Quantitation of oligomeric procyanidin clusters with defined degree of polymerisation from Hypericum perforatum L.

Oligomeric proanthocyanidins (OPC) in medicinal plants are known to modify pharmacokinetic or pharmacodynamic characteristics of active compounds within plant extracts. Quantitation of total oligomeric and polymeric proanthocyanidins is mainly performed by a colorimetric method against pyrogallol (1). This method does not give any information on the distribution of the different oligomers in the respective plant extracts. Additionally the response factors of the different proanthocyanidin oligomers are not comparable to each other, leading to inaccurate values. For unambiguous identification and quantitation of OPC clusters in herbal material and extracts from Hypericum perforatum L. OPC clusters with defined degree of polymerization (DP 3 to 10) were isolated by preparative HPLC from the herbal material and characterized as procyanidins by the respective exact molecular masses. These OPC clusters were used as reference standards for quantitation of these polyphenols from St. John's wort. For qualitative investigation on OPC distribution and quantitation of distinct OPCs naphtodianthrons were removed by SPE on RP18ec, followed by HPLC separation of the OPC clusters on diol phase and fluorescent detection (2, 3). Quantitation was performed by external calibration against the respective reference standards. The method was validated according ICH. Batch analysis indicated DP 3 oligomer being the major cluster in St. John's wort; also the variability of OPC clusters in relation to different herbal materials and time of storage is discussed in detail.

References: 1. monograph 2.8.14 PhEur (2008) Vol6:328.

2. Kelm et al. (2006)J. of Agri. and Food Chem. 54(5):1571–1576.

3. Zumdick et al. (2009) Pharmazie 64:286–288.