scholarly journals α-Photooxygenation of chiral aldehydes with singlet oxygen

2019 ◽  
Vol 15 ◽  
pp. 2076-2084 ◽  
Author(s):  
Dominika J Walaszek ◽  
Magdalena Jawiczuk ◽  
Jakub Durka ◽  
Olga Drapała ◽  
Dorota Gryko
Keyword(s):  
Circular Dichroism ◽  
Singlet Oxygen ◽  
Absolute Configuration ◽  
Dft Methods ◽  
Catalyst Structure ◽  
Electronic Circular Dichroism ◽  
Silyl Ethers ◽  
Td Dft ◽  
The Absolute ◽  
Circular Dichroïsm

Organocatalytic α-oxygenation of chiral aldehydes with photochemically generated singlet oxygen allows synthesizing chiral 3-substituted 1,2-diols. Stereochemical results indicate that the reaction in the presence of diarylprolinol silyl ethers is highly diastereoselective and that the configuration of a newly created stereocenter at the α-position depends predominantly on the catalyst structure. The absolute configuration of chiral 1,2-diols has been unambiguously established based on electronic circular dichroism (ECD) and TD-DFT methods.

scholarly journals Absolute Configuration Sensing of Chiral Aryl- and Aryloxy-Propionic Acids by Biphenyl Chiroptical Probes

Chemosensors ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 154
Author(s):  
Stefania Vergura ◽  
Stefano Orlando ◽  
Patrizia Scafato ◽  
Sandra Belviso ◽  
Stefano Superchi
Keyword(s):  
Circular Dichroism ◽  
Absolute Configuration ◽  
Optical Rotation ◽  
Environmental Pollutants ◽  
Red Shift ◽  
Electronic Circular Dichroism ◽  
Configuration Assignment ◽  
Clear Sign ◽  
The Absolute ◽  
Circular Dichroïsm

The absolute configuration of chiral 2-aryl and 2-aryloxy propionic acids, which are among the most common chiral environmental pollutants, has been readily and reliably established by either electronic circular dichroism spectroscopy or optical rotation measurements employing suitably designed 4,4′-disubstituted biphenyl probes. In fact, the 4,4′-biphenyl substitution gives rise to a red shift of the diagnostic electronic circular dichroism signal of the biphenyl A band employed for the configuration assignment, removing its overlap with other interfering dichroic bands and allowing its clear sign identification. The largest A band red shift, and thus the most reliable results, are obtained by employing as a probe the 4,4′-dinitro substituted biphenylazepine 3c. The method was applied to the absolute configuration assignment of 2-arylpropionic acids ibuprofen (1a), naproxen (1b), ketoprofen (1c) and flurbiprofen (1d), as well as to the 2-aryloxypropionic acids 2-phenoxypropionic acid (2a) and 2-naphthoxypropionic acid (2b). This approach, allowing us to reveal the sample’s absolute configuration by simple optical rotation measurements, is potentially applicable to online analyses of both the enantiomeric composition and absolute configuration of these chiral pollutants.

scholarly journals Use of Circular Dichroism to Determine the Absolute Configuration of a Pimarane Diterpenoid from the Southern African Sclerocroton integerrimus (Euphorbiaceae)

2014 ◽  
Vol 9 (8) ◽  
pp. 1934578X1400900 ◽  
Author(s):  
Vuyelwa J. Tembu ◽  
Moses K. Langat ◽  
Neil R. Crouch ◽  
Dulcie A. Mulholland
Keyword(s):  
Circular Dichroism ◽  
Absolute Configuration ◽  
Spectroscopic Analysis ◽  
Stem Bark ◽  
Electronic Circular Dichroism ◽  
The Absolute ◽  
Circular Dichroïsm

From the stem bark and leaves of Sclerocroton integerrimus, eight compounds, including 17-hydroxy- ent-pimara-8(14),15-dien-3-one (1), were isolated. The structures of the compounds were determined on the basis of spectroscopic analysis. The absolute configuration of 17-hydroxy- ent-pimara-8(14),15-dien-3-one was confirmed from electronic circular dichroism studies.

