Nucleosides and Nucleotides. 232. Synthesis of 2′-C-Methyl-4′-thiocytidine: Unexpected Anomerization of the 2′-Keto-4′-thionucleoside Precursor

The synthesis of 2′-C-methyl-4′-thiocytidine (16) is described. Since the 2′-keto-4′-thiocytidine derivative 2β unexpectedly isomerized to 2α and the methylation of 2β proceeded predominantly from the less hindered α-face to give 7, the desired product 16 was synthesized via the Pummerer reaction of the sulfoxide 14 and N ⁴ -benzoylcytosine.     

Inhibition of a novel subspecies of DNA polymerase α by 2′-deoxy-2′-azidoadenosine 5′-triphosphate

DNA polymerase α₁, a subspecies of DNA polymerase α of Ehrlich ascites tumor cells, was associated with a novel RNA polymerase activity and utilized poly(dT) and single-stranded circular fd DNA as a template without added primer in the presence of ribonucleoside triphosphates and a specific stimulating factor. DNA synthesis in the above system was inhibited by the ATP analogue, 2′-deoxy-2′-azidoadenosine 5′-triphosphate more than the DNA synthesis with poly(dT)·oligo(rA) by DNA polymerase α₁ and RNA synthesis by mouse RNA polymerases I and II. Kinetic analysis showed that the analogue inhibited DNA polymerase α₁ activity on poly(dT) competitively with respect to ATP, suggesting that the analogue inhibited RNA synthesis by the associated RNA polymerase activity.     

The effect of hormones on synthesis of the region linking chondroitin sulfate to protein

1. 1. Particulate fractions of costal cartilage from young rats are capable of catalyzing the formation of the first two monosaccharide units of the chondroitin sulfate-protein linkage region.

2. 2. Hormonal imbalance has been shown to influence the activity of the glycosyltransferases responsible for the sequential transfer of xylose and galactose from UDPxylose and UDPgalactose, respectively, in the formation of the linkage region.

3. 3. The activity of xylosyltransferase was found to be decreased in costal cartilage of diabetic, thyroidectomized and hypophysectomized rats, but not in rats injected with either testosterone or hydrocortisone. In the latter two treatment groups, galactosyltransferase activity was decreased only in the group receiving hydrocorsitone.

4. 4. The combined results of this and previous studies suggest that decreased levels of chondroitin sulfate in diabetic, thyroidectomized and hypophysectomized animals are due to interference in the synthesis of the linkage region of the proteoglycan at the xylosyltransferase level whereas hydrocortisone acts primarily at the level of the galactosyltransferase.

Metabolism to methionine and growth stimulation by 5'-methylthioadenosine and 5'-methylthioinosine in mammalian cells

Viable human and murine lymphoblasts, and normal human tissue extracts, converted the thioether nucleosides 5'-methylthioadenosine (MeSAdo) and 5'-methylthioinosine (MeSIno) to methionine. Both MeSAdo and MeSIno, but not homocysteine, supported the short-term growth of human or murine lymphoblasts in methionine deficient medium. However, MeSAdo at concentrations greater than 25 microM inhibited cell growth. MeSIno was non-toxic at concentrations up to 200 microM, and supported the long-term growth of lymphoblasts in methionine-free medium.     

Six 2′-hydroxyflavonols from Gutierrezia microcephala

Six 2′-hydroxyflavonols were isolated from Gutierrezia microcephala, including four new compounds, 5,7,2′-trihydroxy-3,6,4′,5′-tetramethoxyflavone, 5,7,2′-trihydroxy-3,6,8,4′,5′-pentamethoxyflavone, 5,2′-dihydroxy-3,6,7,8,4′,5′-hexamethoxyflavone and 5,7,2′,4′-tetrahydroxy-3,8,5′-trimethxoyflavone and two known compounds, 5,7,2′,5′-tetrahydroxy-3,6,8,4′-tetramethoxyflavone and 5,7,2′,4′-tetrahydroxy-3,6,8,5′-tetramethoxyflavone.     

Two isomeric flavanones from vitex negundo

Two new flavanoids, characterized as 5,3′-dihydroxy-7,8,4′-trimethoxyflavanone and 5,3′-dihydroxy-6,7,4′-trimethoxyflavanone, have been isolated from the leaves of Vitex negundo.     

Two new C-methylated flavonoids from Myrica gale

From the leaves of Myrica gale 2′,4′-dihydroxy-6′-methoxy-3′,5′-dimethylchalcone has been isolated. The fruits yielded 2′-hydroxy-4′,6′-dimethoxy-3′-methyldihydrochalcone. The constitutions were deduced from spectroscopic data and confirmed by synthesis.     

