1,721,027 research outputs found
A general enantioselective approach to jasmonoid fragrances: synthesis of (+)-(1R, 2S)-methyl dihydrojasmonate and (+)-(1R, 2S)-magnolione
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Enantioselective Divergent Synthesis of (−)-cis-α- and (−)-cis-γ-Irone by Using Wilkinson’s Catalyst
No full textA simple, efficient synthesis is reported for (-)-cis- a- and (-)-cis-g-irone, two precious constituents of iris oils, in > 99 % diastereomeric and enantioselective ratios. The two routes diverge from a common intermediate prepared from (-)-epoxygeraniol. Of general interest in this approach is the installation of the enone moiety of irones through a NHC-AuI-catalyzed Meyer–Schuster-like rearrangement of a propargylic benzoate and the use of Wilkinson’s catalyst for the stereoselective hydrogenation of a prostereogenic exocyclic double bond to secure the critical cis stereochemistry of the alkyl groups at C2 and C6 of the irones. The ste- reochemical aspects of this reaction are rationally supported by DFT calculation of the conformers of the substrates un- dergoing the hydrogenation and by a modeling study of the geometry of the rhodium h2 complexes involved in the dia- stereodifferentiation of the double bond faces. Thus, compu- tational investigation of the h2 intermediates formed in the catalytic cycle of prostereogenic alkene hydrogenation by using Wilkinson’s catalyst could be highly predictive of the stereochemistry of the products
A General and Concise Enantioselective Divergent Approach to 13-Alkyl-Substituted Ionones
No full textA novel enantioselective divergent route to 13-alkyl derivatives of alpha- and gamma-ionone, important components of perfumes and fragrances, is reported. This relatively short and convenient methodology takes advantage of the use of a common intermediate, easily obtained from highly enantiomerically enriched (S)-a-ionone, which avoids the separate installation of the butenone side chain at C(6) for each analog. Olfactory evaluation of synthesized compounds reconfirmed the influence of the hydrophobic interactions of alkyl substituents at C(5) with olfactory receptors (ORs) in the chemoreception of ionones, and suggested that a synperiplanar orientation of C(13) and the lateral chain is the better geometry fitting OR's cavity
First total synthesis of labeled EPA and DHA-derived A-type cyclopentenone isoprostanoids: [D2]-15-A3t-IsoP and [D2]-17-A4t-NeuroP
Full text linkA-type cyclopentenone isoprostanoids are abundantly formed in vivo by radical peroxidation of eico- sapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are consumed daily for the prevention of cardiovascular and neurological pathologies. To facilitate in depth studies concerning the effects of these oxidized isoprostanoids on human health, labeled derivatives are necessary. In this paper, we have accomplished the ␣rst total synthesis of labeled A-type cyclopentenone isoprostanoids, namely 17,18- [D2]-15-A3t-IsoP and 19,20-[D2]-17-A4t-NeuroP. The two enantioselective routes are highly convergent, stemming from a common intermediate, readily available by a JuliaeKocienski reaction, and feature the semihydrogenation of an alkyne moiety for the installation of the labeled lower side chain
Synthesis and Assignement of Absolute Configuration of the Iridoid 9-Deoxygelsemide.
Full text linkThe first enantioselective synthesis of 9-deoxygelsemide, belonging to a rare group of iridoids isolated from Gelsemium plants, is described. The key synthetic steps are a variant of the Woodward-Prevost reaction to install the characteristic cis-r-1,2-dioxygenated system at C-6 and C-7 with complete diastereoselectivity. Construction of the dihydropyran ring was achieved via formylation of lactone I, followed by dehydration of the corresponding lactol. The synthesis allowed assignment of absolute configuration to 9-deoxygelsemide and related iridoids
The Importance of the 5-Alkyl Substituent for the Violet Smell of Ionones: Synthesis of Racemic 5-Demethyl-α-ionone
No full textThe synthesis and the odor tonalities of racemic 5-demethyl-α-ionone are described. This synthetic ionone derivative did not show the typical floral-woody violet smell of α-ionone, definitely proving the importance of a suitably sized and spatially oriented alkyl substituent at C(5) for stimulating olfactory receptors of ionones
Asymmetric synthesis of 14-A(4t)-neuroprostane: hunting for a suitable biomarker for neurodegenerative diseases
No full textOxidative stress has long been associated with aging and age-related pathologies, such as neurodegenerative diseases. One of the direct effects of oxidative stress in vivo is the formation of prostaglandin-like compounds, named isoprostanes, by the action of reactive oxygen species on membrane phospholipids. A particular subclass of isoprostanes, named neuroprostanes, is formed from docosahexaenoic acid (C22: 6ω3, DHA) and is considered to be specific for neuronal oxidative stress. Since isoprostanes are considered as golden standards for oxidative stress, and due to the specificity of neuroprostanes for this condition in neurons and their relation with Alzheimer’s and Parkinson’s diseases, they are envisioned to be suitable biomarkers for these pathologies. Herein we describe the first total synthesis of 14-A4t-NeuroP in an enantioselective and stereoselective fashion, by means of a new and rapid approach for the installation of the ω chain based on a chemoselective Julia-Kocienski olefination. Furthermore, the construction of the 4,5-cis-disubstituted cyclopentenone moiety characteristic of class A neuroprostanes is achieved in a stereospecific fashion, and suitable reaction conditions have been tuned to avoid epimerization of the labile stereogenic centers
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