Gram-scale purification of flavonolignan diastereoisomers from Silybum marianum (milk thistle) extract in support of preclinical in vivo studies for prostate cancer chemoprevention
Extracts of milk thistle (Silybum marianum, Asteraceae), termed ”silymarin,” are used worldwide, primarily for hepatoprotective applications and recently for prostate cancer chemoprevention. Silymarin is a mixture of at least eight compounds, and four major constituents are a group of structurally related flavonolignans: silybin A, silybin B, isosilybin A, and isosilybin B. The initiation of in vivo studies to compare the respective preclinical activities of each compound required that gram quantities of these diastereoisomers be prepared. Procedures were developed and optimized to produce multigram-scale quantities of each of these in > 97 % purity. A hybrid chromatographic/precipitative technique was developed, whereby mixtures were chromatographed at high concentrations so as to induce formation of a precipitate in the column fractions, yielding samples that were more enriched in the desired compounds than would be obtained solely by the chromatographic steps alone.