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Di-glycosylated adenines act as glycosyl donors in the intermoleculartrans-glycosylation of pyrimidine nucleobases under proton beam irradiation conditions. Formamide and chondrite meteorite NWA 1465 increased the yield and the selectivity of the reaction

We report the development of a one-pot synthesis of 2-fluoroadenine from an inexpensive 2,6-diaminopurine starting material using diazonium chemistry in a continuous fashion. Given the sensitivity of this transformation to temperature, we conducted critical experiments to study the exothermicity of the reaction and the heat removal, which were critical for the development of the process. Our goal was to improve the yield and purity of this pharmaceutical intermediate (2-fluoroadenine) and develop a more robust process.

It has recently been demonstrated that mineral self-assembled structures catalyzing prebiotic chemical reactions may form in natural waters derived from serpentinization, a geological process widespread in the early stages of Earth-like planets. We have s

Nucleoside hydrolases (NHs) catalyze the hydrolysis of the N-glycoside bond in ribonucleosides and are found in all three domains of life. Although in parasitic protozoa a role in purine salvage has been well established, their precise function in bacteria and higher eukaryotes is still largely unknown. NHs have been classified into three homology groups based on the conservation of active site residues. While many structures are available of representatives of group I and II, structural information for group III NHs is lacking. Here, we report the first crystal structure of a purine-specific nucleoside hydrolase belonging to homology group III from the nematode Caenorhabditis elegans (CeNH) to 1.65? resolution. In contrast to dimeric purine-specific NHs from group II, CeNH is a homotetramer. A cysteine residue that characterizes group III NHs (Cys253) structurally aligns with the catalytic histidine and tryptophan residues of group I and group II enzymes, respectively. Moreover, a second cysteine (Cys42) points into the active site of CeNH. Substrate docking shows that both cysteine residues are appropriately positioned to interact with the purine ring. Site-directed mutagenesis and kinetic analysis proposes a catalytic role for both cysteines residues, with Cys253 playing the most prominent role in leaving group activation.

Two approaches to the chemoenzymatic synthesis of 2-fluorocordycepin and 2-chlorocordycepin were studied: (i) the use of 3′-deoxyadenosine (cordycepin) and 3′-deoxyinosine (3′dIno) as donors of 3-deoxy- d -ribofuranose in the transglycosylation of 2-fluoro- (2F Ade) and 2-chloroadenine (2Cl Ade) catalyzed by the recombinant E. coli purine nucleoside phosphorylase (PNP), and (ii) the use of 2-fluoroadenosine and 3′-deoxyinosine as substrates of the cross-glycosylation and PNP as a biocatalyst. An efficient method for 3′-deoxyinosine synthesis starting from inosine was developed. However, the very poor solubility of 2Cl Ade and 2F Ade is the limiting factor of the first approach. The second approach enables this problem to be overcome and it appears to be advantageous over the former approach from the viewpoint of practical synthesis of the title nucleosides. The 3-deoxy-α- d -ribofuranose-1-phosphate intermediary formed in the 3′dIno phosphorolysis by PNP was found to be the weak and marginal substrate of E. coli thymidine (TP) and uridine (UP) phosphorylases, respectively. Finally, one-pot cascade transformation of 3-deoxy- d -ribose in cordycepin in the presence of adenine and E. coli ribokinase, phosphopentomutase, and PNP was tested and cordycepin formation in ca. 3.4% yield was proved.

5′-Methylthioadenosine phosphorylase (MTAP) and 5′-methylthioadenosine nucleosidase (MTAN) catalyze the phosphorolysis and hydrolysis of 5′-methylthioadenosine (MTA), respectively. Both enzymes have low KM values for their substrates. Kinetic assays for these enzymes are challenging, as the ultraviolet absorbance spectra for reactant MTA and product adenine are similar. We report a new assay using 2-amino-5′-methylthioadenosine (2AMTA) as an alternative substrate for MTAP and MTAN enzymes. Hydrolysis or phosphorolysis of 2AMTA forms 2,6-diaminopurine, a fluorescent and easily quantitated product. We kinetically characterize 2AMTA with human MTAP, bacterial MTANs and use 2,6-diaminopurine as a fluorescent substrate for yeast adenine phosphoribosyltransferase. 2AMTA was used as the substrate to kinetically characterize the dissociation constants for three-transition-state analogue inhibitors of MTAP and MTAN. Kinetic values obtained from continuous fluorescent assays with MTA were in good agreement with previously measured literature values, but gave smaller experimental errors. Chemical synthesis from ribose and 2,6-dichloropurine provided crystalline 2AMTA as the oxalate salt. Chemo-enzymatic synthesis from ribose and 2,6-diaminopurine produced 2-amino-S-adenosylmethionine for hydrolytic conversion to 2AMTA. Interaction of 2AMTA with human MTAP was also characterized by pre-steady-state kinetics and by analysis of the crystal structure in a complex with sulfate as a catalytically inert analogue of phosphate. This assay is suitable for inhibitor screening by detection of fluorescent product, for quantitative analysis of hits by rapid and accurate measurement of inhibition constants in continuous assays, and pre-steady-state kinetic analysis of the target enzymes.

