The chemical components of Japanese Baizhi (Byakushi), the root of Angelica dahurica BENTH. et HOOK. (Umbelliferae), were investigated. As coumarin components, xanthotoxin, marmesin, scopoletin, anhydrobyakangelicin (isobyakangelicol), and neobyakangelicol (I) were newly isolated, in addition to byakangelicol, byakangelicin, phellopterin, oxypeucedanin, and imperatorin reported previously. The structure of I was elucidated as 5-methoxy-8-(2'-hydroxy-3'-methyl-buten-3'-yl) oxypsoralen from the following reasons. 1) Its ultraviolet (UV) spectrum resembles one of byakangelicin. 2) The elementary analysis and the mass spectrum suggest the molecular formula of C17H16O6, corresponding to an isomer of byakangelicol and anhydrobyakangelicin. 3) Its nuclear magnetic resonance (NMR) (Fig. 1) and infrared (IR) spectra show that I possesses a methyl, a hydroxyl, and a vinyl methylene groups. 4) Treatment of I with formic acid produces 5-methoxy-8-hydroxy-psoralen (II). Furthermore, alloisoimperatorin and II were isolated from the distillattion residue of petroleum-ether extract of the root.
