1,5,7-Trihydroxy-6H-indeno[1,2-b]anthracene-6,11,13-trione (1), proposed to be the antitubercular natural product eucapsitrione, has been synthesized in 43% overall yield and six steps, including a key Suzuki-Miyaura biaryl coupling and a directed remote metalation (DReM)-initiated cyclization. The physical and spectroscopic properties of 1 do not match the data reported for the natural product. At this time there is insufficient information available to enable a structure reassignment. During the optimization of the Suzuki-Miyaura coupling, an unprecedented biaryl coupling ortho to the borono group was observed. The scope of this unusual reaction has been investigated.
The field of biomimetic synthesis seeks to apply biosynthetic hypotheses to the efficient construction of complex natural products. This approach can also guide the revision of incorrectly assigned structures. Herein, we describe the evolution of a concise total synthesis and structural reassignment of hyperelodione D, a tetracyclic meroterpenoid derived from a Hypericum plant, alongside some biogenetically related natural products, erectones A and B. The key step in the synthesis of hyperelodione D forms six stereocentres and three rings in a bioinspired cascade reaction that features an intermolecular Diels–Alder reaction, an intramolecular Prins reaction and a terminating cycloetherification.
The first approaches to the 10′-anthronyl-2anthraquinone skeleton have been devised, allowing two syntheses of the marine natural product albopunctatone. Both routes involve regioselective addition of a nucleophilic masked anthraquinone to a protected chrysazin derivative; the best affords albopunctatone in five steps and 35% overall yield. Albopunctatone exhibits potent inhibitory activity against Plasmodium falciparum and negligible toxicity to a range of other microbial pathogens and mammalian cells.
Michael additions of o-nitrophenylacetonitrile have been investigated. The adducts are formed diastereoselectively under mild conditions. Higher temperatures result in an unusual annulation involving intramolecular nucleophilic attack of an enolate on the nitro group, giving rise to 2,3,4-trisubstituted quinolines. In contrast, under similar conditions ethyl o-nitrophenylacetic acid reacts with N-methylmaleimide to give an N-hydroxyindole. A possible explanation for the divergent chemistry, and mechanisms for these reactions are proposed.
Homochiral (R)- and (S)-3,4-methylenedioxymethamphetamine (MDMA) were prepared in six steps (each) from the chiral pool precursors d- and l-alanine, respectively. The key step, copper-catalysed regioselective ring-opening of an N-tosylaziridine with an aryl Grignard reagent, proceeded in high yield with complete regioselectivity. Elaboration was achieved with preservation of configurational integrity, affording R- and S-MDMA hydrochlorides with enantiopurities of >99.5%, as determined by enantioselective HPLC with fluorescence detection. Attempts to apply the synthetic methodology to the synthesis of the homochiral enantiomers of the α-phenyl analogue of MDMA (UWA-001) were thwarted by a switch in regioselectivity in the key step.
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