Cytokinin (CTK) dehydrogenase is responsible for regulating the endogenous CTK content by oxidative removal of the side chain. Herein, we have applied fluorescence method to study the interaction between CTK dehydrogenase and CTK in vitro and obtain some parameters of their interaction. We found that addition of isopentenyl adenine can quench the fluorescence of CTK dehydrogenase, and the quenching mechanism was to be a static quenching procedure. We have measured the number of binding sites n and the apparent binding constant K and have calculated the thermodynamics parameter ΔH, ΔG, and ΔS by fluorescence quenching method. Based on thermodynamics parameter’s results, we concluded that their binding reaction was both entropy driven and the enthalpy driven, and the Van der Waals force and hydrogen bond force played a major role in the interaction. Based on the synchronous fluorescence spectrometry results, we demonstrated that the binding site between isopentenyl adenine and CTK dehydrogenase is in the microenvironment of both tryptophan and tyrosine. The fluorescence signal of coenzyme, flavin adenine dinucleotide, decreases gradually with the addition of isopentenyl adenine. And this method can be used for isopentenyl adenine routine assay. Under optimized experimental parameters, the linear segment increases from 0.6?μM to 100?μM with a regression equation of ΔF?=?0.04?+?0.15cip (r?=?0.999, cip in μM) with the detection limit of 0.15?μM iP.

The pathway from simple abiotically made organic compounds to the molecular bricks of life, as we know it, is unknown. The most efficient geological abiotic route to organic compounds results from the aqueous dissolution of olivine, a reaction known as serpentinization (Sleep, N.H., et al. (2004) Proc. Natl. Acad. Sci. USA 101, 12818-12822). In addition to molecular hydrogen and a reducing environment, serpentinization reactions lead to high-pH alkaline brines that can become easily enriched in silica. Under these chemical conditions, the formation of self-assembled nanocrystalline mineral composites, namely silica/carbonate biomorphs and metal silicate hydrate (MSH) tubular membranes (silica gardens), is unavoidable (Kellermeier, M., et al. In Methods in Enzymology, Research Methods in Biomineralization Science (De Yoreo, J., Ed.) Vol. 532, pp 225-256, Academic Press, Burlington, MA). The osmotically driven membranous structures have remarkable catalytic properties that could be operating in the reducing organic-rich chemical pot in which they form. Among one-carbon compounds, formamide (NH2CHO) has been shown to trigger the formation of complex prebiotic molecules under mineral-driven catalytic conditions (Saladino, R., et al. (2001) Biorganic & Medicinal Chemistry, 9, 1249-1253), proton irradiation (Saladino, R., et al. (2015) Proc. Natl. Acad. Sci. USA, 112, 2746-2755), and laser-induced dielectric breakdown (Ferus, M., et al. (2015) Proc Natl Acad Sci USA, 112, 657-662). Here, we show that MSH membranes are catalysts for the condensation of NH2CHO, yielding prebiotically relevant compounds, including carboxylic acids, amino acids, and nucleobases. Membranes formed by the reaction of alkaline (pH 12) sodium silicate solutions with MgSO4 and Fe2(SO4)3·9H2O show the highest efficiency, while reactions with CuCl2·2H2O, ZnCl2, FeCl2·4H2O, and MnCl2·4H2O showed lower reactivities. The collections of compounds forming inside and outside the tubular membrane are clearly specific, demonstrating that the mineral self-assembled membranes at the same time create space compartmentalization and selective catalysis of the synthesis of relevant compounds. Rather than requiring odd local conditions, the prebiotic organic chemistry scenario for the origin of life appears to be common at a universal scale and, most probably, earlier than ever thought for our planet.

We have developed a multimodal ion source design that can be configured on the fly for various analysis modes, designed for more efficient and reproducible sampling at the mass spectrometer atmospheric pressure (AP) interface in a number of different applications. This vacuum-assisted plasma ionization (VaPI) source features interchangeable transmission mode and laser ablation sampling geometries. Operating in both AC and DC power regimes with similar results, the ion source was optimized for parameters including helium flow rate and gas temperature using transmission mode to analyze volatile standards and drug tablets. Using laser ablation, matrix effects were studied, and the source was used to monitor the products of model prebiotic synthetic reactions. [Figure not available: see fulltext.]

