Investigation of the No-Donor Activity of the Antimicrobial Drug Tinidazole

Pharmaceutical Chemistry Journal -     

Kinetics and Mechanism of Hydrolysis of Efavirenz

Purpose. To determine the kinetics and mechanism of hydrolysis of efavirenz [(S)-6-chloro-4-(cyclopropylethynyl)-1,4-dihydro-4-(trifluoromethyl)-2H-3,1-benzoxazin-2-one] in aqueous solutions. Methods. The solution stability was examined at 60°C and an ionic strength of 0.3 M over the pH range of 0.6 to 12.8. The loss of efavirenz and the appearance of degradants were followed with a reverse-phase high-performance liquid chromatography assay. Characterization of the degradants was accomplished with liquid chromatography-mass spectrometry. Results. The degradation of efavirenz followed apparent first-order kinetics over the pH range of 0.6 to 12.8 at 60°C. The catalytic effect of phosphate and borate buffers was negligible while acetate and citrate demonstrated buffer catalysis. The overall rate constant indicated a pH minimum (the pH of maximum stability) of approximately 4. Mass spectra data identified a degradant with a molecular weight consistent with hydrolysis of the cyclic carbamate to the corresponding amino alcohol. The degradation route was confirmed with spiking experiments with an authentic sample of the amino alcohol indicating that the carbamate hydrolysis pathway was the predominant reaction throughout the pH range studied. Subsequent degradation of the amino alcohol proceeded at the extremes of the pH range studied via rearrangement to the quinoline. Conclusions. The pH-rate profile was consistent with a combination of a V-shaped profile in the pH range of 0-9 and a sigmoid-shaped profile in the pH range of 4-13. The plateau that began at pH 10-11 is a result of the ionization of the amine of the carbamate inhibiting the base-catalyzed hydrolysis of efavirenz, given that the ionized form of the carbamate is resonance-stabilized toward hydroxide-catalyzed degradation. Thus, increasing the pH resulted in a parallel decrease in the unionized fraction and increase in hydroxide ion concentration resulting in a constant k_obs value.     

Kinetics and Mechanism of the Base-Catalyzed Rearrangement and Hydrolysis of Ezetimibe

The pH-rate profile of the pseudo-first-order rate constants for the rearrangement and hydrolysis of Ezetimibe giving (2R,3R,6S)-N,6-bis(4-fluorophenyl)-2-(4-hydroxyphenyl)-3,4,5,6-tetrahydro-2H-pyran-3-carboxamide (2) as the main product at pH of less than 12.5 and the mixture of 2 and 5-(4-fluorophenyl)-5-hydroxy-2-[(4-fluorophenylamino)-(4-hydroxyphenyl)methyl]-pentanoic acid (3) at pH of more than 12.5 in aqueous tertiary amine buffers and in sodium hydroxide solutions at ionic strength I = 0.1 mol L⁻¹ (KCl) and at 39°C is reported. No buffer catalysis was observed and only specific base catalysis is involved. The pH-rate profile is more complex than the pH-rate profiles for the hydrolysis of simple β-lactams and it contains several breaks. Up to pH 9, the log k_obs linearly increases with pH, but between pH 9 and 11 a distinct break downwards occurs and the values of log k_obs slightly decrease with increasing pH of the medium. At pH of approximately 13, another break upwards occurs that corresponds to the formation of compound 3 that is slowly converted to (2R,3R,6S)-6-(4-fluorophenyl)-2-(4-hydroxyphenyl)-3,4,5,6-tetrahydro-2H-pyran-3-carboxylic acid (4). The kinetics of base-catalyzed hydrolysis of structurally similar azetidinone is also discussed. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:2240–2247, 2014     

北五味子提取物碱性水解主要木脂素增量及其优化

采用80％体积分数的乙醇回流提取方法对北五味子活性成分五味子醇甲、五味子酯甲、五味子甲素和五味子乙素进行提取,采用单因素实验考察水解催化剂的影响,确定以氢氧化钠作为催化剂;应用响应面分析对北五味子乙醇提取物碱水解工艺进行了优化,确定用1 mol/L的氢氧化钠15 mL回流水解2h.然后考察了三氯甲烷、1,2-二氯乙烷、乙酸乙酯和石油醚几种溶剂的萃取效果,确定以1,2-二氯乙烷作为70％浸膏溶液的萃取溶剂.北五味子木脂素的有效成分五味子醇甲、五味子酯甲、五味子甲素和五味子乙素含量分别由原来的150.42、44.02、248.30和514.29mg/kg增加到455.96、58.21、397.69和772.09 mg/kg;经验证后总木脂素的回收率可达到165.91％.     

