Structure and atropisomerisation of new diastereomeric gossypol Schiff bases with (R)-(+)-2-amino-3-benzyloxy-1-propanol studied by NMR,ECD and DFT methods |
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Authors: | Piotr Przybylski Marcin Kwit Krystian Pyta Radosław Pankiewicz Grzegorz Schroeder Jacek Gawroński Bogumil Brzezinski |
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Affiliation: | Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland |
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Abstract: | Gossypol Schiff base with (R)-(+)-2-amino-3-benzyloxy-1-propanol 1 was synthesised and resolved by HPLC method into diastereomers to study their atropisomerisation process. The spectroscopic analysis performed by one- and two-dimensional NMR, UV–vis and FT-IR methods indicated that the compound exists in solution as an enamine-oxo tautomer. The ECD measurements and TD-DFT calculations allowed us to unambiguously determine the configuration about the axially chiral biaryl moiety of 1. The conditions of the atropisomerisation processes of diastereopure gossypol Schiff bases (SAX,R)-1 and (RAX,R)-1 were determined on the basis of ECD and NMR measurements. Exposure of the diastereomers of 1 to sunlight and to the light at λ = 254 nm significantly accelerated the atropisomerisation when compared to its rate in the dark. |
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