Introduction
B-Cyclodextrin (BCD) is a well known host molecule used to prepare inclusion complexes. Considering that the three dimensional array of these complexes depends on the inclusion mode into the BCD cavity, the development of methods to elucidate their structure are highly desired. In this context, the objective of this work is to apply experimental and molecular modeling methods to study the binary complexes: benzoic acid:BCD (BA:BCD) and hipuric acid:BCD (HIP:BCD), and the ternary complex: benzoic acid:BCD:glicine (BA:BCD:GLI). These drugs were chosen as models to compare the presence of aminoacids as multicomponent complexes and as covalently linked to the drug, since HIP is a prodrug of BA with GLI.
Materials and Methods
Experimental: Ligands:BCD interactions were studied in aqueous solutions by NMR (1H NMR and 2D ROESY) on a Bruker® Avance II High Resolution Spectrometer (400.16 MHz). Displacements of 1H chemical shifts caused by complexation were calculated. The effects of complexation on ligands solubility and stoichiometry of the complexes were determined by phase-solubility analyses.
Theoretical: Molecular structures were constructed with Gabedit software, with conformational and energetic analyses performed using Gaussian03. Ligands:BCD (CSD: BCDDEX04) complexes were predicted by molecular docking, using software packages designed by Open Eye Inc (FRED, OMEGA)1,2. Molecular dynamics simulations were performed with Amber12, and visualized using VMD.
Results and Discussion
1H NMR studies evidenced that all ligands and BCD proton resonances were modified upon complexation (Table 1), suggesting the inclusion complex formation. 2D ROESY assays showed correlation between internal BCD protons and aromatic protons of the ligands, evidencing that the aromatic ring is included into BCD cavity.
For all systems studied, a linear increase in ligand solubility occurred at different BCD concentrations, exhibiting an AL-type profile with 1:1 stoichiometry.
Molecular modeling techniques confirmed the formation of the inclusion complexes BA:BCD and HIP:BCD. For BA:BCD, a marked distortion in BCD was observed, consistent with the high displacement calculated (Table 1). The complex BA:BCD:GLI was not stable during the molecular dynamics simulation, suggesting that it is not formed. From energetic decomposition analyses, HIP exhibited a higher affinity for BCD than BA.
Conclusion
A good correlation between the experimental and theoretical methods was found, thus molecular modeling methods may help to predict the geometries and affinities of included ligands. Also, for the studied molecules, the aminoacid present as a prodrug produces a higher affinity than in the multicomponent complexes.
References
1- McGann M. FRED and HYBRID docking performance on standardized datasets. J. Comput. Aided. Mol. Des. 2012;26(8):897-906
2- Bostrom J, Greenwood JR, Gottfries J. Assessing the performance of OMEGA with respect to retrieving bioactive conformations. J. Mol. Graph. Model. 2003; 21 (5): 449-462.
