Real-time monitoring of enzyme-catalyzed phosphoribosylation of anti-influenza prodrug favipiravir by time-lapse nuclear magnetic resonance spectroscopy.

Favipiravir (brand name Avigan), a widely known anti-influenza prodrug, is metabolized by endogenous enzymes of host cells to generate the active form, which exerts inhibition of viral RNA-dependent RNA polymerase activity; first, favipiravir is converted to its phosphoribosylated form, favipiravir-ribofuranosyl-5'-monophosphate (favipiravir-RMP), by hypoxanthine-guanine phosphoribosyltransferase (HGPRT). Because this phosphoribosylation reaction is the rate-determining step in the generation of the active metabolite, quantitative and real-time monitoring of the HGPRT-catalyzed reaction is essential to understanding the pharmacokinetics of favipiravir. However, assay methods enabling such monitoring have not been established. 19 F- or 31 P-based nuclear magnetic resonance (NMR) are powerful techniques for observation of intermolecular interactions, chemical reactions, and metabolism of molecules of interest, given that NMR signals of the heteronuclei sensitively reflect changes in the chemical environment of these moieties. Here, we demonstrated direct, sensitive, target-selective, nondestructive, and real-time observation of HGPRT-catalyzed conversion of favipiravir to favipiravir-RMP by performing time-lapse 19 F-NMR monitoring of the fluorine atom of favipiravir. In addition, we showed that 31 P-NMR can be used for real-time observation of the identical reaction by monitoring phosphorus atoms of the phosphoribosyl group of favipiravir-RMP and of the pyrophosphate product of that reaction. Furthermore, we demonstrated that NMR approaches permit the determination of general parameters of enzymatic activity such as Vmax and Km . This method not only can be widely employed in enzyme assays, but also may be of use in the screening and development of new favipiravir-analog antiviral prodrugs that can be phosphoribosylated more efficiently by HGPRT, which would increase the intracellular concentration of the drug's active form. The techniques demonstrated in this study would allow more detailed investigation of the pharmacokinetics of fluorinated drugs, and might significantly contribute to opening new avenues for widespread pharmaceutical studies.

Metal Ions Sensing by Biodots Prepared from DNA, RNA, and Nucleotides.

Nucleic acids that exhibit a high affinity toward noble and transition metal ions have attracted growing attention in the fields of metal ion sensing, toxic metal ion removal, and the construction of functional metal nanostructures. In this study, fluorescent nanoparticles (biodots) were synthesized from DNA, RNA, and RNA nucleotides (AMP, GMP, UMP, and CMP) using a hydrothermal (HT) method, in order to study their metal ion sensing characteristics. The fluorescent properties of biodots differ markedly between those prepared from purine and pyrimidine nucleobases. All biodots demonstrate a high sensitivity to the presence of mercury cations (Hg2+), while biodots prepared from DNA, RNA, and guanosine monophosphate (GMP) are also sensitive to Ag+ and Cu2+ ions, but to a lesser extent. The obtained results show that biodots inherit the metal ion recognition properties of nucleobases, while the nucleobase composition of biodot precursors affects metal ion sensitivity and selectivity. A linear response of biodot fluorescence to Hg2+ concentration in solution was observed for AMP and GMP biodots in the range 0-250 µM, which can be used for the analytic detection of mercury ion concentration. A facile paper strip test was also developed that allows visual detection of mercury ions in solutions.

Fluorescent Nanoparticles Synthesized from DNA, RNA, and Nucleotides.

Ubiquitous on Earth, DNA and other nucleic acids are being increasingly considered as promising biomass resources. Due to their unique chemical structure, which is different from that of more common carbohydrate biomass polymers, materials based on nucleic acids may exhibit new, attractive characteristics. In this study, fluorescent nanoparticles (biodots) were prepared by a hydrothermal (HT) method from various nucleic acids (DNA, RNA, nucleotides, and nucleosides) to establish the relationship between the structure of precursors and fluorescent properties of biodots and to optimize conditions for preparation of the most fluorescent product. HT treatment of nucleic acids results in decomposition of sugar moieties and depurination/depyrimidation of nucleobases, while their consequent condensation and polymerization gives fluorescent nanoparticles. Fluorescent properties of DNA and RNA biodots are drastically different from biodots synthesized from individual nucleotides. In particular, biodots synthesized from purine-containing nucleotides or nucleosides show up to 50-fold higher fluorescence compared to analogous pyrimidine-derived biodots. The polymeric nature of a precursor disfavors formation of a bright fluorescent product. The reported effect of the structure of the nucleic acid precursor on the fluorescence properties of biodots should help designing and synthesizing brighter fluorescent nanomaterials with broader specification for bioimaging, sensing, and other applications.

