Application of thin-layer chromatography to investigate oscillatory instability of the selected profen enantiomers in dichloromethane

The usefulness of thin-layer chromatography (TLC) as an efficient measuring technique in the studies of oscillatory trans-enantiomerization of profens from the S to the R configuration (and vice versa) during their storage as 70% ethanol solutions is demonstrated in the literature. S-(+)-ibuprofen, S-(+)-naproxen, and S,R-(+/-)-2-phenylpropionic acid are utilized as the test profens. It is proven possible to show oscillatory instability with the racemic S,R-(+/-)-2-phenylpropionic acid also. Correctness of the TLC assessment is successfully confirmed by means of polarimetry. Upon these preliminary results, it is concluded that the most probable mechanism might embrace the keto-enol tautomerism because of a convenient migration of the proton from one moiety of the profen molecule to another in an aqueous medium. To indirectly verify this hypothesis, profens are stored in dichloromethane, deliberately hampering their ability to dissociate and to re-structure. It is obvious though that the (much less pronounced) electrolytic dissociation can occur in the non-aqueous media as well. It is shown that the non-aqueous solvent considerably suppresses, although they do not completely eradicate, the oscillatory trans-enantiomerization of profens. In view of these findings, the reports which claim a predominant therapeutic potential of the respective S-profens become less convincing and certainly need reconsideration.     

Adenosylcobinamide plus exogenous, sterically hindered, putative axial bases: a reinvestigation into the cause of record levels of Co-C heterolysis

A reinvestigation of an earlier Ph.D. thesis (Sirovatka, J. M. Ph.D. Thesis, Colorado State University, Fort Collins, CO, 1999) is reported herein. That thesis examined the thermolysis reaction of AdoCbi(+)BF(4)(-) in ethylene glycol solution with exogenous bases, N-methylimidazole (N-Me-Im) and the sterically hindered 1,2-dimethylimidazole, (1,2-Me(2)-Im), 2-methylpyridine (2-Me-py), and 2,6-dimethylpyridine (2,6-Me(2)-py). In the present work, multiple purities of each base have been utilized as a check to see if impurities in the nitrogenous bases are causing the observed homolysis and heterolysis product distributions as others have implied (Trommel, J. S.; Warncke, K.; Marzilli, L. G. J. Am. Chem. Soc. 2001, 123, 3358). The "impurity hypothesis" is disproven by a series of results, including the following: N-Me-Im displays an invariant 52 +/- 10% heterolysis and the 1,2-Me(2)-Im system displays an invariant 83 +/- 7% heterolysis as a function of different base purification methods. Moreover, 2-Me-py and 2,6-Me(2)-py also display an invariant approximately 16 +/- 5% heterolysis as a function of different purification methods. What is responsible for the high levels of Co-C heterolysis in the AdoCbi(+) plus sterically bulky base thermolyses was uncovered via a revisitation of our four, earlier alternative hypotheses for the enhanced Co-C heterolysis (Sirovatka, J. M.; Finke, R. G. Inorg. Chem. 1999, 38, 1697). Our prior number one alternative hypothesis is shown to be correct: the added bases simply deprotonate the ethylene glycol solvent, forming ethylene glycolate anion and base-H(+)() as the key agents behind the previously ill-understood Co-C heterolyses. Also reported are Co(II)Cbi(+) titrations with five bases (1,2-Me(2)-Im, N-Me-Im, pyridine, 2-MePy, and 2,6-Me(2)-py). These experiments confirm Marzilli and co-workers' (op. cit.) results by showing that sterically hindered bases do not bind to Co(II)Cbi(+); therefore, Co(II)Cbi(+) EPR literature showing binding of bulky pyridines is erroneous as is the previously reported binding of bulky pyridine bases to Co(II)Cbi(+) by UV-vis spectroscopy (Sirovatka, J. Ph.D. Thesis, op. cit.). Also reported is our current best synthesis and purification of AdoCbi(+)BF(4)(-), work that builds off our 1987 synthesis of AdoCbi(+)BF(4)(-) (Hay, B. P.; Finke, R. G. J. Am. Chem. Soc. 1987, 109, 8012). Finally, the multiple, compounding errors which have caused problems in this project are listed, notably errors in the protein X-ray crystallography literature, the EXAFS literature, the Co(II)Cbi(+) plus bulky-bases EPR literature, the misleading B(12)-model literature, the erroneous experimental work (Sirovatka, op. cit.) and thus incorrect conclusions in one of our prior papers, as well as the erroneous implications in parts of the Marzilli and co-workers paper (op. cit.). It is hoped that a forthright reporting of these errors will help others avoid similar mistakes in the future when studying complex, bioinorganic systems.     

