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The chirality of eschscholtzxanthin (all-trans (3S,3′S)-4′,5′-didehydro-4,5′-retro-β,βcarotene-3,3′-diol) at 3,3′ was assigned from the CD correlation of the natural material and the semi-synthetic carotenoid prepared by (NBS-dehydrogenation of natural zeaxanthin ((3R,3′R)-β,β-carotene-3,3′-diol). The δ6(6′)-trans configuration followed from 1H NMR evidence, including nuclear Overhauser experiments with rhodoxanthin, retrodehydro-carotene (4′,5′-didehydro-4,5′-retro-β,β-carotene) and smaller retro model compounds revealing a general preference for the δ6-trans configuration in retro compounds. Biosynthetic considerations are made. 相似文献
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