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

•Gossypol sulfonylation with tosyl chloride in the presence of 4-methoxypyridine N-oxide and triethylamine.•Identification of the reaction products using HPLC, UV-Vis, FT-IR, 1H, 13С and 1Н-1Н COSY NMR and Q-TOF LC/MS spectroscopy and quantum chemistry methods.•Obtaining selective gossypol tosylation product and studying its structure and tautomeric equilibria in dichloromethane.•Tosylation of different hydroxyl groups of gossypol. 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, 1H, 13С and 1Н-1Н 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. [Display omitted]