Recent advances in analysis of hazardous genotoxic impurities in pharmaceuticals by HPLC,GC, and CE

Nowadays, genotoxic impurities in pharmaceuticals at lower levels are of increasing concerns not only to pharmaceutical industries but also for the regulatory agencies due to their risks for human carcinogenesis and, thus, requiring manufacturers to pay extra attention for their analysis and control. The need to determine these impurities at trace levels, based on the threshold of toxicological and daily dose, taking into consideration the often reactive and labile nature of genotoxic impurities, which poses significant analytical challenges. Therefore, sensitive and sophisticated analytical methodologies are deemed necessary in order to be able to test and control genotoxic impurities in drug substances. This review demonstrates the approaches reported in the literature for the analysis of the hazardous genotoxic impurities and the strategies used to enhance the sensitivity such as using ion spray-mass spectrometry and the separation techniques for the analysis of such impurities.     

Literature-based generation of hypotheses on chemical composition using database co-occurrence of chemical compounds

Candidates for identification of unknown constituents in a sample to be chemically analyzed are hypothetical. It is proposed to generate these hypotheses according to the co-occurrence of different chemical compounds with a known sample constituent in the chemical literature. The efficiency of the co-occurrence approach for predicting chemical compositions was tested for 67 impurities in 17 chemical/pharmaceutical products. The relative co-occurrence of impurity compounds and these products in the Chemical Abstracts Service database was evaluated and compared with corresponding values for several reference groups of probability sampled compounds from the literature. Almost all impurities (97%) and only < or = 8% randomly sampled compounds co-occurred with these chemical products. Mean and median values of relative co-occurrence for impurities are much higher than those of probability sampled compounds which co-occurred with the products. For the combination of impurities and the probability sample of 396 interfering compounds, the power to predict the chemical composition using the highest co-occurrences is 0.49-0.59. The co-occurrence value can also be considered as an "empiric" indicator of chemical similarity useful to generate new hypotheses on relationships both between compounds and between compounds and their properties.     

Bond dissociation energies and structures of CuNO(+) and Cu(NO)(2)(+)

The bond dissociation energies of CuNO(+), Cu(NO)(2)(+), and CuAr(+) are determined by means of guided ion beam mass spectrometry and quantum chemical calculations. From the experiment, the values D(0)(Cu(+)-NO) = 1.13 +/- 0.05, D(0)(ONCu(+)-NO) = 1.12 +/- 0.06, D(0)(Cu(+)-Ar) = 0.50 +/- 0.07, and D(0)(Cu(+)-Xe) = 1.02 +/- 0.06 eV are obtained. The computational approaches corroborate these results and provide additional structural data. The relative values of D(0)(Cu(+)-NO) and D(0)(Cu(+)-Xe) are consistent with the approximately thermoneutral formation of CuXe(+) upon interacting CuNO(+) with xenon. The sequential bond dissociation energies of Cu(NO)(2)(+) exhibit a trend similar to those of other Cu(I) complexes described in the literature. Although metathesis of nitric oxide to N(2) and O(2) is of considerable interest, no evidence for N-N- or O-O-bond formations in Cu(NO)(n)(+) ions (with n up to 3) is obtained within the energy range studied experimentally.     

