Effects of Configuration Around the Chiral Carbon Atoms on the Crystal Properties of Ephedrinium and Pseudoephedrinium Salicylates

The physicochemical properties and crystal structures of the crystalline salts formed by the interaction of an achiral anion, salicylate, with homochiral and racemic ephedrinium and pseudoephedrinium cations were determined. The interaction of ephedrinium or pseudoephedrinium with salicylate in aqueous solution yielded crystalline salts with the notable exception of homochiral ephedrinium. Evaporation of the solvent from solutions of homochiral ephedrine and salicyclic acid in various organic solvents, as well as grinding together solid homochiral ephedrine and solid salicylic acid, yielded viscous semisolids suggesting that homochiral ephedrinium salicylate has a low melting point and/or a high aqueous solubility. Mixing of the two viscous solids, obtained by grinding each of the opposite enantiomers of ephedrine with equimolar salicylic acid, resulted in the formation of racemic ephedrine and subsequently, upon heating, in the formation of racemic ephedrinium salicylate. While racemic ephedrinium salicylate exists as a crystalline compound (P2₁/n space group) with an equal number of opposite enantiomers in the unit cell, its diastereomer, racemic pseudoephedrinium salicylate, exists as a conglomerate, i.e. a physical mixture, of the homochiral crystals of the opposite enantiomers (each P2₁ space group). The inability of homochiral ephedrinium to exist as a crystalline salicylate salt at 20–25°C is attributed to its high energy conformation and/or to the poor packing of homochiral ephedrinium salicylate molecules in the crystal lattice.     

Racemic species of sodium ibuprofen: characterization and polymorphic relationships

Racemic and homochiral sodium ibuprofen were characterized by thermal analysis and powder X-ray diffractometry. The melting point phase diagram was constructed and thermodynamic calculation was performed. In contrast to racemic ibuprofen, which is a racemic compound, racemic sodium ibuprofen forms both a racemic conglomerate (termed the gamma-form) as well as two polymorphic racemic compounds, alpha and beta, which are less stable monotropes. From the supercooled liquid, alpha and beta crystallized along with the original gamma-form. Forms alpha and beta are "enantiotropically related" with a transition temperature between 75 degrees and 113 degrees C, but can be considered to be metastable monotropes of the racemic conglomerate, the stable gamma-form.     

Norleucine: a branched-chain amino acid analog affecting feeding behavior of rats

Norleucine, an isomer of leucine and isoleucine and a potent competitor of large neutral amino acid transport into brain, thereby depleting certain amino acid pools, was tested for its effects on growth and feeding behavior of rats fed an amino acid diet limiting in leucine. Growth and food intake were depressed in proportion to the dietary level of norleucine (0.2 to 1.1% of the diet). With suboptimal amounts of indispensable amino acids, leucine at 150% of the requirement reversed the effects of 0.2 and 0.5% norleucine; slight excesses of the other indispensable amino acids were required with extra leucine for maximum growth with 1.1% norleucine. Rats almost exclusively preferred the control to the norleucine diet, but not if the latter diet also contained leucine. Rats also strongly selected a nonprotein rather than norleucine diet when this was the first available choice. If the first choice was between the nonprotein and control diets, rats later almost exclusively selected the norleucine-containing rather than the nonprotein diet for varying periods (2 to 6 days). These studies suggest that amino acid analogs may be useful agents in the study of animal behavior associated with changes in brain amino acid pools.     

Enhanced dissolution rates of piroxicam from the ground mixtures with chitin or chitosan

To increase the dissolution rate of piroxicam, chitin and chitosan which are widely occurring biodegradable natural materials were used as drug carriers. The ground mixtures of piroxicam with chitin or chitosan were prepared by grinding in a ball mill. The dissolution rates of piroxicam from the ground mixtures were enhanced markedly than that from the physical mixtures or from intact piroxicam. The X-ray diffraction peaks disappeared in the ground mixture indicating the production of the amorphous form. The comparison of infrared spectra of the physical mixture and the ground minture showed an interaction such as association between the functional groups of piroxicam and chitin or chitosan in the molecular level. The weight losses in TGA curves showed all the same patterns. However, in the ground mixture by DTA curve, the endothermic peak due to the fusion of piroxicam was disappeared indicating the different thermal property.     

