Rapid Identification of Bibenzyls of Stemona sessilifolia using Hyphenated LC-UV-NMR and LC-MS Methods*

As a part of the ongoing search for new constituents of Stemona species in China, chemical investigation of Stemona sessilifolia, a plant used in the traditional Chinese medicine to treat respiratory disorders, was carried out. To identify the chemical components rapidly, a selected sample of S. sessilifolia containing bibenzyls was tested using LC-ESIMS and analyzed further using stop-flow LC-UV-NMR, which was sensitive for the detection of the main constituents. LC microfractions were collected using the LC-UV-NMR technique and HR-EIMS off-line analysis was carried out on the collected fractions. This chemical screening strategy allowed for the on-line identification of the main constituents of S. sessilifolia and provided information that was useful for a further peak-guided isolation procedure. Using these methods, four bibenzyls were isolated: two known compounds, 3,5-dihydroxy-4-methyl bibenzyl(1) and 3, 5-dihydroxy-2′-methoxy-4-methyl bibenzyl (2), and two novel compounds, 3, 3′-dihydroxy-5, 6′-dimethoxy bibenzyl (3) and 3,5-dihydroxy-2′,5′-dimethoxy bibenzyl (4).