New bakuchiol dimers from Psoraleae Fructus and their inhibitory activities on nitric oxide production

Dried fruits of Psoralea corylifolia L. (Psoraleae Fructus) is one of the most popular traditional Chinese medicine with treatment for nephritis, spermatorrhea, pollakiuria, asthma, and various inflammatory diseases. Bakuchiol is main meroterpenoid with bioactive diversity from Psoraleae Fructus. This study was designed to seek structural diverse bakuchiol derivants with anti-inflammatory activities from this plant.

Various column chromatography methods were used for isolation experiment. Structures and configurations of these compounds were determined by spectroscopic methods and single-crystal X-ray diffraction. Their inhibition on nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages were evaluated by the Griess reaction.

Twelve unpresented bakuchiol dimmers, bisbakuchiols M-U (1-9) and bisbakuchiol ethers A-C (10-12), along with five known compounds (13-17), were isolated from the fruits of Psoralea corylifolia L. Compounds 1-3, 10-12, 16 and 17 exhibited inhibitory activities against LPS-induced NO production in RAW264.7 macrophages, and the inhibition of compound 1 (half maximal inhibitory concentration (IC₅₀) value = 11.47 ± 1.57 μM) was equal to that of L-N(6)-(1-iminoethyl)-lysine (IC₅₀ = 10.29 ± 1.10 μM) as a positive control.

Some compounds exhibited inhibitory activities against NO production, and the study of structure-activity relationship suggested that uncyclized compounds with oxygen substitution at C-12/12' showed strong inhibitory activities, and carbonyl units contributed to enhanced activities.