RESUMO
α-Fluorinated ß-amino thioesters were obtained in high yields and stereoselectivities by organocatalyzed addition reactions of α-fluorinated monothiomalonates (F-MTMs) to N-Cbz- and N-Boc-protected imines. The transformation requires catalyst loadings of only 1â mol % and proceeds under mild reaction conditions. The obtained addition products were readily used for coupling-reagent-free peptide synthesis in solution and on solid phase. The α-fluoro-ß-(carb)amido moiety showed distinct conformational preferences, as determined by crystal structure and NMR spectroscopic analysis.
Assuntos
Amidas/química , Ésteres/síntese química , Peptídeos/síntese química , Quinidina/química , Compostos de Sulfidrila/síntese química , Catálise , Cristalografia por Raios X , Ésteres/química , Halogenação , Modelos Moleculares , Conformação Molecular , Peptídeos/química , Quinidina/análogos & derivados , Estereoisomerismo , Compostos de Sulfidrila/químicaRESUMO
The chemical composition of the essential oils obtained by hydrodistillation from the pastinocello carrot, Daucus carota ssp. major (Vis.) Arcang. (flowers and achenes), and from nine different commercial varieties of D. carota L. ssp. sativus (achenes) was investigated by GC/MS analyses. Selective breeding over centuries of a naturally occurring subspecies of the wild carrot, D. carota L. ssp. sativus, has produced the common garden vegetable with reduced bitterness, increased sweetness, and minimized woody core. On the other hand, the cultivation of the pastinocello carrot has been abandoned, even if, recently, there has been renewed interest in the development of this species, which risks genetic erosion. The cultivated carrot (D. carota ssp. sativus) and the pastinocello carrot (D. carota ssp. major) were classified as different subspecies of the same species. This close relationship between the two subspecies urged us to compare the chemical composition of their essential oils, to evaluate the differences. The main essential-oil constituents isolated from the pastinocello fruits were geranyl acetate (34.2%), α-pinene (12.9%), geraniol (6.9%), myrcene (4.7%), epi-α-bisabolol (4.5%), sabinene (3.3%), and limonene (3.0%). The fruit essential oils of the nine commercial varieties of D. carota ssp. sativus were very different from that of pastinocello, as also confirmed by multivariate statistical analyses.
Assuntos
Daucus carota/química , Frutas/química , Óleos Voláteis/química , Acetatos/análise , Monoterpenos Acíclicos , Alcenos/análise , Monoterpenos Bicíclicos , Análise por Conglomerados , Cicloexenos/análise , Daucus carota/classificação , Flores/química , Cromatografia Gasosa-Espectrometria de Massas , Limoneno , Sesquiterpenos Monocíclicos , Monoterpenos/análise , Análise de Componente Principal , Sesquiterpenos/análise , Terpenos/análiseRESUMO
A combined experimental and computational approach provided insight into the nature and conformational dependence of long-range 4JHF couplings in α-fluoro amides. The dependence of 4JHF on substituents and the solvent was investigated. H-F coupling constants determined by NMR spectroscopy are in agreement with DFT calculations. NBO analysis revealed that a favourable nFâσNH* interaction correlates with the magnitude of 4JHF.
RESUMO
Fluorinated monothiomalonates (F-MTMs) were used as building blocks for the stereoselective synthesis of organofluorine compounds. We present conjugate addition reactions between F-MTMs with nitroolefins that proceed under mild organocatalytic conditions and provide access to α-fluoro-γ-nitro thioesters with adjacent tetrasubstituted and tertiary stereogenic centers. Only 1 mol % of a cinchona alkaloid-urea catalyst is necessary to obtain the addition products in excellent yields and stereoselectivities. The methodology allowed for the straightforward synthesis of a fluorinated analogue of the PAR-2 agonist AC-264613.