Alan R. Oyler

Hydrophilic interaction chromatography on amino-silica phases complements reversed-phase high-performance liquid chromatography and capillary electrophoresis for peptide analysis

Hydrophilic interaction chromatography (HILIC) on amine bonded-phase silica columns provides separations of peptides that are complementary to those obtained with reversed-phase HPLC and free solution capillary electrophoresis. This is illustrated with the peptide drug atosiban and nine diastereomers. Moreover, one of the HILIC methods was suitable for coupling with electrospray mass spectrometry.

Structural characterization of dissolved organic matter: a review of current techniques for isolation and analysis

Natural dissolved organic matter (DOM) in aquatic systems plays many environmental roles: providing building blocks and energy for aquatic biota, acting as a sunscreen in surface water, and interacting with anthropogenic compounds to affect their ultimate fate in the environment. Such interactions are a function of DOM composition, which is difficult to ascertain due to its heterogeneity and the co-occurring matrix effects in most aquatic samples. This review focuses on current approaches to the chemical structural characterization of DOM, ranging from those applicable to bulk samples and in situ analyses (UV-visible spectrophotometry and fluorescence spectroscopy) through the concentration/isolation of DOM followed by the application of one or more analytical techniques, to the detailed separation and analysis of individual compounds or compound classes. Also provided is a brief overview of the main techniques used to characterize isolated DOM: mass spectrometry (MS), nuclear magnetic resonance mass spectrometry (NMR) and Fourier transform infrared spectroscopy (FTIR).

Identification of autoxidation and photodegradation products of ethynylestradiol by on-line HPLC–NMR and HPLC–MS

HPLC-NMR, HPLC-MS, and HPLC-UV were used to characterize the predominant solution autoxidation and photodegradation products of ethynylestradiol (1). A hydroperoxide (2) and a series of isomeric dimeric oxidation products (3-7), were identified.

Separation and identification of retinoic acid photo-isomers

Abstract Retinoic acid was isomerized in ethanol—water (90:10) with fluorescent light. Reversed-phase high-performance liquid chromatography (HPLC) on a 3-μm ODS-2 column with a highly specific mobile phase allowed simultaneous determination of ten retinoic acid isomers that were produced during the photoisomerization. Nine of the isomers were isolated by HPLC and characterized by spectroscopic methods (1H NMR, mass spectrometry and UV). The variation of product distribution with time was determined over the course of the reaction (21 h).

Characterizationf of autoxidation products of retinoic acid

Abstract Retinoic acid underwent autoxidation in 90% ethanol at 25–85.5 °C to give epoxides, dioxetanes, an endoperoxide, and double-bond cleavage products. The majority of these products appear to have resulted from the initial direct oxidation of the olefinic carbons rather than from the expected allylic α oxidation process.

Alkyl Aromatic Synthesis: Nucleophilic Alkyl Lithium Addition

Abstract Alkylated and, in particular, methylated polycyclic aromatic hydrocarbons and heteroaromatic compounds associated with increased coal utilization may be considerably more carcinogenic than the corresponding parent system.1,2 The availability of these alkylated compounds as standards for structural comparison or for biological testing is therefore of some importance. The report describes improvements on methodology for the synthesis of alkyl aromatic compounds by using a nucleophilic addition of an alkyl lithium (often enhanced by UV irradiation)3–11 in combination with the subsequent addition of iodine to conveniently regenerate the aromatic system (Scheme I, Table I).

Forced degradation studies of rapamycin: Identification of autoxidation products

The immunosuppressant drug rapamycin, also known as Sirolimus, underwent autoxidation under mild conditions to give numerous monomeric and oligomeric compounds, which were generally characterized by size-exclusion chromatography and NP-HPLC with UV and MS detection. Some of the more predominant products, epoxides and ketones, were isolated and identified. Two epoxides and 10S-epimer of rapamycin were described for the first time. Observed rapamycin isomers were also addressed. Computational chemistry was used to provide mechanistic insights. Formation of the majority of the rapamycin products could be rationalized with free radical-mediated autoxidation reactions involving alkene and alcohol sites. Methodological aspects of oxidative stress testing are discussed.

Mass balance in rapamycin autoxidation.

The immunosuppressant drug rapamycin is a complex polyene-containing natural product which undergoes autoxidation. The resulting product mixtures contained numerous monomeric and oligomeric compounds, which represented challenges for addressing mass balance in forced degradation studies and in analysis of aged developmental drug-eluting stents. A combination of SEC with ultraviolet and refractive index detection and RP-HPLC was used to account for drug loss and product formation. The mass balance methodology was subsequently validated for the determination of rapamycin and composite rapamycin autoxidation product material in developmental stent samples. This mass balance approach may find general applicability in other situations where drugs degrade to a plethora of products, which cannot be determined individually and summed.

Automation of Chemical Reaction Kinetics and Product Distribution Studies in Pharmaceutical Development

An automated instrument was designed and constructed to facilitate the performance of pharmaceutical degradation studies. A brief theoretical background on degradation kinetics is given to rationalize the design of the instrument and representative data are provided to illustrate its successful application. This system was found to be capable of conducting multiple simultaneous isothermal and nonisothermal kinetic studies with user-defined temperature profiles, sampling periods, and data logging.

Histological effects and bioaccumulation potential of coal particulate-bound phenanthrene in the fathead minnow Pimephales promelas

Abstract Fathead minnows Pimephales promelas were exposed to phenanthrene adsorbed to μm coal particles in a 14-day flow-through exposure to determine changes in histology and bioaccumulation. Based on light microscopic examination, coal particulates caused no obvious damage to external surfaces such as gills or skin and particulates were not observed to have accumulated in internal tissues. However, coal particles were readily ingested and this was followed by extensive mucous secretion by the gut mucosa. In addition, electron micrographs of the gut showed mucous globules in coal-exposed epithelium but no erosion of microvilli. Phenanthrene bioacumulation was compared in fish exposed to dissolved aqueous phenanthrene and fish exposed to dissolved aqueous phenanthrene plus coal particulate-bound phenanthrene. Enhanced phenanthrene uptake was not measured in coal-exposed fish and bioconcentration factors were 1000–4000 during the 14-day exposure period. Elimination of coal from the gut and phenanthrene from the tissues was rapid; both were undetectable after a 24-h depuration period.