This invention provides the compound having the structure wherein n is 1-10; X is C—R11 or N, wherein R11 is H, OH, SH, F, Cl, SO2R7, NO2, trifluoromethyl, methoxy, or CO—R7, wherein R7 is alkyl, alkenyl, alkynyl, C3-C8 cycloalkyl, or aryl; Z is R2 is H or NR3R4, wherein R3 and R4 are each independently H, C1-C6 alkyl, or C3-C8 cycloalkyl; R5 is OH or SH; and R6, R12, R13, and R14 are each independently H, OH, SH, F, Cl, SO2R15, NO2, trifluoromethyl, methoxy, or CO—R15, wherein R15 is alkyl, alkenyl, alkynyl, C3-C8 cycloalkyl, or aryl, or a salt of the compound, which is useful in the treatment of tumors.