Conformational and spectral properties of newly synthesized compounds obtained by reaction of alrestatin with 3-aminocycloalkanespiro-5-hydantoins

Synthesis of new heterocyclic compounds by reaction of alrestatin with 3-aminocyclopentanespiro-5-hydantoin and 3-aminocyclohexanespiro-5-hydantoin is presented. The structures of the products obtained are verified via IR, H-1 and C-13 NMR spectroscopy. Conformational analysis of the newly synthesized compounds is performed at the B3LYP/6-31G(d, p) level both in the gas phase and in solution (DMSO) in order to find the most stable conformers about all single bonds. We find that rotation about the torsion angles O=C-CH2 and C=O-NH is important in the conformational search. The most stable structure has the all trans-conformation. Two more rotamers of comparable energy are located upon rotation about angle O=C-CH2. Calculated energy differences and rotation barriers between the three most stable rotamers in DMSO show that they all should be present in gas phase and solution in fast equilibrium, their population being strongly dependent on solvent polarity. The theoretically predicted IR, H-1 and C-13 NMR spectra of the two compounds are close to experiment.