Structures of lappaphen-a and lappaphen-b. New guaianolides linked with a sulfur-containing acetylenic compound, from Arctium lappa L.

Twonew guaianolides combined with a sulfur-containing acetylenic compoundwere isolated from Arctium lappa (Compositae).Their structures were elucidated on the basis of spectral data.Recently, we have reported the isolation of several of 5'-(1-propynyl)-2,2'-bithieny-5-yl derivatives0 and guaianolides, dehydrodihydrocostus lactone (4) and dehydrocostus lactone,2} from Arctium lappa L.Wecan now report on the isolation and structural elucidation of lappaphen-a (1) and lappaphen-b (2), the first reported compounds in which a sesquiterpenolide was linked to a sulfur-containing acetylenic compound by a carbon-carbon bond.VOH 0 ° ° ,