Search PubMed⌕ Search

Biomedical subjects

W H Hong

Publications and source records attributed to W H Hong.

10 recordsLinked to original sources
PubMed1981

Characteristics of equilibrium reaction of zolazepam.

The equilibrium reaction of zolazepam, a pyrazolodiazepinone, was studied and analyzed using the approach used previously for other pyrazolodiazepinone derivatives. The intrinsic ring closure equilibrium constant for this reaction was approximately 100 times larger than that observed for pyrazolodiazepinones studied previously. This study illustrates that the diazepinone ring can dominate in equilibrium mixtures formed at pH values far below the pKa of the corresponding form.

Azepines↗
PubMed1979

Stability-indicating assay for vidarabine.

A physicochemical procedure for the analysis of vidarabine in aqueous parenteral formulations was needed to assure potency and to define stability. Concurrent with the development of this method, its decomposition products and route in aqueous solution were determined. A quantitative procedure was developed to determine intact drug in the presence of decomposition products, and the results obtained were validated by microbial assay. Spectral (UV and polarimetric) and TLC evidence indicated that, in aqueous solution, hydrolysis without racemization occurs, yielding adenine and arabinose. The sensitivity of the method to decomposition is improved by ion-exchange separation of adenine and drug before UV measurement. Analysis of partially decomposed solutions of the drug by both ion-exchange and microbiological methods gave comparable results.

Chromatography, Thin Layer↗
PubMed1977

Equilibrium reaction of pyrazolodiazepinones in aqueous solution.

This study of the behavior of some pyrazolodiazepinones in aqueous solution at near ambient temperature indicated that they form stable equilibrium mixtures consisting of ring and opened forms. Under isothermal conditions, mixtures are produced whose composition is dependent on pH and may vary from that corresponding to essentially complete ring opening to complete closure. Ring closure equilibrium constants were calculated, and the influence of methyl substitution was determined. Substitution of a methyl group for an amido hydrogen in the open form results in a fivefold increase in this constant. Methylation of the terminal amino group, however, did not cause a corresponding increase and may not significantly affect equilibrium.

Azepines↗
PubMedDate not supplied

Isolation of vindoline from Catharanthus roseus by supercritical fluid extraction.

Vindoline was extracted from the leaves of Catharanthus roseus over the ranges of 35-70 degrees C and 100-300 bar using supercritical carbon dioxide with and without the addition of 3 wt % ethanol as a cosolvent. The vindoline contents in the extracts were determined by HPLC and identified by LC/MS. The remarkable highest vindoline concentration, 58 wt %, was obtained at the lowest temperature, 35 degrees C, and the highest pressure, 300 bar, of this study. The use of a cosolvent only slightly improved the extraction yields or selectivities at some experimental conditions.

Biotechnology↗