New Electrocatalytic Reactions at a Mercury Electrode in the Presence of Homocysteine or Cysteine and Cobalt or Nickel Ions

Homocysteine (Hcy) and cysteine (Cys) mercury thiolate layers were prepared by anodic polarization of a mercury electrode in amino acid containing solutions and then investigated in the cathodic regime in the presence of Ni²⁺ or Co²⁺ ions. The sulfhydryl function in the mercury thiolate undergoes a slow disintegration resulting in surface‐attached mercury sulfide. During the cathodic scan, Hg²⁺ substitution by Ni²⁺ or Co²⁺ yields minute amounts of the relevant metal sulfide. Such a species catalyzes hydrogen evolution at ?1.3 V vs. Ag|AgCl|KCl(3 M). Hcy experiences a faster decomposition and, consequently, displays a stronger catalytic effect. Each compound catalyzes the reduction of Ni²⁺ or Co²⁺, but only Cys (bound in metal complexes) induces typical catalytic hydrogen evolution processes such as the Brdi?ka reaction (with Co²⁺; pH around 9), or the catalytic hydrogen prewave (CHP) (with Ni²⁺; pH near 7). On the other hand, Hcy catalyzes the hydrogen evolution in the presence of Co²⁺ at ?1.5 V in the same way than sulfur derivatives with no amine function do. Metal sulfide formation does not interfere with CHP and Brdi?ka processes. Correlations between the physical state of the metal sulfide (adsorbed molecule or aggregate form) and its catalytic properties are discussed and possible analytical applications suggested.     

Aromatic vs. Carbohydrate Residues in the Major Groove: Synthesis of 5‐[(Benzyloxy)methyl]pyrimidine Nucleosides and Their Incorporation into Oligonucleotides

The synthesis of 5‐[(benzyloxy)methyl]‐substituted pyrimidine 2′‐deoxynucleosides 14 and 15 starting from the uracil derivative 6 and tetra‐O‐acetyl‐D ‐ribose is described (Schemes 1 – 3). These nucleosides were converted to the corresponding cyanoethyl phosphoramidites 18 and 19 , respectively, and incorporated into oligodeoxynucleotide decamers. The 5‐[(benzyloxy)methyl]‐nucleoside building blocks ^boT_d and ^bomC_d (bo=benzyloxy, bom=(benzyloxy)methyl) – shape analogs of the naturally occurring glucosylated nucleosides 1 and 2 (see Fig. 1) – lead to weaker binding affinities of oligodeoxynucleotides pairing to DNA as well as RNA complements. The modification is more destabilizing in the case of ^boT_d than ^bomC_d. Analysis of the thermodynamics of duplex formation shows that ^boT_d and ^bomC_d incorporation leads to a smaller entropy change in duplex formation that is, however, overcompensated by a less favorable enthalpy term. Molecular‐modeling studies suggest that the benzyl groups reside in the major groove which would explain the improved pairing entropy as a result of the exclusion of ordered H₂O.     

Synthesis of Aldehyde‐Linked Nucleotides and DNA and Their Bioconjugations with Lysine and Peptides through Reductive Amination

5‐(5‐Formylthienyl)‐, 5‐(4‐formylphenyl)‐ and 5‐(2‐fluoro‐5‐formylphenyl)cytosine 2′‐deoxyribonucleoside mono‐ ( dC^RMP ) and triphosphates ( dC^RTP ) were prepared by aqueous Suzuki–Miyaura cross‐coupling of 5‐iodocytosine nucleotides with the corresponding formylarylboronic acids. The dC^RTP s were excellent substrates for DNA polymerases and were incorporated into DNA by primer extension or PCR. Reductive aminations of the model dC^RMP s with lysine or lysine‐containing tripeptide were studied and optimized. In aqueous phosphate buffer (pH 6.7) the yields of the reductive aminations with tripeptide III were up to 25 %. Bioconjugation of an aldehyde‐containing DNA with a lysine‐containing tripeptide was achieved through reductive amination in yields of up to 90 % in aqueous phosphate buffer.     

