J. Wagger, S. Grdadolnik, Uroš Grošelj
Mar 12, 2007
Citations
0
Influential Citations
40
Citations
Journal
Tetrahedron-asymmetry
Abstract
Abstract In CDCl 3 solution, enantiopure ( S )-1-benzyl-6-methylpiperazine-2,5-dione ( S )- 1a formed diastereomeric C O ⋯ H –N hydrogen-bonded associates with racemic ( RS , Z )-1-benzyl-3-[(dimethylamino)methylidene]piperazine-2,5-diones 2a and 2b , ( RS )- tert -butyl pyroglutamate ( RS )- 2c and ( RS )- N -benzoylalanine methyl ester ( RS )- 2d . This resulted in splitting (doubling) of the characteristic signals in the 1 H NMR and 13 C spectra of racemic compounds 2a – d in the presence of 1 equiv of ( S )- 1a . The formation of hydrogen-bonded dimers in CDCl 3 solution was studied by 1 H NMR, 13 C NMR and 2D NMR and confirmed by the intermolecular NOE observed between the hydrogen-bonded amide protons from each of the monomeric units, ( S )- 1a and 2a – c . On the other hand, a slightly different binding mode was proposed for association of ( S )- 1a with alaninamide ( RS )- 2d . Enantiomer compositions of known (weighed) mixtures of both enantiomers of tert -butyl pyroglutamate 2c were re-determined by 1 H NMR in the presence of ( S )- 1a in CDCl 3 . The experimental values were in good agreement with the theoretical values, thus indicating the potential applicability of ( S )- 1a and related diketopiperazines as chiral solvating agents in NMR spectroscopy.