Pseudouridine synthesis

The regions of the tRNA molecule teferred to in Chapter 35 (and illustrated in Figure 35-11) now become important. The thymidine-pseudouridine-cyti-dine (T PC) arm is involved in binding of the amino-acyl-tRNA to the ribosomal surface at the site of protein synthesis. The D arm is one of the sites important for the proper recognition of a given tRNA species by its proper aminoacyl-tRNA synthetase. The acceptor arm, located at the 3 -hydroxyl adenosyl terminal, is the site of attachment of the specific amino acid. 

This Section is concerned with the synthesis of C-nucleosides having the Type A arrangement of atoms attached to the glycosylic carbon atom, and covers the synthesis of pseudouridine (1), show-... 

In the course of their studies of pseudouridine,164 Asbun and S. B. Binkley183 reported the synthesis of 5-/3-D-arabinofuranosyl- and 5-/3-D-xylofuranosyl-uracil (258 and 259) by the acid-catalyzed ring-closure of the corresponding alditol derivatives. The configuration at the anomeric carbon atom was determined on the basis of optical rotatory dispersion studies. 

David and Lubineau191 reported the synthesis of pseudocytidine [5-/3-D-ribofuranosylcytosine (270)] and its a anomer by a procedure analogous to that used in preparing pseudouridine.155-157 Thus, 2,4 3,5-di-O-benzylidene-a/de/iydo-D-ribose (223) was condensed with the dilithio derivative of 2-0,4-N-(trimethylsilyl)cytosine, and the resulting, epimeric, acyclic derivatives were subjected to acid-catalyzed cyclization. The anomeric configuration of the free C-nucleosides was ascertained by spectroscopic methods and by their transformation into a- and /3-pseudouridine in the presence of nitrous acid. The anomeric 5-(/3-D-ribofuranosyl)isocytosines have also been prepared by Fox and coworkers.1913... 

Following synthesis, nucleotides in the tRNA molecule may undergo modification to create unusual nucleotides such as 1-methylguanosine (m G), pseudouridine (4/), dihydrouridine (D), inosine (I) and 4-thiouridine (S4U). 

Transfer RNA (Mr s= 25,000) functions as an adapter in polypeptide chain synthesis. It comprises 10-20 percent of the total RNA in a cell, and there is at least one type of tRNA for each type of amino acid. Transfer RNAs are unique in that they contain a relatively high proportion of nucleosides of unusual structure (e.g., pseudouridine, inosine, and 2 -0-methylnucleosides) and many types of modified bases (e.g., methylated or acetylated adenine, cytosine, guanine, and uracil). As examples, the structures of pseudouridine and inosine are shown below. Inosine has an important role in codon-anticodon pairing (Chap. 17). 

Hanessian S, Machaalani R. A highly stereocontrolled and efficient synthesis of a- and fl-pseudouridines. Tetrahedron Lett. 2003 44 8321-8323. 

A selective method which involves the selective pivaloyloxymethyl protection of the N1 of pseudouridine followed by methylation at N3 was developed to prepare the 5-benzhydryloxybis(trimethylsilyloxy)silyl, bis(2-acetoxy-ethoxy)me-thyl- protected phosphoramidite derivative (139) of the nucleoside 3-methylpseu-douridine. The methylated pseudouridine phosphoramidite was successfully used in oligonucleotide synthesis for the NMR study of helix 69 of E. coli 23S rRNA. 2-Thiouridines incorporating 2 -modified nucleoside phosphoramidites... 

In most studies no significant increase in serum uric acid values have been found (Al, T8, Wl), but in some an increase has been reported (B8, S24). The work of Eisen and Seegmiller (E3) is the only report concerned with the metabolic formation of uric acid using radioactive glycine. They did show an increase in the formation of uric acid in extensive psoriasis and a reduction to normal levels with treatment. In addition, the excretion of pseudouridine and uracil was increased in extensive psoriasis (E2) (Table 13). There was a direct correlation in the above studies between the serum uric acid level versus the extent of skin involvement, the excretion of pseudouridine versus the extent of skin involvement, and also the excretion of pseudouridine versus the uric acid excretion (E = 0.81). These findings imply increased nucleic acid synthesis and increased nucleic acid breakdown in the skin, access of the purine breakdown products to the blood stream and from there to the liver ( ) for transformation into uric acid and finally to the kidney for excretion. 

Posttranscription modification of tRNA The synthesis of tRNA involves modification of some uridine nucleotides to unusual nucleotides, such as pseudouridine, ribothymidine, and dihydrouridine. 

Figure 4.1 depicts the cloverleaf structure of a tRNA the bars represent base pairs in the stems. There are four arms and three loops - the acceptor, D, T pseudouridine C, and anticodon arms, and D, T pseudouridine C, and anticodon loops. Sometimes tRNA molecules have an extra or variable loop (shown in yellow in Fig. 4.1). The synthesis of transfer RNA proceeds in two steps. The body of the tRNA is transcribed from a tRNA gene. The acceptor stem is the same for all tRNA molecules and added after the synthesis of the main body. It is replaced often during lifetime of a tRNA molecule. The 3-D structure of a yeast tRNA molecule, which can code for the amino acid serine, shows how the molecule is folded with the...

The term C-nucleoside was only coined after isolation and characterization of the first member of this class pseudouridine, in 1975 [97ACH(ip)]. Before that, alditolyl derivatives of some heterocycles (acyclo C-nucleo-sides) were known both as natural products (alditolyl pteridines or biopterins) as well as products of syntheses (e.g., alditolyl derivatives of imidazoles, benzimidazoles, thiazoles, benzothiazoles, 1,2,3-triazoles, quinoxalines, and flavazoles) and were classified as carbohydrate derivatives of heterocyclic compounds. After isolation of pseudouridine, other naturally occurring members were successively isolated, characterized, and synthesized. It is worth mentioning that synthesis preceded isolation in two cases 9-dea-zaadenosine and pyrrolosine. Comparison with the synthetic compounds facilitated structure elucidation in one case (9-deazaadenosine) and structure reassignment in the other (pyrrolosine). 

---