Catalytic currents of albumin at the hanging mercury drop electrode

Bovine serum albumin (BSA), as well as completely reduced BSA denoted by P (SH)₃₅, are adsorbed on the hanging mercury drop electrode (HMDE) from alkaline buffer solutions. When time is allowed, a monolayer is adsorbed from very dilute (10^?9M) BSA solutions in ammoniacal and borate buffers. With a monolayer of adsorbed protein the voltammograms at the HMDE are then identical in a given ammoniacal or borax buffer containing cobalt(III) or (II) and different BSA concentrations. Voltammograms of P (SH)₃₅ are virtually identical with those of native BSA. At the HMDE the second Brdi?ka current is proportional to concentration of cobalt(III) or (II) and the first current nearly so. Incompletely or completely adsorbed BSA or P (SH)₃₅ is not desorbed on keeping the HMDE for one hour in ammonia buffers. An incomplete layer of adsorbed BSA or P (SH)₃₅ is relatively rapidly desorbed at ?1.6 V (vs. SCE) and a complete film at ?1.65 V, some desorption occurring at ?1.6 V. Upon desorption, the second Brdi?ka current decreases faster than the first one; this is particularly striking in 1 M ammonia buffer. The rate of desorption is increased by calcium chloride, but the rate of adsorption is not, or only slightly, increased in the presence of calcium. Incomplete adsorption occurs at ?1.60 V (vs. SCE) and no adsorption at ?1.65 V. Indications are obtained that “presodium currents” yield a slight plateau at ?1.67 to ?1.70 V, the plateau currents being attributed to adsorbed BSA, while unadsorbed BSA yields catalytic currents without a plateau, the currents merging with the residual one of the buffer. Calcium chloride greatly increases the presodium currents. From many kinetic data obtained at the dropping mercury electrode (DME) and from results at the HMDE it is concluded that, depending on the BSA concentration, Brdi?ka currents at the DME are partly of a kinetic and partly of a surface adsorption nature and partly diffusion-controlled. Adsorption equilibrium is not attained at the DME at 25° at concentrations of BSA smaller than 10^?6M.     

478—Theory of Brdička current and the dependence of the current on cobalt ion concentration

An equation of Brdi?ka current and its experimental verification are presented, in which Brdi?ka current is expressed by a function of the surface concentration of protein, the bulk concentration of cobalt ion and two parameters, n_ck_c and k_f/k_d, characterizing the protein-zero-valent cobalt complex which is to catalize the hydrogen evolution, where n_c is the total number of sites on which the complex can be formed in a protein molecule, and k_c and k_d are the (average) constants representing the intrinsic catalytic activity and the lifetime respectively, of the complex.     

Highly Concise Synthesis of 3'-"Up"-ethynyl-5'-methylbicyclo-[3.1.0]-hexyl Purine and Pyrimidine Nucleoside Derivatives Using Rhodium(II) Carbenoid Cycloaddition and Highly Diastereoselective Grignard Reaction

Synthesis of north‐5'‐methylbicyclo[3.1.0]hexyl purine and pyrimidine nucleosides with an ethynyl group at C‐3' position has been successfully accomplished by a facile method. Methylbicyclo[3.1.0]hexanone (±)‐ 5 having three contiguous chiral centers was remarkably simply constructed only by four steps containing a carbenoid insertion reaction in the presence of rhodium(II) acetate dimer and CuSO₄, giving a correct relative stereochemistry of the generated three chiral centers. Upon Grignard reaction of (±)‐ 5 with ethynylmagnesium bromide, exclusive diastereoselectivity was observed. Condensation of glycosyl donor (±)‐ 9 with purine nucleobase afforded only the desired N⁹‐alkylated nucleoside, while condensation with pyrimidine, N³‐benzoylated uracil gave the desired N¹‐alkylated nucleoside (±)‐ 13 with the undesired O²‐alkylated nucleoside (±)‐ 14 . Probably, (±)‐ 14 would be formed due to steric hindrance caused upon approaching for N¹‐alkylation.     

Application of the modified polarographic Brdička method for cancer testing

This paper reviews the application of a modification of the polarographic Brdi?ka method for cancer testing. The modification comprises the catalytic electroreduction of metal ions (here called Brdi?ka method based on catalytic metal ion reduction for cancer testing—BMMCT) and/or the electrooxidation of proteins, instead of the classical approach based on the catalytic electroreduction of protons, i.e., hydrogen waves (here called Brdi?ka method based on catalytic hydrogen evolution for cancer testing—BMHCT). Further, in the modified method, the mercury electrode has been replaced by a nontoxic solid electrode and the entire measuring system has been automated. The modified method excels in improved testing rates and sensitivity of cancer testing. The cancer testing of vaginal secretions is characterized by high specificity as well.     

2'-deoxycytidines carrying amino and thiol functionality: synthesis and incorporation by Vent (exo-) polymerase

[reaction: see text] The synthesis of 2'-deoxycytidine nucleosides bearing amino and thiol groups appended to the 5-position of the nucleobase via a butynyl linker is described. The corresponding triphosphates were then synthesized from the nucleoside and incorporated into oligonucleotides by Vent (exo(-)) DNA polymerase. The ability of Vent (exo(-)) polymerase to amplify oligonucleotides containing these functionalized cytidine derivatives in a polymerase chain reaction (PCR) was demonstrated for the amino-functionalized derivative.     

