Abstract
Four new chromone glycosides, corymbosins K1-K4 (3–6), together with two known compounds, noreugenin (1) and undulatoside A (2), were isolated from the whole plant of Knoxia corymbosa (Rubiaceae). The structures of the new compounds were established through extensive NMR or X-ray spectroscopic analysis as 7-O-β-d-allopyranosyl-5-hydroxy-2-methylchromone (corymbosin K1, 3), 7-O-β-d-6-acetylglucopyranosyl-5-hydroxy-2-methylchromone (corymbosin K2, 4), 7-O-[6-O-(4-O-trans-caffeoyl-β-d-allopyranosyl)]-β-d-glucopyranosyl-5-hydroxy-2-methylchromone (corymbosin K3, 5) and 7-O-[6-O-(4-O-trans-feruloyl-β-d-allopyranosyl)]-β-d-glucopyranosyl-5-hydroxy-2- methylchromone (corymbosin K4, 6). Compounds 2–5 were subjected to test their immunomodulatory activity in vitro.
Acknowledgements
We are grateful to Dr. Hui-Zi Jin and Dr. Huang-Ping Zhang, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, for their useful suggestions.