Weak Interactions in the Structures of Newly Synthesized (–)-Cytisine Amino Acid Derivatives

Eight new (–)-(N-[(AA)-(N-phtaloyl)]cytisines (where AA is amino acid: glycine, β-alanine, D,L-valine, L-valine, L-isoleucine, L-leucine, D-leucine and D,L-phenyloalanine), were synthesized and fully spectroscopically characterized (NMR, FTIR and MS). For two of these compounds, N-[glycine-(N-phtaloyl)]cytisine and N-[L-isoleucine-(N-phtaloyl)]cytisine, X-ray crystal structures were obtained and used as the basis for an in-depth analysis of intermolecular interactions and packing energies. The structural geometrical data (weak hydrogen bonds, π···π interactions, etc.) were compared with the energies of interactions and the topological characteristics (electron density, Laplacian at the appropriate critical point) based on the atoms-in-molecules theory. The results suggest that there is no straightforward connection between the geometry of point-to-point interactions and the molecule-to-molecule energies. Additionally, the usefulness of the transfer of multipolar parameters in estimating of critical points’ characteristics have been confirmed

Statistical Validation of Absolute Configuration Assignment in Vibrational Optical Activity

Chiroptical spectroscopy usually requires theoretically computed spectra to assist in the elucidation of the absolute configuration of samples for which experimental spectra have been recorded. Due to the inherently different nature of these two types of spectra, perfect agreement is quasi impossible. Several methods exist to quantify the degree of similarity between the two spectra, but rather limited work has been done to evaluate the robustness of the similarity between theory and experiment. In this work, a novel method is described to determine the statistical significance of the numerical degree of similarity between experimental and calculated vibrational circular dichroism spectra and to offer valuable support for performing absolute configuration assignments. The approach is successfully applied to a number of quinolizidine alkaloids

Statistical Validation of Absolute Configuration Assignment in Vibrational Optical Activity

Chiroptical spectroscopy usually requires theoretically computed spectra to assist in the elucidation of absolute configuration of samples for which experimental spectra have been recorded. Due to the inherently different nature of these two types of spectra, perfect agreement is quasi impossible. Several methods exist to quantify the degree of similarity between the two spectra but rather limited work has been done to evaluate the robustness of the similarity between theory and experiment. In this work, a novel method is described to determine the statistical significance of the numerical degree of similarity between experimental and calculated vibrational circular dichroism spectra and to offer a valuable support for performing absolute configuration assignments. The approach is successfully applied to a number of quinolizidine alkaloids