Glutaminase inhibitory activity of umbelliferone isolated from kabosu (Citrus sphaerocarpa Hort. ex Tanaka).

Kabosu (Citrus sphaerocarpa Hort. ex Tanaka) fruits have pleasant and fresh odors and have been used as raw materials for vinegar, seasonings, jams, marmalades and juices in Japan. The n-butanol extracts from kabosu fruits were prepared and a component in the extract was purified by column chromatography and HPLC to afford compounds 1-3. Three compounds, 5-(hydroxymethyl)-2-furaldehyde (1), umbelliferone (2) and oxypeucedanin hydrate (3), have been isolated from kabosu, and the structures of compounds 1-3 were elucidated by 1 D and 2 D NMR as well as EI-MS. Compound 2 exhibited potent glutaminase inhibitory activity with an IC50 value of 1.33 mM. This is the first report on glutaminase inhibitory activity of 2 and the isolation of three compounds 1-3 from kabosu fruits.