Chau Yang Chen

Photochemical decomposition of alkannin/shikonin enantiomers

Abstract Alkannin/shikonin ((±)-5,8-dihydroxy-2-(1-hydroxy-4-methyl-3-pentenyl)-1,4-naphthoquinone), isolated from Macrotomia euchroma , is sensitive to light exposure. A chloroform solution of alkannin/shikonin was exposed to sunlight for 1 month. The major photolytic product, a newly discovered naphthoquinone derivative, was isolated by adsorption chromatography. The chemical structure of the purified photolytic product was identified by NMR, MS and FTIR techniques to be (−)-5,8-dihydroxy-2-(1-hydroxy-3-oxo-4-methyl-4-pentenyl)-1,4-naphthoquinone, indicating that a photo-oxidation reaction had occurred.

Photolysis of indomethacin in methanol

Abstract A novel photo-oxidation product containing a six-membered 1,2-dioxane ring was isolated from the photolysis of indomethacin in methanol and a possible mechanism is proposed.

Inclusion Complex of Carprofen with Hydroxypropyl-β-cyclodextrin

The aim of this study was to investigate the characteristics ofhydroxypropyl-β-cyclodextrin (HPCD) on the solubility,photostability and dissolution of carprofen (CP). It was found that the solubility of carprofen increased 52-fold when16% HPCD was added to H2O (w/v). The phase-solubility diagram revealed the formation of a 1 : 1 inclusion complex of CP-HPCD with a stability constant (ks) of 487 M-1. Formation of the inclusion complex of CP-HPCD was analyzed using differential scanning calorimetry (DSC). Changes in chemical shifts of the 1H-nuclear magnetic resonance spectra of CP-HPCD demonstrated that the inclusion site of CP by HPCD was carbazolyl aromatic ring skeleton rather thanthe side chain of propanoic acid. The photostability study revealed that theCP-HPCD complex could not significantly decrease the rate of photodegradation of CP, implying that the rate-determining step of CP mainly occurredat the side chain. The dissolution rates of CP were significantly enhanced as the proportions of HPCD increasedin the prepared discs. The dissolution of the physical mixture (in a 1 : 3 molarratio) increased by about 6-fold in comparison with the parent drug. The improvement of wettability and solubility of CP by complexing to HPCD was reflected in theenhanced dissolution rate.