Aluminum L-glutamate complex in rat brain cortex: in vivo prevention of aluminum deposit by magnesium D-aspartate

Our previous experiments in the rat showed that aluminum L-glutamate complex (Al L-Glu) crosses the blood-brain barrier and accumulates in selective brain areas and that Al salts may increase D-aspartic acid forms in living brain proteins, probably by inducing more thermodynamically stable structures than L isomers. As magnesium blocks NMDA receptors, D-aspartic acid was used in the present study in the form of magnesium salt to prevent the excitotoxicity of dicarboxylic amino acids. Effects on brain amino acids and Al cortex levels in mature rats were studied after chronic treatment with Al L-Glu or Na L-Glu alone or in association with magnesium D-aspartate (Mg D-Asp). Results demonstrate that treatment with Mg D-Asp induces a decrease in the Al concentration in brain cortex of Al L-Glu-treated rats. In aluminum-free treated controls, treatment with Mg D-Asp in association with Na L-Glu also induces a decrease in Al concentration in brain cortex. These data indicate that Mg D-Asp administration protects rat brain cortex from Al accumulation and suggest that this treatment may be useful in preventing brain Al intoxication.     

Chiral interconversion monitoring of a drug candidate by supercritical fluid chromatography (SFC)

Stereoisomer interconversion of chiral drug substances is of significant importance if it occurs within pharmacological and pharmaceutical time scales and under physiological and shelf life conditions. Several analytical techniques exist for the determination of first order rate constants and enantiomerization energy barriers by dynamic and stopped flow chromatography, mathematical models and functions, and computer programs. The focus of this work is to utilize a simple supercritical fluid chromatography (SFC) chiral assay to determine the possibility of interconversion of the desired R and less active S isomers of a drug candidate. The rate constants of racemization and enantiomerization, the half life of racemization, and enantiomerization energy barriers were determined for the R → S (or, forward) and S → R (or, reverse) conversions. The method was selective and sensitive enough to detect less than 1% interconversion occuring under the conditions studied. The method also demonstrated that R ? S racemization was possible only under extreme conditions of prolonged heating (80 °C) and highly basic pH (9.5).     

Racemization of L-lysine for pharmaceutical synthesis and its chiral separation by GC-MS spectroscopy

In order to improve physico-chemical properties and to enhance stability of drugs, amino acid salt has been widely adopted in pharmaceutical synthesis. Acetylsalicylic acid lysinate is one of the widely used analgesics and it is a good example of this synthesis. In the case of acetylsalicylic acid lysinate synthesis, racemization of naturally occurred lysine is essential because the racemic lysine salt of the drug shows better yield, crystallinity and dryness than that of the L-lysine salt. To establish a simple, practical and economical process for L-lysine racemization, L-lysine treatments with phosphoric acid and with acetic acid were compared and the optimum conditions for its process and derivatization were investigated by chiral separation methods using GC-MS spectroscopy.     

D-青霉胺酰化消旋工艺及动力学研究

目的研究D-青霉胺在酸性条件下进行酰化外消旋的工艺。方法以D-青霉胺为原料,在醋酸溶液中,用乙酰氯为酰化试剂进行消旋化,得到了D-青霉胺酰化消旋物;并以溶剂量、反应温度、反应时间、乙酰氯的量等为因素考察最佳工艺条件;测定反应温度、时间与消旋过程比旋度的关系,计算酰化过程的动力学方程。结果得到最佳工艺条件即青霉胺量-醋酸量-乙酰氯量(1∶7∶2),反应温度80℃,反应时间5h。酰化过程的动力学方程符合一级线性关系。结论该工艺条件缓和,路线简单,为D,L-青霉胺的制备提供了直接原料。     

Chiral purity test of metoprolol enantiomer after derivatization with (−)-menthyl chloroformate by reversed-phase high performance liquid chromatography

A reversed-phase high-performance liquid chromatographic method was developed to determine the optical purity of metoprolol enantiomers. The enantiomers were converted to diastereomeric derivatives using (-)-menthyl chloroformate reagent. Separation of the enantiomers as diastereomers was achieved by reversed-phase HPLC within 30 min using Inertsil C8 column. This method allowed determination of 0.05% of either enantiomer in the presence of its stereoisomer and method validation showed adequate linearity over the required range. Owing to the reaction condition during the derivatization with (-)-menthyl chloroformate, the possibility of racemization had to be established. Different ratios of (S)-(-)-metoprolol and (R)-(+)-metoprolol were prepared. Enantiomeric separation of these mixtures took place on a chiralcel OD column or, after derivatization with (-)-menthyl chloroformate, on a C8 column. The results from the these two independent separation systems were compared with trace racemization and were in very good agreement. No racemization was found during the experiment.     

