Uncommon Reactivity of a Seco-Oxacassane Diterpenoid and Antiproliferative Activity of Some Derivatives

The main diterpenoid of Acacia schaffneri, 7,8-seco-7,8-oxacassa-13,15-dien-7-ol-17-al (1), has two aldehydes of which one is protected as a ?-lactol. The free aldehyde resisted to afford the carboxylic acid using reagents with different oxidative strength, although 1 gave oxime 2 when treated with hydroxylamine, ?-hydroxyketone 3 after addition of acetone, aldo-?-lactone 4 whereby only the lactol was oxidized when using Jones reagent, and epoxyformate 5 after Baeyer-Villiger treatment. Hydrolysis of 5 with NaHCO3 gave 6. Structures 2?6 followed from physical and spectral data including X-ray diffraction. All compounds showed antiproliferative activity similar to some chemotherapeutic drugs against C2C12, L929, SiHa, and MDA-MB-231 cell lines.