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This article describes an application of the host‐guest chiral recognition approach called tweezer methodology for the determination of the absolute configuration of 3‐hydroxy‐β‐lactams. These substrates represent challenging cases due to their chemical reactivity, the presence of multiple stereogenic centers and several functional groups which offer various possibilities of binding to the Zn‐porphyrin...
A direct semipreparative HPLC enantioseparation of two chiral thiazolidinone derivatives having cyclooxygenase‐2 inhibition activity was performed on the Chiralpak IA chiral stationary phase. Semipreparative amounts of enantiopure forms were collected using acetonitrile‐ethanol‐trifluoroacetic acid mixtures as mobile phase. The absolute configuration of both compounds was unequivocally established...
Density Functional Theory (DFT) calculations of optical rotation (OR) and vibrational circular dichroism (VCD) have been used to assign the absolute configuration (AC) of a recently prepared (3‐phenyloxirane‐2,2‐diyl)bis(phenylmethanone), 3, by asymmetric epoxidation of the corresponding 2‐arylidene‐1,3‐diketone. The experimental OR at 589.3 nm and the VCD spectrum of the (+)‐ and (−)‐enantiomer of...
We describe herein the use of a flexible biphenyl moiety as efficient chirality probe in the assignment of the absolute configuration (AC) of aliphatic, non‐chromophoric diols. The diols are transformed in the corresponding biphenyl dioxolanes in which the biphenyl system has either a P or M torsion depending on the chirality of the diol. As the correlation between biphenyl torsion and diol AC has...
The absolute configuration of semisynthetic (−)‐3α,6β‐acetoxytropane 1, prepared from (−)‐6β‐hydroxyhyoscyamine 2, has been determined using vibrational circular dichroism (VCD) spectroscopy. The vibrational spectra (IR and VCD) were calculated using DFT at the B3LYP/DGDZVP level of theory for the eight more stable conformers which account for 99.97% of the total relative abundance in the first 10...
In‐depth conformational analyses of 10 known eremophilane (= (1S,4aR,7R,8aR)‐decahydro‐1,8a‐dimethyl‐7‐(1‐methylethyl)napththalene) sesquiterpenes, 1–10, from Petasites hybridus were performed with molecular mechanics as well as density functional theory methods. Electronic transition energies and rotational strengths of these eight eremophilane lactones and two petasins were calculated by time‐dependent...
Time‐dependent density functional theory (TD‐DFT) has been employed to simulate the circular dichroism (CD) spectra of bipyridyl ruthenium(II) complexes as well as zinc(II) and copper(II) complexes containing tris(2‐pyridylmethyl)amine (TPA) derivatives. A qualitative model is used to account for the mechanism by which the bis‐ and tris‐bipyridine complexes (or analogous systems) exhibit exciton CD...
The conversion into 6,7‐dihydro‐5H‐dibenz[c,e]azepine (DAZ) N‐protected amides is a viable route for the determination of the absolute configuration of chiral 2‐substituted carboxylic acids. The biphenyl moiety of DAZ, besides being a probe of chirality for the electronic circular dichroism (ECD) spectroscopy, makes these systems suitable for configuration assignment by exploiting the chirality amplification...
The transfer of chirality from a guest molecule to an achiral host is the subject of significant interest especially when, upon chiral induction, the chiroptical response of the host/guest complex can effectively report the absolute configuration (AC) of the guest. For more than a decade, dimeric metalloporphyrin hosts (tweezers) have been successfully applied as chirality probes for determination...
Secoscabronine M (1) is a hemiacetal cyathane diterpenoid that was isolated from the fruiting bodies of the basidiomycete Sarcodon scabrosus (Fr.) Karst. Compound 1 possesses a novel structure with a bond cleavage between C‐3 and C‐4. The structure of the new compound was elucidated by means of spectroscopic methods, including two‐dimensional nuclear magnetic resonance experiments. The absolute configuration...
The effect of conformational flexibility on the chiroptical properties of a series of synthetic (3R)‐3‐hydroxy‐4‐aryl‐β‐lactams of known stereochemistry (1–6) was investigated by means of electronic circular dichroism (ECD) measurements and time‐dependent density functional theory (TD‐DFT) calculations. The application of the β‐lactam sector rules allowed a correct stereochemical characterization...
A synthesis of diastereomeric bicyclic dibenzoyl esters derived from enantiomerically pure (1S,5S)‐bicyclo[3.3.1]nonane‐2,6‐dione was accomplished. Molecules containing two benzoyl chromophores with different configuration in the bicyclic framework were obtained. Chiroptical properties of the synthesized enantiomerically pure molecules were studied. Diastereomeric esters exhibited exciton couplets...
The hemicryptophane racemate (±)‐M-1, P-1 was optically resolved by semipreparative HPLC on Chiralpak IC column. The absolute configuration of each isolated enantiomer was established from the analysis of their electronic circular dichroism spectra. Enantiodifferentiation of the chiral cationic cage (±)‐M-1, P-1 was evidenced in solution using Δ‐TRISPHAT as chiral solvating agent, and the diastereomeric...
Absolute configurations (ACs) of 3‐alkylphthalides including natural products (−)‐3‐n‐butylphthalide ((S)‐1) and fuscinarin have been studied using chiroptical properties and quantum chemical calculation. Electronic circular dichroism and optical rotatory dispersion spectra of (S)‐1 predicted adopting time‐dependent density functional theory and hybrid functionals coincide very well with the experimental...
The preparation of tetrakis((+)‐hfbc) lanthanide(III) complexes with an encapsulated alkali metal and ammonium ions M[Ln((+)‐hfbc)4] (hereafter abbreviated as M‐Ln : (+)‐hfbc, (+)‐heptafluorobutyrylcamphorate; M, ammonium or benzyl ammonium ions as well as alkali metal ions) was reported and discussed. The electronic circular dichroism (CD) spectra in the intraligand π−π* transition of M–Ln were examined...
Four known hydroxyanthraquinones (1–4) together with four new derivatives having a tetralone moiety, namely coniothyrinones A–D (5–8), were isolated from the culture of Coniothyrium sp., an endophytic fungus isolated from Salsola oppostifolia from Gomera in the Canary Islands. The structures of the new compounds were elucidated by detailed spectroscopic analysis and comparison with reported data....
Coatline A (1) and α‐epi‐coatline A (4) co‐occur in the trunk extract of Andira coriacea. Inspection of their chiroptical properties led to intriguing results. After a careful examination of the experimental data used for the previously reported absolute configuration of these compounds, some uncertainties were identified. A combined theoretical approach including conformational analyses and calculation...
This article reports, for the first time, on the absolute configuration of (+)‐9‐benzyloxy‐α‐dihydrotetrabenazine (8), as determined from the perspective of X‐ray crystallography. Compound 8 was prepared by a six‐step reaction using 3‐benzyloxy‐4‐methoxybenzaldehyde (1) as a starting material. The X‐ray crystal diffraction structure of two compounds, racemic 9‐benzyloxy‐tetrabenazine (5) and the diastereomeric...
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