消旋棉酚拆分的研究——Ⅱ.手性α-甲基苯乙胺及α-甲基苄胺为拆分剂

本文报道用中压柱色谱快速分离S或R-α-甲基苯乙胺及S或R-α-甲基苄胺缩(±)-棉酚的方法,可得光学活性胺缩(+)或(一)-棉酚非对映体,经水解分别得到(+)或(一)-棉酚。并证明胺缩光学活性棉酚非对映体之间有互相转化的性质,此特性可利用于棉酚对映体的转化。     

晶状体蛋白的外消旋化及其在白内障发病机制中的研究进展

外消旋化是老年人晶状体蛋白中重要的翻译后修饰类型.多项研究发现,随着年龄的增长,α-、β-及γ-晶状体蛋白中的部分L型氨基酸残基倾向于通过外消旋化反应转化为D型氨基酸残基,导致晶状体蛋白的构象改变,聚合形成的大分子蛋白质在晶状体核区和皮质中逐渐积累,晶状体蛋白失去了原有功能而不能维持晶状体的透明度.外消旋化在晶状体蛋白年龄相关性改变中的效应和参与程度,及其对白内障发生与进展的具体机制都值得进一步研究.     

Compared pharmacological characteristics in humans of racemic cetirizine and levocetirizine, two histamine H1-receptor antagonists

The potent histamine H(1)-receptor antagonist cetirizine (Zyrtec) is a racemic mixture of levocetirizine (now available under the trademark Xyzal and dextrocetirizine. In this Commentary, we examine some biological properties of cetirizine and levocetirizine, namely enantioselectivity in pharmacological activity and pharmacokinetic properties, with emphasis on the possibility of racemization, the compared behavior of the two enantiomers, and the potential for interactions with other drugs. Recent data demonstrate that the antihistaminergic activity of the racemate is primarily due to levocetirizine. Levocetirizine is rapidly and extensively absorbed, poorly metabolized, and not subject to racemization. Its pharmacokinetic characteristics are comparable after administration alone or in the racemate. Its apparent volume of distribution is smaller than that of dextrocetirizine (0.41 L kg(-1) vs. 0.60 L kg(-1)). Moreover, the non-renal (mostly hepatic) clearance of levocetirizine is also significantly lower than that of dextrocetirizine (11.8 mL min(-1) vs. 29.2 mL min(-1)). Our conclusion is that levocetirizine is indeed the eutomer of cetirizine. The evidence reviewed here confirms preclinical findings and offers a rationale for the chiral switch from the racemate to levocetirizine.     

The problem of racemization in drug discovery and tools to predict it

Introduction: Racemization has long been an ignored risk in drug development, probably because of a lack of convenient access to good tools for its detection and an absence of methods to predict racemization risk. As a result, the potential effects of racemization have been systematically underestimated.

Areas covered: Herein, the potential effects of racemization are discussed through a review of drugs for which activity and side effects for both enantiomers are known. Subsequently, drugs known to racemize are discussed and the authors review methods to predict racemization risk. Application of a method quantitatively predicting racemization risk to databases of compounds from the medicinal chemistry literature shows that success in clinical trials is negatively correlated with racemization risk.

Expert opinion: It is envisioned that a quantitative method of predicting racemization risk will remove a blind spot from the drug development pipeline. Removal of the blind spot will make drug development more efficient and result in less late-stage attrition of the drug pipeline.     

Temperature-rate profiles by polarimetric variable-temperature kinetic experiments to study racemization reactions

The racemization of (−)-adrenaline was followed by polarimetric variable-temperature kinetic experiments obtaining activation parameters and k_obs(T) profile in one tenth of the time usually spent for traditional kinetic runs. A polarimeter connected to a computer for the acquisition and processing of the analytical data was used. The kinetic profiles were processed by both an integral method and a differential method. The results are in good agreement with each other and with those obtained by constant-temperature kinetics.