the bases. Some of these modifications change the basicity of primary metal-binding sites. 

Treatment of bromomethyl acetate with the sodium salt of a dialkyl phosphite, followed by deacetylation with methoxide affords the corresponding dialkyl hydroxymethanephosphonate. If this is tosylated with tosyl chloride, and the product treated with nucleosides [protected at the 3 -(and 2 -, if present) hydroxy groups] and sodium hydride in DMF, the monoalkyl ester of a 5 -0-phosphonyl-methyl nucleoside (60) is obtained after deblocking the sugar, and subsequent dealkylation with TMS-iodide affords (61). Like alkyl esters of 5 -mononucleotides, (60) is resistant to acid and alkaline hydrolysis, while (61) is stable in acidic and alkaline media, and is also resistant to hydrolysis by alkaline phosphomono-esterase and snake venom 5 -nucleotidase. Treatment of (61) with DCC and morpholine, and subsequently with orthophosphate or pyrophosphate, affords (62) and (63), respectively. Alkaline phosphomonoesterase from E. co/i hydrolyses the pyrophosphate links in (62) and (63) to give (61) and orthophosphate. The UTP and CTP analogues (63 B = U or C) are inhibitors of uridine kinase from... 

Base-catalysed equilibration of 2,2-0-cyclo- 3-D-arabinofuranosyl-uracil with the 2,3-(7-cyclo-j3-D-xylofuranosyl isomer strongly favours the former compound 2, 3 -anhydrouridine is an intermediate in the reaction, and with sodium methoxide in boiling methanol the xylo and arabino isomers of uridine could also be isolated, together with the 2-O-methyl-nucleoside (28). ... 

A study has been made of the FAB mass spectra of a number of nucleosides euid nucleotides.Exhaustive methylatlon with CO -labelled trlmethylanlllnivim hydroxide, followed by g.c.-m.s., has been developed as a way of distinguishing native methyl groups in methylated nucleosides from those Introduced during derivatiz-... 

Lane, B. G., Ofengand, J., and Gray, M. W. (1995). Pseudouridine and 02 -methylated nucleosides. Significance of their selective occurrence in rRNA domains that function in ribosome-catalyzed synthesis of the peptide bonds in proteins. Biochimie T7(l-2), 7-15. 

Koole LH, Moody HM, Buck HM, Groullier A, Essadiq H, Vial J-M, Chattopadhyaya J (1988) Synthesis and confonnatitHi of l-(3 -C-methyl-2 -deoxy-p-D-xyloftffanosyl)uracil and 9-(3 -C-methyl-2 -deoxy-p-D-xylofijranosyl) adenine two novel sugar-methylated nucleoside analogs. Reel Trav Chim Pays-Bas 107 343-346... 

A number of nucleosides were therefore tested for delaying effects on division 2 when added at EH in combination with methotrexate. It appears that 8 out of 10 nucleosides when tested at a 5 mM concentration have a delaying effect. Only the 2 methylated nucleosides, thymidine and 5-methyldeoxycytidine, do not. Uridine and deoxyuridine both delay division number 2 by 125 to 135 minutes. By itself methotrexate causes a delay of 5 minutes and uridine alone causes no delay. Uridine was used in all later experiments because it is cheaper than deoxyuridine. (Uracil or uridylic acid will not replace uridine in these tests). 

INCREASES IN METHYLATED NUCLEOSIDES DURING HUMAN PREGNANCY... 

Table 1. Amniotic fluid concentrations of methylated nucleosides...

Table 4. Plasma concentrations of methylated nucleosides in pregnant women and in men and a non-pregnant woman.

URINARY EXCRETION OF METHYLATED NUCLEOSIDES IN DIFFERENT STATES OF FAILURE TO THRIVE... 

The excretion of "one way" methylated nucleosides reflects the activity of RNA turnover. Therefore it can be interpreted as a new indicator of catabolism-anabolism. 

Quantitative Determination of Methylated Nucleosides and Pseudouridine in Urine by Gas-Liquid Chromatograptiy J. Lab. Clin. Med. 83(5) 816-830 (1974) CA 81 46985a... 

The synthesis of 4-C-methyl-D-ribofuranose derivatives as key intermediates for 4 C-methyl nucleosides from D-glucose has been reported. ... 

Table 4. Chemical shifts cs ) and assignments of C-methyl for methylated nucleosides of E.coU tRNA ...

Two new antibiotics containing a branched-chain sugar are reported in Chapter 19. The synthesis of some 2 - -methyl and 3 -Q-methyl nucleosides is covered in Chapter 20. The assignment of the resonances of the and C n.m.r. spectra of novobiocin is referred to in Chapter 21. 

A brief review of the synthesis and properties of -methyl nucleosides has been published, as has a further account of the s)mthesis of 2 -i2 niethyl nucleosides via 2-hydro3gmiethyl 2,3-Q-isopropylidene-5- -trityl-D-... 

Thin-layer Chromatography.— Improved or more-rapid separations by t.l.c. have been reported for mono-, di-, tri- and oligo-saccharides, naturally occurring pentitols and hexitols, iridoid D-glucopyranosides, methylated nucleosides, " and D-arabinosyl-, o-ribosyl-, and 2-deoxy-D-ery Aro-pentosyl-nucleotides. " ... 

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