Synthesis and in vitro antitumour activity of crassalactone D, its stereoisomers and novel cinnamic ester derivatives

Naturally occurring styryl lactone, crassalactone D (1), unnatural 4-epi-crassalactone D (2), and the corresponding 7-epimers (3 and 4) have been synthesized starting from d-glucose. The key step of the synthesis is a new one-pot sequence that commenced with a Z-selective Wittig olefination of suitably functionalized sugar lactols with a stabilized ylide, (methoxycarbonylmethylene)-triphenylphosphorane, in dry methanol, to afford 1 or 3, in the mixtures with the corresponding 4-epimers (2 or 4, respectively). A number of 6-O-cinnamoyl derivatives of styryl lactones 1-4 have been prepared, bearing electron donating or electron withdrawing functionalities in the C-4 position of cinnamic acid residue. The synthesized products were evaluated for their in vitro antiproliferative activity against selected human tumour cell lines, whereupon very potent cytotoxicities have been recorded in many cases. SAR analysis indicated some important structural features responsible for biological activity, such as stereochemistry at the C-4 and C-7 positions, as well as the nature of a substituent at the C-4 position in the aromatic ring of cinnamoate moiety. Flow cytometry and Western blot analysis data gave insight in the mechanism underlying antiproliferative effects of the synthesized compounds.