1. Contribution from the Department of Analytical Chemistry and Laboratory of NMR Spectroscopy, Institute of Chemical Technology, Technická 5, 16628 Praha 6, Czech Republic, Department of Chemistry and Biochemistry, Institute for Cellular and Molecular Biology, The University of Texas at Austin, 1 University Station, A5300, Austin, Texas 78712-0165, and Institute of Organic Chemistry and Biochemistry, Flemingovo nám. 2, 16610 Praha 6, Czech Republic