Gas-phase isolation of diethyl guanosine 5'-monophosphate and its conformational assignment.

We show that intact neutral molecules of guanosine 5'-monophosphate can be vaporized by laser desorption when its phosphate group is esterified. The UV and IR spectroscopic measurements of this nucleotide reveal the existence of a novel internal hydrogen-bonding conformation of the phosphate group and guanine moiety.

Equilibrium of homochiral oligomerization of a mixture of enantiomers. Its relevance to nonlinear effects in asymmetric catalysis.

The origin of nonlinear effects (no proportionality between enantiomeric excess (ee) of chiral auxiliary and ee of product) is first summarized in general terms, underlining the importance of the presence of molecular species bearing several moieties deriving from the chiral auxiliary. The presence of a heterochiral species, produced from enantioimpure chiral auxiliaries, usually explains well the deviation to linearity, especially asymmetric amplification. In this article it is shown that the absence of a heterochiral species is not incompatible with an asymmetric amplification. The demonstration has been done on a simple model, the equilibrium of homochiral dimerization. The monomers R and S being in equilibrium with the dimers R(2) and S(2), it was possible to calculate ee(monomer) and ee(dimer) as a function of the initial concentration and the initial ee of the monomer. The asymmetric amplification can be quite substantial for the dimer, while asymmetric depletion characterizes the residual monomers. Similar conclusions apply to homochiral tri- and tetramerizations. The extension to irreversible reactions was briefly analyzed as well as the use of these results.

Two cases of polymorphic ventricular tachycardia induced by the administration of verapamil against paroxysmal supraventricular tachycardia.

Verapamil is widely used for the termination of paroxysmal supraventricular tachycardia (PSVT) with little proarrhythmic effect. We describe two cases of PSVT that changed to non-sustained polymorphic ventricular tachycardia after administration of verapamil. Electrophysiological study revealed atrioventricular nodal reentrant tachycardia in the first case, and atrioventricular reentrant tachycardia due to a concealed left lateral accessory pathway in the second case. Catecholamine-induced automaticity was one of the possible mechanisms of VT in the first case, but the mechanism is unknown in the second case.

Controlling Glycosyl Bond Conformation of Guanine Nucleosides: Stabilization of the anti Conformer in 5'-O-Ethylguanosine.

Nucleosides that consist of base and sugar moieties can adopt two main conformations, syn and anti, about the glycosidic bond. We have investigated the conformational properties of guanine nucleosides in the gas phase by using laser desorption combined with IR-UV double resonance spectroscopy. In guanosine, syn conformation is preferred as a result of internal hydrogen bonding between the 5'-OH group of the sugar and the N3 site of the guanine moiety. We have therefore employed a chemically modified nucleoside 5'-O-ethylguanosine, in which possible glycosyl bond conformations are restricted upon ethylation of the 5'-OH group. The result shows that anti conformer is stabilized by the formation of hydrogen bonding involving the 2'-OH group.

Systolic outward motion of the left ventricular apical wall as detected by magnetic resonance tagging in patients with apical hypertrophic cardiomyopathy.

Patients with apical hypertrophic cardiomyopathy (APH) associated with paradoxic jet flow (ie, diastolic flow away from the apex) may gradually develop an apical aneurysm, which often leads to arrhythmia and mural thrombus formation. We observed systolic outward motion of the left ventricular apical myocardium in patients with APH using a magnetic resonance tagging procedure and examined the relationship of the outward motion to echocardiographic and scintigraphic findings and to cardiac events. Systolic displacement of the myocardial tags of the apical region perpendicular to the long axis in the 4-chamber view was recorded in 31 patients with APH. Of these patients, 14 showed no outward movement of tags (group A), and 17 showed outward movement (group B). In group B, apical hypertrophy was more severe (35 +/- 7 mm vs. 29 +/- 6 mm, p < 0.05), paradoxic jet flow was more frequent (64% vs. 14%, p < 0.05) and the defect score in I-123-beta-methyliodophenylpentadecanoic acid scintigraphy was higher (2.1 +/- 0.7 vs. 1.3 +/- 0.7, p < 0.01). During a mean follow-up period of 55 months, only 1 patient experienced paroxysmal atrial fibrillation in group A. In group B, 1 patient died suddenly, 1 was admitted to hospital because of congestive heart failure, 2 developed angina pectoris, 2 exhibited non-sustained ventricular tachycardia, and 1 showed multifocal premature ventricular contraction; in these 7 patients the outward movement was greater than in the 10 patients in Group B who had no cardiac events (1.00 +/- 0.59 vs. 0.52 +/- 0.40, p < 0.05). Hence, our results show that outward tag displacement is frequently associated with severe apical hypertrophy, paradoxic jet flow, apical ischemia, and cardiac events. The tagging method may be useful in assessing the severity of APH and predicting the occurrence of cardiac events at an early stage.

