Biomedical subjects

Thomas R Sharp

Publications and source records attributed to Thomas R Sharp.

3 recordsLinked to original sources

PubMed2004

Identification of low-level degradants from low dose tablets.

A multifaceted approach was successfully used to identify three of four unknown degradants in degraded low dose tablets. Accelerated solvent extraction (ASE) was found to be an invaluable tool in this multifaceted approach. ASE was capable of extracting four individual degradants of an active pharmaceutical component from 10 tablets into 15 mL of solvent with approximately 100% recovery for each degradant. Using ASE instead of manual extraction led to the extraction and isolation of the degradants in 1 day instead of 7 days. One of the degradants was extracted by ASE, isolated by semi-prep HPLC, and identified by LC-MS and NMR spectroscopy. The structures of two of the remaining three degradants were confirmed by synthesis of authentic samples, while the fourth degradant is yet to be identified.

Chromatography, High Pressure Liquid↗

PubMed2004

Pharmaceutical impurity identification: a case study using a multidisciplinary approach.

A multidisciplinary team approach to identify pharmaceutical impurities is presented in this article. It includes a representative example of the methodology. The first step is to analyze the sample by LC-MS. If the structure of the unknown impurity cannot be conclusively determined by LC-MS, LC-NMR is employed. If the sample is unsuitable for LC-NMR, the impurity needs to be isolated for conventional NMR characterization. Although the technique of choice for isolation is preparative HPLC, enrichment is often necessary to improve preparative efficiency. One such technique is solid-phase extraction. For complete verification, synthesis may be necessary to compare spectroscopic characteristics to those observed in the original sample. Although not widely practiced, an effective means of getting valuable structural information is to conduct a degradation study on the purified impurity itself. This systematic strategy was successfully applied to the identification of an impurity in the active pharmaceutical ingredient 1-(1,2,3,5,6,7-hexahydro-s-indacen-4-yl)-3-[4-(1-hydroxy-1-methyl-ethyl)-furan-2-sulphonylurea. Identification required the use of all of the previously mentioned techniques. The instability of the impurity under acidic chromatographic conditions presented an additional challenge to purification and identification. However, we turned this acidic instability to an advantage, conducting a degradation study of the impurity, which provided extensive and useful information about its structure. The following discussion describes how the information gained from each analytical technique was brought together in a complementary fashion to elucidate a final structure.

Drug Contamination↗

PubMed2004

Soft ionization mass spectrometry of chromanols produces radical cation molecular ions.

Several chromanol drug substance candidates exhibit unconventional behavior under the soft ionization conditions of fast atom bombardment and electrospray ionization in the mass spectrometer. Under FAB, these compounds produce radical cation molecular ions rather than protonated molecular ions. Similarly, under acidic mobile phase conditions in an electrospray LC-MS experiment, they produce radial cation molecular ions. Upon changing to a neutral, ammonium acetate-containing mobile phase, the molecular ion species is an ammonium adduct. The two example compounds behave conventionally under negative ion detection, both being free carboxylic acids and forming abundant [M - H](-). Examination of structural analogs indicates that the chromanol, methoxyl and chroman compounds behave this way. Oxidation to a chromanone causes formation of a conventional [M + H](+). Oxidation to a chromene produces even more complex behavior-namely a mixture of [M - H](+), M(+') and [M + H](+). We propose that, for these compounds, elimination of a valence electron to form the radical cation is the more energetically favored reaction than attachment of a proton.

Antioxidants↗