1. Institute for Chemistry, Technology and Metallurgy, Njegoševa 12, 11000 Belgrade, Institute for Medicinal Plant Research, “Dr. Josif Pančić”, Tadeuša Košćuška 1, 11000 Belgrade, School of Medicine, Department of Chemistry, Višegradska 26, 11000 Belgrade, Yugoslavia, Department of Biochemistry, Mayo Graduate School, Mayo Fondation, Rochester, Minnesota 55905, and Faculty of Chemistry, University of Belgrade, Studentski trg 16, P.O. Box 158, 11001 Belgrade, Yugoslavia