RESUMEN
This study was to investigate the chemical constituents from the aerial parts of Thymus przewalskii. The chemical consti-tuents were separated and purified by column chromatography on silica gel, ODS, Sephadex LH-20 and semi-prepared HPLC, and their structures were determined by physicochemical properties and spectroscopic data. Four flavanones were isolated from the ethanol extract of the aerial parts of T. przewalskii, and identified as(2S)-5,6-dihydroxy-7,8,4'-trimethoxyflavanone(1), 5,4'-dihydroxy-6,7-dimethoxyflavanone(2),(2S)-5,4'-dihydroxy-7,8-dimethoxyflavanone(3), sakuranetin(4), respectively. Compound 1 was a new compound and its configuration was determined by CD spectrum, compound 3 was natural product which was isolated for the first time and their configurations were determined by CD spectra. Compound 2 was isolated from the genus Thymus for the first time and compound 4 was isolated from T. przewalskii for the first time. Furthermore, cytotoxicity test was assayed for the four flavanones. They exhibited weak cytotoxicity against human lung cancer cells(A549), with the IC_(50) from 74.5 to 135.6 μmol·L~(-1).