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Hydrogen-bonding interactions in some benzopyranopyridine esters

Weak interatomic interactions, such as hydrogen bonds, play a dominant role in many chemical and biochemical processes. Hydrogen bonds in four different molecules of benzopyranopyridine esters (Fig.1), which exert their antibacterial activity by inhibiting DNA gyrase, [1-3] have been investigated by means of NMR and IR spectroscopy and quantum chemical calculations. All NMR spectra were recorded in DMSO-d6 solution while IR spectra were recorded in DMSO solution and solid state. Quantum chemical calculations were performed at the semi-empirical level using PM3 Hamiltonian. Significant changes in vibrational frequencies, NMR chemical shifts and calculations have pointed toward the formation of different interactions in solid state and solution. In compound 2 the observed tautomeric equilibrium is slow on the NMR time scale and is governed by strong intramolecular hydrogen bonds.

coumarin; benzopyranopyridine; hydrogen bond

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