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Chiral Discrimination of Some Annelated Xanthine Derivatives by the Dirhodium Method
Author(s) -
Rockitt Sven,
Duddeck Helmut,
Drabczynska Anna,
KiecKoowicz Katarzyna
Publication year - 2000
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200010)2000:20<3489::aid-ejoc3489>3.0.co;2-9
Subject(s) - chemistry , diastereomer , imidazole , molecule , chemical shift , stereochemistry , homo/lumo , methylene , xanthine , computational chemistry , organic chemistry , enzyme
Complete 1 H and 13 C signal assignments and conformation analyses of the title compounds (racemic mixtures) were performed. Most 1 H and 13 C NMR signals were resolved in the presence of the enantiomerically pure dirhodium complex Rh 2 (MTPA) 4 ( Rh* ) allowing for clear and simple chiral recognition. A detailed interpretation of the signal shifts (Δδ) and dispersions (Δν) in the diastereomeric complexes suggested that the π‐system around the C‐4/C‐5 bond of the central imidazole ring ( B ) is a binding site of the xanthine derivatives. This assumption was based on HOMO−LUMO considerations including back‐donation and on the fact that diastereotopic dispersions for protons within methylene groups are very different. Signal shifts are in the range of 0.5 to 1 ppm for carbon atoms close to the binding site and fade away at the periphery of the molecule. Dispersions are spread all over the molecule.