Synthesis,chiroptical properties and absolute configuration of α-phenylglycidic acid

The (+)- and (-) enantiomers of potassium α-phenylglycidate, an irreversible inhibitor of the enzyme mandelate racemase, were synthesized by resolution of the diastereomeric esters with R-(-)-2-octanol. Base-catalyzed ring-opening of the resolved α-phenylglycidate esters gave the enantiomers of 2,3-dihydroxy-2-phenylpropanoic acid, also obtained by resolution of the racemic dihydroxy acid using ephedrine. A comparison of the chiroptical properties of the esters of α-phenylglycidic and 2,3-dihydroxy-2-phenylpropanoic acids with those of the structurally similar atrolactic and mandelic acids and their 2-methoxy-derivatives showed that the (-)-methyl 2,3-dihydroxy-2-phenylpropanoate corresponding to the (+)-enantiomer of potassium α-phenylglycidate, as well as the esters of α-phenylglycidic acid derived from the same (+)-potassium salt, were all configurationally related to S-(+)-atrolactic and mandelic acids. The configurational assignments made on the basis of the chiroptical data were confirmed by lithium aluminum hydride reduction of the (-)-2-octyl S- and R-α-phenylglycidates, which led exclusively to the R-(-)- and S-(+)-2-phenyl-1, 2-propanediols, respectively, previously related configurationally to R-(-)- and S-(+)-atrolactic acids.     

Recognition and simultaneous determination of ofloxacin enantiomers by synchronization-1st derivative fluorescence spectroscopy

Under controlling pH 3, R-(+)- and S-(-)-ofloxacin (OFLX) enantiomers can be well recognized and resolved by the synchronization-1st derivative fluorescence spectroscopic techniques, and the interference from urine blank also can be eliminated. The linear dynamic ranges are 0.36-2.16 (R), 0.36-2.89 and 3.16-31.6 mug/ml (S), respectively, for determining OFLX in urine samples. The limits of detection are 0.36 mug/ml (R) and the recoveries of R-(+)- and S-(-)-OFLX in urine samples are 97-104%. Relative standard deviation is <6.6%. Pharmacokinetic study of OFLX and levofloxacin shows that R-(+)- and S-(-)-ofloxacin reach their peak concentration in urine samples after a healthy subject has taken tablets for approximately 3 and 6 h, respectively. R-(+)-OFLX can be obviously detected in 5-6 h after a healthy subject has taken tablets, indicating the transformation of S-(-)- to R-(+)-OFLX enantiomer in human body (in vitro).     

Evolution of regulatory aspects of genotoxic impurities in pharmaceuticals: Survival of the fittest

The genotoxic impurities (GIs) are carcinogenic hence its management during synthesis of pharmaceuticals is very important to be detected even in trace level for the safe use of the drugs. The presence of drug substance/drug product DNA-reactive impurities poses a significant problem for drug regulators as well as industry. There are several regulatory guidelines and position papers focused on controlling the amount of impurities within the specified limits. The present compilation gives an account of updated information about GIs and reviews the regulatory aspects for GIs in active pharmaceutical ingredients/drug formulations. A detailed discussion about control strategies in the context of GIs is also described precisely. The analysis of GIs is a challenging and complex aspect of the drug development process. Control and determination of these impurities at ppm or ppb levels are significant challenges for analysts, therefore the approaches for the analysis of GIs have also been discussed.     

Enantiomeric difference in percutaneous penetration of propranolol through rat excised skin.

The percutaneous penetration of R-(+)- and S-(-)-propranolol (PL) through rat excised skin was investigated in vitro. The flux of S-(-)-PL after application to normal skin was high compared with that of R-(+)-PL. On the other hand, in damaged rat skin, the flux of R-(+)-PL was almost equivalent to that of S-(-)-PL. It is suggested that there is an enantiomeric difference between S-(-)- and R-(+)-PL in terms of penetration through rat stratum corneum.     

Enhancing the detection sensitivity of trace analysis of pharmaceutical genotoxic impurities by chemical derivatization and coordination ion spray-mass spectrometry

Many pharmaceutical genotoxic impurities are neutral molecules. Trace level analysis of these neutral analytes is hampered by their poor ionization efficiency in mass spectrometry (MS). Two analytical approaches including chemical derivatization and coordination ion spray-MS were developed to enhance neutral analyte detection sensitivity. The chemical derivatization approach converts analytes into highly ionizable or permanently charged derivatives, which become readily detectable by MS. The coordination ion spray-MS method, on the other hand, improves ionization by forming neutral-ion adducts with metal ions such as Na⁺, K⁺, or NH₄⁺ which are introduced into the electrospray ionization source. Both approaches have been proven to be able to enhance the detection sensitivity of neutral pharmaceuticals dramatically. This article demonstrates the successful applications of the two approaches in the analysis of four pharmaceutical genotoxic impurities identified in a single drug development program, of which two are non-volatile alkyl chlorides and the other two are epoxides.     

