Saturday, 23 October 2010

Conformational analysis of cyclic compounds using Mspin and RDCs

On the occasion of the release of a new version of Mspin (BTW, this is the very first multiplatform version of Mspin: it works now in Windows, Mac OS X and Linux), I would like to bring into your attention one of the many applications where this software plays an instrumental role: The application of Mspin to the study of seven-membered rings compounds by NMR.

The NMR study of seven-membered ring compounds is a classical problem in conformational analysis. They are commonly studied by means of NOE-based experiments or 3J coupling analysis using Karplus-Altona relationships. In a recent work, recently published in Chemical Communications, [ Chem. Commun. , 2010, 46, 5879–5881 ]from the groups of Roberto Gil (Carnegie Mellon University) and Navarro-Vázquez ( Universidade de Vigo ) have demonstrated that the conformation of a 3-benzazepine compound can be completely determined by using 1DCH residual dipolar couplings (RDCs). These RDCs were easily obtained by performing HSQC experiments coupled in the direct dimension using a polydimethylsiloxane gel as oriented medium

Conformational search indicated the presence of 11 possible conformations for this molecule. In agreement with computed DFT energies for these conformers, as well as observed 3J couplings, chemical shifts, and NOE's RDC analysis shows the preference of the system for a crown-chair conformation with equatorial disposition of the substituents.
Here you can download the rdc data file ( click here ) in the MSpin format and a multiconformer XYZ file with the DFT optimized conformations (click here) . Load them into the RDC module of Mspin, select the singular value decomposition method (SVD), just click the calculate button and see how convenient is to perform the RDC analysis with Mspin