Characterization of racemic species of chiral drugs using thermal analysis, thermodynamic calculation, and structural studies

The identification of the racemic species, as a racemic compound, a racemic conglomerate, or a racemic solid solution (pseudoracemate), is crucial for rationalizing the potential for resolution of racemates by crystallization. The melting points and enthalpies of fusion of a number of chiral drugs and their salts were measured by differential scanning calorimetry. Based on a thermodynamic cycle involving the solid and liquid phases of the enantiomers and racemic species, the enthalpy, entropy and Gibbs free energy of the racemic species were derived from the thermal data. The Gibbs free energy of formation, is always negative for a racemic compound, if it can exist, and the contribution from the entropy of mixing in the liquid state to the free energy of formation is the driving force for the process. For a racemic conglomerate, the entropy of mixing in the liquid state is close to the ideal value of R ln 2 (1.38 cal.mol-1. K-1). Pseudoracemates behave differently from the other two types of racemic species. When the melting points of the racemic species is about 30 K below that of the homochiral species, is approximately zero, indicating that the racemic compound and racemic conglomerate possess similar relative stabilities. The powder X-ray diffraction patterns and 13C solid-state nuclear magnetic resonance spectra are valuable for revealing structural differences between a racemic compound and a racemic conglomerate. Thermodynamic prediction, thermal analysis, and structural study are in excellent agreement for identifying the nature of the racemic species.     

Isolation of a new peptide antibiotic, permetin A, from Bacillus circulans.

Permetin A was purified from the culture filtrate of Bacillus circulans AJ 3902 by extraction with n-butanol, precipitation with sodium helianthate, CM-cellulose column chromatography and Sephadex LH-20 column chromatography. The compound was found to be a new peptide antibiotic containing 2,4-diaminobutyric acid (Dab), leucine, isoleucine, phenylalanine, valine, serine (in a molar ratio of 3:2:1:1:1:1) and a fatty acid. This antibiotic showed activity in vitro against Gram-negative, Gram-positive and some anaerobic bacteria.     

Chiral Self Assembled Monolayers as Resolving Auxiliaries in the Crystallization of Valine

Chiral drugs are a subgroup of drug substances that contain one or more chiral centers. For reasons of safety and efficacy, the pure enantiomer is usually preferred over the racemate in many marketed dosage forms. Thus, resolution ofracemic mixtures is an active area of research. In this work, chiral self assembled monolayers (SAMs) on gold were employed as resolving auxiliaries in the crystallization of the amino acid valine. Results showed the ability to obtain one enantiomer in excess on the crystals grown on the chiral SAMs when starting with racemic solutions. The enantiomer obtained in excess was the one having opposite chirality to the monolayer being used. In addition, it was possible to obtain crystals of the pure enantiomer when starting with a solution having an enantiomeric excess value of 50%. Control experiments carried out without chiral SAMs showed that at equilibrium, mixtures of the pure enantiomer and racemic compound were obtained under these conditions. The enantiomer obtained on the chiral SAMs was the one that was initially present in excess regardless of the chirality of the monolayer being used.     

Ultrasonication as a Potential Tool to Predict Solute Crystallization in Freeze-Concentrates

Purpose

We hypothesize that ultrasonication can accelerate solute crystallization in freeze-concentrates. Our objective is to demonstrate ultrasonication as a potential predictive tool for evaluating physical stability of excipients in frozen solutions.

Methods

The crystallization tendencies of lyoprotectants (trehalose, sucrose), carboxylic acid buffers (citric, tartaric, malic, and acetic) and an amino acid buffer (histidine HCl) were studied. Aqueous solutions of buffers, lyoprotectants and mixtures of the two were cooled from room temperature to ?20°C and sonicated to induce solute crystallization. The crystallized phases were identified by X-ray diffractometry (laboratory or synchrotron source).

Results

Sonication accelerated crystallization of trehalose dihydrate in frozen trehalose solutions. Sonication also enhanced solute crystallization in tartaric (200 mM; pH 5), citric (200 mM pH 4) and malic (200 mM; pH 4) acid buffers. At lower buffer concentrations, longer annealing times following sonication were required to facilitate solute crystallization. The time for crystallization of histidine HCl progressively increased as a function of sucrose concentration. The insonation period required to effect crystallization also increased with sucrose concentration.

Conclusions

Sonication can substantially accelerate solute crystallization in the freeze-concentrate. Ultrasonication may be useful in assessing the crystallization tendency of formulation constituents used in long term frozen storage and freeze-drying.     