麻黄碱衍生物噁唑烷水解反应动力学参数的光度法测定

用光度法研究了仿生理条件下黄碱（伪麻黄碱）和水杨醛缩合产物恶唑烷的水解反应过程。证实了它们的水解均为一级反应，半衰期分别为34s和8．9s，水解反应速度与它们自身结构相关。     

Hydrolysis of Partially Saturated Egg Phosphatidylcholine in Aqueous Liposome Dispersions and the Effect of Cholesterol Incorporation on Hydrolysis Kinetics

Abstract— Hydrolysis kinetics of partially hydrogenated egg phosphatidylcholine (PHEPC) were studied as a function of pH, temperature, buffer concentration, ionic strength, and the effect of cholesterol incorporation. Results showed that PHEPC has a maximum stability at around pH 6·5. General acid base catalysis was observed for acetate, HEPES and Tris buffers. Increasing the ionic strength of the buffer solutions did not influence the hydrolysis kinetics. The relationship between the observed hydrolysis rate constants and the temperature could adequately be described by the Arrhenius equation. Incorporation of cholesterol did not affect the hydrolysis kinetics. This result indicates that the hydrolysis kinetics of PHEPC do not depend on the changes in bilayer rigidity induced by cholesterol incorporation. Cholesterol is stable under the experimental conditions used in this study; no changes were observed in cholesterol concentration over the experimental time interval.     

Stability of Phenobarbital N-Glucosides: Identification of Hydrolysis Products and Kinetics of Decomposition

The two diastereomers of l-(l--D-glucopyranosyl)phenobarbital, (1A) and (1B), decompose to l-(l--D-glucopyranosyl)-3-(2-ethyl-2-phenylmalonyl)urea (2A or 2B) followed by decarboxylation to l-(l--D-glucopyranosyl)-3-(2-phenylbutyryl)urea (3A and 3B) under physiological conditions of temperature and pH. The sigmoidal pH–rate profile and the Arrhenius parameters indicate that degradation takes place by hydroxide ion attack on the undissociated and monoanion forms of 1A and 1B. The rates of hydrolysis of the nonionized species of 1A and 1B are more than two orders of magnitude faster than those of common 5,5-disubstituted or 1,5,5-trisubstituted barbiturates. Molecular modeling studies suggest that rate enhancement is due to intramolecular hydrogen bonding in the transition state of the C₂ hydroxyl with the tetrahedral hydrated C₆ carbonyl as well as hindered rotation around the N₁–C₁ of phenobarbital and glucose. Based on these studies it is recommended that any data related to the quantitation of 1A and 1B be reevaluated depending on how the samples were collected, stored, and analyzed.     

The Relationship of Diastereomer Hydrolysis Kinetics to Shelf-Life Predictions for Cefuroxime Axetil

Cefuroxime axetil, an ester prodrug of cefuroxime, is comprised of a 50:50 mixture of diastereomers A and B. The first-order hydrolysis kinetics of cefuroxime axetil were investigated as a function of pH, temperature, buffers, and ionic strength. Chromatographically identified hydrolysis products were cefuroxime, ²-cefuroxime axetil, and ,-sulfoxides. Buffer catalysis was observed in acetate and phosphate buffers. No significant kinetic effect was observed for ionic strength in the range µ = 0.1-1.0. The pH–rate profiles for hydrolysis of cefuroxime axetil isomeric mixture were obtained at 45, 35, and 25°C. The equation defining the cefuroxime axetil hydrolysis rate constant as a function of pH was k _obs = k _H(a _H) + k _s + k _OH(K _w/a _H), exhibiting maximal stability in the pH range 3.5 to 5.5. The predicted profile at 5°C was in excellent agreement with experimental data in the pH range 3.6 to 5.5. In the pH range 1 to 9, the maximum difference observed for individual hydrolysis constants of isomers was 27%. Shelf-life estimates based on the hydrolysis rate constants for cefuroxime axetil as an isomeric mixture were shown to be equivalent to those based on individual hydrolysis rate constants for isomers A and B.     

僧帽牡蛎碱性磷酸酶在变性剂作用下构象与催化活力变化的研究

从僧帽牡蛎（Ostrea Cucullata）整体中提取一种经聚丙烯酸胺凝胶电泳鉴定为均一纯的碱性磷酸酶。经不同浓度的胍和脲处理,以荧光光谱为监测手段。研究其变性和大活动力学过程,发现酶的荧光强度随着变性剂浓度的增大而逐渐下降,330.2nm处的吸收峰峰值位置也出现了一定程度的“红移”和“蓝”。测定该酶的失活和变性速度常数发现,不论该酶在胍或脲溶液中变性,其失活速度常数都较其变性速度常数大。呈现出“快失活慢构象变化”的过程。     

人工虫草碱提取物的降血糖作用研究

人工虫草菌丝的碱(1.25 mol·L~(-1)NaOH)提醇沉淀物CsOH(产率2.58％)经纸层析(PPC)和气相层析分析证实为含5种单糖的杂多糖。口服给予CsOH在剂量500、250mg·kg~(-1)时和腹腔给予CsOH在剂量100、50 mg·kg~(-1)时对正常小鼠、四氧嘧啶糖尿病模型小鼠和链脲佐菌素糖尿病模型小鼠均有显著的降血糖作用.且呈现一定的量效关系。     

