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'.

Psorospermin, a new antileukemic xanthone from Psorospermum febrifugum.

An ethanolic extract of Psorospermum febrifugum was fractionated with antileukemic activity in vivo in the P388 lymphocytic leukemia in mice and in vitro in the KB cell culture system used as a guide. The new antileukemic xanthone psorospermin 1 was isolated, and its structure was elucidated. The chlorohydrin of O-methylpsorospermin 2 was also isolated after treatment of the fraction containing psorospermin chlorohydrin 6 with diazomethane.

Structure-activity relationships among in vivo active germacranolides.

Nine structurally related germacranolides from Eupatorium semiserratum and Eriophyllum confertiflorum were assayed in two standard tumor systems (PS and KB) to determine the structural features required for in vivo antileukemic activity. The moieties necessary for in vivo activity were found to be an alpha,beta-unsaturated ester side chain adjacent to the gamma-lactone and either a primary or secondary allylic alcohol or both.

Structural requirements for antileukemic activity among the naturally occurring and semisynthetic maytansinoids.

In an effort to determine the structural requirements for the significant antileukemic, cytotoxic, antitubulin, and antimitotic activity exhibited by the novel ansa macrolide, maytansine (1), four new C-3 ester and six new C-9 ether homologues were synthesized. The biological activities of these compounds were assayed and compared to the activities of previously reported, naturally occurring maytansinoids. From the data, it is apparent that presence of the C-3 ester is necessary for significant activity, and variations in the ester group are not accompanied by marked changes in activity.