New macrocyclic trichothecenes from Baccharis megapotamica.

: The isolation and structural elucidation of biologically active baccharinoids B1 [11a], B2 [12a], B3 [5a], and B7 [6a] are reported with crystal structure determinations of baccharinoid B7 and of the triacetate of baccharinoid B2. All four compounds are isomeric with 11a/12a and 5a/6a being epimeric at C13'.