Richard Dunphy

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.

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.

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.

Characterization of autoxidation products of the antifungal compounds econazole nitrate and miconazole nitrate

Abstract Econazole nitrate 1 and miconazole nitrate 2 underwent autoxidation in 90% ethanol at 77 °C in the presence of AIBN and oxygen. The benzylic methylene carbons of 1 and 2 , the benzylic methine carbon of 2 , and the imidazole ring of 2 were sites of oxidation.