Absolute configuration determinations

MPA, either the [/ ]- or the [S]-form) recorded at two different temperatures. This approach, requiring just one derivatizing reaction, also simplifies the NMR-based methodologies for absolute configuration determination.82... 

The reported determinations of nonequivalence sense for configurationally known compounds are presented or referenced in this section. The NMR method of absolute configuration determination, when it works, is often more reliable and positive than chiroptic... 

CSAs have found stereochemical applications in areas other than those of enantiomeric purity and absolute configuration determination. 

Single-crystal studies allow the absolute configurational determination of polymeric materials that have high degrees of crystallinity. Such determinations are costly with respect to time because of the complexity of polymeric materials. 

Other examples of absolute configuration determination by the exciton coupling between a chromophore and a benzoate derived from the alcohol include ... 

Absolute configuration determined by optical rotations and comparison of the retention orders with known literature data. 

Both 1- and 1 -A -alkylated ethylenediamine ligands are prochiral and coordination completes the asymmetry at the nitrogen atom. Under favorable conditions, such complexes can be resolved and the absolute configuration determined by X-ray or other methods. Structures (17)-(22) show some representative configurations. 

The CD properties of a number rf -polyene) Fe(CO)3 complexes containing carbonyl group have been described336,337. Tricarbonyliron complex of 2,3-dihydrotropone (149) was resolved by HPLC and its absolute configuration determined by X-ray and CD338. 

Many diasteromeric peptides of type (R,S)-27 and (S,S)-28 (Scheme 1) could be crystallized and their absolute configuration determined based on the known ( -configuration of L-phenylalanine. Table 1 shows a compilation of the relevant torsional angles (4>1/ P1) derived from crystal structures of the peptides shown.108 It is interesting to note that the (S,S)-diastereomers show a high prevalence for P-tum type I conformations in the crystal state. 

Epoxidation of bullvalene with ozone gave racemic trisepoxide. The enantiomers were separated and the absolute configuration determined by X-ray analysis. Acid-catalysed isomerization of the enantiomerically pure (+)-(44) proceedes without... 

The experimental CD spectra of these donor-acceptor cyclophanes were very well reproduced by the theoretical calculations at the TD-DFT-BH-LYP/TZV2P level [32]. The amount of the exact exchange in the functional to be used turned out to be important for better agreement with experiment. The analysis of the configuration contributions showed that the observed CD spectra essentially resulted from simple overlap of the Cotton effects of pure n-n transitions in the donor and acceptor parts, in addition to the CT transitions. Thus, the exciton chirality method cannot be applied to the absolute configuration determination for these cyclophanes. The experimental CD spectrum of more congested donor-acceptor cyclophane 22 was reproduced in a less satisfactory manner compared to the cases of 20 and 21. The absolute configuration was safely determined by a comparison of the experimental spectrum with the theoretical data at the TD-DFT level however, the satisfactory reproduction of the whole CD spectrum of 22 was only possible by... 

Freedman TB, Cao X, Dukor RK, Nafie LA (2003) Absolute configuration determination of chiral molecules in the solution state using vibrational circular dichroism. Chirality 15 743-758... 

Furo T, Mori T, Origane Y, Wada T, Izumi H, Inoue Y (2006) Absolute configuration determination of donor-acceptor [2.2]paracyclophanes by comparison of theoretical and experimental vibrational circular dichroism spectra. Chirality 18 205-211... 

Perhaps the best known clinical agent is the heptaene polyene, amphotericin B 50, isolated from Streptomyces nodosus and first reported in 1956. The full structure was not elucidated until 1970 when it was determined by X-ray crystallography,56 closely followed by a description of the absolute configuration determined by utilising the iodo-derivative for X-ray and by mass spectroscopy.57 Quite recently, 50 years after its initial discovery, a full review giving the highlights of the chemistry around the compound was published by Cereghetti and Carreira.58... 

Table 1. Some absolute configurations determined by Bijvoet X-ray method...

Because of the biological importance of many chelating organic molecules such as a-amino acids many of their absolute configurations (determined by the Bijvoet method (57)), are available. This means that the known absolute configuration of one centre in a molecule can be used to deduce that of other centres. This can be done in several ways, and has proved extremely useful in coordination chemistry. 

THF) has been synthesized starting with (iS)-/ -phenyl-/ -alanine. From this, the structure of homaline (194) has been confirmed and the absolute configuration determined (138). 

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