Silybin A and B were separated from commercial silibinin using the preparative HPLC method. The described method is rapid and effective in obtaining gram-scale amounts of two diastereoisomers with minimal effort. In our approach, silibinin was dissolved in THF (solubility greater than 100 mg/mL), an alternative solvent to H₂O or MeOH in which silibinin has a very low solubility (ca 0.05-1.5 mg/mL), and then separated into its two components using preparative RP-HPLC. By starting with purified diastereoisomers, it was possible to obtain the two enantiomers of 2,3-dehydrosilybin in good yields and optically pure using an efficient oxidation procedure. All of the purified products were fully characterised using NMR (¹H, ¹³C), CD, [α](D), and ESI MS analyses. The purities of the products, which were evaluated using analytical HPLC, were greater than 98% in all cases.
Georg Thieme Verlag KG Stuttgart · New York.