A non-specific nucleoside hydrolase from Escherichia coli (RihC) has been cloned, overexpressed, and purified to greater than 95% homogeneity. Size exclusion chromatography and sodium dodecyl sulfate polyacrylamide gel electrophoresis show that the protein exists as a homodimer. The enzyme showed significant activity against the standard ribonucleosides with uridine, xanthosine, and inosine having the greatest activity. The Michaelis constants were relatively constant for uridine, cytidine, inosine, adenosine, xanthosine, and ribothymidine at approximately 480 μM. No activity was exhibited against 2′-OH and 3′-OH deoxynucleosides. Nucleosides in which additional groups have been added to the exocyclic N6 amino group also exhibited no activity. Nucleosides lacking the 5′-OH group or with the 2′-OH group in the arabino configuration exhibited greatly reduced activity. Purine nucleosides and pyrimidine nucleosides in which the N7 or N3 nitrogens respectively were replaced with carbon also had no activity.

The effect of exposing 2′-deoxyadenosine (dA), 5′-dAMP, 3′-dAMP, dApA, dA(pdA)19, and poly(dA): oligo(dT) to iron/H2O2 in the presence and absence of ethanol or NADH has been studied. HPLC retention times, enzyme treatments, radiolabeled substrates, UV absorption spectra, and fast atom bombardment mass spectrometry (FABMS) have been used to distinguish 20 products arising from the reaction, of which 16 have been identified and four anomers proposed by comparison with earlier gamma radiation studies. The radical responsible for the reactions seems to be analogous to radiation-derived ·OH, has many products in common, but has some novel ones probably specific for Fenton-induced damage. Two new dimeric adducts arising from the generation of hydroxylamine at N7 and its subsequent condensation with two known sugar damage products, dR-adenine-N1-oxide, and two isomers of dR-FAPy arising from radical attacks at C4 and C5, may be considered novel in the present study. Unlike radiation-derived ·OH, the radical under study is difficult to eliminate due to its generation in the proximity of the substrate molecules. It is proposed that the iron binds to the phosphate group and generates the radical in its vicinity. Strand breaks in dA(pdA)11 resulting from the Fenton reaction are of two types, spontaneous and alkali-labile. Duplex DNA is less sensitive to attack by this radical, as its various degradation products are a subset of those obtained with monomer substrates and only dR-FAPy production is relatively enhanced for poly (dA): oligo (dT) as compared to those from other substrates. Copyright

Thiazole synthase in Escherichia coli is an αβ heterodimer of ThiG and ThiH. ThiH is a tyrosine lyase that cleaves the Cα-Cβ bond of tyrosine, generating p-cresol as a by-product, to form dehydroglycine. This reactive intermediate acts as one of three substrates for the thiazole cyclization reaction catalyzed by ThiG. ThiH is a radical S-adenosylmethionine (AdoMet) enzyme that utilizes a [4Fe-4S]+ cluster to reductively cleave AdoMet, forming methionine and a 5′-deoxyadenosyl radical. Analysis of the time-dependent formation of the reaction products 5′- deoxyadenosine (DOA) and p-cresol has demonstrated catalytic behavior of the tyrosine lyase. The kinetics of product formation showed a pre-steady state burst phase, and the involvement of DOA in product inhibition was identified by the addition of 5′-methylthioadenosine/S-adenosylhomocysteine nucleosidase to activity assays. This hydrolyzed the DOA and changed the rate-determining step but, in addition, substantially increased the uncoupled turnover of AdoMet. Addition of glyoxylate and ammonium inhibited the tyrosine cleavage reaction, but the reductive cleavage of AdoMet continued in an uncoupled manner. Tyrosine analogues were incubated with ThiGH, which showed a strong preference for phenolic substrates. 4-Hydroxyphenylpropionic acid analogues allowed uncoupled AdoMet cleavage but did not result in further reaction (Cα-Cβ bond cleavage). The results of the substrate analogue studies and the product inhibition can be explained by a mechanistic hypothesis involving two reaction pathways, a product-forming pathway and a futile cycle.

