New germacrane derivatives from Nanothamnus sericeous. X-Ray molecular structure of (1R,4R,5R,6R,10R)-1,10;4,5-diepoxy-11-hydroxygermacran-6-yl (Z)-2-methylbut-2-enoate

Four new closely related germacrane derivatives have been isolated from the acetone extract of Nanothamnus sericeous. Based on spectral data and some chemical evidence, the structures of these compounds have been established as (1R,4R,5R,6R,10R)-1,10;4,5-diepoxy-11-hydroxygermacran-6-yl (Z)-2-methylbut-2-enoate (1a), (4R,5R,6R)-4,5-epoxy-11-hydroxygermacr-1(10)-en-6-yl (Z)-2-methylbut-2-enoate (6a), (1R,4R,5R,6R,10S)-1,10;4,5-diepoxy-11-hydroxygermacrane-6,14-diyl bis-[(Z)-2-methylbut-2-enoate](7a), and 4ξ,5ξ,11-trihydroxygermacran-6-yl (Z)-2-methylbut-2-enoate (9a). The structure and stereochemistry of compound (1a) have been confirmed by X-ray crystallography.