Prodrugs of Peptides. 11. Chemical and Enzymatic Hydrolysis Kinetics of N-Acyloxymethyl Derivatives of a Peptide-like Bond

Various carboxylic acid esters of the N-hydroxymethyl derivative of N-benzyloxycarbonylglycine benzylamide, used as a peptide-like model, were prepared and their decomposition kinetics studied in aqueous solution and in human plasma solutions. These N-acyloxymethylamide derivatives were found to undergo a facile decomposition by a pH-independent process in the pH range 4–8.5, the half-lives being 1–11hr at 37°C. The cause of this limited stability was suggested to be due to the occurrence of an elimination-addition mechanism involving a reactive N-acyliminium ion intermediate. In alkaline solutions (pH > 10) the derivatives showed a normal ester stability. The ester group in the N-acyloxymethyl derivatives was readily hydrolyzed by plasma enzymes to yield the N-hydroxymethyl amide, which subsequently decomposed to the parent amide. The results obtained suggest that N-acyloxymethylation of a peptide bond may be a useful prodrug approach to obtain derivatives with varying lipophilicities and a ready ability to undergo conversion to the parent peptide in vivo. However, the stability of the derivatives in aqueous solutions is limited.     

In-vivo Activity of Retinoid Esters in Skin is Related to In-vitro Hydrolysis Rate

BMS-181163 (4-acetamidophenyl retinoate, previously reported as BMY-30123), the acetamidophenyl ester of all-trans-retinoic acid (tRA), is topically active in various retinoid-sensitive animal models, but was recently shown to be ineffective for the treatment of acne in patients. To determine whether BMS-181163 functions as a prodrug of tRA in mice but not in man, the relative rates of ester hydrolysis in mouse and human skin homogenates were determined. In-vitro hydrolysis assays showed that BMS-181163 was substantially hydrolysed in mouse skin homogenates and minimally in human skin preparations. In addition, a series of phenyl esters of tRA and several known active synthetic retinoids (Ch-80: (E)-4-[3-oxo-3-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)-1-propenyl] benzoic acid; CD-271: 6-[3-(1-adamantyl)-4-methyoxyphenyl]-2-naphthoic acid; and TTNPB: (E)-4-[2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)-1-propenyl] benzoic acid) was prepared and hydrolysis rates and in-vivo (rhino mouse utriculi reduction) activities were compared. The hydrolysis rates of the six test retinoid phenyl esters, ranging from 0·06 to 2·0 h^?1 were found to correlate with the in-vivo activity. Those esters (BMS-181163 and acetamidophenyl esters of Ch-80 and TTNPB) with a higher hydrolysis rate exhibited in-vivo activity only slightly lower than their parent free acid retinoids. In contrast, the three phenyl esters with a hydrolysis rate less than 0·3 h^?1 were inactive in-vivo. Data from both approaches suggest that the breakdown of the phenyl ester linkage in this series is essential for the respective in-vivo activity and that the active phenyl esters of retinoids function as prodrugs.     

Kinetics of drug decomposition. Part 38. Hydrolysis and autoxidation of sodium phenylbutazone and aminophenazone in binary kinetic system.

The kinetics of hydrolysis and autoxidation of sodium phenylbutazone (PhB-Na) and aminophenazone (APh) was studied in ammonia-acetate, Carmody and Welford buffers at different buffer concentration, pH, ionic strengths and temperatures. The reaction in N2 atmosphere and under a constant O2 pressure, carried out in calibrated ampoules, followed the first order reaction kinetics. The assay of PhB-Na and APh in the presence of their degradation produces was carried out spectrophotometrically in the degraded solutions.     

Potential Improvement in the Shelf Life of Parenterals Using the Prodrug Approach: Bacampicillin and Talampicillin Hydrolysis Kinetics and Utilization Time

The utilization time for a parenteral prodrug solution with a bioavailable fraction of unity was defined as the time during which the total of the prodrug concentration and the drug concentration equals or exceeds 90% of the initial prodrug concentration. This utilization time was calculated as a function of pH, buffer, and temperature using the experimentally determined rate expressions for bacampicillin and talampicillin. The results were compared to the shelf life of ampicillin solutions under identical storage conditions. First-order rate constants were determined for conversion of the prodrugs to ampicillin (k _c), for -lactam degradation of the prodrugs (k _nc), for the overall loss of prodrugs (k _sum), and for -lactam degradation of ampicillin (k _h) in aqueous solutions at 25.0 to 60.0°C, µ = 0.5, in the pH range 0.90 to 8.4. Loss of bacampicillin proceeded primarily by degradation at pH levels below 4 but was due predominantly to conversion at pH levels above 5. Loss of talampicillin was due primarily to conversion throughout the entire pH range. While the prodrug utilization times were approximately twice the shelf life of ampicillin in acidic solutions, ampicillin was significantly better in neutral solutions. The results illustrate the potential for increased prodrug storage periods when utilization time is defined on the basis of the bioactivity rather than on the prodrug concentration alone.