Synthesis and study of cytotoxicity of 3β-acetoxyurs-12-en-28-oyl-thiourea derivatives

The interaction of 3β-acetoxyurs-12-en-28-oyl chloride with potassium rhodanide afforded 3β-acetoxyurs-12-en-28-oyl isothiocyanate. A series of substituted 3β-acetoxy-urs-12-en-28-oyl-thioureas was synthesised in yields of 69–88% by condensation of triterpene acyl isothiocyanate with a series of amino derivatives. The CuAAC cycloaddition reaction of N-(2-azidoethylcarbamothioyl)-3-acetoxyurs-12-en-28-oyl-amide with propargyl alcohol and 3-(prop-2-inyloxy)-4,5-((R,S)-methoxymethylenedioxy)-benzoate led to the formation of hybrid acylthioureas containing a 1,2,3-triazole linker in 72 and 75% yields. In CuAAC reactions of N-(prop-2-ynylcarbamothioyl)-3β-acetoxyurs-12-en-28-oylamide with substituted acylthiourea azides containing 1,2,3-triazole were isolated in moderate yields of 48–62%. The use of one-pot-reactor version of the synthesis with the preparation of substituted (1H-1,2,3-triazol-4-yl)methanamines in the reaction of propargylamine with substituted azides followed by condensation with 3β-acetoxyurs-12-en-28-oyl isothiocyanate increased the yield of 1,2,3-triazole-containing acylthioureas to 65–85%. Polar triterpene acylthioureas containing carboxyl or alcohol groups exhibited high inhibitory activity against HepG2 cells, significantly superior to the parent compound ursolic acid, and were also more selective than the drug doxorubicin. Among the acylthioureas, products of CuAAC cycloaddition, the most active was the polar derivative with (1H-1,2,3-triazol-4-yl)methanol substituent, which was cytotoxic to all cells tested, including the non-tumour control, but superior in selectivity to doxorubicin. Ursane hybrids with acylthiourea derivatives are of interest for further investigation as promising antitumour agents.