Voltammetric sensor for tinidazole based on poly(carmine) film-modified electrode and its application

A poly(carmine) film-modified glassy carbon electrode (GCE) was fabricated and the electrochemical behavior of tinidazole at the modified electrode was investigated by electrochemical methods. A well-defined reduction peak was observed at 0.61 V and was applied for the determination of tinidazole. Compared with that at a bare GCE, the reduction peak potential of tinidazole shifted negatively and the reduction peak current increased significantly. The influences of some parameters on the reduction of tinidazole were also examined. Based on the experimental data, a possible mechanism was proposed for the electrochemical reaction of tinidazole at the modified electrode. It was found that the reduction peak current was proportional to the concentration of tinidazole in the range from 1.0 x 10(-7) to 5.0 x 10(-5)mol L(-1). The detection limit was about 1.0 x 10(-8)mol L(-1) after accumulation 90 s at a constant potential of 0.0 V. The proposed method was applied to determine tinidazole in drugs and the result was satisfied.     

Reactive sulfur species: kinetics and mechanism of the hydrolysis of cysteine thiosulfinate ester

The kinetics and mechanisms of the hydrolysis of cysteine thiosulfinate ester (CyS(O)SCy ( x- ), x = 0-2) have been investigated by stopped-flow spectrophotometry between pH 6 and pH 14. The rate-limiting reaction of hydroxide is observed for pH < 13. More complicated kinetics are observed above pH 13, where the hydrolysis of CyS(O)SCy (2-) can be fast relative to subsequent reactions. The eventual products of hydrolysis are a 1:1 molar ratio of cystine (CySSCy) and cysteine sulfinic acid (CySO 2H) under all reaction conditions. The rate of hydrolysis is dependent upon the proton state of CyS(O)SCy ( x- ). Furthermore, cysteine thiosulfonate ester (CyS(O) 2SCy) was observed as an intermediate during the hydrolysis of CyS(O)SCy ( x- ) at lower pH. CyS(O) 2SCy eventually hydrolyzes to give stoichiometric amounts of CySSCy and CySO 2H. However, CySO 2H is observed under some conditions for which hydrolysis of CyS(O) 2SCy is relatively slow, thus suggesting multiple hydrolysis pathways for CyS(O)SCy ( x- ). The mechanism up to the rate-limiting step is proposed to be as follows: CyS(O)SCy (0) = H (+) + CyS(O)SCy (-), p K a3 = 7.32; CyS(O)SCy (-) = H (+) + CyS(O)SCy (2-), p K a4 = 7.92; CyS(O)SCy (0) + OH (-) --> products, P 0 k 0 = (5.0 +/- 0.01) x 10 (3) M (-1) s (-1); CyS(O)SCy (-) + OH (-) --> products, P 1 k 1 = 60 +/- 18 M (-1) s (-1); and CyS(O)SCy (2-) + OH (-) --> products, P 2 k 2 = 0.36 +/- 0.01 M (-1) s (-1), where P x is a constant (1 相似文献   

Enzymatic hydrolysis of 7-phenylacetamidodesacetoxycephalosporanic acid by immobilized penicillin G acylase

Enzymatic parameters such as pH, temperature and substrate concentration were studied for the hydrolysis of 7-PADCA by penicillin G acylase. Optimum pH and temperature were 8.0 and 50 degrees C, respectively. Km value of soluble and immobilized enzyme for 7-PADCA was 2.3 x 10(-5) M and 7.5 x 10(-5) M, respectively. At 7-PADCA concentration of 5% and an IME: 7-PADCA ratio of 1:2.5, the hydrolysis was complete in 110 min.     

The voltammetric behavior of nizatidine and its determination in biological fluids

The voltammetric behavior of nizatidine (a newly introduced antiulcer drug) was studied using direct current (DCt), alternating current and differential pulse polarography (DPP). Well-defined cathodic waves were obtained over the whole pH range in Britton-Robinson buffers, in addition to 0.1 and 1 M HCl media. The main reduction wave was characterized as being irreversible and diffusion-controlled, although adsorption phenomena played a limited role in the electrode process. The current-concentration relationship was found to be rectilinear over the range 1x10(-5)-6x10(-4) and 2x10-6) -2x10(-4) M using DCt and DPP modes respectively, with a minimum detectability (S/N = 2) of 2x10(-7) M using the latter technique. The number of electrons involved in the reduction process was established, and the mechanism of electrode reaction was verified. The proposed method was successfully applied to determination of nizatidine in spiked human plasma and urine and the percentage recoveries were 96.12+/-0.40 and 97.12+/-0.17, respectively.     

