Involucratustones A-C (1-3), three cadinane dimers containing multiple contiguous quaternary carbons, were isolated from the rhizomes of Stahlianthus involucratus. Their structures were determined by a combination of NMR spectroscopy, chemical conversion, and X-ray diffraction analysis. Compounds 1 and 2 are rearranged homodimers of cadinane sesquiterpene fused with a unique fully substituted 1-oxaspiro[4.4]nonane core observed for the first time in natural products, and 3 is a novel 3',4'-seco-cadinane-dimer. Compounds 1 and 2 exhibited potent cytotoxic activities, and 3 showed notable anti-inflammatory effect.
Keywords: cadinane sesquiterpene dimer; natural products; quaternary carbons; spiro compounds; structure elucidation.
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