Activation of Nucleoside Hydrogenphosphonates by Use of Aryl Sulfonyl Chlorides

Abstract

The reaction of nucleoside 3′-hydrogenphosphonates with 2,4,6-triisopropylbenzenesulfonyl chloride (TPS-CI) has been studied using P NMR spectroscopy, and a general scheme of transformations occuring during this activation process is proposed.     

Reactions of Nucleoside Hydrogenphosphonates with Diphenyl Chlorophosphate and Sterically Hindered Aromatic Acyl Chlorides

Abstract

The final product of the reaction of H-phosphonate monoesters with diphenylchlorophosphate was found to be the corresponding dichlorophosphite. Stericalty hindered aromatic acyl chlorides react with H-phosphonate diesters affording C-phosphonate derivatives.     

Studies on Ribonucleoside Hydrogenphosphonates. Effect of a Vicinal Hydroxyl Function on the Stability of H-Phosphonate Diester Bond

Abstract

Stability of hydrogenphosphonate diester bond in the presence of a free vicinal hydroxyl function has been investigated on the example of ribonucleoside H-phosphonates. It was found that H-phosphonate diesters undergo immediate intramolecular cyclization, both with or without a base, affording 2′, 3′-cyclic H-phosphonate diesters.     

Studies on Aryl H-Phosphonates. Synthesis of Nucleoside N-Alkylphosphonamidates

Abstract

The aminolysis of aryl nucleoside H-phosphonate diesters with various amines was studied. The new simple and efficient method of synthesis of nucleoside phosphonamidates is described.     

Recent Studies in Nucleoside Phosphonate Chemistry

Abstract

New activation pathways have been found for H-phosphonate monoesters subjected to a reaction with alkyl chlorophosphates or sterically hindered aromatic acyl chlorides. Studies on synthesis of nucleoside methylphosphnate diesters using a new condensing system are also discussed.     

Studies on Nucleoside H-Phosphonothioates as Synthons in the Synthesis of Oligonucleotide Analogues

Abstract

Recently, we have reported that H-phosphonothioate diesters¹ are versatile synthetic intermediates for the preparation of phosphorothioates, phosphorodithioates, or other phosphodiester analogues. The most suitable coupling agents to produce Hphosphonothioate diesters were found to be various chlorophosphates¹ [e.g., 2-chloro-5,5-dimethyl-2-oxo-2λ⁵-1,3,2-dioxaphosphinane (NEP), diphenyl phosphorochloridate]. These reagents secure the required chemoselectivity during the condensation and are unreactive towards the P-H function in H-phosphonothioate diesters^1,2.     

Studies on Reactions of Nucleoside H-Phosphonates with Bifunctional Reagents. Part III. Further Studies on Transesterification of Nucleoside H-Phosphonate Diesters with Amino Alcohols

Abstract

Reactions of 5′-O-(4,4′-dimethoxytrityl)thymidin-3′-yl 2-cyanoethyl phosphonate with alcohols, amines and amino alcohols in pyridine are described Transesterification was found to be faster than β-elimination of 2-cyanoethyl group     

Stereoselective Nucleoside Deuteration for NMR Studies of DNA

A procedure has been elaborated for stereoselective deuterium substitution of one of the diastereotopic 5′-protons in 2′-deoxynucleotides. The synthetic scheme uses the reduction of the 5-oxosugar derivative with deuterated Alpine-Borane. The resulting deuterosugar is converted into pyrimidine nucleosides and incorporated into DNA using standard protocols. Comparison of two-dimensional NMR spectra of the fully protonated and partially deuterated duplexes allowed us to assign diastereotopic 5′ protons, increasing the number of experimental restraints used for structure determination.     

Studies on the Oxidation Mechanism of Vitamin E

α-Tocopherol model compound, 2,2,5,7,8-pentamethyl-6-hydroxychroman was oxidized under oxygen bubbling. Four oxidation products of 2-(γ,γ-dimethylallyl)-3,5,6-trimethyl-1,4-benzoquinone (B), 2,2,7,8-tetramethyl-5-formyl-6-hydroxychroman (C), trimer (D) and tocopherylethane (G) were identified, and spirodimer (E) was tentatively identified by TLC. Two of them, (B) and (C) have not been obtained in the oxidation of α-tocopherol model compound with p-quinone, alkaline ferricyanide and other compounds as oxidizing agent. A scheme of oxidation mechanism of α-tocopherol model compound was also proposed.     

Studies on the Oxidation of Steroids by Fungi

As a result of seeking for suitable microorganisms which catalize the hydroxylation of steroids at C-11 position, Corticium sasakii, the fungus of sheath spot disease of rice, was found among the culture specimens of 28 genera of Basidiomycetes. This organism converted Reich-stein’s compound S to hydrocortisone, epi-hydrocortisone and 17α, 19-dihydroxydesoxycorticosterone.     

Studies on Disaccharide Nucleoside Synthesis. Mechanism of the Formation of Trisaccharide Purine Nucleosides

Abstract

The unexpected formation of trisaccharide nucleosides during synthesis of purine 5′-O-β-D-ribofuranosylnucleosides in the presence of Lewis acids was observed.     

