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.     

Alkaline Hydrolysis Kinetics and No-Donor Activity of Tenonitrozole

The kinetics of alkaline hydrolysis of N-(5-nitro-2-thiazolyl)-2-thiophenylcarboxamide (tenonitrozole or atrican) has been studied by photometric and polarographic techniques, and the thermodynamic parameters in the intermediate state of this process were determined. A mechanism explaining the nitric oxide (NO) production during the hydrolytic decomposition of tenonitrozole is proposed. It is suggested that the antiprotozoal and antimicrobial activity of this drug under anaerobic conditions is related to the formation of nitro radical anions and NO. Under aerobic and microaerophilic conditions, the hydrolysis of tenonitrozole may lead to the formation of a peroxynitrite anion, which is a strong cytotoxic agent. __________ Translated from Khimiko-Farmatsevticheskii Zhurnal, Vol. 39, No. 6, pp. 15 – 18, June, 2005.     

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.     

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。     

Ezetimibe的合成

(4S)-3-[(5S)-5-(4-氟苯基)-5-羟基-1-氧代戊基]-4-苯基-2-(?)唑烷酮与4-(4-氟苯基亚氨基)甲酚缩合后再经环合、脱硅烷保护得ezetimibe。前一中间体可以氟苯为原料,与戊二酸酐经付-克反应得到的5-(4-氟苯基)-5-氧代戊酸,与特戊酰氯缩合得到混合酸酐,再与(4S)-4-苯基-2-(?)唑烷酮缩合得(4S)-3-[5-(4-氟苯基)-1,5-二氧代戊基]-4-苯基-2-(?)唑烷酮,经(3αR)-1-甲基-3,3-二苯基-1H,3H-四氢吡咯并[1,2-c][1.3.2](?)唑硼烷[(R)-MeCBS]／BH3·S(CH3)2催化还原制得。总收率24％。     

依折麦布的合成

对氟苯甲醛经Wittig反应和水解反应得到(Z)-5-(4-氟苯基)-4-戊烯酸(3),与(S)-4-苯基-2-噁唑烷酮(4)缩合、N-[4-(苄氧基)苯亚甲基]-4-氟苯胺(6)加成后,在N,O-双(三甲基硅烷基)乙酰胺和氟化四正丁铵三水合物的作用下环合,经Shi氧化得到(3R,4S)-4-[4-(苄氧基)苯基]-1-(4-氟苯基)-3-[[(2S,3R)-3-(4-氟苯基)-2-环氧基]甲基]-2-氮杂环丁酮(10),再经二苯联硒开环、钯炭催化氢化得到胆固醇吸收抑制剂依折麦布,总收率约7％,(S)-羟基de值大于99％.     

Ezetimibe and vascular inflammation

Atherosclerosis is an inflammation-based complex vascular disorder which causes coronary artery disease, stroke and peripheral artery disease. Its pathophysiological process consists of endothelial dysfunction, monocyte adhesion to endothelial cells, lipid and inflammatory cell accumulation in the vascular wall, and migration and proliferation of smooth muscle cells. Both hyperlipidemia and inflammation are profoundly involved in each step. Cholesterol lowering by HMG-CoA reductase (statin) is beneficial for treating atherosclerotic coronary artery disease and stroke, together with reducing a surrogate-marker of inflammation, C-reactive protein (CRP). Another recently established cholesterol lowering tool using an intestinal cholesterol absorption inhibitor, ezetimibe, has been applied for clinical treatment of hypercholesterolemia for several reasons. First, hypercholesterolemia is associated with increased intestinal cholesterol absorption. Second, low cholesterol absorption prevents cardiovascular events. Third, cholesterol metabolism analysis provides evidence that the long-term use of statin increases cholesterol absorption. In terms of low-density lipoprotein cholesterol (LDL-C) and CRP reductions, the more powerful effect of ezetimibe has been seen when the agent is combined with statins. However, the effect of ezetimibe monotherapy on CRP reduction has not been well defined. This review provides information on recently described clinical trials of ezetimibe monotherapy, stain monotherapy, and combined therapy for LDL-C lowering and vascular inflammation.     

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.     

Ezetimibe and vascular endothelial function

Hypercholesterolemia is a major risk factor for cardiovascular diseases that has been managed mostly with 3-hydroxy-3-methyl glutaryl coenzyme A reductase inhibitors (statins) that suppress de novo cholesterol synthesis in the liver. Statins also have beneficial pleiotropic effects on the atherosclerotic process that are independent of their ability to lower lipid values. However, the levels of low-density lipoprotein cholesterol (LDL-C) in most hypercholesterolemic patients at high risk for cardiovascular disease do not reach the goals proposed by guidelines even when prescribed with statins. Ezetimibe is a new lipid-lowering agent that blocks the intestinal absorption of dietary and biliary cholesterol and reduces LDL-C levels, especially when combined with statins. However, its effect on cardiovascular events remains unknown. We reviewed the effects of ezetimibe on cardiovascular diseases, in particular, vascular endothelial function, which is initially impaired during the atherogenetic process and is an important predictor of cardiovascular events. The simultaneous inhibition of cholesterol synthesis by statin and of cholesterol absorption by ezetimibe might retard the atherogenetic process. These effects are considered to be mainly mediated by lipid lowering. However, further studies should elucidate the mechanism of the anti-atherosclerotic effects induced by ezetimibe; for instance, whether or not it directly affects atherogenesis independently from its lipid-lowering effects.     