Epimer interconversion, isomerization, and hydrolysis of tetrahydrouridine: implications for cytidine deaminase inhibition

Tetrahydrouridine (THU) is an inhibitor of cytidine deaminase (CDA), the enzyme responsible for the deactivation of ara-C and other cytidine analogues in vivo, and therefore is capable of improving the therapeutic efficacy of these antitumor agents. In aqueous solution formulations, THU exists as a mixture of epimers differing in stereochemistry of the 4-OH substituent. The aims of this study were to investigate the interconversion kinetics of the epimers of THU, the CDA inhibitory effects of these epimers, and the stability and degradation mechanisms of THU epimer mixtures in aqueous solution with the ultimate goal of developing optimal conditions for a parenteral formulation of THU. A stability indicating HPLC assay utilizing a derivatized beta-cyclodextrin column was developed to separate the two epimers of THU and to monitor their reversible isomerization to their beta-ribopyranosyl counterparts and their hydrolysis to form N-glycosidic bond cleavage products. MS and one- and two-dimensional (1)H- and (13)C-NMR measurements were conducted to identify THU epimers and degradation products and to quantitatively model the degradation kinetics. The interconversion reaction between the two THU epimers is acid catalyzed with a first-order rate constant for conversion of epimer 1(1) to epimer 1(2) of (7.4 +/- 0.3) x 10(-3) h(-1) and an equilibrium constant ([1(2)]/[1(1)] of 1.7 +/- 0.1 at pH 7.4 and 25 degrees C. Epimer interconversion was therefore sufficiently slow at pH 7.4 to allow the isolation of each and evaluation of their CDA inhibitory activities utilizing 1% (w/v) mouse kidney homogenates as a source for cytidine deaminase and cytidine as a substrate. Inhibition constants for the two THU epimers (1(1) and 1(2)) were determined to be 8 +/- 1 x 10(-7) M and 6.2 +/- 0.2 x 10(-8) M, respectively. Studies at elevated temperature suggested that THU degradation from epimer mixtures is biphasic with the initial rate of disappearance being acid catalyzed and first order in initial THU concentration, thus ruling out dimerization as a potential reaction mechanism. NMR/MS analyses revealed that the major degradation products included the beta-ribopyranosyl THU isomers (two epimers), the reduced pyrimidinone base (tetrahydrouracil), and various anomers of D-ribose formed through N-glycosidic bond cleavage, and the products of subsequent reactions of the base. Kinetic modeling of the data obtained from both HPLC and NMR measurements indicated that in an acidic solution THU beta-ribofuranosyl --> beta-ribopyranosyl isomerization is a rapid equilibrium reaction, which proceeds through an intermediate observable in 1H-NMR, and is followed by slower N-glycosidic bond hydrolysis. All the reactions between THU, its ribopyranosyl isomers, the intermediate, and the base are acid catalyzed and appear to proceed through the same sugar ring-opened intermediate (carbinolamine), consistent with previous literature.     

Voltammetric study of danazol and its determination in capsules and spiked biological fluids

The voltammetric behaviour of danazol DZ (antigonadotropin) was studied using cyclic voltammetry, direct current, differential pulse polarography (DPP) and alternating current polarography. Danazol exhibited irreversible cathodic waves over the pH range of 1-5 in Britton Robinson buffers. At pH 1 (the analytical pH), a well-defined wave with E1/2 of -1.04 V versus Ag/AgCl reference electrode was obtained. The diffusion current constant (Id) was 4.8+/-0.14 microA.L.m mole(-1) and the current-concentration plot was rectilinear over the range from 5 x 10(-6) to 1 x 10(-4) M with correlation coefficient (n = 11) of 0.995. The calculated detection limit was 1 x 10(-6) M using the DPP mode. The wave was characterized as being irreversible, diffusion-controlled although adsorption phenomenon played a limited role in the electrode process. The proposed method was applied to commercial capsules and the average percentage recovery was in agreement with that obtained by the official USP method. The method was extended to the in vitro determination of DZ in spiked human urine and plasma samples, the percentage recoveries were 96+/-4 and 97+/-5, respectively. A proposal of the electrode reaction was postulated.     

