American Chemical Society
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NMR Structure Elucidation of Naphthoquinones from Quambalaria cyanescens

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posted on 2020-12-19, 13:35 authored by Eliška Procházková, Oleksandr Kucherak, Eva Stodůlková, Zdeněk Tošner, Ivana Císařová, Miroslav Flieger, Miroslav Kolařík, Ondřej Baszczyňski
Naphthoquinones isolated from Quambalaria cyanescens (quambalarines) are natural pigments possessing significant cytotoxic and antimicrobial properties. Determining the structure of naphthoquinone compounds is important for the understanding of their biological activities and the informed synthesis of related analogues. Identifying quambalarines is challenging, because they contain a hydroxylated naphthoquinone scaffold and have limited solubility. Here, we report a detailed structural study of quambalarine derivatives, which form strong intramolecular hydrogen bonds (IMHBs) that enable the formation of several tautomers; these tautomers may complicate structural investigation due to their fast interconversion. To investigate tautomeric equilibria and identify new quambalarines, we complemented the experimental NMR spectroscopy data with density functional theory (DFT) calculations.