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Absolute Configuration of Chiral Molecules by VCD

This week in the world of BioTools:

Enantiopure C5 Pentaindenocorannulenes: Chiral Graphenoid Materials

Jay Steven Siegel, Tianjian Guo, Ansu Li, Jun Xu, Kim K. Baldridge

 

First published: 06 September 2021     https://doi.org/10.1002/anie.202109946

Abstract

Chiral carbon nanomaterials offer numerous prospects for material science . As a fundamental building block for non-planar graphenoid materials, pentaindenocorannulene (PIC) with its C 5 v symmetrical structure presents a platform for the creation of supramolecular chiral carbon materials. Specifically, when uniformly penta-substituted on its periphery, PIC generates C 5 symmetrical chiral buckybowls capable of columar stacking. The synthesis and resolution of such PICs are achieved. Assignment of absoulte configuration is established by comparison of ECD and VCD spectra with those from theory. Material characterization of these curved PAHs are reported. Evidence for columnar stacking in solution as well as in the crystal is presented.

Abstract

The advent of cisplatin as a cancer drug in the late 1960s generated considerable interest in the use of transition metal complexes as cancer therapy agents. Despite enhanced research in this area, there has yet to be any non-platinum-based transition metal complex cancer drugs approved by the Food and Drug Administration (FDA). Recently a Ru(II) metal-organic dyad (TLD1433) has provided promising results as a photodynamic therapy (PDT) agent for some types of cancer. This particularly effective PDT compound has an oligothiophene chain appended to an imidazophenanthroline ligand which chelates Ru(II). The entire complex is chiral and is synthesized as a racemate. Five such chiral Ru(II) and Os(II) PDT agents were synthesized and their enantiomers separated for the first time. The enantiomers of these compounds are not easily crystalized. However, preparative LC provided sufficient amounts of these novel PDT agents to determine their absolute configurations by vibrational circular dichroism (VCD). The synthesis, separation and absolute configuration determinations are described and discussed in detail.

Absolute Configuration Reassignment of Natural Products: An Overview of the Last Decade

Andrea N. L. Batista,  Bianca R. P. Angrisani,  Maria Emanuelle D. Lima, Stephanie M. P. da Silva,  Vitória H. Schettini, Higor A. Chagas, Fernando M. dos Santos Jr., João M. Batista Jr., and Alessandra L. Valverd

Departamento de Química Orgânica, Instituto de Química, Universidade Federal Fluminense, Outeiro de São João Batista s/n, 24020-141 Niterói-RJ, Brazil

Departamento de Ciência e Tecnologia, Instituto de Ciência e Tecnologia, Universidade Federal de São Paulo, Rua Talim No. 330, 12231-280 São José dos Campos-SP, Brazil

Abstract

The assignment of absolute configuration (AC) is a crucial step in the structural characterization of natural products, especially for those subjected to biological assays. Methods such as X-ray crystallography, stereocontrolled organic synthesis, nuclear magnetic resonance (NMR), and chiroptical spectroscopies are commonly used to determine the AC of chiral natural compounds. Even with these well-established techniques, however, unambiguous stereochemical assignments of natural products remain a challenge, resulting in an increasing number of structural misassignments being reported every year. Herein, we will present the main techniques that have been used in AC reassignments of natural products over the last 10 years, along with some selected examples. Special attention will be paid to the strengths and weaknesses of each approach. With this, we expect to provide the readers with critical information to help them to choose the appropriate methods for correct AC determinations.

 Number of articles dealing with absolute configuration reassignments of natural products over the last decade, according to the search criteria used.

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