Chromophoric derivatives

Three other substituted benzaldehydes, p-dimethylaminobenzaldchydc (130), julo-lidinecarboxaldehyde (131) and p-dimethylaminocinnamaldehyde (132), have been reported for use in the preparation of chromophoric derivatives of chiral amines116117. 

Azotobactin is a highly fluorescent hexadentate mixed siderophore containing a pyoverdin-like bidentate ligating chromophore, derived from 2,3-diamino-6,7-dihydroxyquinoline, a hydroxamate and a a-hydroxycarboxylic acid for Fe(in) coordination. ... 

As shown in this section, CD spectroscopy has the potential to provide reliable configurational assignments for many products of stereoselective synthesis, requiring only small amounts of material (usually 1 mg or less) and simple analytical procedure. In addition, many nonchro-mophoric functional groups (c.g. amino, hydroxy groups) can be converted to chromophoric derivatives suitable for chiroptical studies. 

The power of the exciton chirality method lies in its applicability to molecules having functional groups which are not chromophores in the usual sense (such as hydroxy, amino or thiol groups), but can be converted to a chromophoric derivative, such as an unsaturated or aromatic acyl derivative. This procedure is extremely useful for the determination of the absolute configuration of products of stereoselective synthesis having a hydroxy, amino or thiol group at the stereogenic center. 

Table 11. Exciton Cotton Effects of Bi-chromophoric Derivatives of 1-Deoxy-D-alditols (Ae Acetonitrile Solution)...

Other useful chromophoric derivatives of the primary amino group include phthalimide199 and Schiff bases200. 

Chromophoric derivatives for the optically transparent amino group, such as dimedone derivatives 103-106, were prepared for assigning the absolute configuration of primary and secondary amines. The vinylogous planar amide chromophore (280-290 nm ji — n ... 

Predicted chromophores derived from natural retinoids... 

A variety of fluorescent chromopeptide siderophores, termed pseudobactins and pyoverdins, are synthesized by Pseudomonas species. The chromophores, derived from 2,3-diamino-6,7-dihydroxyquinoline (Figure 2(d)), are linked to a peptide chain exhibiting either two hydroxamate groups or one hydroxamate and one a-hydroxycarboxylate group. 

Double-Layered Chromophores Derived from [2.2] Paracyclophane. . 126... 

Myers, A. G., Cohen, S. B., Kwon, B.-M. (1994). DNA cleavage by neocarzinostatin chromophore. Establishing the intermediacy of chromophore-derived cumulene and biradical species and their role in sequence-specific cleavage, J. Am. Chem. 

The word chromophore" derives from the ancient Greek chroma (colour) and phoros (bearing). It is the term used to signify any group or part of a molecule that is coloured or has UV/visible absorbing properties... 

Of the number of chromophoric derivatives of chiral amines for potential use in the establishment of their absolute configuration by BCD measurement only a few have proven to be generally useful. Of these, intensive investigation of the Af-salicylidene (Schiff base) derivatives of chiral primary amines, including unsubstituted and ring-substituted a- and S-arylalkylamines, a-amino acids, unsaturated and satnrated aliphatic and alicyclic amines, and amino sugars, has resulted in the formulation of the salicylidenamino chirality rule ° °. The application of this rule has recently been reviewed and has been successfully used for the establishment of absolute configuration of chiral primary amines in connection with other stereochemical studies. In related studies, the conformations of a series of pyridoxyl-L-a-amino acid Schiff bases were deduced from their CD spectra ... 

IV. CHIROPTICAL PROPERTIES OF METAL COMPLEXES AND CHROMOPHORIC DERIVATIVES OF a-AMINO ACIDS... 

Although the Cotton effects of a-amino acids can be measured directly with up-to-date ORD/CD equipment, more often it is advantageous to form chromophoric derivatives or complexes whose chiroptical properties reflect the absolute configuration of the a-carbon atom. This is especially important when adequate instrumentation is not available or chromophoric substituents other than COOH or NH2 are present. For instance, in the case of aromatic amino acids, more complex chirospectral patterns have to be considered which might prevent the unequivocal assignment of absolute stereochemistry. Also, minor optically active impurities might interfere with spectral data in the 200-250-nm area. 

The chromophoric derivatives (1) have a chromophore that is optically inactive by nature but becomes optically active in the vicinity of the asymmetric a-carbon atom (2) absorb in the near-uv or visible spectral range (above 300 nm, where the aromatic and other chromophoric substituents are transparent) and (3) preferably have a rather high Kuhn s dissymmetry factor... 

In several review articles (Djerassi, 1964, pp. 206-210 Crabbe, 1965, pp. 307-316 1972, pp. 72-84 Velluz et a/., 1965, pp. 154-165 Ripperger, 1966 Sjoberg, 1967, pp. 173-192 Anonymous, 1969-1979) a number of chromo-phoric reagents and the chiroptical properties of the chromophoric derivatives have been described. In this chapter, these are discussed briefly but more attention is given to the newest developments. 

The Cu(II) complex of L-alanine was the first chromophoric derivative of an amino acid whose anomalous ORD spectrum was observed (Lifschitz, 1925). Subsequently, Pfeiffer and Christeleit (1937a,b) studied a series of Cu(II)-amino acid complexes (6) and found a close relationship between... 

Subsequently, it was demonstrated that the chromophoric reaction between MDPF and an amino acid [Eq. (7)] can be carried out in a test tube and that CD spectra can be obtained from the resulting reaction mixtures without the isolation of the chromophoric derivatives (Toome and Reymond, 1975). The first two Cotton effects are easily accessible and the intensity of the Cotton effects is ca. 30-70% of those of the isolated standards. Since the Cotton effects are strong, these yields are sufficient for in situ determina-... 

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