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 IC ₅₀ 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.