One hundred and seventy crude drugs were screened for prolyl endopeptidase (PEP) inhibitors. Among them, 80% methanolic extract of 18 medicinal plants such as Polygonum cuspidata, Sanguisorba officinalis, Eugenia caryophyllata, Rubus coreanus, Cinnamomum cassia (Cassiae Cortex and Cinammomi Ramulus), Rheum palmatum, Ulmus pumila, Sorbus commixta, Areca catechu, Uncaria sinensis, Terminalia chebula, Caesalpinia sappan, Nelumbo nucifera, Machilus thunbergii, Paeonia moutan, Elscholtzia patrini and Cynomorium coccineum inhibited more than 70% of PEP activity at a concentration of 40 ppm. The active principles of P. moutan, M. thunbergii, T chebula, A. catechu, S. commixta, R. palmatum, R. coreanus, E. caryophyllata and P. cuspidata were transferred into organic solvents, which showed more than 75% inhibition at 5 ppm.
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