title: Stereoselective biotransformation of timosaponin A-III by Saccharomyces cerevisiae.
abstract: Bioconversion of timosaponin A-III (TA-III), one of the major steroidal saponins isolated from the rhizomes of Anemarrhenae asphodeloides Bunge (Liliaceae), was investigated in Saccharomyces cerevisiae. Five bioconversion products, denoted compounds 2-6, were obtained. Biotransformation metabolite 2 was a stereoisomer of TAIII with a specific isotype F-ring and beta-ranged CH3-21, which rarely occurs in nature. The structure of 2 was elucidated by extensive spectroscopic analysis (H-H COSY, HSQC, HMBC), as well as by high-resolution mass spectral analysis. The growth inhibitory activity of compounds 1-6 was assayed against four human cancer cell lines, HepG2, H-1299, HT-29, and HCT-116. Compounds 1 and 2 obviously inhibited the growth of the four types of cancer cells with IC50 values being less than 19 micrometer. A structure-activity relationship is discussed, and the spirostane-ring F in compounds 1 and 2 appears to be the critical bioactive moiety for the cell growth inhibitory property.
authors.affiliation: Centre for Cancer and Inflammation Research, School of Chinese Medicine, Hong Kong Baptist University, Kowloon Tong, Hong Kong, China.
authors.forename: Yong-Mei
authors.initials: YM
authors.lastname: Hu
authors.forename: Zhi-Ling
authors.initials: ZL
authors.lastname: Yu
authors.forename: Wang-Fun
authors.initials: WF
authors.lastname: Fong
mesh_terms: D031403:Anemarrhena / Q000737:chemistry; D001711:Biotransformation; D045744:Cell Line, Tumor; D019073:HT29 Cells; D006801:Humans; D027343:Rhizome / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D012503:Saponins / Q000737:chemistry* / Q000378:metabolism*; D013237:Stereoisomerism; D013256:Steroids / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D012503:Saponins; D013256:Steroids; C543146:timosaponin AIII