RESUMO
Tolpyralate, a new selective postemergence herbicide developed for the weed control in corn, possesses a unique chemical structure with a 1-alkoxyethyl methyl carbonate group on the N-ethyl pyrazole moiety. This compound shows high herbicidal activity against many weed species, including glyphosate-resistant Amaranthus tuberculatus. Tolpyralate targets 4-hydroxyphenylpyruvate dioxygenase (4-HPPD), which is involved in the tyrosine degradation pathway. Inhibition of the enzyme destroys the chlorophyll, thereby killing the susceptible weeds. Details of tolpyralate discovery, structure optimization, and biological activities are described.
RESUMO
The first total synthesis of the cytotoxic alkaloid ritterazine B is reported. The synthesis features a unified approach to both steroid subunits, employing a titanium-mediated propargylation reaction to achieve divergence from a common precursor. Other key steps include gold-catalyzed cycloisomerizations that install both spiroketals and late stage C-H oxidation to incorporate the C7' alcohol.
Assuntos
Antineoplásicos/síntese química , Fenazinas/síntese química , Compostos de Espiro/síntese química , Esteroides/síntese química , Animais , Antineoplásicos/química , Catálise , Ouro/química , Conformação Molecular , Fenazinas/química , Compostos de Espiro/química , Estereoisomerismo , Esteroides/química , Urocordados/químicaRESUMO
The proof of the pudding: The first asymmetric total synthesis of the marine tetracyclic oxasqualenoid (+)-omaezakianol features a convergent olefin cross-metathesis between a monotetrahydrofuran fragment and a triepoxy alkene, and cascade oxacyclizations of a triepoxy alcohol to form the right-hand three ether rings. The total synthesis proved the absolute configuration of (+)-omaezakianol to be that shown.
Assuntos
Esqualeno/análogos & derivados , Terpenos/síntese química , Conformação Molecular , Esqualeno/síntese química , Esqualeno/química , Estereoisomerismo , Terpenos/químicaAssuntos
Compostos Heterocíclicos de 4 ou mais Anéis/síntese química , Rodófitas/química , Esqualeno/análogos & derivados , Esqualeno/química , Compostos Heterocíclicos de 4 ou mais Anéis/química , Conformação Molecular , Estrutura Molecular , Esqualeno/síntese química , Estereoisomerismo , Terpenos/química , Terpenos/isolamento & purificaçãoRESUMO
The asymmetric synthesis of tetraol (+)-3, a degradation product derived from a C2 symmetric oxasqualenoid intricatetraol 1, has been achieved through the two-directional synthesis starting from diol 7, realizing the further additional assignment of the incomplete stereostructure of 1, the stereochemistry of which is difficult to determine otherwise.
Assuntos
Esqualeno/análogos & derivados , Esqualeno/química , Álcoois/síntese química , Álcoois/química , Compostos de Epóxi/síntese química , Compostos de Epóxi/química , Modelos Moleculares , Conformação Molecular , Esqualeno/síntese químicaRESUMO
[structure: see text] The first asymmetric total synthesis of a structurally novel cis-cyclopent[c]isoxazolidine alkaloid, (-)-pyrinodemin A (3), which exhibits potent cytotoxicity, has been accomplished through a highly diastereoselective intramolecular nitrone-olefin cycloaddition reaction as the key step. Thus, it has been found that the hitherto unknown absolute configuration of pyrinodemin A is as indicated in the structural formula 3.
