LAUSR

Abstract 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.