Synthesis, protonation constants and biological activity determination of amino acid–salicylaldehyde-derived Schiff bases

Schiff bases represent a class of molecules widely studied for their importance in organic and coordination chemistry. Despite the large amount of studies on the chemical and biological properties of the Schiff bases, the different experimental conditions prevent a useful comparison to search for a correlation structure–activity. Moreover, literature is lacking in comprehensive data on the spectroscopic characterization of these compounds. For this reason, six Schiff bases, derived from salicylaldehyde and natural amino acids were fully characterized by nuclear magnetic resonance and infrared spectroscopy, and their aqueous solution equilibria, antiproliferative activity and DNA-binding activity were examined. All experimental conditions were kept constants to achieve comparable information and useful insights about their structure–activity correlation. The synthesized compounds showed DNA binding constants in the 101–102 M−1 range, depending on the substituent present in the amino acid side-chain, and resulted devoid of significant cytotoxic activity against the different human tumor cell lines showing IC50 values higher than 100 µM.