Enantioselective synthesis of a marine antibiotic (-)-atrop-abyssomicin C was accomplished in 21 steps, in 1.8% overall yield (4%, based on the recovered starting material). The key steps of the synthesis are the formation of the functionalized cyclohexane core by an organocatalyzed Tsuji-Trost reaction, the formation of a tricyclic spirotetronate unit by a gold-catalyzed reaction sequence and the highly efficient eleven-membered ring closure by a Nozaki-Hiyama-Kishi reaction. Biological tests showed all abyssomicin derivatives to possess strong antibacterial activity against methicillin resistant S. aureus strains; however, they also proved to be cytotoxic, both to malignant and to normal somatic cells.
Synergic combination of organotransition metal catalysis and organocatalysis allows, for the first time, the Tsuji-Trost cyclization of aldehydes. A catalytic asymmetric variant of the reaction is also possible.
The total synthesis of desmethylabyssomicin C analogue 1 was accomplished using diastereotopos-selective ring closing metathesis and Nozaki-Hiyama-Kishi cyclization as the key steps. The synthetic analogue retained its antibacterial activity against methicillin-resistant S. aureus strains, whereas its cytotoxicity decreased for three orders of magnitude, as compared to atrop-abyssomicin C.
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