抄録
We have extended our systematic study of the genus Iva (Compositae, Heliantheae, subtribe Ambrosiinae) to Iva dealbata Gray, whose distribution is limited to west Texas and New Mexico. In the present paper, we discuss the structure of ivalbatin, a new sesquiterpene lactone from this species. Ivalbatin, C_<15>H_<20>O_4; [α]^<29>_D-84°, which easily polymerized to give an insoluble gum in ordinary solvents, was acetylated to furnish crystalline acetate (3), C_<17>H_<22>O_5; m.p. 128-128.5°; [α]^<20>_D-136°. A Michael adduct (8) obtained by the treatment of (3) with MeONa-MeOH, was acetylated to give crystalline acetate (9), C_<18>H_<26>O_6; m.p. 90-91°. (8) was dehydrated with MsCl-pridine or TsCl-lutidine to give a diene product (10). C_<16>H_<22>O_4; b.p. 130-140°/0.001 mmHg. The structure of ivalbatin has been established as (2) on the basis of the chemical and spectral data of (3), (9), and (10). The R-configuration of the asymmetric center at C-9 shown as (26) was determined by the Horeau method. The absolute configuration of ivalbin (1) which had been previously isolated from the same plant, is also discussed.