Synthesis of Disaccharide Nucleosides by the O‐Glycosylation of Natural Nucleosides with Thioglycoside Donors

Disaccharide nucleosides constitute an important group of naturally‐occurring sugar derivatives. In this study, we report on the synthesis of disaccharide nucleosides by the direct O‐glycosylation of nucleoside acceptors, such as adenosine, guanosine, thymidine, and cytidine, with glycosyl donors. Among the glycosyl donors tested, thioglycosides were found to give the corresponding disaccharide nucleosides in moderate to high chemical yields with the above nucleoside acceptors using p‐toluenesulfenyl chloride (TolSCl) and silver triflate (AgOTf) as promoters. The interaction of these promoters with nucleoside acceptors was examined by ¹H NMR spectroscopic experiments.     

Synthesis of Selectively 15N‐Labeled 2′‐O‐{[(Triisopropylsilyl)oxy]methyl}(=tom)‐Protected Ribonucleoside Phosphoramidites and Their Incorporation into a Bistable 32Mer RNA Sequence

We present optimized reaction conditions for the conversion of 2′‐O‐{[(triisopropylsilyl)oxy]methyl}(=tom) protected uridine and adenosine nucleosides into the corresponding protected (3‐¹⁵N)‐labeled uridine and cytidine and (1‐¹⁵N)‐labeled adenosine and guanosine nucleosides 4, 6, 12 , and 18 , respectively (Schemes 1–4). On a DNA synthesizer, the resulting ¹⁵N‐labeled 2′‐O‐tom‐protected phosphoramidite building blocks 19 – 22 were efficiently incorporated into five selected positions of a bistable 32mer RNA sequence 23 (known to adopt two different structures) (Fig. 1). By 2D‐HSQC and HNN‐COSY experiments in H₂O/D₂O 9 : 1, the ¹⁵N‐signals of all base‐paired ¹⁵N‐labeled nucleotides could be identified and attributed to one of the two coexisting structures of 23 .     

Post‐Synthetic Monovalent Central‐Metal Exchange,Specific I2 Sensing,and Polymerization of a Catalytic [3×3] Grid of [CuII5CuI4L6]⋅(I)2⋅13 H2O

From a predesigned grid, [Cu^II₅Cu^I₄L₆] ? (I)₂ ? 13 H₂O ( 1 ), in which LH₂ was a pyrazinyl‐triazolyl‐2,6‐substituted pyridine, we successfully synthesized an extended 3D complex, ¹_∞[{Cu^II₅Cu^I₈L₆}{μ‐[Cu^I₃(CN)₆]}₂ ? 2 CH₃‐ CN] ( 2 ), that displayed unprecedented coexistence of all the five known coordination geometries of copper. Grid 1 displayed monovalent central metal exchange (CME) of Cu^I for Ag^I for the first time, as well as the formation of tri‐iodide in the crystalline state. These systems were investigated for their magnetic properties. Remarkably, grid 1 showed much higher catalytic activity than the Ag‐exchanged product for synthesis of a substituted triazole, 1‐benzyl‐4‐phenyl‐1H‐1,2,3‐triazole.     

Determination of Bromide Production in Radiolysis of Nucleobases,Nucleosides, and Nucleotides Using HPLC

Abstract

Determination of the formation of bromide ions in intermolecular electron transfer in 5-bromouracil (BrUr) and its nucleoside and nucleotide derivatives with nucleobases, nucleosides, and nucleotides was carried out with high performance liquid chromatography (HPLC). Initial electron attachment, at high concentration of nucleobases, nucleosides, or nucleotides, is mainly on these molecules; intermolecular electron transfer then occurs between theses molecules and BrUr and the derivatives. The elimination of bromide ions from BrUr and the derivatives then follows. It is concluded that in neutral and basic solution (pH 6 to 10) there is a significant electron transfer from thymine (T), uracil (Ur), thymidine (dT), 2′-deoxyuridine (dU), or 2′-deoxyuridine-5′-monophosphate (dUMP) to BrUr and the derivatives. For example, at a concentration ratio of BrUr and T of 1 : 100, the yield of bromide ions is about 1.6, amounting to 59% of hydrated electron (e^{aq .}) yield in the radiolysis, in which the pseudo-first-order rate constants predict a bromide yield of less than 0.03.     

