Methods of using a compound, its pharmaceutically acceptable salts, and / or its pro-
drug esters, in isolated form, to treat
cancer, and methods for isolating, for formulating, and for administering the compound, salt, and / or pro-
drug ester as an antitumor agent, wherein the compound, salt, or pro-
drug ester has the following structure: wherein:R1, R2, R5, R7, and R8 are each separately selected from the group consisting of a
hydrogen atom, a
halogen atom, and saturated C1-C24
alkyl, unsaturated C1-C24 alkenyl, cycloalkyl, cycloalkenyl, alkoxy, cycloalkoxy,
aryl, substituted
aryl, heteroaryl, substituted heteroaryl, amino, substituted amino, nitro, substituted nitro, phenyl, and substituted phenyl groups,R3, R4, and R6 are each separately selected from the group consisting of a
hydrogen atom, a
halogen atom, and saturated C1-C12
alkyl, unsaturated C1-C12 alkenyl, cycloalkyl, alkoxy, cycloalkoxy,
aryl, substituted aryl, heteroaryl, substituted heteroaryl, amino, substituted amino, nitro, and substituted nitro groups,X1 and X2 are separately selected from the group consisting of an
oxygen atom, and a
sulfur atom, andthe dashed bond represents a bond selected from the group consisting of a carbon-carbon
single bond and a carbon-carbon
double bond. Most preferably, R3 and R4 are
hydrogen, and each are involved in hydrogen bonds, and / or the dashed bond is a
double bond, such that the chemical backbone of the compound substantially retains a substantially planar conformation.