Crystallographic Consequences of Molecular Dissymmetry

The molecular chirality associated with an optically active molecule is manifested in the bulk crystallography of the compound. The historical development of optical activity was greatly aided by systematic studies of the habits of enantiomorphic crystals. The concepts of molecular dissymmetry, crystallography, and chirality are therefore linked. Racemic materials can be characterized by means of their melting-point phase diagrams, and this information used to design rational separations of racemic mixtures into their component enantiomers. Certain compounds are found to resolve spontaneously upon crystallization, and the enantiomers of these conglomerate species may be separated by direct crystallization. Compounds which crystallize as true racemates require resolution through the formation and separation of dissociable diastereomer species. The choice of resolution pathway is therefore determinable through an evaluation of the melting-point phase diagrams. When possible, resolution through direct crystallization represents the simplest, most cost-effective means of enantiomer resolution.     

Urea-PETT compounds as a new class of HIV-1 reverse transcriptase inhibitors. 3. Synthesis and further structure-activity relationship studies of PETT analogues.

The further development of allosteric HIV-1 RT inhibitors in the urea analogue series of PETT (phenylethylthiazolylthiourea) derivatives is described here. The series includes derivatives with an ethyl linker (1-5) and racemic (6-16) and enantiomeric (17-20) cis-cyclopropane compounds. The antiviral activity was determined both at the RT level and in cell culture on both wild-type and mutant forms of HIV-1. Most compounds have anti-HIV-1 activity on the wt in the nanomolar range. Resistant HIV-1 was selected in vitro for some of the compounds, and the time for resistant HIV-1 to develop was longer for urea-PETT compounds than it was for reference compounds. Preliminary pharmacokinetics in rats showed that compound 18 is orally bioavailable and penetrates well into the brain. The three-dimensional structure of complexes between HIV-1 RT and two enantiomeric compounds (17 and 18) have been determined. The structures show similar binding in the NNI binding pocket. The propionylphenyl moieties of both inhibitors show perfect stacking to tyrosine residues 181 and 188. The cyclopropyl moiety of the (+)-enantiomer 18 exhibits optimal packing distances for the interactions with leucine residue 100 and valine residue 179.     

超临界流体萃取拆分手性外消旋伪麻黄碱

目的用超临界CO₂流体萃取技术拆分伪麻黄碱异构体。方法用单通路法,毛细管电泳分析。将消旋伪麻黄碱转化为非对映体盐,用超临界二氧化碳作为萃取溶剂,可从反应混合物中选择性萃取出伪麻黄碱的一个异构体,达到拆分伪麻黄碱的目的。结果酒石酸是伪麻黄碱良好的拆分剂,半摩尔法形成非对映体盐以超临界二氧化碳流体萃取拆分,一次萃取产物e.e.值可达100%。结论对拆分剂及非对映体盐进行分子构键的计算结果表明拆分剂与被拆分物质成盐的反应规律为R构型优先与S构型反应,理论预测与拆分结果基本吻合。     

Formation of the Racemic Compound of Ephedrine Base from a Physical Mixture of Its Enantiomers in the Solid,Liquid, Solution,or Vapor State

Physical mixtures (conglomerates) of the two enantiomers of ephedrine base, each containing 0.5% (w/w) of water, were observed to be converted to the 1:1 racemic compound in the solid, liquid, solution, or vapor state. From a geometrically mixed racemic conglomerate of particle size 250–300 µm (50–60 mesh), the formation of the racemic compound follows second-order kinetics (first order with respect to each enantiomer), with a rate constant of 392 mol^–1 hr^–1 at 22°C. The reaction appears to proceed via the vapor phase as indicated by the growth of the crystals of the racemic compound between diametrically separated crystals of the two enantiomers in a glass petri dish. The observed kinetics of conversion in the solid state are explained by a homogeneous reaction model via the vapor and/or liquid states. Formation of the racemic compound from the crystals of ephedrine enantiomers in the solution state may explain why Schmidt et al. (Pharm. Res. 5:391–395, 1988) observed a consistently lower aqueous solubility of the mixture than of the pure enantiomers. The solid phase in equilibrium with the solution at the end of the experiment was found to be the racemic compound, whose melting point and heat of fusion are higher than those of the enantiomers. An association reaction, of measurable rate, between the opposite enantiomers in a binary mixture in the solid, liquid, solution, or vapor state to form the racemic compound may be more common than is generally realized.     

