Spectroscopic study of stepwise gossypol sulfonylation with tosyl chloride in the presence of 4-methoxypyridine N-oxide and triethylamine

Sulfonylation of gossypol with stepwise increase of tosyl chloride content in the presence of 4-methoxypyridine N-oxide and triethylamine was carried out. The sequence of gossypol's hydroxyl groups tosylation was studied using HPLC, FT-IR and UV-Vis spectroscopy. It was shown that 4-methoxypyridine N-oxide is a much more effective catalyst compared to triethylamine, and its use allows to selectively tosylate gossypol to 7,7'-ditosyloxygossypol. The structure and tautomeric equilibria of obtained 7,7'- ditosyloxygossypol in dichloromethane were studied using FT-IR, UV-Vis, H-1, C-13 and H-1-H-1 COSY NMR, Mass spectroscopy, and quantum chemistry methods. It was found that dilactol tautomeric form is more preferable for 7,7'-ditosyloxygossypol in dichloromethane, contrary to gossypol. It was proven that the combined use of triethylamine and 4-methoxypyridine N-oxide allows to tosylate different hydroxyl groups of gossypol. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The sulfonylation of gossypol was conducted with stepwise increase of tosyl chloride content in the presence of 4-methoxypyridine N-oxide and triethylamine. It was found that 4-methoxypyridine N-oxide is a more effective catalyst compared to triethylamine, allowing selective tosylation of gossypol to 7,7'-ditosyloxygossypol. The study also investigated the structure and tautomeric equilibria of the obtained product in dichloromethane, showing that a dilactol tautomeric form is more preferable for 7,7'-ditosyloxygossypol.