Absolute configuration assignments by experimental and theoretical approaches of ent-labdane- and cis-ent-clerodane-type diterpenes isolated from Croton glabellus

2006 ◽  
Vol 84 (12) ◽  
pp. 1593-1602 ◽  
Author(s):  
Abraham García ◽  
Teresa Ramírez-Apan ◽  
J Antonio Cogordan ◽  
Guillermo Delgado
Keyword(s):  
Circular Dichroism ◽  
Absolute Configuration ◽  
Spectroscopic Data ◽  
Theoretical Approaches ◽  
Configuration Assignment ◽  
Td Dft ◽  
Bioassay Guided Fractionation ◽  
Labdane Diterpene ◽  
The Absolute ◽  
Circular Dichroïsm

The bioassay-guided fractionation of the moderately cytotoxic extract from Croton glabellus resulted in the isolation of bioactive compounds, which were characterized as austroinulin (2), 6-O-acetylaustroinulin (3), the acetonide artifact of 2 (4), and 3-O-methylkaempferol (9). In addition, a new natural cis-ent-clerodane lactone diterpene named marrubiagenin (1), trans-dehydrocrotonin (6), the epimeric mixture of cajucarinolide (7/8), and 5,7,3′,4′-tetrahydroxy-3-methoxyflavonoid (10) were also characterized and identified as nonbioactive compounds. The structures of all compounds were determined by analyses of their physical and spectroscopic data and by comparison with those reported in the literature. The absolute configuration assignment of 3 was carried out by means of the modified Mosher method and by the experimental and theoretical circular dichroism method establishing that 3 belongs to the ent-labdane diterpene series. Furthermore, the absolute configuration of 1 was established by analysis of its chiroptical properties concluding that 1 belongs to the cis-ent-clerodane diterpene series.Key words: Croton glabellus, ent-labdane-type diterpenes, cis-ent-clerodane-type diterpenes, circular dichroism, TD-DFT.

Stereodynamic Analysis of New Atropisomeric 4,7-Di(naphthalen-1-yl)-5,6-dinitro-1H-indoles

Synlett ◽  
2018 ◽  
Vol 29 (16) ◽  
pp. 2161-2166 ◽  
Author(s):  
Giovanni Petrillo ◽  
Michele Mancinelli ◽  
Angela Pagano ◽  
Emanuela Marotta ◽  
Andrea Mazzanti ◽  
...  
Keyword(s):  
Kinetic Analysis ◽  
Absolute Configuration ◽  
Indole Ring ◽  
Electronic Circular Dichroism ◽  
X Ray ◽  
Dft Simulation ◽  
Rotational Barriers ◽  
Td Dft ◽  
The Absolute ◽  
Circular Dichroïsm

A series of atropisomeric molecules containing the indole ring and two stereogenic axes were prepared. The four atropisomers were resolved by enantioselective HPLC. The rotational barriers of the indole–naphthyl axes were evaluated by means of kinetic analysis either by NMR or enantioselective HPLC. The absolute configuration of the ­atropisomers was determined by a combination of X-ray spectroscopy and TD-DFT simulation of electronic circular dichroism spectra.

scholarly journals The Assignment of the Absolute Configuration of Non-Cyclic Sesquiterpenes by Vibrational and Electronic Circular Dichroism: The Example of Chiliadenus lopadusanus Metabolites

Biomolecules ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1902
Author(s):  
Giuseppe Mazzeo ◽  
Alessio Cimmino ◽  
Giovanna Longhi ◽  
Marco Masi ◽  
Antonio Evidente ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Circular Dichroism ◽  
Statistical Analysis ◽  
Absolute Configuration ◽  
Density Functional ◽  
Human Pathogens ◽  
Functional Theory ◽  
Electronic Circular Dichroism ◽  
The Absolute ◽  
Circular Dichroïsm

9-Hydroxynerolidol, 9-oxonerolidol, and chiliadenol B are three farnesane-type sesquiterpenoids isolated from Chiliadenus lopadusanus that have shown an interesting activity against human pathogens as Gram+ and Gram− bacteria resistant to antibiotics. However, the absolute configuration (AC) of these interesting sesquiterpenes has not been assigned so far. Vibrational and electronic circular dichroism spectra have been recorded and correlations are pointed out for the three compounds. Density functional theory (DFT) calculations are used in conjunction with Mosher’s method of investigation to assign AC. Statistical analysis is considered to quantitatively define the choice of AC from VCD spectra.

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