RESUMO
A C29 phytoecdysteroid named amarasterone A (1) has been isolated from Cyathula capitata (Amaranthaceae), Leuzea carthamoides (Asteraceae), and Microsorum scolopendria (Polypodiaceae). We recently isolated amarasterone A from C. officinalis. Amarasterone A has been postulated as a biosynthetic intermediate of cyasterone in Cyathula sp. The stereochemistry at the C-24 and C-25 positions of these amarasterone A samples was investigated by comparing the NMR spectroscopic data with those of stereodefined model compounds, (24R,25S)-, (24R,25R)-, (24S,25S)-, and (24S,25R)-isomers of (20R,22R)-3ß-methoxystigmast-5-ene-20,22,26-triol (2a-d), which were synthesized in the present study. Amarasterone A isolated from Cyathula officinalis was determined to be the (24R,25S)-isomer (1a), while amarasterone A from L. carthamoides was found to be the (24R,25R)-isomer (1b). Amarasterone A from M. scolopendria was found to be a mixture of 1a and 1b. The biosynthesis of cyasterone in Cyathula sp. is discussed on the basis of the identical C-24 configuration of sitosterol and amarasterone A.
Assuntos
Estigmasterol/análogos & derivados , Espectroscopia de Ressonância Magnética , Estereoisomerismo , Estigmasterol/síntese química , Estigmasterol/química , Estigmasterol/isolamento & purificaçãoRESUMO
Chemical investigation of ecdysteroidal constituents of the roots and stems of Cyathula officinalis led to the isolation of two cyasterone stereoisomers, 2 and 3, together with the known cyasterone 1. The structures of compounds 2 and 3 were determined to be 28-epi-cyasterone and 25-epi-28-epi-cyasterone, respectively, by means of spectroscopic analysis. X-Ray structures of 1 and 2 confirmed the 24S,25S,28R configuration for 1 and 24S,25S,28S for 2.