Synthesis, Antitumor Evaluation, and Apoptosis-Inducing Activity of Hydroxylated (E)-Stilbenes Cedric J. Lion, Charles S. Matthews, Malcolm F. G. Stevens, and Andrew D. Westwell* Cancer Research U.K. Experimental Cancer Chemotherapy Research Group, Centre for Biomolecular Sciences, School of Pharmacy, University of Nottingham, Nottingham, NG7 2RD, U.K. Received September 17, 2004 The parallel solution-phase synthesis of a series of 30 monohydroxylated (E)-stilbene analogues is described. In vitro screening revealed low micromolar activity (GI 50 ) against the MDA MB 468 breast cancer cell line. Activity in MDA MB 468 cells correlated with the ability to induce apoptosis following drug treatment by the most potent agents in the series, e.g., 5dy and 5jy, an observation further reinforced by AnnexinV-FITC analysis and fluorescence microscopy. Introduction A number of hydroxylated stilbenes derived from natural sources with a range of interesting biological activities have been reported. 1 Most notable among these from the antitumor perspective are the trihy- droxylated trans-stilbene resveratrol 2 (isolated from edible materials such as grape skins, peanuts, and red wine) and the hydroxylated cis-stilbene combretastatin A-4 3 (from the African bush willow Combretum caf- frum), shown in Figure 1. The intriguing cardioprotective and cancer chemo- preventative activity associated with resveratrol has prompted several reports describing the synthesis and antitumor evaluation of resveratrol analogues. For example, Roberti and co-workers have described the synthesis and biological evaluation of resveratrol ana- logues as apoptosis-inducing agents. 4 Also, Kim and co- workers have reported the synthesis of a range of (protected) trans-stilbene analogues and their evalua- tion as human cytochrome P450 (CYP) inhibitors to find a potent and selective inhibitor of the isoform CYP1B1. 5 Because of our ongoing interest in the antitumor evaluation of novel chemical structures arising from the chemical oxidation of bioactive phenols, 6 we became interested in the synthesis of novel monohydroxylated stilbenes structurally related to resveratrol. Our reasons for choosing monohydroxylated (rather than polyhy- droxylated) stilbenes at this stage were twofold: first, to enable the rapid parallel synthesis of a range of substituted analogues for antitumor evaluation and, second, to simplify and control subsequent oxidation chemistry. In this paper we report the solution-phase parallel synthesis and antitumor evaluation of a library of 30 monohydroxylated trans-stilbenes containing a variety (H, OMe, and F) of ring substituents. Chemistry Interest in the biological properties of resveratrol has resulted in the development of a number of synthetic methods toward this trihydroxystilbene, most commonly using the Wittig reaction and its variants to install the ethylenic bridge. Unfortunately these methods often lead to low yields of trans product and/or low E/Z selectivity and produce triphenylphosphine oxide as a byproduct, necessitating chromatographic purification. Recently Guiso and co-workers have reported the syn- thesis of resveratrol, exclusively in the (E)-form in good yield, via Heck reaction between a protected styrene derivative and protected p-iodophenol. 7 We wished to develop our own strategy toward the solution-phase synthesis of (E)-stilbenes to produce new products in parallel without the need to resort to column chromatography and in quantities for full characteriza- tion and biological profiling (>50 mg). We chose to make use of Horner-Wadsworth-Emmons olefination chem- istry, methodology possessing the key advantages of both (E)-specificity and easy removal of the water- soluble dialkylphosphoric acid byproduct. 8 A related strategy toward the synthesis of a substituted (E)- stilbene library for evaluation as human cytochrome P450 1B1 inhibitors was recently reported. 5 The overall scheme for the parallel solution-phase synthesis of our hydroxylated (E)-stilbene library is shown in Scheme 1. Reaction of the (10) substituted benzylphosphonic acid diethyl esters (1a-j) under Hor- ner-Emmons-Wadsworth conditions with 2-, 3-, or 4-methoxymethyl-substituted hydroxylbenzaldehydes (2x-z) afforded 30 novel protected monohydroxystilbene derivatives (3ax-jz) exclusively in the (E)-conformation in each case (no (Z)-isomer could be detected by 1 H NMR analysis). Among a range of protecting groups exam- ined, the methoxymethyloxy (MOM) protecting group was found to be optimal, offering both easy attachment to and removal from the phenol and stability under Horner-Emmons-Wadsworth reaction conditions. Parallel reactions could be carried out on either Carousel reaction systems mounted on conventional hot- plate stirrers or on a Stem block format. A slight excess of benzaldehyde (2x-z) was required in each case to * To whom correspondence should be addressed. Phone: +44 115 9513419. Fax: +44 115 953412. E-mail: andrew.westwell@ nottingham.ac.uk. Figure 1. Structures of (E)-resveratrol and (Z)-combretastatin A-4. 1292 J. Med. Chem. 2005, 48, 1292-1295 10.1021/jm049238e CCC: $30.25 © 2005 American Chemical Society Published on Web 02/02/2005