A Revised Conformational Code for the Exhaustive Analysis of Conformers with One-to-One Correspondence between Conformation and Code: Application to the VCD Analysis of (S)-Ibuprofen

A revised conformational code for the exhaustive analysis of conformers of all classes of molecules is proposed and applied to the vibrational circular dichroism (VCD) analysis of (S)-ibuprofen. The revised code can strictly define the conformation of compounds with relatively high-symmetry substituents and is especially useful for visualizing conformational changes in ligands and proteins. The conformational analysis of (S)-ibuprofen using the code in the solution state reveals that the four energetically preferred conformations, ibut-3α2ασ(phpa-3ασ2α), ibut-3α2ατ(phpa-3ατ2α), ibut-2β3βτ(phpa-3ατ2α), and ibut-2β3βσ(phpa-3ασ2α), exist in the monomer and dimer forms. In CDCl3 solution, the dimer form is stabilized as the “U”-shape, and the ease of crystallization is largely ascribed to the conformation of phpa-3α2α for (S)-ibuprofen. The new version of the conformational code has the possibility to be used as a tool for the exhaustive analysis of conformers of all kinds of chemical compounds, conformome an...