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Stereoselective Formation of Ternary Copper(II) Complexes of ( S )‐Amino‐acid Amides and ( R )‐ or ( S )‐Histidine and ( R )‐ or ( S )‐Tyrosine in Aqueous Solution
Author(s) -
Dallavalle Francesco,
Folesani Giuseppina,
Leporati Enrico,
Galaverna Gianni
Publication year - 1996
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19960790707
Subject(s) - chemistry , stereoselectivity , histidine , imidazole , stereochemistry , denticity , ternary operation , dipeptide , amino acid , medicinal chemistry , crystallography , organic chemistry , catalysis , crystal structure , biochemistry , computer science , programming language
Abstract Formation constants of ternary complexes of Cu II with ( S )‐amino‐acid amides (( S )‐phenylalaninamide, ( S )‐prolinamide, and ( S )‐tryptophanamide) and ( R )‐ or ( S )‐histidine and ( R )‐ or ( S )‐tyrosine were determined potentiometrically in aqueous solution. Significant stereoselectivity was presented by all three amides towards histidine, the diastereoisomeric complexes with ‘heterochiral’ ligands being more stable than those with ‘homochiral’ ligands (see Table 3 ). The stereoselectivity observed with ( S )‐phenylalaninamide and ( S )‐tryptophanamide may be explained on the basis of hydrophobic stacking interactions between 1 H ‐imidazole and the aromatic side chain, favoured by the terdentate behaviour of histidine (see Fig.2 ), whereas repulsive effects seem to be prevalent with ( S )‐prolinamide. Only ( S )‐prolinamide and ( S )‐phenylalaninamide show appreciable stereoselectivity with tyrosine, which is bidentate, probably on account of repulsive interactions. The present results on the stability of ternary complexes in solution allow to draw some conclusions on the mechanism of chiral discrimination performed by Cu II complexes of ( S )‐amino‐acid amides added to the mobile phase in HPLC (reversed phase).