Mechanism and Kinetics of Punch Sticking of Pharmaceuticals

Adherence of powder onto tablet tooling, known as punch sticking, is one of the tablet manufacturing problems that need to be resolved. An important step toward the resolution of this problem is to quantify sticking propensity of different active pharmaceutical ingredients (APIs) and understand physicochemical factors that influence sticking propensity. In this study, mass of adhered material onto a removable upper punch tip as a function of number of compression is used to monitor sticking kinetics of 24 chemically diverse compounds. We have identified a mathematical model suitable for describing punch sticking kinetics of a wide range of compounds. Chemical analyses have revealed significant enrichment of API content in the adhered mass. Based on this large set of data, we have successfully developed a new punch sticking model based on a consideration of the interplay of interaction strength among API, excipient, and punch surface. The model correctly describes the general shape of sticking profile, that is, initial rise in accumulated mass followed by gradual increase to a plateau. It also explains why sometimes sticking is arrested after monolayer coverage of punch surface by API (punch filming), while in other cases, API buildup is observed beyond monolayer coverage.     

Kinetics and Mechanism of Isomerization of Cyclosporin A

The kinetics of isomerization of cyclosporin A to isocyclosporin A were studied in various nonaqueous solvents as a function of temperature and added methanesulfonic acid. The rate of isomerization was found to be acid-catalyzed over the acid concentration range studied. The choice of organic solvent significantly altered the rate of isomerization. For a series of alcohols, the rate was enhanced with increasing dielectric constant of the media, however, this correlation did not hold upon introduction of the dipolar aprotic solvent, tetrahydrofuran. Conversion of cyclosporin A to isocyclosporin A in tetrahydrofuran was found to contain diminished side reactions as compared to alcoholic solvents. The rate of conversion of isocyclosporin A to cyclosporin A was determined in aqueous buffers as a function of pH, buffer concentration, and temperature. The rates of conversion were extremely rapid compared to the forward reaction. Based on the pH dependencies of dilute solution reactivities, isocyclosporin A displayed a kinetically generated pK _a value of 6.9 for the secondary amine moiety. From pH 8 to pH 10 the pH–rate profile plot is linear, with a slope approximately equal to unity, indicating apparent hydroxide ion catalysis. The break in pH–rate profile suggests a change in the rate-determining step upon protonation of isocyclosporin A. The rate of isomerization in plasma was comparable with that found in a pH 7.4 buffer solution, indicating that plasma proteins do not significantly alter the isomerization kinetics of isocyclosporin A to cyclosporin A.     

Ezetimibe and reactive oxygen species

Ezetimibe is a potent inhibitor of cholesterol absorption that has been approved for the treatment of hypercholesterolemia. Statin, 3-hydroxy-3 methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, is an inhibitor of cholesterol synthesis. Statin is the first-choice drug to reduce low-density lipoprotein (LDL)-cholesterol for patients with hypercholesterolemia, due to its strong effect to lower the circulating LDL-cholesterol levels. Because a high dose of statins causes concern about rhabdomyolysis, it is sometimes difficult to achieve the guideline-recommended levels of LDL-cholesterol in patients with high LDL-cholesterol treated with statin monotherapy. Ezetimibe has been reported to reduce LDL-cholesterol safely with both monotherapy and combination therapy with statins. Ezetimibe is especially expected to be the best pharmacological option for the treatment of patients unable to achieve LDL-cholesterol goals with statins. Reactive oxygen species (ROS) are produced at low levels to maintain physiological redox balance. Oxidative stress results when ROS production exceeds the ability of cells to detoxify ROS. Overproduction of ROS damages cellular components, including lipids, leading to decline in physiological function and cell death. Oxidative stress exacerbates atherosclerosis, the major risk factor for coronary artery disease and ischemic stroke, at every step involves the accumulation of oxidized LDL in the arteries, leading to foam cell formation, plaque development, and plaque rupture. This review focuses on the recent findings of ezetimibe-related atheroprotective effects in vasculature. Moreover, known and proposed mechanisms of how ezetimibe could improve ROS-induced pro-atherosclerotic conditions in vasculature are discussed; these effects may help to explain the mechanisms by which ezetimibe may protect vascular from atherosclerosis.     

