Towards seeking the right chiroptical tool to assign the stereochemistry of bioactive compounds: Effectiveness, challenges, and perspectives

Epoxydibenzo[b,f][1,5]diazocines: From a Hidden Structural Motif to an Efficient Solvent-Free Synthetic Protocol

Epoxydiazocines belong to the rare class of small V-shaped molecules, closely related to Tröger’s base. Due to their intriguing, unique structure, they could serve as molecular building blocks for supramolecular chemistry. An extensive review on their synthesis is contained in this article. Moreover, our recent findings devoted to efficient and easily scalable synthesis of fluorinated epoxy[1,5][b,f]diazocines through solvent-free base-catalyzed condensation of ortho-aminophenones is provided. The unique V-shaped structure was confirmed by X-ray crystal structure analysis. Furthermore, the rigidity of the epoxy­diazocine skeleton allowed for racemate separation and the configuration of enantiomers was established by combining quantum chemical calculations and chiroptical methods.

1 Introduction

2 Synthetic Efforts Towards Epoxydibenzo[b,f][1,5]diazocines

3 Synthetic Efforts Towards Fluorinated Epoxydibenzo[b,f][1,5]diazocines

4 Conclusion

A Holistic Approach to Determining Stereochemistry of Potential Pharmaceuticals by Circular Dichroism with β-Lactams as Test Cases

This paper's main objective is to show that many different factors must be considered when solving stereochemical problems to avoid misleading conclusions and obtain conclusive results from the analysis of spectroscopic properties. Particularly in determining the absolute configuration, the use of chiroptical methods is crucial, especially when other techniques, including X-ray crystallography, fail, are not applicable, or give inconclusive results. Based on various β-lactam derivatives as models, we show how to reliably determine their absolute configuration (AC) and preferred conformation from circular dichroism (CD) spectra. Comprehensive CD analysis, employing both approaches, i.e., traditional with their sector and helicity rules, and state-of-the-art supported by quantum chemistry (QC) calculations along with solvation models for both electronic (ECD) and vibrational (VCD) circular dichroism ranges, allows confident defining stereochemistry of the β-lactams studied. Based on an in-depth analysis of the results, we have shown that choosing a proper chiroptical method/s strictly depends on the specific case and certain structural features.