"Chemical equation presented" S-Adenosylmethionine (AdoMet or SAM)-dependent methyltransferases belong to a large and diverse family of group-transfer enzymes that perform vital biological functions on a host of substrates. Despite the progress in genomics, structural proteomics, and computational biology, functional annotation of methyltransferases remains a challenge. Herein, we report the synthesis and activity of a new AdoMet analogue functionalized with a ketone group. Using catechol O-methyltransferase (COMT, EC 2.1.1.6) and thiopurine S-methyltransferase (TPMT, EC 2.1.1.67) as model enzymes, this robust and readily accessible analogue displays kinetic parameters that are comparable to AdoMet and exhibits multiple turnovers with enzyme. More importantly, this AdoMet surrogate displays the same substrate specificity as the natural methyl donor. Incorporation of the ketone group allows for subsequent modification via bio-orthogonal labeling strategies and sensitive detection of the tagged ketone prod cts. Hence, this AdoMet analogue expands the toolbox available to interrogate the biochemical functions of methyltransferases.

We describe the one-pot synthesis of a large panel of nucleic bases and related compounds from formamide in the presence of iron sulfur and iron-copper sulfur minerals as catalysts. The major products observed are purine, 1H-pyrimidinone, isocytosine, adenine, 2-aminopurine, carbodiimide, urea, and oxalic acid. Isocytosine and 2-aminopurine may recognize natural nucleobases by Watson-Crick and reverse Watson-Crick interactions, thus suggesting novel scenarios for the origin of primordial nucleic acids. Since the major problem in the origin of informational polymers is the instability of their precursors, we also investigate the effects of iron sulfur and iron-copper sulfur minerals on the stability of ribooligonucleotides in formamide and in water. All of the iron sulfur and iron-copper sulfur minerals stimulated degradation of RNA. The relevance of these findings with respect to the origin of informational polymers is discussed.

(Chemical Equation Presented) A variant of the semipinacol rearrangement that was observed in our laboratory has been applied to the synthesis of several furanose and pyranose derivatives. The process consists of an "orchestrated" [1,2]-hydride shift with

The synthesis of C5'-aldehydes 1a,b and preliminary results concerning their reactivity under radical conditions was analyzed. Treatment of C5'-aldehydes 4a, b under mildly basic conditions led to the formation of 3' 4' -didehydroaldehydes 1a, b and furfu

The present invention is directed to purine nucleoside analogs of the general Formula (I), or tautomers thereof, physiologically acceptable salts, solvents and physiologically functional derivatives thereof, and pharmaceutical compositions comprising such compounds, salts and derivatives, which are useful as anti-bacterial and anti-protozoan agents. The invention is also directed to methods for treating a bacterial or protozoan infection in a mammal and use of the compounds for inhibiting the growth of a bacteria or protozoa.

The structure-based design, chemical synthesis, and biological evaluation of novel MTAP substrates are described. These compounds incorporate various C5′-moieties and are shown to have different kcat/Km values compared with the natural MTAP substrate (MTA).

The hydrolysis of diadenosine 5′,5′-triphosphate to AMP and ADP has been studied over a wide pH-range. Under acidic conditions the reaction shows a first-order dependence on the hydronium ion concentration. Below pH 3 the rate-increase begins to level off. From pH 6 to 9 the hydrolysis is slow and pH-independent. Base-catalysed hydrolysis is observed in NaOH-solutions. Under alkaline conditions an intramolecular nucleophilic attack on the phosphate producing 3′,5′-cAMP is also observed, but it is slower than the intermolecular reaction. Depurination of the adenosine moieties competes with the hydrolysis both under acidic and alkaline conditions, but the mechanisms are different. The temperature-dependence of the hydrolysis of Ap3A and the depurination of adenosine moieties were studied under acidic conditions, and the activation parameters of the reactions were calculated. The results of the work reflect the fact that the negatively charged polyphosphate group is very resistant towards nucleophilic attack. An efficient catalysis is only observed under acidic conditions, where the phosphate group becomes protonated. General acids or bases did not catalyse the hydrolysis. Furthermore, hydroxide ion catalysed cleavage is only observed at high base concentrations and other negatively charged nucleophiles did not attack the phosphate groups of diadenosine polyphosphates.

