Isolation and Structure of the New Sesquiterpene Lactone 3-oxo-10β-hydroxy-5,7α(H),4,6β(H)-guai-1,11(13)-diene-6,12-olide

The article presents the results of a chemical study of Tanacetopsis Pjataevae, which is an endemic plant in Kazakhstan. The amount of extractive substances was obtained by extraction with chloroform from the air-dry crushed above-ground part of the plant collected in the flowering phase. Isolation of compounds was carried out by column chromatography on a column of silica gel brand KSK at a ratio of sum - carrier = 1:20. A colorless crystalline substance of the composition C15H18O4 with m.p. 189-191°C (recrystallized from diethyl ether) was found when the column was eluted with a mixture of petroleum ether-ethyl acetate (87.5:12.5). The structure of the obtained new compound (3-oxo-10β-hydroxy-5,7α(Н),6β(Н)-guai-1,11(13)-diene-6,12-olide) was established on the basis of IR, NMR analysis and mass spectra. The spatial structure was determined by the X-ray diffraction method. It has been established that the 3-oxo-10β-hydroxy-5,7α(Н),6β(Н)-guai-1,11(13)-diene-6,12- olide molecule in the crystal is disordered over two conformational states in the 6 :4 ratio. The stability of these conformers was confirmed by semi-empirical quantum-chemical calculations. It was established that the difference in the heats of formation of two conformers was 6.3 kJ/mol for a free molecule.