A Full Conformational Characterization of Natural Ionones and Irones, as well as 13‐Alkyl‐Substituted α‐Ionones

Legnani, Laura; Luparia, Marco; Zanoni, Giuseppe; Toma, Lucio; Vidari, Giovanni

doi:10.1002/ejoc.200800429

Cited by 9 publications

(7 citation statements)

References 24 publications

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“…The structures with the cis arrangement around τ 1 were predicted to be transition-state structures of the first order and not minima on the PES. The low-energy forms found in this work are in agreement with the minima presented by Legnani et al, computed at a lower theory level (B3LYP/6-31G(d)). According to our calculations, the same six structures constitute the whole population of E -β-ionone at room temperature.…”

Section: Resultssupporting

confidence: 92%

Influence of Cage Confinement on the Photochemistry of Matrix-Isolated E-β-Ionone: FT-IR and DFT Study

2013

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β-ionone, a model compound of carotenoids ring structure, was investigated by FT-IR spectroscopy in a low-temperature argon matrix as well as using B3LYP/6-311++G(d,p) and MP2/6-311++G(d,p) quantum-chemical calculations. The spectrum of matrix-isolated E-β-ionone was analyzed and attributed to six conformers of the compound. Then, matrix-isolated E-β-ionone was submitted to UV irradiation using either a broadband source (with different cutoff filters) or a narrowband laser/MOPO system (at various wavelengths). Upon 240 nm narrowband irradiation, the formation of both Z-retro-γ-ionone and Z-β-ionone was observed, the reactant and the photoproducts being in a photostationary equilibrium. Under these conditions, the matrix environment was found to hamper subsequent reactions of Z-retro-γ-ionone and Z-β-ionone, so that this last species could be observed directly for the first time. Furthermore, the formation of Z-retro-γ-ionone was shown to occur directly via an intramolecular [1,5] H-atom shift and thereby, under the constraints imposed by the matrix confinement, the conformations assumed by this photoproduct were found to be strictly determined by those initially assumed by the reactant molecules. Broadband irradiation resulted in the completion of the reaction (disappearance of the reactant) and the sole observation of Z-retro-γ-ionone. These results imply that under these conditions the Z-β-ionone is unstable, very likely decaying to additional conformers of Z-retro-γ-ionone, as reflected in the broader bands due to this photoproduct observed in the infrared spectra of the broadband irradiated matrix.

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Section: Resultssupporting

confidence: 92%

Influence of Cage Confinement on the Photochemistry of Matrix-Isolated E-β-Ionone: FT-IR and DFT Study

2013

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“…The analog that Poirier and Yadav used in the latter study is almost identical to our compound 11 ( vide infra ). In 2008, 6 low-energy conformers of β-ionone were determined using the B3LYP/6-31G(d,p) level of theory, but the s-gauche conformers were similar in energy to the s-trans conformers (only 2 kJ/mol higher in energy than s-gauche )[21]. Using a variety of semi-empirical or ab initio computational approaches, the low-energy conformers of carotenes (including β-carotene) have also been reported in the literature.…”

Section: Introductionmentioning

confidence: 99%

Conformational analysis of retinoic acids: Effects of steric interactions on nonplanar conjugated polyenes

Cox

Muccio

Hamilton

2013

Computational and Theoretical Chemistry

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Retinoic acids and other vitamin A analogs contain a trimethylcyclohexenyl ring in conjugation with a polyene chain joined at carbon-6 (C6) and carbon-7 (C7). A MP2-SCS/cc-pVDZ// B3LYP/6-31G(d) 2-D potential energy surface was computed for all-trans retinoic acid, which had 6 minima (3 enantiomeric pairs). The global minima were distorted s-gauche enantiomers (6–7 = 53°) with half-chair conformations of the ring. Distorted s-gauche enantiomers (6–7 = 55°) with inverted half-chair ring conformations were 1.7 kJ/mol above the global minima. The s-trans enantiomers (6–7 = 164°) were 11.3 kJ/mol above the global minima. Steric energies were computed by the method of Guo and Karplus to identify key structural elements in retinoic acids which determines their conformation. Small molecule crystal structures in the CCDC database with trimethylcyclohexenyl ring and exocyclic double bonds have ring-chain geometries near to one of the 6 energy minima of retinoic acids, except for retinaldehyde iminium cations.

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“…Along this reasoning, in order to examine the influence of the C-5 alkyl substituent in the chemoreception of ionones, in previous studies we compared the olfactory properties of three synthetic 13-alkyl-substituted homologues 4 − 6 with parent ( S )-α-ionone ( 1 ) . It resulted that the three compounds maintained a predominant violet odor whose intensity dramatically depended on the steric hindrance of this group.…”

Section: Introductionmentioning

confidence: 99%

Enantioselective Synthesis and Olfactory Evaluation of Bicyclic α- and γ-Ionone Derivatives: The 3D Arrangement of Key Molecular Features Relevant to the Violet Odor of Ionones

et al. 2009

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Violet smelling ionones 1-3, occurring in the headspace of different flowers, are well-known perfumery raw materials. With the goal to recognize the still ill-defined spatial arrangement of structural features relevant to the binding of ionones to olfactory G-protein coupled receptors, through B3LYP/6-31G(d) modeling studies we identified bicyclic compounds 7-9 as conformationally constrained 13-alkyl-substituted analogues of monocyclic alpha- and gamma-ionones. They were thus synthesized to evaluate the olfactory properties. The enantioselective syntheses of 7-9 entailed two common key steps: (i) a Diels-Alder reaction to construct the octalinic core and (ii) a Julia-Lythgoe olefination to install the alpha,beta-enone side chain. The odor thresholds of synthetic 7 and 9 were significantly lower than the corresponding parent ionones, and 9 showed the lowest threshold value among violet-smelling odorants examined so far. Modeling studies suggested a nearly identical spatial orientation of key hydrophobic and polar moieties of compounds 1, 3, and 4-9. Presumably, interaction of these moieties with ionone olfactory receptors (ORs) triggers a similar receptor code that is ultimately interpreted by the human brain as a pleasant woody-violet smell. These results open the way to studies aimed at identifying and modeling complementary binding sites on alpha-helical domains of ionone receptor proteins.

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A Full Conformational Characterization of Natural Ionones and Irones, as well as 13‐Alkyl‐Substituted α‐Ionones

Cited by 9 publications

References 24 publications

Influence of Cage Confinement on the Photochemistry of Matrix-Isolated E-β-Ionone: FT-IR and DFT Study

Influence of Cage Confinement on the Photochemistry of Matrix-Isolated E-β-Ionone: FT-IR and DFT Study

Conformational analysis of retinoic acids: Effects of steric interactions on nonplanar conjugated polyenes

Enantioselective Synthesis and Olfactory Evaluation of Bicyclic α- and γ-Ionone Derivatives: The 3D Arrangement of Key Molecular Features Relevant to the Violet Odor of Ionones

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