A new method for the phosphorylation of nucleosides

Development of MTH1-Binding Nucleotide Analogs Based on 7,8-Dihalogenated 7-Deaza-dG Derivatives

MTH1 is an enzyme that hydrolyzes 8-oxo-dGTP, which is an oxidatively damaged nucleobase, into 8-oxo-dGMP in nucleotide pools to prevent its mis-incorporation into genomic DNA. Selective and potent MTH1-binding molecules have potential as biological tools and drug candidates. We recently developed 8-halogenated 7-deaza-dGTP as an 8-oxo-dGTP mimic and found that it was not hydrolyzed, but inhibited enzyme activity. To further increase MTH1 binding, we herein designed and synthesized 7,8-dihalogenated 7-deaza-dG derivatives. We successfully synthesized multiple derivatives, including substituted nucleosides and nucleotides, using 7-deaza-dG as a starting material. Evaluations of the inhibition of MTH1 activity revealed the strong inhibitory effects on enzyme activity of the 7,8-dihalogenated 7-deaza-dG derivatives, particularly 7,8-dibromo 7-daza-dGTP. Based on the results obtained on kinetic parameters and from computational docking simulating studies, these nucleotide analogs interacted with the active site of MTH1 and competitively inhibited the substrate 8-oxodGTP. Therefore, novel properties of repair enzymes in cells may be elucidated using new compounds.

Enzymatic synthesis of ribo- and 2'-deoxyribonucleosides from glycofuranosyl phosphates: An approach to facilitate isotopic labeling

Milligram quantities of α-D-ribofuranosyl 1-phosphate (sodium salt) (αR1P) were prepared by the phosphorolysis of inosine, catalyzed by purine nucleoside phosphorylase (PNPase). The αR1P was isolated by chromatography in >95% purity and characterized by ¹H and ¹³C NMR spectroscopy. Aqueous solutions of αR1P were stable at pH 6.4 and 4 °C for several months. The isolated αR1P was N-glycosylated with different nitrogen bases (adenine, guanine and uracil) using PNPase or uridine phosphorylase (UPase) to give the corresponding ribonucleosides in high yield based on the glycosyl phosphate. This methodology is attractive for the preparation of stable isotopically labeled ribo- and 2'-deoxyribonucleosides because of the ease of product purification and convenient use and recycling of nitrogen bases. The approach eliminates the need for separate reactions to prepare individual furanose-labeled ribonucleosides, since only one ribonucleoside (inosine) needs to be labeled, if desired, in the furanose ring, the latter achieved by a high-yield chemical N-glycosylation. 2'-Deoxyribonucleosides were prepared from 2'-deoxyinosine using the same methodology with minor modifications.

Recent Trends in Nucleotide Synthesis

Focusing on the recent literature (since 2000), this review outlines the main synthetic approaches for the preparation of 5'-mono-, 5'-di-, and 5'-triphosphorylated nucleosides, also known as nucleotides, as well as several derivatives, namely, cyclic nucleotides and dinucleotides, dinucleoside 5',5'-polyphosphates, sugar nucleotides, and nucleolipids. Endogenous nucleotides and their analogues can be obtained enzymatically, which is often restricted to natural substrates, or chemically. In chemical synthesis, protected or unprotected nucleosides can be used as the starting material, depending on the nature of the reagents selected from P(III) or P(V) species. Both solution-phase and solid-support syntheses have been developed and are reported here. Although a considerable amount of research has been conducted in this field, further work is required because chemists are still faced with the challenge of developing a universal methodology that is compatible with a large variety of nucleoside analogues.

Binding of non-natural 3'-nucleotides to ribonuclease A

2'-Fluoro-2'-deoxyuridine 3'-phosphate (dU(F)MP) and arabinouridine 3'-phosphate (araUMP) have non-natural furanose rings. dU(F)MP and araUMP were prepared by chemical synthesis and found to have three- to sevenfold higher affinity than uridine 3'-phosphate (3'-UMP) or 2'-deoxyuridine 3'-phosphate (dUMP) for ribonuclease A (RNase A). These differences probably arise (in part) from the phosphoryl groups of 3'-UMP, dU(F)MP, and araUMP (pK(a) = 5.9) being more anionic than that of dUMP (pK(a) = 6.3). The three-dimensional structures of the crystalline complexes of RNase A with dUMP, dU(F)MP and araUMP were determined at < 1.7 A resolution by X-ray diffraction analysis. In these three structures, the uracil nucleobases and phosphoryl groups bind to the enzyme in a nearly identical position. Unlike 3'-UMP and dU(F)MP, dUMP and araUMP bind with their furanose rings in the preferred pucker. In the RNase A.araUMP complex, the 2'-hydroxyl group is exposed to the solvent. All four 3'-nucleotides bind more tightly to wild-type RNase A than to its T45G variant, which lacks the residue that interacts most closely with the uracil nucleobase. These findings illuminate in atomic detail the interaction of RNase A and 3'-nucleotides, and indicate that non-natural furanose rings can serve as the basis for more potent inhibitors of catalysis by RNase A.

Antineoplastic agents 500. Narcistatin

An efficient procedure was found for synthetic conversion of the sparingly soluble anticancer isocarbostyril narciclasine (1), a component of various Narcissus species, to a cyclic phosphate designated narcistatin (3b). The reaction between narciclasine, tetrabutylammonium dihydrogen phosphate, and p-toluenesulfonic acid in pyridine afforded pyridinium narcistatin (3a) in reasonable yields. Transformation of narcistatin (3a) to, for example, the water-soluble prodrug sodium narcistatin (3d) was easily achieved by cation exchange chromatography. Narcistatin (3b) and 15 salt derivatives were evaluated against a panel of human cancer cell lines, and the range (0.1-0.01) of GI(50) values in micro g/mL was found to parallel that shown by the parent narciclasine.

HIV integrase as a target for antiviral chemotherapy

One of the three key enzymes encoded by the pol gene of HIV is a M(r) 32 000 protein called HIV integrase. This viral enzyme is involved in the integration of HIV DNA into host chromosomal DNA. There appears to be no functional equivalent of the enzyme in human cells. The biochemical mechanism of integration of HIV DNA into the host cell genome involves a carefully defined sequence of DNA tailoring (3'-processing) and coupling (joining or integration) reactions. In spite of some effort in this area targeted at the discovery of therapeutically useful inhibitors of this viral enzyme, there are no drugs for HIV/AIDS in clinical use where the mechanism of action is inhibition of HIV integrase. Thus, new knowledge on inhibitors of this enzyme is of critical importance in the anti-HIV drug discovery area. The focus of this review will be on several classes of compounds, including nucleotides, dinucleotides, oligonucleotides and miscellaneous small molecules such as heterocyclic systems, natural products, diketo acids and sulfones, that have been discovered as inhibitors of HIV integrase. Special emphasis in the review will be placed on discoveries from my laboratory on HIV integrase inhibitors that are non-natural, nuclease-resistant dinucleotides. Comments on future directions and the prospects for developing integrase inhibitors as therapeutic antiviral agents are discussed.