Effect of acute nitrogen dioxide exposure on the free amino acids of rat serum

Female Wistar rats were acutely exposed to 20 ppm nitrogen dioxide (NO₂). After 20 h exposure, the concentrations of valine, leucine, isoleucine and phenylalanine in serum significantly increased. Significant decreases were observed for aspartic acid, threonine, serine, glutamic acid, glycine alanine, cystine, methionine, tyrosine, lysine, arginine and proline. The concentrations of free amino acids of rats exposed to NO₂ for 40 h were close to the values for rats starved for 40 h.     

Characterization and dissolution behavior of nifedipine and phosphatidylcholine binary systems

Physicochemical properties and the dissolution behavior of binary systems of nifedipine (NIF) and dipalmitoylphosphatidylcholine (DPPC) or dimyristoylphosphatidylcholine (DMPC) as physical mixtures, solid dispersions and ground mixtures at 9:1 w/w were investigated. The drug and formulations were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy (FTIR) and differential thermal analysis (DTA). The dissolution and solubility of NIF was increased in the order physical mixture < solid dispersion < ground mixture. The powder X-ray diffraction patterns and FTIR spectra indicated absence of major crystalline or molecular changes of NIF or the PCs. The fraction of NIF dissolved after 1 h was approximately 30 and 34% from NIF/DMPC and NIF/DPPC ground mixtures, respectively, and the dissolution was only slightly reduced from NIF/DPPC, 9.75:0.25 w/w systems. The crystal lattice parameter, c, of DPPC and DMPC in the solid dispersion was longer than that of PC alone but each was considered to be in an amorphous state in the ground mixture because of the absence of an X-ray diffraction peak. Full-width at half-maximum (half width) of the X-ray diffraction peak of NIF in the ground mixture was greater than NIF in the physical mixture or solid dispersion, suggesting that the lattice distortion of NIF crystals was increased by grinding. Thermal analysis confirmed the crystalline state of DPPC and DMPC in the physical mixture and the solid dispersion but an amorphous state in the ground mixture. Thus, an increase in lattice distortion of NIF crystals due to grinding and an amorphous state of DPPC or DMPC in the ground mixtures are considered mainly responsible for the larger increase in dissolution rate and extent of dissolution of NIF after 1 h compared to the solid dispersion formulation.     

Thermodynamic and kinetic characterization of polymorphic transformation of famotidine during grinding

Two polymorphs of famotidine were prepared by recrystallization from acetonitrile for form A and methanol for form B, respectively. The effect of grinding process on the polymorphic transformation of famotidine was investigated. Each famotidine sample ground for various grinding times in a ceramic mortar was determined by differential scanning calorimetry (DSC), conventional and thermal Fourier transform infrared (FT-IR) microspectroscopy. The results indicate that the raw material of famotidine was proved to be a form B. A unique IR absorption band at 3505 cm(-1) for famotidine form B gradually decreased its intensity with the grinding time, while two newer IR absorption bands at 3451 and 1671 cm(-1) for famotidine form A slowly appeared. The peak intensity ratio of 3451/350 5 cm(-1) was linearly (r=0.9901) increased with the grinding time, suggesting that the grinding process could induce the polymorphic transformation of famotidine from form B to form A by a zero-order process. The DSC endothermic peaks also confirmed this polymorphic transformation from famotidine form B (167 degrees C, DeltaH: 165J/g) to famotidine form A (174 degrees C, DeltaH: 148J/g) in which the values of enthalpy were linearly reduced with the increase of grinding time (r=0.9943). The phase transition temperature of the different ground famotidine samples could be easily and only evidenced by using thermal FT-IR microspectroscopy, rather than by DSC analysis. These phase transition temperatures of the famotidine form B ground for 5-20 min quickly reduced from 144 to 134 degrees C and maintained a constant at 134 degrees C even after 20-30 min grinding. The grinding process not only decreased the crystallinity of famotidine form B but also reduced the particle size of famotidine form B, resulting in easy induction of the polymorphic transformation of famotidine from form B to form A in ground famotidine sample.     

