Our group recently reported the isolation of two new
sesquiterpenes, englerins A (1) and B (2), from the root
bark and stem bark of Phyllanthus engleri Pax (Euphorbiaceae).1
Englerin A displayed remarkable potency and selectivity in its
inhibition of renal cancer cell line growth. Consequently,
englerin A (1) has been under intensive preclinical investigation
at the National Cancer Institute, and several groups
have published the synthesis of englerin A2−7 and analogues.8,9
At an early stage of this project, seven related bioactive
compounds (3−9) were isolated, with these considered to be
artifacts produced during the isolation procedure. Reported
here are their structures and biological activity and the synthesis
from 1 of the most active compound.