Malondialdehyde is a ubiquitous product of lipid peroxidation that reacts with DNA to form premutagenic lesions. Principal among them is pyrimido-[1,2-α]purin-10(3H)-one (M1G). M1G has recently been found to be a reactive electrophile in DNA that couples with amines at basic pH or hydroxylamines at neutral pH. We explored the reaction of M1G with hydrazines because of the possibility that the latter could act as bifunctional nucleophiles to strip the malondialdehyde equivalent from DNA. Pentafluorophenylhydrazine reacted rapidly with M1G to form a hydrazone conjugate. This hydrazone was stable at room temperature and did not cyclize to form the corresponding pyrazole. In contrast, phenylhydrazine and benzylhydrazine reacted with M1G to form phenylpyrazole and benzylpyrazole, respectively. Pentafluorobenzylhydrazine reacted rapidly with M1G to form pentafluorobenzylpyrazole and dG in near quantitative yield. This reaction formed the basis for a quantitative assay for the presence of M1G or M1G equivalents in DNA or protein that utilized gas chromatography/negative chemical ionization mass spectrometry. The assay was extended to the oxopropenyl donors, M1A, base propenal, and Nε-3-oxopropenyl-lysine. Analysis of DNA treated with bleomycin demonstrated a linear increase in the level of oxopropenyl groups that plateaued at approximately 1 oxopropenyl group/100 bases at a bleomycin concentration of 200 μM. Parallel analysis of M1G in the samples revealed that this adduct represents a small fraction of the total oxopropenyl units generated in DNA by treatment with bleomycin.

The synthesis of prebiotic molecules is a major problem in chemical evolution as well as in any origin-of-life theory. We report here a plausible new prebiotic synthesis of naturally occurring purine and pyrimidine derivatives from formamide under catalytic conditions. In the presence of CaCO3 and different inorganic oxides, namely silica, alumine, kaolin, and zeolite (Y type), neat formamide undergoes the formation of purine, adenine, cytosine, and 4(3H)-pyrimidinone, from acceptable to good yields. The role of catalysts showed to be not limited to the improvement of the yield but it is also relevant in providing a high selectivity in the products distribution.

A new method for monitoring hydrothermal reactions on the millisecond time scale has been developed using a microtube flow reactor. The system was designed based on a high-pressure pump, a sample-loop injector, a narrow-bore size capillary, a cooling bath, back-pressure tubing, and a sampling port. Samples were analyzed using high-performance liquid chromatography. Kinetic analyses of the hydrolyses of adenosine 5'-triphosphate (ATP) and adenosine 5'-monophosphate (AMP) on the millisecond time range at 250 - 315 °C were demonstrated so as to evaluate the performance of the method. In conclusion, monitoring was successful for the hydrolysis of ATP and AMP in 2 - 50 ms using fused-silica capillary tubing with 0.015 and 0.025 mm inner diameter (ID). The method enables real-time monitoring of hydrothermal reactions in about 100-times shorter time range than other techniques. This paper proposes apparent rate constants and activation energy for the consecutive hydrolysis of ATP to adenine at high temperatures that were difficult to determine by a conventional batch method. On the basis of the rate constants, kinetics and mechanistic analyses of the step-wise decomposition of ATP were investigated from the viewpoint of the RNA world hypothesis under hydrothermal environments.

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

Treatment of 5'-O-nitro esters of nucleosides with tributylstannane and AIBN at elevated temperatures caused β-scission of the resulting 5'-oxygen radical to give formaldehyde and dehomologated erythrofuranosyl nucleosides. Analogous treatment of 6'-O-nitro esters of homonucleosides [(5-deoxy-β-D- ribo-hexofuranosyl)adenine or uracil nucleosides derived from D-glucose] resulted in generation of a 6'-oxygen radical followed by abstraction of H3' by a [1,5]-hydrogen shift. Radical quenching with tributyltin deuteride gave 3'-[2H]homonucleosides. This deuterium transfer, and inversion of configuration at C3' with unprotected homonucleosides, confirmed the relay- generation of C3' free radicals. Analogous treatment of 6'-O-nitro esters of homonucleosides containing a 2'-chloro (30) or 2'-O-tosyl (40) substituent resulted in complete disappearance of starting material and generation of (R)-2-(2-hydroxyethyl)-3(2H)-furanone (33). Generation of a 6'-oxygen radical, [1,5]-hydrogen shift of H3' to give a C3' radical, and loss of the 2'-substituent would give unstable intermediates that could lose the heterocyclic base from Cl' to give 33. This radical-initiated cascade simulates reactions postulated to occur at the active site of ribonucleotide reductases. Generation of a C3' radical from 40 and loss of toluenesulfonic acid via a [1,2]-electron shift would generate a radical intermediate that could undergo deuterium transfer followed by β-elimination of the base to give the deuterated furanone 33 as observed. This is in harmony with a new mechanism for substrate reduction of nucleotides to give 2'-deoxy products. Generation of a C3' radical from 30 and loss of a chlorine atom by β- radical elimination would result in conjugate elimination of base and generation of 33 without incorporation of deuterium, as observed. Thus, one- electron elimination processes (as well as the previously postulated two- electron loss with groups from C2') must be considered with mechanism-based inactivators of ribonucleotide reductases. Biomimetic reactions and new mechanistic considerations are discussed.

