Silybin A

Natural Product Communications, 2011, 6(6):1653-1656.

A Comparison of the Diastereoisomers, Silybin A and Silybin B, on the Induction of Apoptosis in K562 cells[Pubmed: 22224281]

Two diastereoisomers of silybin, Silybin A and silybin B, were separated from silymarin by HPLC in our previous study.
METHODS AND RESULTS:
The present study assessed the effects of the diastereoisomers on cell apoptosis, and compared these with their mixture, silybin, in human chronic myeloid leukemia K562 cells. Both isomers showed stronger effects on cell growth inhibition and apoptosis induction than silybin. Compared with silybin B, Silybin A showed higher effects on the production of intracellular reactive oxygen species and Ca2+.
CONCLUSIONS:
These results suggest that Silybin A and silybin B have similar potency on apoptosis induction with different oxidative effects. Antagonistic effects may exist between Silybin A and silybin B, partially through ROS production and Ca2+ increase.

J Nat Prod. 2003 Sep;66(9):1171-4.

Molecular structure and stereochemistry of silybin A, silybin B, isosilybin A, and isosilybin B, Isolated from Silybum marianum (milk thistle).[Pubmed: 14510591 ]

METHODS AND RESULTS:
Two pairs of diastereoisomeric flavonolignans, Silybin A, silybin B, isoSilybin A, and isosilybin B, were successfully separated from Silybum marianum by sequential silica gel column chromatography, preparative reversed-phase HPLC, and recrystallization. Complete stereochemical assignments at C-2, C-3, C-7', and C-8' of these flavonolignans have been achieved.
CONCLUSIONS:
On the basis of X-ray crystallographic analysis and optical rotation data, coupled with comprehensive (1)H and (13)C NMR spectral data interpretation including COSY, HMQC, and HMBC, the stereochemistry of these diastereoisomers was determined unambiguously as Silybin A (4), 2R, 3R, 7'R, 8'R; silybin B (5), 2R, 3R, 7'S, 8'S; isoSilybin A (6), 2R, 3R, 7'R, 8'R; and isosilybin B (7), 2R, 3R, 7'S, 8'S.