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In order to find anti-dementia drugs from natural products, prolyl endopeptidase inhibitors were purified from Puerariae Flos by consecutive solvent partition, followed by silica gel, Sephadex LH-20, and HPLC. Four isoflavonoid inhibitors were isolated and identified as tectorigenin, genistein, 5,7-dihydroxy-4´,6-dimethoxyisoflavone, and 5-hydroxy-6,7,4´-trimethoxyisoflavone by means of instrumental analyses including ¹H-, ^(13)C-, ²D-NMR and MS and IC_(50) values against PEP were 5.30 ppm(17.7 μM), 10.39 ppm(38.5 μM), 13.92 ppm(44.3 μM), and 20.61 ppm (62.8 μM), respectively. Some previous mistakes in ^(13)C-NMR assignment were revised by careful investigation of HMBC and HMQC data.
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