Activity-guided isolation of steroidal alkaloid antiestrogen-binding site inhibitors from Pachysandra procumbens

Four novel steroidal alkaloids, (+)-(20S)-20-(dimethylamino)-3-(3'alpha-isopropopyl)-lactam-5 alpha-pregn-2-en-4-one (1), (+)-(20S)-20-(dimethylamino)-16 alpha-hydroxy-3-(3'alpha-isopropyl)-lactam-5 alpha-preg-2-en-4-one (2), (+)-(20S)-3-(benzoylamino)-20-(dimethylamino)-5 alpha-pregn-2-en-4 beta-yl acetate (3), and (+)-(20S)-2 alpha-hydroxy-20-(dimethylamino)-3 beta-phthalimido-5 alpha-pregnan-4 beta-yl acetate (4), as well as five known compounds, (-)-pachyaximine A (5), (+)-spiropachysine (6), (+)-axillaridine A (7), (+)-epipachysamine D (8), and (+)-pachysamine B (9), were isolated from Pachysandra procumbens, using a bioassay-guided fractionation based on inhibition of H-3-tamoxifen binding at the antiestrogen binding site (AEBS). Compounds 1-7 and 9 demonstrated significant activity as AEBS-inhibitory agents, and compounds 3, 5 and 9 were found to potentiate significantly the antiestrogenic effect mediated by tamoxifen in cultured Ishikawa cells. The structure elucidation of compounds 1-4 was carried out by spectral data interpretation.