31P NMR Studies on Oxidative Transformations of Aryl Nucleoside H-Phosphonate Diesters

Abstract

Various aspects of oxidative coupling of nucleoside aryl H-phosphonate diesters with nucleosides to produce important synthetic intermediates in the phosphotriester approach to oligonucleotide synthesis, dinucleoside aryl phosphotriesters, was investigated.     

Interactions of Calf Spleen Purine Nucleoside Phosphorylase with Antiviral Acyclic Nucleoside Phosphonate Inhibitors: Kinetics and Emission Studies

Abstract

Association between calf spleen purine nucleoside phosphorylase and a series of phosphonylalkoxyalkyl derivatives of purine bases was studied by inhibition kinetics and fluorimetric titrations. Dissociation constants, determined by fluorimetric titration in phosphate-free conditions, were lower than inhibition constants in 1 mM phosphate, and inhibition was still weaker in 50 mM phosphate, in accord with the postulated bisubstrate analogue character of this class of inhibitors.     

Studies on the Mechanism of the Oxidation of Tea Leaf Catechins

In order to understand the mechanism of the enzymic oxidation of epigallocatechin, ethyl gallate was taken up as a model substrate on account of its close structural similarity to the w-trihydroxyphenyl group, which indeed is supposed to be attacked by oxidase, when epigallocatechin is oxidized enzymically. By the action of tea or apple oxidase at pH 5.5, it gave a characteristic polyphenolic substance, which was obtained in prisms, C₁₈H₁₈O₁₀·2H₂O, and proved to be diethyl 4,4′,5,5′,6,6′-hexahydroxydiphenate, as the product was converted into ellagic acid by hydrolysis of ester linkage and then lactone formation.     

Studies on the Mechanism of the Oxidation of Tea Leaf Catechins

Oxidations of epigallocatechin in the presence of catechol or pyrogallol with tea oxidase as well as with an oxidizing reagent and the isolation of the oxidation products, categallin (II) and pyrogallin (III), in crystalline form are described. Their absorption spectra are compared with those of pigment P(I) obtained by the oxidation of epigallocatechin and epicatechin, and their structural relationships are discussed.     

Studies on the Mechanism of the Oxidation of Tea Leaf Catechins

A study is made on the oxidation of a mixture containing epigallocatechin and epicatechin with tea oxidase as well as a oxidizing reagent, in order to understand the formation of red pigments in tea manufacture. As the reaction proceeds a remarkable colored substance is formed, which can be obtained in reddish orange needles (from water) and is supposed to be a troponoid compound having a 3′,4′-dihydroxybenzotropolone nucleus as suggested by a tentative structural formula III from a consideration of its spectral characteristics.     

Use of 4-Thiouridine and 4-Thiothymidine in Studies on Pyrimidine Nucleoside Phosphorylases

The new substrates 4-thiouridine and 4-thiothymidine were proposed for spectrophotometric measurement of the activity of uridine (UP) and thymidine (TP) phosphorylases. At pH 7.5, 4-thiouridine has an absorbance maximum at 330 nm, and the difference in extinction coefficient () between 4-thiouridine and 4-thiouracil is 3000 ^–1cm^–1. 4-Thiouridine proved to be a good substrate for UP: the Michaelis ( ) and catalytic (k _cat) constants were estimated respectively at 130 M and 49 s^–1 at 25°C. Even a greater (5000 M^–1cm^–1 at 336 nm) was observed for the 4-thiothymidine/4-thiothymine pair.     

Enzymatic Studies on the Oxidation of Sugar and Sugar Alcohol

During the course of studies on the oxidative metabolism of d-sorbitol by acetic acid bacteria, it was found that d-sorbitol was almost quantitatively converted to 5-keto-d-fructose via l-sorbose by a certain strain of Gluconobacter suboxydans. In addition to 5-keto-d-fructose, three γ-pyrone compounds, kojic acid, 5-oxymaltol, and 3-oxykojic acid, 2-keto-l-gulonate, and several organic acids such as succinic, glycolic, and glyceric acids were confirmed in the culture filtrate of this bacterium.

• The most suitable carbon source for 5-ketofructose fermentation by Gluconobacter suboxydans Strain 1 was confirmed to be d-sorbitol or l-sorbose using growing and resting cells. d-Fructose had little effect on the formation of this dicarbonylhexose.

• The optimal pH for the formation from l-sorbose by intact cells was found to be at 4.2.

• The activity of the pentose phosphate cycle in the resting cells was calculated as 13~17 μatoms/hr/mg of dry cells by the use of the manometric techniques.

• There was no strain tested so far which could accumulate a large amount of 5- keto-d-fructose from d-sorbitol except this bacterium.

• The experimental results shown in this paper makes the prediction that a certain dehydrogenating system of l-sorbose is functional in the organism, and the metabolic pathways of d-sorbitol via l-sorbose and 5-keto-d-fructose is proposed.