scholarly journals Assignment of Absolute Configuration of Bromoallenes by Vacuum-Ultraviolet Circular Dichroism (VUVCD)

Molecules ◽  
2021 ◽  
Vol 26 (5) ◽  
pp. 1296
Author(s):  
Taiki Umezawa ◽  
Nakaba Mizutani ◽  
Koichi Matsuo ◽  
Yuugo Tokunaga ◽  
Fuyuhiko Matsuda ◽  
...  
Keyword(s):  
Circular Dichroism ◽  
Absolute Configuration ◽  
Vacuum Ultraviolet ◽  
Specific Rotation ◽  
Ultraviolet Region ◽  
Cotton Effects ◽  
The Absolute ◽  
Circular Dichroïsm ◽  
Absolute Stereochemistry ◽  
Unambiguous Assignment

A new application of vacuum-ultraviolet circular dichroism (VUVCD), which enables the measurement of CD spectra in the vacuum-ultraviolet region (140–200 nm), for the assignment of the absolute configurations of bromoallenes is described. Bromoallene moieties are found in natural products obtained from many marine organisms. To date, the absolute configuration of bromoallenes has been assigned almost exclusively with Lowe’s rule, which is based on specific rotation. However, exceptions to Lowe’s rule have been reported arising from the presence of other substituents with large specific rotations. For the unambiguous assignment of the absolute configuration of the bromoallene moiety with its characteristic absorption wavelength at 180–190 nm due to the π–π* transition, VUVCD was applied to four pairs of bromoallene diastereomers prepared by modifying the synthetic scheme of omaezallene. The VUVCD spectra clearly showed positive or negative Cotton effects around 180–190 nm according to the configuration of the bromoallene employed, revealing the potential of VUVCD for determining absolute stereochemistry.

Absolute stereochemistry of the spiroxins

2001 ◽  
Vol 79 (11) ◽  
pp. 1786-1791 ◽  
Author(s):  
Tao Wang ◽  
Osamu Shirota ◽  
Koji Nakanishi ◽  
Nina Berova ◽  
Leonard A McDonald ◽  
...  
Keyword(s):  
Circular Dichroism ◽  
Absolute Configuration ◽  
Phenolic Hydroxyl ◽  
Hydroxyl Group ◽  
Exciton Coupling ◽  
The Absolute ◽  
The Difference ◽  
Circular Dichroïsm ◽  
Absolute Stereochemistry

The absolute configuration of spiroxin A has been determined by exciton-coupled circular dichroism (CD). Namely, the difference CD between spiroxin A – bis-methoxycinnamate, as well as that between spiroxin A – bis-retinoate, both exhibit negative exciton couplings between the acylated phenolic hydroxyl group chromophores. This establishes the absolute configuration as 2S,3R,4S,2'S,3'R,4'S.Key words: circular dichroism, exciton coupling, spiroxins, antitumor, antifungal.

Capsidiol and 1-epicapsidiol: absolute configuration, nmr, and optical spectra of the dibenzoates

1981 ◽  
Vol 59 (15) ◽  
pp. 2303-2305 ◽  
Author(s):  
M. J. Stillman ◽  
J. B. Stothers ◽  
A. Stoess
Keyword(s):  
Circular Dichroism ◽  
Absolute Configuration ◽  
Magnetic Circular Dichroism ◽  
Optical Spectra ◽  
Circular Dichroism Spectra ◽  
The Absolute ◽  
Circular Dichroïsm ◽  
Magnetic Circular Dichroism Spectra ◽  
Absolute Stereochemistry

Application of the exciton chirality method has confirmed that capsidiol, a unique eremophilane, has the absolute stereochemistry depicted in 1. The 1H and 13Cmr, circular dichroism, and magnetic circular dichroism spectra of capsidiol and 1-epicapsidiol dibenzoates are discussed.

(-)-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.

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.

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.

Sign in / Sign up

Export Citation Format

Share Document