Proton delineation of conformational parameters of constituents of Silybum marianum in solution

Silybin, silydianin and silychristin, the 3 major constituents of the crude ext. of Silybum marianum, were investigated by means of 1H-NMR in (CD2)2CO. Non selective, single-selective and double-selective 1H-NMR spin-lattice relaxation rates were measured and interpreted in terms of dipolarly interacting proton pairs. The motional correlation time was in the range 0.50-0.60 ns for all compds. The flavanonol moiety was in the same configuration whereas slight conformational differences were seen in the substituents. The Dreiding models of the 3 preferred conformations in soln. were built and projections were sketched.