Degradation kinetics and mechanisms of moricizine hydrochloride in acidic medium.

The degradation kinetics of moricizine hydrochloride (1) were examined over a pH range of 0.6 to 6.0 at an ionic strength of 0.3 and 60 degrees C. The disappearance of intact 1 was followed by a stability-indicating HPLC assay. The degradation products, which had approximate solubilities of less than 100 micrograms/mL, precipitated in aqueous solution. The precipitate was collected for HPLC analysis and identification of degradation products. Degradation of 1 was catalyzed by acetate and phosphate buffers and was pH dependent, with the pH of the minimum rate constant located between 2.8 and 3.2. At pH 0.6-2.0, 1 degraded via amide hydrolysis to yield first ethyl (10H-phenothiazin-2-yl) carbamate (2), an amide hydrolysis product, which further oxidized in parallel to give ethyl (3-oxo-3H-phenothiazin-2-yl) carbamate (3), ethyl (10H-phenothiazin-2-yl) carbamate S-oxide (4), and diethyl (3,10'-bi-10H-phenothiazine-2,2'-diyl)bis(carbamate) (5), the dimer of the amide hydrolysis product. At pH 2.2-6.0, 1 degraded via a reverse Mannich reaction, to form the reverse Mannich product ethyl [10-(1-oxo-2-propenyl)-10H-phenothiazin-2-yl] carbamate (6), and by parallel reaction via the described amide hydrolysis pathway. The dimer of the amide hydrolysis product was not detectable at pH greater than 2.8. At pH greater than 4.0, the reverse Mannich product was the predominant degradation product. Degradation of 1 was subject to positive and negative kinetic salt effects at pH 1.0 and 4.0, respectively. Arrhenius plots determined at pH 1.0 and 6.0 were linear between 37 and 70 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)     

In-vitro hydrolysis, permeability, and ocular uptake of prodrugs of N-[4-(benzoylamino)phenylsulfonyl]glycine, a novel aldose reductase inhibitor

To enhance the ocular uptake of N-[4-(benzoylamino)phenylsulfonyl]glycine (BAPSG), two ester (methyl and isopropyl) prodrugs were synthesized and evaluated for their stability in various buffers (pH 1-9), hydrolysis in rabbit ocular tissues (cornea, conjunctiva, iris-ciliary body, lens, aqueous humor, and vitreous humor), transport across cornea and conjunctiva, and in-vivo uptake following topical administration. Over the pH range of 1-9, the rate constants for degradation ranged from 5.67 to 218.9 x 10(-3) h(-1) for the methyl ester and from 3.14 to 4.45 x 10(-3) h(-1) for the isopropyl ester. At all pH conditions, the isopropyl ester was more stable when compared with the methyl ester. A change in buffer concentration at pH 7.4 did not influence the stability of the prodrugs. The prodrugs were rapidly hydrolysed in the tissue homogenates, with the rate constants for hydrolysis ranging from 1.98 to 7.2x 10(-3) min(-1) for the methyl ester and 3.32 to 6.53 x 10(-3) min(-1) for the isopropyl ester. The in-vitro permeability of the methyl ester was less than the parent drug across cornea and conjunctiva. Isopropyl ester levels were not detectable in the receiver chamber even at the end of the 4-h transport study. Following topical administration of BAPSG and the two prodrugs at a dose of 60 microg/eye, the lowest levels were seen in vitreous humor for parent compound and its methyl ester. In general, the tissue uptake of methyl ester was less than BAPSG. Isopropyl ester levels were below detection limits in all the ocular tissues. Lipophilic ester prodrugs of BAPSG showed good aqueous solution stability in tissue homogenates. However, these prodrugs lacking the free carboxylate anion exhibited reduced in-vitro permeability and in-vivo uptake, suggesting the importance of free carboxylate anion in the delivery of BAPSG.     

Interaction of tetrahydroaminoacridine with acetylcholinesterase and butyrylcholinesterase.

