Cis-diastereoselectivity in pictet-spengler reactions of L-tryptophan and electronic circular dichroism studies.

Allama Iqbal Open University, Department of Chemistry, Islamabad, Pakistan. .
Chirality (Impact Factor: 1.72). 07/2012; 24(10):789-95. DOI: 10.1002/chir.22070
Source: PubMed

ABSTRACT The diastereoselective synthesis of optically active 1,3-disubstituted tetrahydro-β-carbolines using polar protic Pictet-Spengler cyclization of (S)-tryptophan methyl ester with five aldehydes RCHO (R═CH(3) , C(2) H(5) , C(3) H(7) , C(4) H(9) , and C(6) H(5) ) was studied. As an alternate route, the cyclization of (S)-tryptophan with the same aldehydes and subsequent methylation of the resulting tetrahydro-β-carboline carboxylic acids were also performed for comparison. (13) C NMR and electronic circular dichroism (ECD) studies and time-dependent density functional theory ECD calculations data established the relative 1,3 cis/trans and the absolute configuration (1S,3S/ 1R,3S) of the synthesized compounds. The solid-state and solution ECD study of the prepared compounds, supported by ECD calculation and X-ray data, afforded a reliable ECD method for the configurational assignment of 1,3-disubstituted tetrahydro-β-carbolines and revealed the stereochemical factors that determine the characteristic ECD data. Chirality 24:789-795, 2012. © 2012 Wiley Periodicals, Inc.

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    ABSTRACT: A series of 13 enantiopure aryl benzyl sulfoxides () with different substituents on the two aromatic rings has been previously analyzed by means of electronic circular dichroism (CD) spectroscopy. Most of these compounds are crystalline and their X-ray structure is established. For almost one-half of the series, CD spectra measured in the solid state were quite different from those in acetonitrile solution. We demonstrate that the difference is due to strong exciton couplings between molecules packed closely together in the crystal. The computational approach consists of time-dependent density functional theory (TDDFT) calculations run on "dimers" composed of nearest neighbors found in the lattice. Solid-state CD spectra are well reproduced by the average of all possible pairwise terms. The relation between the crystal space group and conformation, and the appearance of solid-state CD spectra, is also discussed. Chirality 00:000-000, 2013. © 2013 Wiley Periodicals, Inc.
    Chirality 12/2013; · 1.72 Impact Factor


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