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: 1.89). 10/2012; 24(10):789-95. DOI: 10.1002/chir.22070
Source: PubMed


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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