TLC chromatographic-densitometric assay of ibuprofen and its impurities

A simple and sensitive thin-layer chromatographic (TLC)-densitometric method for the quantitative estimation of S(+)-2-[4-isobutylphenyl]propionic acid (ibuprofen) and its impurities in pharmaceutical preparations has been developed. The chromatographic separation was carried out on silica gel 60 F(254) TLC plates using toluene-ethyl acetate-glacial acetic acid (17:13: 1, v/v/v) as the mobile phase. Detection was carried out densitometrically with a UV detector. The developed method has detection and quantitation limits ranging from 0.13 μg per spot to 0.72 μg per spot. For individual constituents the recovery ranged from 96.8% to 99.0%. In addition, the stability of ibuprofen solutions was investigated, including the effect of pH, temperature, and incubation time. The method is rapid, simple, and suitable for routine quality-control analysis of pharmaceuticals containing ibuprofen.     

The chemical constituents of the tissue culture cells of Daphne giraldii cullus

Three compounds were isolated from the tissue culture cells of Daphne giraldii cullus,their structures were identified as daphneolone(1),S-(+)-1-(4-hydroxy-3-methoxyphenyl)-3-hydroxy-5-phenyl-1-pentanone(2),S-(+)-1-(4-methoxyphenyl)-3- hydroxy-5-phenyl-1-pentanone(3),and among them,2 was a new compound,3 was a novel natural product.     

Analytical Method Development for 19 Alkyl Halides as Potential Genotoxic Impurities by Analytical Quality by Design

Major issues in the pharmaceutical industry involve efficient risk management and control strategies of potential genotoxic impurities (PGIs). As a result, the development of an appropriate method to control these impurities is required. An optimally sensitive and simultaneous analytical method using gas chromatography with a mass spectrometry detector (GC–MS) was developed for 19 alkyl halides determined to be PGIs. These 19 alkyl halides were selected from 144 alkyl halides through an in silico study utilizing quantitative structure–activity relationship (Q-SAR) approaches via expert knowledge rule-based software and statistical-based software. The analytical quality by design (QbD) approach was adopted for the development of a sensitive and robust analytical method for PGIs. A limited number of literature studies have reviewed the analytical QbD approach in the PGI method development using GC–MS as the analytical instrument. A GC equipped with a single quadrupole mass spectrometry detector (MSD) and VF-624 ms capillary column was used. The developed method was validated in terms of specificity, the limit of detection, quantitation, linearity, accuracy, and precision, according to the ICH Q2 guideline.     

Trace Impurity Removal from Air

In addition to Nitrogen, Oxygen and Argon, ambient air contains many trace impurities. These impurities include moisture, Carbon Dioxide, Oxides of Nitrogen and light Hydrocarbons. Prior to cryogenic distillation of air to produce Nitrogen, Oxygen and Argon these trace impurities have to be removed since, some of these constitute a safety hazard in the cryogenic plant. A significant amount of information is available in the literature for the removal of Water and Carbon Dioxide from air. However, only limited information is available for the removal of other trace impurities. We discuss the results of an experimental study on the removal of these trace impurities from air.These days, air pre purification is carried out primarily by adsorption based technologies. There are two main choices: Thermal Swing Adsorption (TSA) processes, and Pressure Swing Adsorption (PSA) processes. Main differences between these two approaches and the trace impurity removal results are discussed.     

Stereochemistry of some reactions between alkyl S-methyl methylphosphonothioates and chiral alkoxides

With R-(+) ethyl (or methyl) S-methyl methylphosphonothioate and (+)-pinacolyl alkoxide competitive and highly stereoselective displacements of O-alkyl and S-methyl occur, both reactions being with inversion of configuration. With the enantiomeric S-(-) ethyl (and methyl) S-methyl methylphosphonothioates and (+)-pinacolyl alkoxide the reactions, although still competitive, are no longer stereoselective. In contrast similar reactions with the sodium salt of (-)-menthol, (which might be considered to be the mirror image of (+)-pinacolyl alkoxide) occur highly stereoselectively with the S-(-) but not with R-(+) enantiomers. The displacement of O-alkyl from alkyl S-methyl methyl-phosphonothioates by ethoxide, pinacolyl alkoxide and menthyl alkoxide is not observed when methoxide is the nucleophile; in this case only displacement of S-alkyl group occurs.     