Novel synthesis and characterization of bioconjugate block copolymers having oligonucleotides.

Novel and efficient synthesis of polymers terminated with nucleotides via the phosphoramidite method has been developed. A hydroxyl-terminated polymer was converted into a polymer capped with a nucleotide in three steps, where the conversion of the reactions was very high, almost 100%. By repetition of this synthetic method, a block copolymer composed of a synthetic polymer, polystyrene, and biological oligonucleotides with thymidine units has been successfully synthesized. A microphase-separated structure of this block copolymer was observed by both transmission electron microscopy and small-angle X-ray scattering, and a cylindrical structure was confirmed.

Is it possible to estimate the enantioselectivity of a chiral catalyst from its racemic mixture?

The evaluation of a racemic catalyst was investigated in the case of oxazaborolidine (OAB)-catalyzed borane reduction of 1,5-diphenyl-1,5-pentanedione, giving the corresponding diol. On the basis of the diastereoselectivity of the diols, it is possible to estimate the enantioselectivity (ee) of the first step, which correlates well with the ee in the reaction of the structurally similar phenyl n-pentyl ketone with enantiopure OAB catalyst. The measure of diastereoselectivity could be a tool for screening racemic catalysts without the need for resolving the individual enantiomers, if in the second step of the process there is no substrate control and no catalyst scrambling.

Internucleotide-linkage formation via the phosphoramidite method using a carboxylic acid as a promoter.

This paper describes utility of a carboxylic acid, such as 2,4-dinitrobenzoic acid, as a promoter for internucleotide-linkage formation via the phosphoramidite method.

Mechanism of asymmetric hydrogenation of alpha-(acylamino)acrylic esters catalyzed by BINAP-ruthenium(II) diacetate.

The mechanism of asymmetric hydrogenation of alpha-(acylamino)acrylic esters with Ru(CH(3)COO)(2)[(S)-binap] (BINAP = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl), giving the S saturated products in >90% ee, has been investigated by means of a kinetic study, deuterium labeling experiments, isotope effect measurements, and NMR and X-ray analysis of certain Ru complexes. The hydrogenation in methanol under a low H2 pressure proceeds via a monohydride-unsaturate mechanism that involves the initial RuH formation followed by a reaction with an olefinic substrate. The migratory insertion in the enamide-RuH chelate complex occurs reversibly and endergonically in an exo manner, giving a five-membered metallacycle intermediate. The cleavage of the Ru-C bond is achieved with either H2 (major) or CH3OH (minor). Both of the pathways result in overall cis hydrogenation products. The hydrogen at C3 is mainly from an H2 molecule, and the C2 hydrogen is from another H2 or protic CH3OH. The major S and minor R enantiomers are produced via the same mechanism involving diastereomeric intermediates. The turnover rate is limited by the step of hydrogenolysis of a half-hydrogenated metallacyclic intermediate. The participation of two different hydrogen donor molecules is in contrast to the pairwise dihydrogenation using a single H2 molecule in the RhI-catalyzed reaction which occurs via a dihydride mechanism. In addition, the sense of asymmetric induction is opposite to that observed with S-BINAP-RhI catalysts. The origin of this phenomenon is interpreted in terms of stereocomplementary models of the enamide/metal chelate complexes. A series of model stoichiometric reactions mimicking the catalytic steps has indicated that most NMR-observable Ru complexes are not directly involved in the catalytic hydrogenation but are reservoirs of real catalytic complexes or even side products that retard the reaction.