This paper examines inhibition of acetylcholinesterase (AchE) and butyrylcholinesterase (BuchE) by tetrahydroaminoacridine (THA), an acridine analog under consideration for palliative treatment of Alzheimer's dementia. THA causes linear mixed inhibition of AchE hydrolysis of acetylthiocholine, a cationic substrate (KI = 3.8 x 10(-9) M), and linear competitive inhibition of AchE hydrolysis of 7-acetoxy-4-methylcoumarin, an uncharged substrate (KI = 6.8 x 10(-9) M), and N-methyl-7-dimethylcarbamoxyquinolinium, a cationic carbamate (KI = 1.5 x 10(-8) M). Propidium association with AchE in the presence of saturating concentrations of THA is characterized by a dissociation constant of 7.7 +/- 0.7 x 10(-6) M, a value within 2-fold of the dissociation constant in the absence of THA. Association of THA with AchE is, therefore, not mutually exclusive with association of propidium at the peripheral anionic site. Moreover, THA causes dissociation of decidium complexes with AchE at concentrations compatible with a dissociation constant of 7.0 +/- 0.4 x 10(-9) M. Similar relationships were observed for THA inhibition of BuchE hydrolysis of butyrylthiocholine (KI = 2.5 x 10(-8) M) and dissociation of decidium complexes with BuchE (KD = 1.9 +/- 0.1 x 10(-8) M). These kinetic and equilibrium data uniformly indicate that THA associates with AchE and BuchE with high affinity and that the subsequent inhibition comes about through ligand association at the active center rather than at a peripheral site. The noncompetitive component of inhibition reflects association of THA with the acyl-enzyme intermediate, with subsequent effects on the rate of deacylation.     

Polarographic behavior and determination of finasteride

The polarographic behavior of finasteride at the dropping mercury electrode (DME) was studied adopting direct current (DC(t)), alternating current (AC(t)) and differential-pulse polarography (DPP) modes. In Britton-Robinson buffer (BRb), finasteride exhibited cathodic waves over the pH range 6-12. At pH 10, a well-defined cathodic wave was obtained. The latter could be characterized as being irreversible, diffusion-controlled and partially affected by adsorption phenomenon. The number of electrons involved in the reduction process was accomplished and a proposal of the electrode reaction was presented. The current-concentration plots were rectilinear over the ranges 8-40 and 2-30 microg ml(-1) using DC(t) and DPP modes, respectively. The minimum delectability was 0.2 microg ml(-1) (5.4 x 10(-7) M), for the latter. The proposed method was successfully applied to the determination of finasteride in its commercial capsules and the results obtained were in good agreement with those given with a reference method.     

Determination of the rate constants and activation energy of acetaminophen hydrolysis by capillary electrophoresis

A method based on capillary electrophoresis with electrochemical detection (CE-ED) was developed for the simultaneous determination of p-aminophenol and acetaminophen in the hydrolysates of acetaminophen. Effects of several important factors such as the acidity and concentration of running buffer, separation voltage, injection time, and working potential were investigated to acquire the optimum conditions. The detection electrode was a 300 microm carbon disc electrode at a working potential of +0.80 V (versus SCE). The two analytes can be well separated within 6 min in a 50 cm length fused silica capillary at a separation voltage of 18 kV in a 25 mM phosphate buffer (pH 6.5). The rate constants of acetaminophen hydrolysis in 0.5 M HCl at different temperatures were determined by monitoring the concentration changes of acetaminophen. At 70, 80, 90 and 100 degrees C, the measured rate constants of acetaminophen hydrolysis were 5.027 x 10(-3), 8.522 x 10(-3), 18.60 x 10(-3) and 32.76 x 10(-3) min(-1), respectively. The activation energy for acetaminophen hydrolysis was calculated to be 68.13 kJ mol(-1), which is in good agreement with the value in the literature.     

