Solution-state conformational study of the hevamine inhibitor allosamidin and six potential inhibitor analogues by NMR spectroscopy and molecular modeling

The solution-state conformations of the hevamine inhibitor allosamidin and six potential inhibitor analogues were studied by various NMR spectroscopic techniques and molecular modeling using force field calculations. Determination solely of the global energy minimum conformation was found to be insufficient for consensus with the NMR results, and agreement between the NMR experimental data and the theoretical calculations was only reached by assessing the structures as population-weighted average conformers on the basis of Boltzmann distributions derived from the calculated relative energies. The conformations of the glycosidic linkages in the compounds were found to be similar when the sugar residues were the same, but differences were markedly evident otherwise and also for the various heterocyclic group linkages. The binding of the compounds to hevamine, which may also complex to chitinases in general, was assessed using HMQC, transfer-NOESY, and both 1-D and 2-D saturation transfer difference NMR experiments. Under the conditions employed, only allosamidin was implicated to be bound to hevamine, and then only by HMQC with the dipolar coupling-based experiments failing to substantiate the formation of the complex. However, the results are consistent with the biochemical activities of the compounds whereby only allosamidin has been shown to act as a competitive inhibitor.