抗肿瘤药物的研究 Ⅲ.含氨基酸的氮芥磷酰胺衍生物的合成

以N-磷酰氨基酸为载体而形成的氮芥磷酰胺衍生物,可能具有较好的抗肿瘤专属性。双-(β-氯乙基)氨基磷酰二氯(Ⅰ)与二当量的甘、丙、缬、亮、笨丙、天冬及谷氨酸乙酯(Ⅱ)缩合,生成相应的N,N-双-(β-氯乙基)-N′,N″-二-(乙氧羰甲基)磷三酰胺衍生物(Ⅲ);与当量的丝氨酸乙酯(Ⅹ)缩合时生成环状衍生物,2-双-(β-氯乙基)氨基-4-乙氧羟基-四氢-1,2,3-氧膦氮茂,2-氧化物(Ⅺ)。这类化合物经动物实验有显著的抗肿瘤活性。     

Injection-Molded Coamorphous Tablets: Analysis of Intermolecular Interaction and Crystallization Propensity

The processing steps involved in converting from a powder to a tablet entail numerous operations in a which the coamorphous system is recrystallized and dissociated easily. This research focused on (i) a single-step preparation of a coamorphous tablet during injection molding (IM) from the bulk powder, and (ii) a mechanistic characterization of the coamorphous formulation. We selected several organic acids [citric acid, succinic acid, tartaric acid, and malic acid] in an effort to compound with basic loratadine (a poorly water-soluble drug). Loratadine–acids coamorphous tablets were produced via an IM process, and the dissolution was more enhanced than in the pure loratadine amorphous. The interaction was analyzed by FT-IR and terahertz spectroscopies. Each tablet was stored at 40 °C/75%RH, and then XRD patterns were acquired at the desired timepoints. In summary, loratadine exhibited ionic interaction with each acid, and the physical stability of the coamorphous tablet was in proportion to the loratadine–acids interaction strength. Terahertz spectra detected the molecular mobility, which plays an important role in the crystallization propensity of a coamorphous system. This understanding offers a framework for robust coamorphous tablet formulation using the IM methodology.     

Tartaric acid derivatives as chiral sources for enantioseparation in liquid chromatography

Based on a systematic review of the usage of tartaric acid as a chiral source to resolve enantiomeric compounds, a concept is presented for synthesizing new chiral stationary phases utilizing tartaric acid derivatives as the chiral selector. The results indicate that the conformational change of one of the three optically active centres of the chiral selector strongly affects its enantioselectivity for certain types of compound.     

Effect of acute tyrosine depletion in using a branched chain amino-acid mixture on dopamine neurotransmission in the rat brain.

Central dopamine function is reduced by decreasing the availability of the catecholamine precursor, tyrosine, using a tyrosine-free amino acid mixture containing multiple large neutral as well as branched chain amino-acids, which compete with tyrosine for uptake into the brain. Current mixtures are cumbersome to make and administer, and unpalatable to patients and volunteers. Here, we investigate whether individual or limited amino-acid combinations could reduce brain tyrosine levels and hence dopamine function. Measurements of regional brain tyrosine levels, catecholamine and indoleamine synthesis (L-DOPA and 5-HTP accumulation, respectively) were used to identify an effective paradigm to test in neurochemical, behavioral and fos immunocytochemical models. Administration of leucine or isoleucine, or a mixture of leucine, isoleucine, and valine reduced tyrosine and 5-HTP, but not L-DOPA accumulation. A mixture of leucine, valine, and isoleucine supplemented with tryptophan reduced brain tyrosine and L-DOPA, but not 5-HTP. In microdialysis experiments this amino-acid mixture reduced basal and amphetamine-evoked striatal dopamine release, as well as amphetamine-induced hyperactivity. This mixture also reduced amphetamine-induced fos expression in striatal areas. In conclusion, the present study identified a small combination of amino acids that reduces brain tyrosine and dopamine function in a manner similar to mixtures of multiple amino acids. This minimal mixture may have use as a dopamine reducing paradigm in patient and volunteer studies.     

Stereoselective synthesis of L‐[15N] amino acids with glucose dehydrogenase and galactose mutarotase as NADH regenerating system

We have developed an efficient stereospecific enzymatic synthesis of L‐[¹⁵N]‐valine, L‐[¹⁵N]‐leucine, L‐[¹⁵N]‐norvaline, L‐[¹⁵N]‐norleucine and L‐[¹⁵N]‐isoleucine from the corresponding α‐keto acids by coupling the reactions catalysed by leucine dehydrogenase and glucose dehydrogenase/galactose mutarotase. Giving high yields of L‐amino acids, the procedure is economical and easy to perform and to monitor at a synthetically useful scale (1–10 g). Copyright © 2008 John Wiley & Sons, Ltd.