Study on Disulfur-Backboned Nucleic Acids: Part 3. Efficient Synthesis of 3′,5′-Dithio-2′-Deoxyuridine and Deoxycytidine

A general method is described for synthesizing 3′,5′-dithio-2′-deoxypyrimidine nucleosides 6 and 13 from normal 2′-deoxynucleosides. 2,3′-Anhydronucleosides 2 and 9 are applied as intermediates in the process to reverse the conformation of 3′-position on sugar rings. The intramolecular rings of 2,3′-anhydrothymidine and uridine are opened by thioacetic acid directly to produce 3′-S-acetyl-3′-thio-2′-deoxynucleosides 3 or 5. To cytidine, OH^? ion exchange resin was used to open the ring and 2′-deoxycytidine 10 was abtained in which 3′-OH group is in threo-conformation. The 3′-OH is activated by MsCl, and then substituted by potassium thioacetate to form the S,S′-diacetyl-3′,5′-dithio-2′-deoxycytidine 12. The acetyl groups in 3′,5′ position are removed rapidly by EtSNa in EtSH solution to afford the target molecules 6 and 13. The differences of synthetic routes between uridine and cytidine are also discusssed.     

Polyphosphate anions increase the activity of bovine spleen cathepsin D

Bovine spleen cathepsin D is activated by polyphosphate anions when bovine serum albumin is used as substrate at pH 4.6. In the presence of ATP at 10 mM, the catheptic activity at this pH is enhanced as high as 17 times over the control. Similar activating effects were observed, though to varying degrees, with sodium tripolyphosphate, nucleotides, nucleotide analogues, CoA, polyU and yeast RNA. The possible mechanism and biological significance of the activation were discussed with regard to the intralysosomal polyanionic substance.     

SYNTHESIS OF 2′-C-METHYL-4′-THIO RIBONUCLEOSIDES

Starting from 2-C-methyl-ribonolactone, 1,2,3,5-tetra-O-acetyl-2-C-methyl-4-thioribofuranose was synthesized and condensed with heterocyclic bases to afford 2′-C-methyl-4′-thioribonucleosides.     

Flavones from Eupatorium leucolepis

Chloroform extraction of Eupatorium leucolepis gave the new flavones 3′-hydroxy-5,6,7,8,4′,5′-hexamethoxyflavone, 4′-hydroxy-5,6,7,8,3′,5     

Synthesis and Properties of DNA Containing Cyclonucleosides

Here, we present efficient syntheses of the R and S diastereomers of 8,5′-cyclo-2′-deoxyadenosine and 6,5′-cyclo-2′-deoxyuridine. We incorporated these interesting nucleosides into DNA to study how the cyclo linkage affects the stability of duplex formation.     

Synthesis of 2′-O-Photocaged Ribonucleoside Phosphoramidites

The chemical synthesis and incorporation of the phosphoramidite derivatives of 2?′-O-photocaged ribonucleosides (A, C, G and U) with o-nitrobenzyl, α-methyl-o-nitrobenzyl or 4,5-dimethoxy-2-nitrobenzyl group into oligoribonucleotides are described. The efficiency of UV irradiated uncaging of these 2′-O-photocaged oligoribonucleotides was found in the order of α-methyl-o-nitrobenzyl < 4,5-dimethoxy-2-nitrobenzyl < 2′-O-o-nitrobenzyl.     

Calorimetric determination of thermodynamic parameters of 2′-dUMP binding to Leishmania major dUTPase

We have investigated the binding of 2′-deoxyuridine 5′-monophosphate (2′-dUMP) to Leishmania major deoxyuridine 5′-triphosphate nucleotide hydrolase (dUTPase) by isothermal titration microcalorimetry under different experimental conditions. Binding to dimeric L. major dUTPase is a non-cooperative process, with a stoichiometry of 1 molecule of 2′-dUMP per subunit. The utilization of buffers with different ionization enthalpies has allowed us to conclude that the formation of the 2′-dUMP–dUTPase complex, at pH 7.5 and 30 °C, is accompanied by the uptake of 0.33±0.05 protons per dUTPase subunit from the buffer media. Moreover, 2′-dUMP shows a moderate affinity for the enzyme, and binding is enthalpically driven across the temperature range studied. Besides, whereas ΔG° remains practically invariant as a function of temperature, both ΔH and ΔS° decrease with increasing temperature. The T_S and T_H were 23.4 and 13.6 °C, respectively. The temperature dependence of the enthalpy change yields a heat capacity change of ΔC_p°=?618.1±126.4 cal·mol^?1·K^?1, a value low enough to discard major conformational changes, in agreement with the fitting model. An interpretation of this value in terms of solvent-accessible surface areas is provided.