A. Synthesis and biochemical evaluation of estrogen analogs. B. Synthetic strategies for constructing benzopyrone combinatorial libraries

4-Hydroxy estradiol (4-OHE2) is an oxidative metabolite of estrogens that is implicated as a possible causative agent in estrogen-induced tumorigenesis. The tumorigenic potential of 4-OHE2 may be a result of its ability to bind ER and initiate mitogenic events or its oxidative metabolism and redox-cycling properties resulting in DNA lesions. In order to separate the receptor activation and redox cycling properties, a series of C-4 hydroxyalkylestradiol analogs were synthesized as metabolically stable analogs of 4-OHE2. These compounds lack the catechol moiety and were not expected to undergo redox cycling and produce oxidative stress. On the other hand, the hydroxyl groups at position 3- and 4- in these compounds were expected to mimic the binding interactions of 4-OHE2 with receptors and enzymes. The Stille cross-coupling and the carboxymethylation reactions used for the synthesis of these analogs represent two efficient and previously unexplored synthetic routes for the functionalization of the 4-position of estradiol. The 4-hydroxyalkyl estrogens and catechol estrogens were compared in potentiometric and DNA-damaging studies. These studies revealed that the non-redox cycling estrogen analogs are unable to induce DNA damage, where as catechol estrogens produce DNA damage. A novel synthetic route was developed for synthesis of catechol estrogens based on Baeyer-Villiger oxidation of 2- and 4-substituted formyl estradiols. In addition several estrogen analogs were synthesized as potential inhibitors of estrogen-hydroxylases, the enzymes responsible for metabolizing estrogens into catechol estrogens. 2-Methoxymethylestradiol (2MME2) was identified as a novel inhibitor of tubulin polymerization in vitro.;The benzopyrone ring system is present in various natural products that interact with enzymes and receptors of therapeutic importance in breast and prostate cancer. In an another project, a novel synthetic route was developed for constructing benzopyrone libraries. Readily available salicylic acids and terminal alkynes were used as building blocks for the benzopyrone ring system. A series of o-(O-t-butylsilyloxy)benzoyl chlorides generated from salicylic acids were coupled with a range of terminal alkynes to afford alkynyl ketones. The alkynyl ketones were converted to enaminoketones and cyclized to yield a benzopyrone ring system. Piperazinyl resin was used to effect a resincapture of the alkynones to yield support bound enaminoketones, which underwent an on-resin cyclization to provide the benzopyrone ring system. This synthetic approach utilizes readily available starting materials, mild and high yielding reactions with good functional group tolerance, and is ideal for developing combinatorial libraries centered around the benzopyrone ring system. Synthesis and screening of benzopyrone combinatorial libraries would allow us to harvest the biological potential of these molecules.