During the last few years, many gene therapy strategies have been developed for various disease targets. The development of anticancer gene therapy strategies to selectively generate cytotoxic nucleoside or nucleotide analogs is an attractive goal. One such approach involves the delivery of herpes simplex virus thymidine kinase followed by the acyclic nucleoside analog ganciclovir. We have developed another gene therapy methodology for the treatment of cancer that has several significant attributes. Specifically, our approach involves the delivery of E. coli purine nucleoside phosphorylase, followed by treatment with a relatively non-toxic nucleoside prodrug that is cleaved by the enzyme to a toxic compound. .This presentation describes the concept, details our search for suitable prodrugs, and summarizes the current biological data. Copyright

Monitoring of hydrothermal reactions in the time range of 3-1000 ms was succeeded by flow reactor using fused-silica capillary tubing. The technique was applied for measuring the hydrolysis rate of ATP at 250 °C in which the minimum monitoring time was 3.1 ms. The rate constants of ATP hydrolysis was consistent with that was extrapolated of the Arrhenius plots in our previous study. This method enables milli-second monitoring of hydrothermal reactions.

Ribonucleotide reductases are enzymes that catalyze the conversion of ribonucleotides to 2'-deoxyribonucleotides. This important reaction is initiated by the generation of a C-3' nucleotide radical and subsequent loss of the 2'-hydroxyl group. In order to model certain steps in this mechanism, selenol ester 23 was prepared and photolyzed providing the first selective chemical access to the 3'-adenosyl radical. From product analysis it could be shown that elimination of the 2'-OH function readily takes place under general base catalysis. The rate coefficient for this reaction was determined by competition kinetics to be 1.5 · 106 s-1 in the presence of 1 M triethylammonium acetate buffer at pH 7. Without catalyst the elimination rate is about 103 times slower. It can be concluded that a similar mechanism is also feasible for the key steps of the enzyme catalyzed reaction.

The treatment of nucleic acid bases, nucleosides, and nucleotides with peroxodisulfate ion in a phosphate buffer solution at pH 7.0 or water at 70-75°C was investigated. The reaction of thymine and 5-methylcytosine nucleosides and nucleotides resulted in the oxidation of the 5-methyl groups. The oxidation products from 1,3-dimethyluracils and the time-course of the reaction of uracils led to two plausible reaction mechanisms for the oxidation of uracils.

Preparation of 2'- and 3'-bromo derivatives of 2',3'-unsaturated uracil and adenine nucleosides has been carried out starting from the corresponding β-hydroxyselenides by way of bromination and successive selenoxide elimination.These compounds have been shown to serve as versatile synthons for the preparation of anti-HIV candidates, 2'-C- and 3'-C-branched 2',3'-unsaturated nucleosides, through palladium-catalyzed cross-coupling and halogen-lithium exchange reactions. Key Words: β-hydroxyselenide; bromovinyl structure; branched-sugar nucleoside; anti-HIV agent; 2',3'-unsaturated nucleoside.

First-order rate constants for mutual isomerization and hydrolytic cleavage of the monomethyl and monoisopropyl esters of adenosine 2'- and 3'-monophosphates (2'- and 3'-AMP) have been determined by HPLC over a wide pH range.Both reactions preceed at comparable rates under acidic conditions, exhibiting a second-order dependence of rate on hydronium ion concentration at 1 -> -3.No sign of mutual isomerization was detected under these conditions.With the isopropyl esters alkaline degradation of the adenine moiety is considerably faster than the phosphodiester hydrolysis.Mechanisms of phosphate migration and phosphodiester hydrolysis under various conditions have been discussed.

N-arylmethyladenines are photolyzed in water, giving adenine and the corresponding arylmethanols.The reaction is not only observed when the arylmethyl group is a metasubstituted benzyl, but also with more complex substituents like imidazopyridin-6-ylmethyl.Meta-substituted arylmethyl groups are proposed as photoremovable N-protective groups in adenine chemistry.

