Inter- and intramolecular Mitsunobu reaction and metal complexation study: synthesis of S-amino acids derived chiral 1,2,3,4-tetrahydroquinoxaline, benzo-annulated [9]-N3 peraza, [12]-N4 peraza-macrocycles

Substituted 1,2,3,4-tetrahydroquinoxaline, benzo-annulated unsymmetrical chiral [9]-N-3 peraza, and [12]-N-4 peraza-macrocycles have been synthesized employing an inter-and intramolecular Mitsunobu reaction from an amino acid derived common synthetic intermediate 3. The metal complexation study of these macrocycles has been investigated by UV-visible spectroscopic technique with binding constant (K-b) value 1.84 x 10(3) dm(3) mol(-1) using the Benesi-Hildebrand equation and a Gibbs free energy (Delta G) -19.4 kJ mol(-1) at 35 degrees C for 14d with Co2+. The binding properties of the metal were dependent on the structure of polyaza-macrocycles that were confirmed by the DFT optimized structure of two macrocycles. A detailed investigaton of UV-visible spectra of macrocycles and their complete interpretation with the help of TD-DFT along with the frontier molecular orbital calculations are presented.