Sixteen 2-cyclohexenone and 6-(ethoxycarbonyl)-2-cyclohexenone analogs of combretastatin-A4 (CA-4, 1) were synthesized, and their ability to inhibit the growth of two murine cancer cell lines (B16 melanoma and L1210 leukemia) was determined using an MTT assay. One of the cyclohexenone analogs, 8, which contains the same substituents as CA-4 (1) is the most potent (IC 50 = 0.91 µM, L1210). Exposure of A-10 aortic cells to cyclohexenone 8 and its ester congener 7 produced significant reduction in cellular microtubules, with EC 50 values of 27 and 37 µM, respectively. Molecular modeling studies indicate that analog 8 adopts a twisted conformation, similar to CA-4, suggesting that conformation and structure are crucial for activity. These compounds are worthy of further investigation as potential tubulin inhibitors in the quest for novel anti-cancer agents.

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Abstract:Analogs of the seco-cyclopyrroloindoline (seco-CPI), the DNA alkylation pharmacophore of CC-1065 and the duocarmycins, can be prepared through a 5-exo-trig radical cyclization of a free radical and a 3-chloro-2-allylic moiety. This manuscript reports an unexpected discovery that, depending on the structure and stability of the free radical, the cyclization process leads to the production of an appreciable amount of secocyclopropyltetrahydroquinolines 7a-d along with the seco-cyclopropoyltetrahydroindoline products (6a-e). For instance, free radical reaction of the bromoallylic chloride 5a produced an equal amount of 6-benzyloxy-N-t-butoxycarbonyl-3-(chloromethyl)furano[e]indoline (6a), and 7-benzyloxy-N-t-butoxycarbonyl-3-chloro-1,2,3,4-tetrahydrofurano[f]quinoline (7a). Three other examples that produced mixtures of indoline and quinoline products are provided. In only one of the examples reported in this manuscript, the 6-benzyloxy-N-t-butoxycarbonyl-3-(chloromethyl)benzo[e]indoline, was a seco-CBI precursor 6e formed exclusively, consistent with literature precedents.

Preparation of a series of substituted diquinones is reported. In most examples, inverse order of addition (addition of a dimethoxybenzene derivative to a CAN solution) has been found to produce higher yields of diquinones than the traditional protocol in which the oxidant is added to the arene.