Influence of calcium ions on the polarographic behaviour of serum albumin

The increase of the catalytic Brdi?ka current of serum albumin in the presence of calcium ions was attributed to the conformational change of its molecule, caused by the binding of calcium. In the changed molecule the buried disulfide groups are freed and therefore the Brdi?ka current, as well as the reduction current due to the reduction of the disulfide groups, increase. The proposal explanation is supported by spectrophotometric measurements.     

ATP‐Releasing Nucleotides: Linking DNA Synthesis to Luciferase Signaling

A new strategy is reported for the production of luminescence signals from DNA synthesis through the use of chimeric nucleoside tetraphosphate dimers in which ATP, rather than pyrophosphate, is the leaving group. ATP‐releasing nucleotides (ARNs) were synthesized as derivatives of the four canonical nucleotides. All four derivatives are good substrates for DNA polymerase, with K_m values averaging 13‐fold higher than those of natural dNTPs, and k_cat values within 1.5‐fold of those of native nucleotides. Importantly, ARNs were found to yield very little background signal with luciferase. DNA synthesis experiments show that the ATP byproduct can be harnessed to elicit a chemiluminescence signal in the presence of luciferase. When using a polymerase together with the chimeric nucleotides, target DNAs/RNAs trigger the release of stoichiometrically large quantities of ATP, thereby allowing sensitive isothermal luminescence detection of nucleic acids as diverse as phage DNAs and short miRNAs.     

Triazole‐based ligands functionalized silica: Effects of ligand denticity and donors on catalytic oxidation activity of Pd nanoparticles

Triazole‐based ligands, tris (triazolyl)methanol (Htbtm), bis (triazolyl)‐phenylmethanol (Hbtm), and phenyl (pyridin‐2‐yl)(triazolyl)methanol (Hpytm), with differences in ligand denticity (i.e., bidentate and tridentate) and type of N donors (i.e., triazole and pyridine) were functionalized onto a silica support to produce the corresponding SiO₂‐ L ( L  = tbtm, btm, pytm). Subsequent reactions with Pd (CH₃COO)₂ in CH₂Cl₂ yielded Pd/SiO₂‐ L . ICP‐MS reveals that Pd loadings are higher with increased N loadings, resulting in the following trend: Pd/SiO₂‐tbtm (0.83 mmol Pd g^?1) > Pd/SiO₂‐btm (0.65 mmol Pd g^?1) ~ Pd/SiO₂‐pytm (0.63 mmol Pd g^?1). Meanwhile, TEM images of the used Pd/SiO₂‐ L catalysts after the first catalytic cycle show that the mean size of Pd NPs is highest with Pd/SiO₂‐pytm (8.5 ± 1.5 nm), followed by Pd/SiO₂‐tbtm (6.4 ± 1.6 nm) and Pd/SiO₂‐btm (4.8 ± 1.3 nm). Based on TONs, catalytic studies toward aerobic oxidation of benzyl alcohol to benzaldehyde at 60 °C in EtOH showed that Pd/SiO₂‐pytm possessed the most active surface Pd(0) atoms, most likely as a result of more labile properties of the pyridine–triazole ligand compared to tris‐ and bis (triazolyl) analogs. ICP‐MS and TEM analysis of Pd/SiO₂‐btm indicate minimal Pd leaching and similar average Pd NPs sizes after 1^st and 5^th catalytic runs, respectively, confirming that SiO₂‐btm is an efficient Pd NPs stabilizer. The Pd/SiO₂‐btm catalyst was also active toward aerobic oxidation of various benzyl alcohol derivatives in EtOH and could be reused for at least 7 reaction cycles without a significant activity loss.     

A Direct Synthesis for a New Series of 2‐Oxo(thioxo)nicotinonitrile Nucleosides as Antimicrobial Agents

A facile synthesis of a new series of cyclic and acyclic nucleosides of polyfunctionalized 2‐oxo(thioxo)nicotinonitrile derivatives 1 and 2 was performed. Glycosylation of 2‐pyridone 1 and 2‐thiopyridone 2 with glycosyl/galactosyl bromides in the existence of KOH afforded the N‐nucleoside and S‐nucleoside analogues 3 , 5 , 7 , and 9 , respectively. Deacetylation of nucleosides 3 , 5 , 7 , and 9 gave the deacetylated nucleosides 4 , 6 , 8 , and 10 , respectively. Alkylation of 2‐pyridone 1 with glycone analogues [namely, 4‐bromobutyl acetate, (2‐acetoxyethoxy)methyl bromide, 3‐chloropropane‐1,2‐diol, and allyl and / propargyl bromides] in the existence of K₂CO₃ afforded the corresponding O‐acyclic nucleoside analogues 11 , 13 , and 15–17 , respectively. Finally, treating of compounds 11 and 13 with a small amount of Et₃N tolerated the 6‐hydroxy deacetylated derivatives 12 and 14 , respectively. The synthesized nucleosides and alkylated products were tested against Gram (+ve) (Staphylococcus aureus and Bacillus cereus) and (Pseudomonas aeruginosa and Escherichia coli) as Gram (?ve) and Fungi (Aspergillus flavus and Aspergillus niger) and showed moderate antibacterial and antifungal activity.     