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On reaction of 1-aminopurinium mesitylenesulfonates with methanolic ammonia N-deamination occurs.For 1-amino-, 1-amino-8-(methylthio)-, 1-amino-8-phenyl-, 1-amino-2-methyl-, 1-amino-6-methyl- and 1-amino-8-phenyl-9-methylpurinium mesitylenesulfonate this reaction proceeds for at least 75percent via ring opening as shown by the isolation of 1-15N-labelled purines when 15N-labelled methanolic ammonia was used. 1-Amino-9-methylpurinium mesitylenesulfonate gave N-deamination without ring opening.The reaction of 1-amino-6-(methylthio)purinium mesitylenesulfonate with methanolic ammonia involves, besides deamination, partial substitution of the methylthio group; no ring opening is involved.However, ring opening followed by substitution occurs in the reaction of 1-amino-2-(methylthio)purinium mesitylenesulfonate; the reaction proceeds via an adduct at position 2.

Reaction of 1-aminoadenosinium mesitylenesulphonate, 1a, with methanolic ammonia for 10 h at 80 deg C yields adenosine, 7a, and nebularine, 6a.With methanolic methylamine 1a gives 6-methylamino-9-β-D-ribofuranosylpurine, 8a, and adenosine, 7a, respectively.Similar results are obtained with the salt of 1-amino-2',3'-O-isopropylideneadenosine, 1b. 1-Aminoadeninium mesitylenesulphonate, 1c, with methanolic methylamine only yields 6-(methylamino)purine, 8c.In contrast, the mesitylenesulphonate salt of 1,2-diaminopurine, 11, with methanolic methylamine gives only deamination at N1, affording 2-aminopurine, 12.Studies with 15N-labelled methanolic ammonia or 15N-labelled purinium compounds show that in all these reactions, except that of 11, a ring-opening mechanism (ANRORC-mechanism) is involved.

The hydrolysis of adenosine in aqueous alkali has been studied by liquid chromatography (LC), NMR spectroscopy, and isotopic labeling techniques.The first step of the multistage reaction pathway has been shown to be a nucleophilic attack of hydroxide ion on the C8 atom with concomitant opening of the imidazole ring.The equilibrium mixture of 4-amino-5-formamido-6-(ribosylamino)pyrimidines obtained undergoes three competitive reactions, viz., intramolecular cyclization to adenine nucleosides and N6-ribosyladenines and degradation to nonchromophoric products, most probably via intermediary formation of 4,5-diamino-6-(ribosylamino)pyrimidines.Isomeric N6-ribosyladenines are further hydrolyzed to adenine and D-ribose.The rate constants for the different partial reactions have been determined at various concentrations of hydroxide ion.The mechanisms of individual steps are discussed.Comparative kinetic studies with 2'-deoxy-, 2',3'-O-isopropylidene-, and 5'-O-methyladenosine and 9-β-D-arabinofuranosyladenine and its 5'-O-methyl derivative are interpreted to indicate that the glycon moiety hydroxyl groups do not play any important role in the alkaline cleavage of adenine nucleosides.

A series of arenesulfenyl chlorides and methanesulfenyl chloride were reacted in pyridine solution with 6-N-dibenzoyl-9-(2',3'-dideoxy-β-D-glycero-pent-2-enofuranosyl)adenine (1b).In each case, the relative abundance of isomeric β-chloroarene/alkene sulfides was estimated and used to assess the relative thermodynamic stabilities of the lyxo and ribo thiiranium ion intermediates and their steric susceptibilities to attack by nucleophile (Cl-).Subsequently, the β-chloroarene/alkene sulfides 8a-d to 13 a-d, upon alkaline treatment, underwent an unprecedented ylide-mediated β elimination of the intermediary lyxo and ribo thiiranium ions, to give only 2'-ene-thiol ethers 14-19.

It has been reported, and confirmed by the present investigation, that N-(purin-6-yl)aspartic acid heated with copper(II) affords adenine.The fate of the side chain has been established by labelling the succinyl moiety uniformly with (14)C; (14)CO2 and (14)CH3(14)CHO are formed, thus showing that an oxidative degradation takes place.The same type of degradation is observed with the 9-β-D-ribofuranoside and with the 9-β-D-ribofuranoside-5'-phosphate of the title compound.

Reaction of 1-aminoadeninium mesitylenesulfonate (1) and 1,2-diaminopurinium mesitylenesulfonate (8) with methanolic ammonia for 17 h at 100 deg C leads to deamination at N(1), yielding adenine and 2-aminopurine, respectively, as well as dideamination, yielding purine.It is very likely that 6-hydrazinopurine is formed in the dideamination of 1 and that 2- hydrazinopurine is an intermediate in the dideamination of 8.From both hydrazinopurines, purine is formed.Labelling studies, using 15N-labelled methanolic ammonia, show that, in the deamination reactions, a ring-opening reaction (ANRORC mechanism) is involved.