Short-range interactions within molecular complexes formed in supersonic beams: structural effects and chiral discrimination

One- and two-color, mass-selected R2PI spectra of the S1<--S0 transitions in the bare chiral chromophore R-(+)-1-phenyl-1-propanol (R) and its complexes with a variety of alcoholic solvent molecules (solv), namely methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, S-(+)-2-butanol, R-(-)-2-butanol, 1-pentanol, S-(+)-2-pentanol, R-(-)-2-pentanol, and 3-pentanol, were recorded after a supersonic molecular beam expansion. Spectral analysis, coupled with theoretical calculations, indicate that several hydrogen-bonded [R.solv] conformers are present in the beam. The R2PI excitation spectra of [R.solv] are characterized by significant shifts of their band origin relative to that of bare R. The extent and direction of these spectral shifts depend on the structure and configuration of solv and are attributed to different short-range interactions in the ground and excited [R.solv] complexes. Measurement of the binding energies of [R.solv] in their neutral and ionic states points to a subtle balance between attractive (electrostatic and dispersive) and repulsive (steric) forces, which control the spectral features of the complexes and allow enantiomeric discrimination of chiral solv molecules.     

胶束模拟酶的研究2:手性胶束中硫醚氧化为亚砜的不对称诱导

从(+)-和(-)-α-甲基苄胺和天然麻黄素(ephedrine)合成三个手性表面活性剂,由这些表面活性剂组成的手性胶团体系可用作最简单的酶模型和立体专一性催化的研究,在手性胶团体系中,手性亚砜可以用NaIO4或H2O2不对称氧化硫醚而获得,讨论了表面活性剂结构与不对称诱导之间的关系.     

A validated enantioselective HPLC assay of dexibuprofen in dexibuprofen tablet formulations

A high-performance liquid chromatography-diode array detector (HPLC-DAD) method was developed and validated for the quantitation of dexibuprofen in dexibuprofen tablets using ovomucoid chiral stationary phase (Ultron ES-OVM). The mobile phasewas composed of 0.025 M potassium phosphate dibasic (pH 4.5)-methanol-ethanol (85:10:5 v/v/v). The method was validated for specificity, linearity, range, accuracy, precision and robustness. The method was enantiomerspecific for the determination of dexibuprofen [S-(+)-isomer ibuprofen] in the presence of R-(-)-isomer ibuprofen in bulk drug, pharmaceutical dosage form and under stress degradation. The method was linear over the range 15-35 mg/mL with r2 = 0.9995; accuracy and precision were acceptable with %RSD < 2.0%. The method was found to be specific, precise, accurate, robust and stability-indicating, and can be successfully applied for the routine analysis of dexibuprofen in bulk drug and pharmaceutical dosage form.     

Identification,control strategies,and analytical approaches for the determination of potential genotoxic impurities in pharmaceuticals: A comprehensive review

Potential genotoxic impurities in pharmaceuticals at trace levels are of increasing concern to both pharmaceutical industries and regulatory agencies due to their possibility for human carcinogenesis. Molecular functional groups that render starting materials and synthetic intermediates as reactive building blocks for small molecules may also be responsible for their genotoxicity. Determination of these genotoxic impurities at trace levels requires highly sensitive and selective analytical methodologies, which poses tremendous challenges on analytical communities in pharmaceutical research and development. Experimental guidance for the analytical determination of some important classes of genotoxic impurities is still unavailable in the literature. Therefore, the present review explores the structural alerts of commonly encountered potential genotoxic impurities, draft guidance of various regulatory authorities in order to control the level of impurities in drug substances and to assess their toxicity. This review also describes the analytical considerations for the determination of potential genotoxic impurities at trace levels and finally few case studies are also discussed for the determination of some important classes of potential genotoxic impurities. It is the authors’ intention to provide a complete strategy that helps analytical scientists for the analysis of such potential genotoxic impurities in pharmaceuticals.