Voltammetric determination of montelukast sodium in dosage forms and human plasma

The voltammetric behaviour of montelukast (MKST) was studied using cyclic voltammetry, direct current (DCt), differential pulse polarography (DPP) and alternating current (ACt) polarography. MKST exhibited well-defined cathodic waves over the range pH range 1-5. No anodic waves were produced over the same pH range. At pH 1, the analytical pH; the diffusion current constant (Id) was 2.2+/-0.01 microA l mmol-1. The current concentration plot was rectilinear over the range 2-20 microg ml-1 with correlation coefficient (n=10) of 0.9943. The lower limit of detection (S/N=2) was 0.2 microg ml-1 (3.41x10(-7) M). The wave has been characterised as being diffusion-controlled, although adsorption phenomenon played a limited role in the electrode reaction. The proposed method was successfully applied to the determination of MKST in commercial tablets, and results were in agreement with those given with a reference HPLC method. The method was further extended to the in vitro determination of the drug in spiked human plasma. The mean % recovery (n=5) was 101.38+/-3.85. The number of electrons transferred in the reduction process could be accomplished and a proposal of the electrode reaction was proposed.     

Voltammetric analysis of certain 4-quinolones in pharmaceuticals and biological fluids

The voltammetric behaviour of Enrofloxacin (I), Sparfloxacin (II) and Fleroxacin (III) was studied using direct current (DCt), differential pulse (DPP) and alternating current (ACt). All the drugs manifest cathodic waves in Britton Robinson buffer over the pH range of 4.0-11.98. The waves were characterized as being irreversible, diffusion-controlled with limited adsorption properties. The diffusion current concentration relationships were found to be rectilinear over the ranges 4 x 10(-5) x 10(-4) M, 1 x 10(-5)-2 x 10(-4) M, 1 x 10(-5)-4 x 10(-4) M using DCt mode for I, II and III, respectively and 1 x 10(-6)-4 x 10(-5) M, 1 x 10(-6)-1 x 10(-4) M, and 2 x 10(-6)-8 x 10(-5) M, using DPP mode for I, II and III respectively, with minimum detectability (S/N = 3) of 1 x 10(-7) M for I, II and 2 x 10(-7) M for III. The proposed method was successfully applied to the determination of the studied compounds either per se or in formulations and biological fluids. The results obtained were concordant to those given using reference methods.     

拉氧头孢钠的极谱行为及其痕量测定方法

在HCI-KCI（ｐＨ1～2）介质中，用循环伏安和示差脉冲极谱（ＤＰＰ）等电化学方法研究了拉氧头孢钠（噻吗灵）的电极反应机理，并建立了用ＤＰＰ测定的新方法。其峰电位为-0.62V（ｖｓＡｇ/ＡｇＣｌ），峰电流与拉氧头孢钠浓度在1×10^-8～5×10^-6ｍｏｌ·Ｌ^-1（富集时间t_ac＝９０ｓ），5×10^-6～5×10^-5ｍｏｌ·Ｌ^-1（t_ac＝７０ｓ），5×10^-5～８×１０^-4ｍｏｌ·Ｌ^-1（t_ac＝30ｓ）范围内成线性关系。检测限为４×１０^-9ｍｏｌ·Ｌ^-1（t_ac＝９０ｓ）。本法可用于注射剂中该物质的测定，同时也探讨了直接测定尿中拉氧头孢钠的可能性。     

Kinetics and mechanistic studies of the hydrolysis of diisocyanate-derived bis-thiocarbamates of cysteine methyl ester

Diisocyanates (dNCOs) are the most commonly reported cause of chemically induced occupational asthma, but the ultimate antigenic form is unknown. Reactions of the three most common monomeric dNCOs, hexamethylene dNCO (HDI), methylene diphenylisocyanate (MDI), and toluene dNCO (TDI), with cysteine methyl ester (CME) gave the corresponding bis-dithiocarbamates (HDI-CME, TDI-CME, and MDI-CME). The dissociation kinetics of these bis-thiocarbamates, in aqueous conditions, was followed spectrophotometrically under varying pH and temperature conditions. Reaction of the adducts with methylamine or human serum albumin (HSA) produced diurea, monourea, and diamine products, and this was consistent with the base-catalyzed elimination reaction (E1cB) pathway being the dominant, but not exclusive, dissociation mechanism. The hydrolysis of the adducts was first-order with respect to OH(-) concentration and overall second-order (HDI-CME, k = 3.36 x 10(2) M(-)(1) min(-)(1); TDI-CME, k = 2.49 x 10(4) M(-)(1) min(-)(1); and MDI-CME, k = 5.78 x 10(4) M(-)(1) min(-)(1) at pH 7.4) with deviation from second-order when the dNCO had an aromatic functional group. Arrhenius plots gave activation energies (HDI-CME, E(a) = 70.6 kJ/mol; TDI-CME, E(a) = 46.1 kJ/mol; and MDI-CME, E(a) = 44.5 kJ/mol) that were consistent with the following order of stability: HDI-CME > TDI-CME > MDI-CME. Therefore, the stability of different dNCO-derived thiocarbamates in aqueous environments can vary greatly. Thiocarbamate dissociation rates and type of products formed may potentially influence antigenicity and subsequent hypersensitivity/toxic reactions following dNCO exposures.     