The structure elucidation and total synthesis of chryscandin (1), a new antifungal antibiotic produced by Chrysosporium pannorum No.4629, is reported.

In barley seedling extracts, p-coumaroyl-CoA is rapidly hydrolysed to p-coumaroyl-dephospho-CoA, p-coumaroyl-4'-phosphopantetheine and p-coumaroyl-pantetheine. p-Coumaroyl-4'-phosphopantetheine is active as a substrate of agmatine coumaroyl transferase in the formation of p-coumaroyl agmatine, but p-coumaroyl-pantetheine is inactive.The phosphohydrolysis can be partly inhibited by inorganic pyrophosphate, sodium fluoride and purine nucleotides.A simplified method for the synthesis of N-hydroxysuccinimide esters of hydroxycinnamic acids, used in the synthesis of CoA thioesters, is also described.Key Word Index -- Hordeum vulgare; Gramineae; barley seedlings; plant extracts; phosphohydrolysis; hydroxycinnamoyl-CoA; p-coumaroylagmatine.

A number of 2',5'- or 3',5'-diprotected ribonucleosides and 5'-protected 2'- or 3'-deoxy-β-D-erythro-pentofuranosyl nucleosides have been oxidized to the corresponding 3' or 2'-ketonucleoside derivatives using chromium trioxide/pyridine/acetic anhydride or dimethyl sulfoxide/acetic anhydride.Reduction of the carbonyl functions with sodium borohydride gave the inverted arabino, xylo, or deoxy-threo isomers as predominant products by attack at the less hindered α-face of the sugar ring.Parallel reductions using sodium borodeuteride corroborated the epimeric ratios by demonstrating that complete oxidation of the original hydroxyl groups had occured.The deuterium labeling also aided in making NMR spectral assignments.

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Cytokinin oxidase has been highly purified from mature Zea mays kernels.Adenine has been unambiguously identified, by HPLC co-chromatography, UV and mass spectroscopy, to be the oxidation product of N6-(Δ2-isopentenyl)adenine by this enzyme.No other products were detected.The results are in agreement with metabolic studies and suggest that cytokinin oxidase plays an important role in the catabolism of exogenously applied cytokinins. - Key Word Index: Zea mays; Gramineae; kernels; cytokinin oxidase; N6-(Δ2-isopentenyl) adenine; adenine; HPLC.

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Adenine (1) is formed in substantial amounts (about 1percent yield) by heating ammonium cyanide absorbed in zeolithe X for several days at 120 deg C.If both, ammonium cyanide and cyanic acid have been absorbed, 1 and guanine (2) are synthesized under the same conditions.These experiments provide the first demonstration of the possibility of a spontaneous synthesis of these essential constituents of nucleic acids and of important coenzymes in a silicate. - Key words: Adenine, Guanine Zeolithe X, Prebiotic Synthesis

A few 6-substituted 9-(1-ethoxyethyl)purines have been prepared and the rates of their base-catalyzed hydrolysis were measured by UV spectroscopy.The product mixtures were fractionated by preparative TLC and characterized by NMR and UV spectroscopy.The results obtained suggest that the alkaline cleavage of 9-(1-ethoxyethyl)purines generally proceeds by nucleophilic attack of hydroxide ion on C8 of the purine moiety, resulting in formation of appropriate 4,5-diaminopyrimidine and 8-methylpurine as final products.With 6-methoxy, 6-methylthio, and 6-chloro derivatives nucleophilic attack of hydroxide ion of C6 giving 9-(1-ethoxyethyl)hypoxanthine competes with this reaction.

The newly synthesized adenosylsulphonium ion, (2), undergoes a facile ring closure reaction in aqueous oxyanion buffers; in contrast, amine buffers effect an intermolecular dealkylation in competition with the lyate reaction.

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Adenine, adenosine, and 5'-adenylic acid react readily with benzenediazonium ion and its derivatives at pH 8-11 to yield derivatives of (E)-6-(3-phenyl-2-triazen-1-yl)purine.The structural assignments for these compounds, some of which are unstable, are based on their spectroscopic properties and their degradation reactions in acid solution and with sodium dithionite to yield 6-hydrazinopurine.The triazenes decompose in basic aqueous solution at 60-90 deg C to produce 8-aryladenines.For adenosine and 5'-adenylic acid, the ribose residues are cleaved during this process.Several lines of evidence indicate that the triazenes are converted to 8-aryladenines in intermolecular processes.Both the benzenediazonium ion and the phenyl radical can be intercepted during the reaction.Consequently, the phenylation reaction may be confidently formulated as an intermolecular free-radical substitution reaction.