Antitumor agents. 32. Synthesis and antitumor activity of cyclopentenone derivatives related to helenalin

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Abstract
Several new cyclopentenones related to helenalin were synthesized as potential alkylating antitumor agents. The procedure involved the transformation of 2-methyl-2-carbethoxycyclopentanone (2) to an ethylene ketal 3, bromination of 3 followed by dehydrobromination to yield a ketal olefin 5, reduction of 5 to the alcohol 6, conversion of 6 to the corresponding hydroxycyclopentenone 7, and esterification of 7 to afford the cyclopentenone esters 8-11. Biological assays indicated that only cyclopentenones possessing a conjugated ester side chain demonstrated significant in vitro cytotoxicity against the growth of tissue culture cells originating from human epidermoid carcinoma of the larynx (H.Ep.-2) as well as in vivo antitumor activity in Walker 256 carcinosarcoma in rats and P-388 lymphocytic leukemia in mice.