A compound, or a pharmaceutically acceptable salt or ester thereof, having a formula I of: R20—(Z)b—(Y)c—(R21)a—X—R22—R23 wherein R20 is an aryl, substituted aryl, heteroaryl, substituted heteroaryl, heterocycloalkyl, substituted heterocycloalkyl, alkoxy, aryloxy, a silyl-containing group, a boryl-containing group, a phosphine-containing group, amino, a thio-containing group, a seleno-containing group, halide, or a nitro-containing group; Z is alkanediyl, substituted alkanediyl, cycloalkanediyl, or substituted cycloalkanediyl; Y is S, O, or NR10, wherein R10 is H or alkyl; R21 is alkanediyl, substituted alkanediyl, cycloalkanediyl, substituted cycloalkanediyl, alkadienyl, substituted alkadienyl, alkatrienyl, substituted alkatrienyl; X is —C(=0)- or —S(=0)(=0)-; R22 is a moiety that includes at least one divalent amino radical; R23 is an aryl, substituted aryl, heteroaryl, substituted heteroaryl, heterocycloalkyl, substituted heterocycloalkyl, alkoxy, aryloxy, a silyl-containing group, a boryl-containing group, a phosphine-containing group, amino, a thio-containing group, a seleno-containing group, halide, or a nitro-containing group; a is 0 or 1; b is 0 or 1; and c is 0 or 1; provided that if X is —C(=0)- then Y is not S.