Determination of levodopa methyl ester and its metabolites in rat serum by CZE with amperometric detection

Rapidly identifying bioactive compounds from Zhisou oral liquid by immobilized receptor-based high-performance affinity chromatography

The identification of bioactive compounds in complex matrices remains a major challenge due to the lack of highly efficient and specific methods. This work developed an approach based on high-performance affinity chromatography to identify the potential antitussive compounds from Zhisou oral liquid . The main methods include the synthesis of immobilized beta2-adrenoceptor by a one-step method, the screening and identification of the potential bioactive compounds by the receptor column coupled with mass spectrometry, and the binding mechanism analysis of the compounds to the receptor by the in vivo experiment, injection amount dependent method and molecular simulation. We identified the potential bioactive compounds of Zhisou oral liquid as glycyrrhizic acid, platycodin D, tuberostemonine, and hesperidin. In vivo experiment showed that the combinational utilization of the four compounds was possible to present an equivalent antitussive effect to the formula. The docking results demonstrated that hydrogen bonds and Van der Waals forces were the main forces to drive the binding of the four compounds to beta2-adrenoceptor. We concluded that the four compounds are the effective components in Zhisou oral liquid. The proposed strategy is possible to provide an alternative for the development of highly efficient methods to pursue the bioactive compounds of complex matrices.

Assay of levodopa in brain by CE

This article reports a CE (capillary electrophoresis) method for the determination of Levodopa (L-DP) in rabbit brain tissue. L-DP was separated and determined on a fused quartz capillary (75 microm ID, 75 cm length, 50 cm effective length, Beckman Co.) with a mobile phase of phosphate buffer (pH = 2.5, 20 mmol/L THAM, 3% carboxymethyl-beta-cyclodextrin), sample pressure 0.6 kPa x 6 s, separation voltage 20 KV, detected at 280 nm and temperature 25 degrees C. The calibration curve was linear (r = 0.9999, n = 6) within the range of 0.5-16 microg/ml for L-DP. The recovery ratio was 87.87%. The mean relative standard deviation (RSD) was 2.73% (n = 5). This method is convenient, rapid, accurate, and brings about good recovery; it can be used for content determination of levodopa in rabbit brain tissue.

Determination, purity assessment and chiral separation of levodopa methyl ester in bulk and formulation pharmaceuticals

A sensitive, reliable and reproducible HPLC method with electrochemical detection (HPLC-ECD) has been developed for the separation and quantification of levodopa methyl ester (LDME) and its impurities such as levodopa (l-DOPA), 3-methoxytyrosine (MTS) and l-tyrosine (TS) in bulk drug and pharmaceutical dosage form. The separation was performed on an LC18 column by isocratic elution with methanol-acetonitrile-50 mm potassium dihydrogen phosphate (8:2:90, v/v/v) containing 5 mm sodium 1-hexanesulfonate, 5 mm EDTA and 5 mm sodium chloride, adjusted with phosphoric acid to a pH of 3.2 as mobile phase. The correlation coefficients of linear regression for LDME, L-DOPA, MTS and TS were more than 0.999. The detection limits for L-DOPA, MTS and TS were 3.15, 2.04 and 2.88 ng/mL, respectively. The precision was checked in terms of F-test variance ratio using potentiometric titration as reference. The separation of dopa methyl ester enantiomers by chiral chromatography is also described. This method is capable of separating the two enantiomers with a selection of 1.4 and a resolution of 8.4. Both methods were found to be stable and useful in the quality control of the bulk material and formulations.