Degradation of busulfan in aqueous solution

The influence of pH, phosphate buffer components and temperature on the degradation rate of busulfan was studied. The analysis was performed using gas chromatography with electron capture detection and reversed-phase liquid chromatography with radioactivity monitoring. The degradation rate of busulfan showed no pH dependence in the range pH 1.5-11 and increased at higher pH values. The degradation rate constant was 0.034 +/- 0.001 h(-1) (S.E.M.) for the degradation of busulfan in pure water and 0.45 +/- 0.01 h(-1)M(-1) (S.E.M.) for the reaction of busulfan with the hydroxide ion at 37 degrees C. The reactivity of HPO(4)(-2) was six times higher than the reactivity of H(2)PO(4)(-1) towards busulfan. The hydrolysis products were identified as tetrahydrofuran and methanesulphonic acid by nuclear magnetic resonance spectroscopy.     

Dependence of hydrolysis of beta-lactams with a zinc(II)-beta-lactamase produced from Serratia marcescens (IMP-1) on pH and concentration of zinc(II) ion: dissociation of Zn(II) from IMP-1 in acidic medium

The pH dependence for the hydrolysis of beta-lactam antibiotics by a metallo-beta-lactamase (IMP-1) produced from Serratia marcescens was investigated varying the concentration of Zn(II). The activity of IMP-1 for imipenem was decreased at pH less than pH 5.3 without external addition of Zn(II) ions but was recovered with addition of Zn(II). Varying the concentration of external Zn(II), the molar activity of the enzyme, k(obs), that was defined by the velocity of hydrolysis of imipenem/concentration of IMP-1 was expressed by k(obs)=v(init)/[E](T)=k(max)[Zn]/(K(d)+[Zn]) in which K(d) stands for the dissociation constant between Zn(II) and IMP-1. The dissociation constants, K(d), vary with pH; K(d)=840 x 10(-6) M at pH 4.3 and K(d)=0.19 x 10(-6) M at pH 6.0. The plot of -log K(d) against pH showed a straight line having a slope of 4.0 below pH 5.0, showing the existence of four functional groups which may be protonated upon dissociation of Zn(II) ion(s). The k(cat), K(m), and k(cat)/K(m) of hydrolysis of imipenem and cephalothin in the presence of sufficient concentration of Zn(NO(3))(2) for saturation of IMP-1 with Zn(II) showed similar dependency to each other on pH between pH 6.0 and 9.0.     

Comparative studies of (--)-, (+/-)-propranolol, atenolol, guanethidine, bretylium and tetracaine on adrenergic transmission.

1 Effects of (--)-, (+/-)-, and (+)-propranolol, atenolol, guanethidine, bretylium and tetracaine were studied on relaxation responses of rabbit ileum and contractile responses of rabbit pulmonary artery and guinea-pig vas deferens to electrical nerve stimulation (2 to 50 Hz). 2 In the ileum, inhibition by tetracaine 3.3 x 10(-6) M occurred at high frequencies of stimulation, while bretylium 1.2 x 10(-4) M and guanethidine 2 x 10(-5) M inhibited responses at all frequencies, the latter producing greater inhibition at low frequencies. 3 (+/-)-Propranolol 10(-5) M produced a tetracaine-type inhibition after 1 h and a bretylium-pattern after 2 h in the ilea and pulmonary arteries and a transition from bretylium- to guanethidine-pattern in the vas deferens, while atenolol 2 x 10(-5) to 10(-4) M produced guanethidine-type inhibition in all preparations. 4 (--)-, (+/-)-, and (+)-Propranolol 3 x 10(-6) to 3.3 x 10(-5) M were equipotent in the vas deferens and ileum. However, inhibition by (--)-propranolol 3.3 x 10(-5) M persisted in the ileum, while that by the (+)-isomer was partially restored by washing. 5 (--)- or (+)-Propranolol 3.3 x 10(-5) M or atenolol 2 x 10(-5) M did not inhibit relaxation of the ileum after the bath temperature was maintained at 4 degrees C for 2 h during drug application. 6 In conclusion, propranolol and atenolol both have gradually developing guanethidine-like adrenergic neurone blocking actions.     

