The South American medicinal plant called Pau ferro is a tall tree belonging to the leguminous genus Caesalpinia. Little chemical constituents other than gallic acid and ellagic acid in this plant have been reported so far. The acetone extracts of this bark exhibited the remarkable inhibitory activity on DNA topoisomerase II, and induced potent apoptosis in human leukemia cell line HL-60. In search of the bioactive substances, a variety of flavonoids including novel chalcone oligomers (1-5), prenyl flavone (7) and known compounds (amentoflavone (6), karanjachromene (8), 3',5'-dimethoxy-[2",3": 7,8]-furano flavone (9), desmethoxy kanugin (10)) were found from the bark extracts. In this paper, we report their compounds concerning the chemical structures and the biological activities. The molecular formulas of 1-5 and 7 were determined by HR-FABMS and HR-EIMS. Their planar structures were elucidated by the MS fragmentations and by using various NMR techniques (^1H, ^<13>C,^1H^1H-COSY, HMQC, and HMBC). The relative configurations of fran ring in 1-5 were deduced to be trans positions from NOESY. The stereochemistry around cyclobutane ring of 5 was presumed from the NOE difference spectra. Interestingly, 5 was a first example of chalcone trimer having cyclobutane structure. The chemical structures of all known compounds were identified by the comparison with published spectroscopic data. The isolated compounds were mainly evaluated for three bioactivities: inhibitory activity on DNA topoisomerase II, apoptosis induction in human leukemia cell line HL-60, and antidiabetic efficacy. 5 and 6 exhibited the inhibitory activities on topo II with IC_<50>-value of 2.1 and 8.3μM, respectively. 5 also revealed apoptosis in HL-60 with IC_<50> = 5.2μM. 8 showed cytotoxicity reaction of IC_<50> = 8.2μM. PPARα or γ activation potency as to antidiabetic efficacy was recognized on 9.

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