Thiolysis-HPLC/MS characterization of oligomeric and polymeric proanthocyanidins in Ephedra sinica

Proanthocyanidins (PAs) can be found in a wide variety of edible plants such as green tea, cranberry and peanuts. They have been reported to have anticancer, antiallergical and antimicrobial activity and are effective antioxidants. Ephedra sinica Stapf (Ephedraceae), a plant widely used in TCM, is known to contain PAs, but so far only unusual dimeric PAs, e.g. ephedrannin A or B, have been identified as constituents of this plant [1].

The aim of this work was the characterization of oligomeric and polymeric PAs from aerial parts of E. sinica. By means of silica gel column chromatography and precipitation from methanol and chloroform mixtures, PA enriched fractions varying in their degree of polymerization were obtained. Samples were analyzed by a thiolytic degradation/HPLC-MS assay. Reference compounds were prepared by thiolytic degradation of a larger amount of Ephedra-PAs followed by isolation and structure elucidation via LC-MS and NMR. Analysis of the precipitated fractions revealed a mean degree of polymerization between 15 (precipitate 50% methanol) and 6 (precipitate 25% methanol). Monomeric units were identified as gallocatechin and epigallocatechin (81 – 83% of total units) as well as catechin and epicatechin. Interestingly, the investigated PAs turned out to be a complex mixture of double linked A-type and single linked B-type units.

Results of this study suggest that aerial parts of E. sinica are a useful source of oligomeric and polymeric PAs mainly consisting of epigallocatechin and gallocatechin monomers. Studies to investigate the contribution of these compounds to the pharmacological activity of E. sinica are ongoing.

References:

[1] Tao et al.(2008) Planta Medica 74: 1823 – 5