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Absolute Configuration of Chiral Molecules by VCD

This week in the world of BioTools:

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.

FTIR Spectroscopy Detects Intermolecular β-Sheet Formation Above the High Temperature Tm for Two Monoclonal Antibodies

Garrett Baird, Chris Farrell, Jason Cheung, Andrew Semple, Jeffery Blue & Patrick L. Ahl

The Protein Journal  39, pages 318–327 (2020)

Abstract

 

The temperature-dependent secondary structure of two monoclonal IgG antibodies, anti-IGF1R and anti-TSLP, were examined by transmission mode Fourier Transform Infrared (FTIR) spectroscopy. Anti-IGF1R and anti-TSLP are IgG monoclonal antibodies (mAbs) directed against human Insulin-like Growth Factor 1 Receptor for anti-tumor activity and Thymic Stromal Lymphopoietin cytokine for anti-asthma activity, respectively. Differential scanning calorimetry (DSC) clearly indicates both antibodies in their base formulations have a lower temperature protein conformational change near 70 °C (Tm1) and a higher temperature protein conformational change near 85 °C (Tm2). Thermal scanning dynamic light scatting (TS-DLS) indicates a significant particle size increase for both antibodies near Tm2 suggesting a high level of protein aggregation. The nature of these protein conformational changes associated with increasing the formulation temperature and decreasing sucrose concentration were identified by transmission mode FTIR and second derivative FTIR spectroscopy of temperature controlled aqueous solutions of both monoclonal antibodies. The transition from intra-molecular β sheets to inter-molecular β sheets was clearly captured for both monoclonal antibodies using FTIR spectroscopy. Finally, FTIR Spectroscopy was able to show the impact of a common excipient such as sucrose on the stability of each monoclonal antibody, further demonstrating the usefulness of FTIR spectroscopy for studying protein aggregation and formulation effects.

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