ABSTRACT
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.
ABSTRACT
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.
Subject(s)
Antineoplastic Agents/chemical synthesis , Phenazines/chemical synthesis , Spiro Compounds/chemical synthesis , Steroids/chemical synthesis , Animals , Antineoplastic Agents/chemistry , Catalysis , Gold/chemistry , Molecular Conformation , Phenazines/chemistry , Spiro Compounds/chemistry , Stereoisomerism , Steroids/chemistry , Urochordata/chemistryABSTRACT
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.
Subject(s)
Squalene/analogs & derivatives , Terpenes/chemical synthesis , Molecular Conformation , Squalene/chemical synthesis , Squalene/chemistry , Stereoisomerism , Terpenes/chemistrySubject(s)
Heterocyclic Compounds, 4 or More Rings/chemical synthesis , Rhodophyta/chemistry , Squalene/analogs & derivatives , Squalene/chemistry , Heterocyclic Compounds, 4 or More Rings/chemistry , Molecular Conformation , Molecular Structure , Squalene/chemical synthesis , Stereoisomerism , Terpenes/chemistry , Terpenes/isolation & purificationABSTRACT
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.
Subject(s)
Squalene/analogs & derivatives , Squalene/chemistry , Alcohols/chemical synthesis , Alcohols/chemistry , Epoxy Compounds/chemical synthesis , Epoxy Compounds/chemistry , Models, Molecular , Molecular Conformation , Squalene/chemical synthesisABSTRACT
[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.
