1. Department of Organic Chemistry, Palacký University, Tř. Svobody 8, 771 46 Olomouc, Czech Republic, Farmak a.s., 771 17 Olomouc, Czech Republic, Laboratory of Growth Regulators, Palacký University, Šlechtitelo̊ 11, 783 71 Olomouc, Czech Republic, and Dipartimento di Chimica and Centro di Strutturistica Diffrattometrica, University of Ferrara, Via L. Borsari, 46, 44100 Ferrara, Italy hradil@farmak.cz