Complementarity of Electronic and Vibrational Circular Dichroism Spectroscopy in Structure Determination of Vic-Amino Alcohols

Abstract

EditorialThere is no doubt that determination of the absolute configuration of isolated natural products or synthesized compounds remains one of the most important tasks in all fields of chemistry, biochemistry, structural biology and medicinal chemistry. This is unquestionably due to the fact that biological activity is closely related to the stereostructure of bioactive compounds. Therefore, access to methods allowing simple and primarily unequivocal determination of their absolute configuration (AC) and/or conformation is of particular significance. Such a role is at present fulfilled by chiroptical techniques. In the last two decades chiroptical spectroscopy has been one of the most rapidly developing areas of chiral analysis due to the availability of modern, highly specialized and dedicated to particular chiroptical techniques commercial instruments. Recent progress in ab initio simulations of chiroptical properties has also significantly contributed to the increase of the use of chiroptical spectroscopy as a stereochemistry probe [1]. It is generally accepted that combined experimental and theoretical analysis opens much broader application opportunities for chiroptical spectroscopy by giving theoretical basis to experimental results [1][2][3][4]. Moreover, utilization of multiple (at least two) chiroptical techniques increases the confidence level of the stereochemical assignment and is nowadays considered by many authors to be the best practice [1][2][3][4][5].In this Editorial, we will focus on such a combined experimental and theoretical approach of electronic circular dichroism (ECD), and vibrational circular dichroism (VCD) to determine the absolute configuration and conformation. We intend to demonstrate that both these chiroptical techniques are well cooperating and mutually complementary. Moreover, we want to show that the concerted use of the two methods clearly provides more definitive ACs although in many cases stereochemistry can be determined by using only a single chiroptical property. As a model compound for this study (1S,2R)-2-amino-1,2-diphenylethanol (1) with formula shown here below and representing vic-amino alcohols was chosen (Figure 1).Information obtained through ECD concerns chromophore and its nearest surroundings whereas the data from VCD covers the whole molecule. Therefore, in the case of ECD the acquired information is restricted to the chromophore unit and its nearest surroundings. Consequently, the assignment of AC can be easily achieved by semiempirical and empirical rules known as sector and helicity rules supported by quantum mechanics calculations. In contrast to ECD, the advantage of VCD spectroscopy comes mainly from the presence of numerous well-resolved vibrational transitions from the skeleton of the whole chiral molecule. Thus, high information content about vibrations of the electronic ground state is provided. Since the functional groups responsible for vibrations are distributed over the entire skeleton of the molecule, the VCD contains information on the geo...