Adenosine 5'-O-(1-boranotriphosphate) derivatives as novel P2Y(1) receptor agonists

P2-receptors (P2-Rs) represent important targets for novel drug development. Most ATP analogues proposed as potential drug candidates have shortcomings such as limited receptor-selectivity and limited stability that justify the search for new P2-R agonists. Therefore, a novel series of nucleotides based on the adenosine 5'-O-(1-boranotriphosphate) (ATP-alpha-B) scaffold was developed and tested as P2Y(1)-R agonists. An efficient four-step one-pot synthesis of several ATP-alpha-B analogues from the corresponding nucleosides was developed, as well as a facile method for the separation of the diastereoisomers (A and B isomers) of the chiral products. The potency of the new analogues as P2Y(1)-R agonists was evaluated by the agonist-induced Ca2+ release of HEK 293 cells stably transfected with rat-brain P2Y(1)-R. ATP-alpha-B A isomer was equipotent with ATP (EC50 = 2 x 10(-7) M). However, 2-MeS- and 2-Cl- substitutions on ATP-alpha-B (A isomer) increased the potency of the agonist up to 100-fold, with EC50 values of 4.5 x 10(-9) and 3.6 x 10(-9) M, compared to that of the ATP-alpha-B (A isomer). Diastereoisomers A of all ATP-alpha-B analogues were more potent in inducing Ca2+ release than the corresponding B counterparts, with a 20-fold difference for 2-MeS-ATP-alpha-B analogues. The chemical stability of the new P2Y(1)-R agonists was evaluated by 31P NMR under physiological and gastric-juice pH values at 37 degrees C, with rates of hydrolysis of 2-MeS-ATP-alpha-B of 1.38 x 10(-7) s-1 (t1/2 of 1395 h) and 3.24 x 10(-5) s-1 (t1/2 = 5.9 h), respectively. The enzymatic stability of the new analogues toward spleen NTPDase was evaluated. Most of the new analogues were poor substrates for the NTPDase, with ATP-alpha-B (A isomer) hydrolysis being 5% of the hydrolysis rate of ATP. Diastereoisomers A and B exhibited different stability, with A isomers being significantly more stable, up to 9-fold. Furthermore, A isomers that are potent P2Y(1)-R agonists barely interact with NTPDase, thus exhibiting protein selectivity. Therefore, on the basis of our findings, the new, highly water-soluble, P2Y(1)-R agonists may be considered as potentially promising drug candidates.     

Determination of the antihyperlipidemic simvastatin by various voltammetric techniques in tablets and serum samples

The electrochemical behavior and determination of simvastatin (SMV), a lipid-lowering drug, were studied in aqueous alcohol medium at a stationary glassy carbon electrode. Cyclic voltammetry studies showed one main, well-defined, sharp oxidation peak between pH 2 and 8. The oxidation was irreversible and exhibited a diffusion controlled mechanism. Differential pulse and square wave voltammetric methods for the quantitative determination of SMV in pharmaceutical dosage forms and spiked serum samples were developed based on the linear relationship between the peak current and the concentration. Differential pulse and square wave voltammetric techniques for the determination of SMV in 0.1 M H2SO4 and a constant amount of methanol (20%), which allow quantitation over the 2 x 10(-6)-1 x 10(-4) M range in supporting electrolyte with a detection limit of 2.71 x 10(-7) M and 5.50 x 10(-7) M for differential pulse and square wave voltammetric methods, respectively, are proposed. The repeatability and reproducibility of the methods were determined. Precision and accuracy were also checked. These methods were used for the determination of SMV in tablets. The standard addition method was used in biological media. No electroactive interferences from endogenous substances and excipients were found in biological fluids and pharmaceutical dosage forms, respectively.