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.

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 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.

(-)-Strempeliopine, stereoselective total synthesis and the determination of absolute configuration

1986 ◽  
Vol 51 (8) ◽  
pp. 1731-1742 ◽  
Author(s):  
Josef Hájíček ◽  
Jan Trojánek
Keyword(s):  
Circular Dichroism ◽  
Total Synthesis ◽  
Absolute Configuration ◽  
Determination Of Absolute Configuration ◽  
Natural Base ◽  
The Absolute ◽  
Circular Dichroïsm

A synthesis of (±)-strempeliopine (II) is described, the key step of which is the stereoselective reductive rearrangement of 18-methylene-1,2-dehydroaspidospermidine (XI). The absolute configuration of the natural (-)-base II was determined as (2S, 7R, 20R, 21R) on the basis of its synthesis from (+)-18-methylenevincadifformine (XVII) the configuration of which was derived from a comparison of circular dichroism properties of bases with a β-anilinoacrylate chromophore. The biogenesis of the alkaloids of the schizozygane type is discussed.

Absolute configuration determination of theanti-head-to-head photocyclodimer of anthracene-2-carboxylic acid through cocrystallization withL-prolinol

2013 ◽  
Vol 69 (11) ◽  
pp. 1411-1413 ◽  
Author(s):  
Yuko Kawanami ◽  
Hidekazu Tanaka ◽  
Jun-ichi Mizoguchi ◽  
Nobuko Kanehisa ◽  
Gaku Fukuhara ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Circular Dichroism ◽  
Carboxylic Acid ◽  
Absolute Configuration ◽  
Void Space ◽  
Circular Dichroism Spectra ◽  
The Absolute ◽  
Circular Dichroïsm ◽  
Hydrogen Bonded

The absolute configuration has been established of the enantiopureanti-head-to-head cyclodimer of anthracene-2-carboxylic acid (AC) cocrystallized with L-propinol and dichloromethane [systematic name: (S)-2-(hydroxymethyl)pyrrolidin-1-ium (5R,6S,11R,12S)-8-carboxy-5,6,11,12-tetrahydro-5,12:6,11-bis([1,2]benzeno)dibenzo[a,e][8]annulene-2-carboxylate dichloromethane monosolvate], C5H12NO+·C30H19O4−·CH2Cl2. In the crystal structure, the AC dimer interacts with L-prolinol through a nine-membered hydrogen-bonded ring [R22(9)], while the dichloromethane molecule is incorporated to fill the void space. The absolute configuration determined in this study verifies a recent assignment made by comparing theoreticalversusexperimental circular dichroism spectra.

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