Isoguanine and 5‐Methyl‐Isocytosine Bases,In Vitro and In Vivo

The synthesis, base‐pairing properties and in vitro and in vivo characteristics of 5‐methyl‐isocytosine (isoC^Me) and isoguanine (isoG) nucleosides, incorporated in an HNA(h) (hexitol nucleic acid)–DNA(d) mosaic backbone, are described. The required h‐isoG phosphoramidite was prepared by a selective deamination as a key step. As demonstrated by T_m measurements the hexitol sugar showed slightly better mismatch discrimination against dT. The d‐isoG base mispairing follows the order T>G>C while the h‐isoG base mispairing follows the order G>C>T. The h‐ and d‐isoC^Me bases mainly mispair with G. Enzymatic incorporation experiments show that the hexitol backbone has a variable effect on selectivity. In the enzymatic assays, isoG misincorporates mainly with T, and isoC^Me misincorporates mainly with A. Further analysis in vivo confirmed the patterns of base‐pair interpretation for the deoxyribose and hexitol isoC^Me/isoG bases in a cellular context, through incorporation of the bases into plasmidic DNA. Results in vivo demonstrated that mispairing and misincorporation was dependent on the backbone scaffold of the base, which indicates rational advances towards orthogonality.     

Synthesis,Base Pairing,and Fluorescence Properties of Oligonucleotides Containing 1H‐Pyrazolo[3,4‐d]pyrimidin‐6‐amine (8‐Aza‐7‐deazapurin‐2‐amine) as an Analogue of Purin‐2‐amine

The synthesis of the N⁹‐ and N⁸‐(β‐D ‐2′‐deoxyribonucleosides) 2 and 10 , respectively, of 8‐aza‐7‐deazapurin‐2‐amine (=1H‐pyrazolo[3,4‐d]pyrimidin‐6‐amine) is described. The fluorescence properties and the stability of the N‐glycosylic bond of 2 were determined and compared with those of the 2′‐deoxyribonucleosides 1 and 3 of purin‐2‐amine and 7‐deazapurin‐2‐amine respectively. From the nucleoside 2 , the phosphoramidite 14 was prepared, and oligonucleotides were synthesized. Duplexes containing compound 1 or 2 are slightly less stable than those containing 2′‐deoxyadenosine, while their CD spectra are rather different. The fluorescence of the nucleosides is strongly quenched (>95%) in single‐stranded as well as in duplex DNA. The residual fluorescence was used to determine the melting profiles, which gave T_m values similar to those determined from the UV melting curves.     

Coordination‐Driven Macrocyclization for Locking of Photo‐ and Thermal cis→trans Isomerization of Azobenzene

Both trans and cis isomers of azobenzene‐linked bis‐terpyridine ligand L1 were incorporated in rigid macrocycles linked by Fe^II(tpy)₂ (tpy: terpyridine) units. The complex of the longer trans‐ L1 is dinuclear [(trans‐ L1 )₂ ? Fe^II₂], whereas the complex of the shorter cis‐ L1 is mononuclear [cis‐ L1? Fe^II]. The complex cis‐ L1? Fe^II was not only thermally stable but also photochemically inactive. These results indicate a perfectly locked state of cis‐azobenzene. The stable macrocyclic structure of cis‐ L1? Fe^II causes locking of the isomerization. To the best of our knowledge, this is first example of dual locking of photo‐ and thermal isomerization of cis‐azobenzene.     

Solid‐Phase Synthesis of (Poly)phosphorylated Nucleosides and Conjugates

Succinyl‐cycloSal‐phosphate triesters of ribo‐ and 2′‐deoxyribonucleosides were attached to aminomethyl polystyrene as an insoluble solid support and reacted with phosphate‐containing nucleophiles yielding nucleoside di‐ and triphosphates, nucleoside diphosphate sugars, and dinucleoside polyphosphates in high purity after cleavage from the solid support. Here, reactive cycloSal‐phosphate triesters were used as immobilized reagents that led to a generally applicable method for the efficient synthesis of phosphorylated biomolecules and phosphate‐bridged bioconjugates.