CRYSTAL-STRUCTURE OF A MIXTURE OF LUPEOL-ACETATE TAUTOMERS ISOLATED FROM HIERACIUM-PLUMULOSUM KERNER,A., ASTERACEAE

Transparent single crystals obtained from the purified extract of the plant Hieracium plumulosum A. Kerner, Asteraceae were submitted to spe ctroscopic and X-ray studies. The spectroscopic (infra-red, mass spect rometry, H-1 and C-13 nuclear magnetic resonance) investigations sugge sted the presence of two isomers of lupeol acetate (C32H52O2) with tau tomeric relationship. Their mixture crystallizes in the monoclinic sys tem with space group P2(1): a = 19.170(2) Angstrom, b = 8.128(1) Angst rom, c = 21.832(2) Angstrom, beta = 90.24(1)degrees, V = 3401.7(6) Ang strom(3), Z = 4 (two molecules in the asymmetric unit), D-x = 1.095 g cm(-3), mu(CuKalpha) = 0.488 mm(-1). The structure was solved by direc t methods and refined to a final R = 0.071 for 6636 reflections with I > 2 sigma(I). The bond lengths around C20/(C60) are between single an d double bonds indicating the superposition of the tautomers, i.e., lu p-20(29)-en-3 beta-ol and lup-19(20)-en-3 beta-ol acetates. They are d istributed with different ratio in the symmetry-independent positions. In addition, the difference maps revealed that toluene solvent molecu les are also captured in the lattice. They substantially hindered the refinement of atomic positions in particular for the C19/(C59) functio ns. (C) 1997 Elsevier Science B.V.