Subepicardial aneurysm associated with ventricular septal perforation showing a normal coronary angiogram.

Subepicardial aneurysm is a rare complication of acute myocardial infarction and the present case was associated with ventricular septal perforation. Echocardiography showed the subepicardial aneurysm adjoining the true apico-anteroseptal aneurysm, with the former being discontinuous with the myocardium at its neck, which was narrower than the diameter of the aneurysm. In addition, color Doppler imaging showed shunt flow from the aneurysm to the right ventricle. Coronary angiography revealed extension only of the anterior descending artery without any discernible stenosis. The apical aneurysm was excised and the defect closed with an epicardial patch. The myocardial infarction was probably caused by coronary spasm. Echocardiography was useful for diagnosing the anatomy and hemodynamic condition of the subepicardial aneurysm.

Idiopathic long QT syndrome with early afterdepolarization induced by epinephrine. Acase report.

A patient with idiopathic long QT syndrome had repeated syncopal episodes. The QTc interval on the electrocardiogram at rest was 530 ms and was prolonged by exercise up to 740 ms with T wave alternation. Intravenous epinephrine (0.1 microg/kg weight per min), but not isoproterenol (0.7 microg/min), produced early after depolarization of the monophasic action potential recorded at the right ventricular apex. Epinephrine prolonged the QTc interval to 710 ms. After the addition of propranolol to the epinephrine, the QTc (580 ms) was longer than at baseline. Methoxamine also prolonged the QTc to 580 ms. The QT interval in long QT syndrome is generally considered to be prolonged by a beta-adrenergic effect, but in the present case alpha-adrenergic stimulation had an additional effect on the prolongation of the QT interval.

Echocardiographically documented acute aortic insufficiency induced by Amplatz left guide catheter.

This paper examines a case of sudden systolic pressure fall, tachycardia, low pulse pressure, and high pulmonary artery wedge pressure due to acute aortic insufficiency which was induced by an Amplatz left (AL-1) guide catheter used for better guide support during percutaneous transluminal coronary angioplasty of the right coronary artery. AL guide catheters can cause acute aortic insufficiency, of which practitioners should be aware when sudden hemodynamic collapse occurs.

Fractional flow reserve in a patient with intermediate coronary stenosis and hypertrophic cardiomyopathy.

We discuss the case of a 61-year-old male patient with hypertrophic cardiomyopathy and chest pain on exertion. Coronary angiography and intravascular ultrasound revealed an intermediate stenosis in the proximal site of the left anterior descending artery, while Tc-99m myocardial scintigraphy revealed exercise-induced myocardial ischemia in the anteroseptal wall and apical portion. Flow velocity-derived coronary flow reserve (CFR) and pressure-derived fractional flow reserve (FFRmyo) were both low (1.1 and 0.59), suggesting that the stenosis was functionally significant. Directional coronary atherectomy greatly improved the FFRmyo (0.99), the scintigraphic findings, and anginal pain but did not improve the CFR (1.2). FFRmyo was useful in assessing the functional significance of an equivocal coronary stenosis and its interventional resolution.

A case of cardiomyopathy induced by premature ventricular complexes.

Tachycardia-induced cardiomyopathy is a well-known and reversible condition, but the left ventricular dysfunction caused by frequent isolated premature ventricular complexes (PVCs) has been rarely reported. Apparent dilated cardiomyopathy was resolved in a patient after the focal source of PVCs was eliminated by radiofrequency catheter ablation. Echocardiography showed progressive improvement of the abnormal wall motion. Frequent PVCs could be the cause of left ventricular dysfunction in a subset of patients with dilated cardiomyopathy and radiofrequency ablation should be the choice of therapy in those patients.

Rate-dependent QRS prolongation during exercise testing associated with hyperkalemia.

The present case showed gradual increase of QRS duration from 100 ms up to 180 msec during an ergometer exercise test along with the heart rate increase. After exercise, QRS duration shortened and normalized. Laboratory test showed hyperkalemia (K = 8.0 mEq/l). T1 myocardial scintigraphy revealed exercise-induced transient ischemia in posterolateral region of left ventricle. Coronary angiography showed significant stenosis in the distal portion of left circumflex coronary artery. The increase of QRS duration was possibly due to the combination of hyperkalemia and the effect of mexiletine. The rate dependent blocking effect on sodium channel of mexiletine might be intensified under hyperkalemia.