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Protein tyrosine phosphatase 1B plays a major role in the negative regulation of insulin signaling, and this establishes protein tyrosine phosphatase 1B as an attractive therapeutic target for diabetes. Bioassay-guided fractionation of the EtOAc-soluble extract of the seeds of Psoralea corylifolia afforded two protein tyrosine phosphatase 1B inhibitory compounds, psoralidin (1) and bakuchiol (2), along with inactive corylin. Compounds 1 and 2 inhibited PTP1B activity in a dose-dependent manner, displaying IC50 values of 9.4 +/- 0.5 microM and 20.8 +/- 1.9 microM, respectively.

Activity-guided fractionation of the EtOAc and MeOH extract of the leaves of Syringa dilatata NAKAI furnished one free radical scavenger, the secoiridoid glucoside oleuropein together with ligstroside and an iridoid glucoside, syringopicroside. Oleuropein interacted with the stable free radical, 1,1-diphenyl-2-picrylhydrazyl (DPPH), and showed an IC(50) value of 40.4 microM. L-Ascorbic acid as a positive control showed an IC(50) value of 50.3 microM., (Copyright 2003 John Wiley & Sons, Ltd.)

Chemical investigation of the EtOH extract of Morus alba L. (Moraceae), as guided by free radical scavenging activity, furnished 5,7-dihydroxycoumarin 7-methyl ether (1), two prenylflavones, cudraflavone B (2) and cudraflavone C (3), and oxyresveratrol (4). Compounds 1 and 4 showed superoxide scavenging effects with the IC(50) values of 19.1 +/- 3.6 and 3.81 +/- 0.5 microM, respectively. Compound 4 exhibited a DPPH free radical scavenging effect (IC(50) = 23.4 +/- 1.5 microM). Compounds 2 and 4 showed hepatoprotective effects with EC(50) values of 10.3 +/- 0.42 and 32.3 +/- 2.62 micro, respectively, on tacrine-induced cytotoxicity in human liver-derived Hep G2 cells.