Anthraquinone distribution in the hypogeal apparatus of Rubia peregrina L. growing wild in Sardinia.

The isolation, characterisation and quantification of anthraquinones, from hypogeal apparatus of Rubia peregrina L. (Wild Madder) growing wild in Sardinia (Italy) are described. The present study allowed us to perform an easy and fast HPLC analytical method for the detection of anthraquinones in all underground parts of plant. Concentrations of these compounds are variable in the different hypogeal parts before and after hydrolysis of the crude methanolic extracts. Before hydrolysis, we found that pseudopurpurin was 0.18% in rhizomes, alizarin 0.02% in rhizomes and principal stolons, and purpurin 0.56% in stolons of second order. Rubiadin is the major constituent of R. peregrina and reached a higher concentration in principal stolons of up to 4.8%. After hydrolysis, we found some drastic changes: an increase of purpurin in rhizomes (0.04%) and pseudopurpurin in all hypogeal parts (around 0.57%), and a decrease of purpurin in all parts of hypogeal apparatus. The most important change was found in rubiadin concentration, which reached its maximum in principal stolons (11.3%). No anthraquinones were found in the aerial parts of the plant.