LC-MS/MS测定人血浆中依折麦布和总依折麦布的含量及其应用

目的 建立人血浆中依折麦布（ezetimibe,EZE）和总依折麦布（total ezetimibe,EZE-T）的LC-MS/MS测定方法,并用于依折麦布片人体生物等效性（bioequivalency,BE）研究。方法 分别采用直接沉淀法和酶解后沉淀法处理血浆样品。内标为依折麦布-d4（EZE-d4）,色谱柱为Waters ACQUITY UPLC^® BEH C₁₈（2.1 mm×50 mm,1.7 μm）,流动相为0.1%乙酸-乙腈（A）,0.1%乙酸-水（B）,梯度洗脱,流速0.2 mL·min^-1。在ESI源负离子模式下使用离子对m/z 408.2→271.0（EZE）和m/z 412.2→271.1（EZE-d4）进行MRM定量分析。对口服相同剂量受试制剂或参比制剂依折麦布片的健康受试者的血药浓度进行定量分析。结果 血浆中内源性物质不干扰待测物定量,EZE、EZE-T及EZE-d4不存在相互干扰和/或相互转化。人血浆中EZE和EZE-T的线性范围分别为0.1~20,1~200 ng·mL^-1,线性关系良好。待测物与内标提取回收率均为102.4%~109.8%;内标归一化基质效应因子均为98.5%~99.4%,变异系数（CV）均<5%;批内、批间准确度偏差均<15%,CV均<10%。用本法测定得到的EZE和EZE-T的浓度水平及获取的药动参数与文献报道一致,生物样品再分析复测值与原测值的偏差均<10%。结论 本法特异性强、灵敏、准确,重复性好,所需样本体积少,满足依折麦布片人体BE研究的定量分析需求。     

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.     

Agacutase体外水解牛纤维蛋白原机制的研究(英文)

Agacutase是自尖吻蝮蛇蛇毒中分离出的新的具有止血功能的蛇毒类凝血酶,它能够将纤维蛋白原转化为纤维蛋白单体。通过SDS-PAGE和ELISA方法,我们研究了Agacutase体外水解牛纤维蛋白原的分子机制。实验结果显示,Agacutase仅仅水解牛纤维蛋白原的α亚基并释放血纤肽A,而对牛纤维蛋白原的β和/或γ亚基没有影响。研究表明Agacutase属于血纤肽A类(FP-A类型)的类凝血酶。     

Ezetimibe合成路线图解

Ezetimibe(SCH-58235,1),化学名为(3R,4S)-1-(4-氟苯基)-3-[(3S)-3-(4-氟苯基)-3-羟丙基]-4-(4-羟苯基)-2-氮杂环丁酮,是由Merck/Schering-Plough公司研发的新型胆固醇拮抗剂,2002年11月在德国首次上市,同期在美国上市,商品名ezetrol.本品不同于胆酸螯合剂[1],可选择性抑制胆固醇的吸收,同时口服1和HMG-CoA还原酶抑制剂可降低低密度脂蛋白-胆固醇(LDL-C)和总胆固醇(TC)含量[2].1单独给药或与HMG-CoA还原酶抑制剂联合给药耐受性均良好,不良事件发生率与安慰剂相似.按起始原料不同主要有4种合成方法(图1).     

头孢地嗪钠的热分解机理及动力学

目的测定头孢地嗪钠（CDZ）的热性质,研究CDZ的热分解机理、热分解动力学和CDZ的热稳定性。方法采用热重法（TG）和差示扫描量热法（DSC）测定CDZ在氮气氛和空气氛中的热分解过程,测定CDZ及其在热分解过程中不同阶段残存物的红外光谱,运用量子化学GAMESS软件计算CDZ分子的键级,根据不同升温速率下的热重曲线计算CDZ热分解反应的动力学参数,采用Dakin方程计算CDZ在各种温度下的预期寿命。结果CDZ的热分解过程是多阶段过程。在氮气氛中热分解表观活化能Ea=173．9kJ·mol^-1,指前因子A=1．175×10^17min^-1;在空气氛中热分解表观活化能Ea=172.3kJ·mol^-1,指前因子A=2．692×10^17min^-1。结论CDZ在常温下有很好的热稳定性。     

Ezetimibe plus simvastatin for the treatment of hypercholesterolemia

Introduction: Cardiovascular disease is a major cause of death, and hypercholesterolemia is a major risk factor. Statins, with simvastatin among the most widely used, have ample evidence demonstrating prevention of cardiovascular events and mortality. Ezetimibe is effective at improving serum lipids in combination with statins or alone, but its role has been controversial.

Areas covered: Here, we provide an overview of the pharmacokinetics and pharmacodynamics of each component of the combination, as well as pharmacogenetic contributors. Regarding clinical efficacy, our focus will be on the post-marketing clinical trials of ezetimibe–simvastatin combination therapy. We broach the controversy around the role of ezetimibe, particularly in light of the results of the IMProved Reduction of Outcomes: Vytorin Efficacy International Trial (IMPROVE-IT).

Expert opinion: Ezetimibe in combination with simvastatin or other statins provides an excellent means of incremental lipid-lowering effect, although the clinical benefit has been uncertain. IMPROVE-IT is the first to demonstrate incremental cardiovascular risk reduction with the addition of ezetimibe to simvastatin. What the literature lacks is evidence around the common use of ezetimibe as monotherapy or add-on therapy to lower doses of statins in patients who fail to achieve adequate lipid lowering or do not tolerate high-dose statins.