Phytochemistry of cimicifugic acids and associated bases inCimicifuga racemosaroot extracts

Abstract Introduction Earlier studies reported serotonergic activity for cimicifugic acids (CA) isolated from Cimicifuga racemosa . The discovery of strongly basic alkaloids, cimipronidines, from the active extract partition and evaluation of previously employed work‐up procedures has led to the hypothesis of strong acid/base association in the extract. Objective Re‐isolation of the CAs was desired to permit further detailed studies. Based on the acid/base association hypothesis, a new separation scheme of the active partition was required, which separates acids from associated bases. Methodology A new 5‐HT 7 bioassay guided work‐up procedure was developed that concentrates activity into one partition. The latter was subjected to a new two‐step centrifugal partitioning chromatography (CPC) method, which applies pH zone refinement gradient (pHZR CPC) to dissociate the acid/base complexes. The resulting CA fraction was subjected to a second CPC step. Fractions and compounds were monitored by 1 H NMR using a structure‐based spin‐pattern analysis facilitating dereplication of the known acids. Bioassay results were obtained for the pHZR CPC fractions and for purified CAs. Results A new CA was characterised. While none of the pure CAs was active, the serotonergic activity was concentrated in a single pHZR CPC fraction, which was subsequently shown to contain low levels of the potent 5‐HT 7 ligand, N ω ‐methylserotonin. Conclusion This study shows that CAs are not responsible for serotonergic activity in black cohosh. New phytochemical methodology (pHZR CPC) and a sensitive dereplication method (LC‐MS) led to the identification of N ω ‐methylserotonin as serotonergic active principle. Copyright © 2009 John Wiley & Sons, Ltd.