Triphenyltin (IV) derivatives of N-acetyl amino acids,N-acetyl dipeptides and tripeptides: Preparation,NMR investigations and NMR spectroscopic resolution of the enantiomeric composition

Triphenyltin(IV) derivatives of N-acetyl amino acids ( 1a–g ) and N-acetyl di- ( 2a–f ) or tripeptides ( 3 ) mostly in the (L )- and the racemic (DL )-form have been prepared from bis(triphenyltin)oxide and the appropriate N-acetyl amino acid or N-acetyl peptide using various dehydrating agents. The compounds were characterized by NMR spectroscopy and elemental analysis. These compounds were studied at different concentrations and temperatures, revealing a strong self-association tendency. NMR investigations were undertaken in order to highlight preferred conformations of the peptide derivatives due to possible strong intramolecular associations between tin and nucleophilic donor atoms of the peptide moiety in weakly polar solvents. No preferred conformation was found which was in accordance with the underivatized peptides. The enantiomeric composition was determined by means of ¹H NMR spectroscopy using (−)-quinine hydrochloride and S-(−)-1-phenylethylamine as chiral solvating agents.