1. Dept. of Organic and Nuclear Chemistry, Faculty of Science, Charles University in Prague, Hlavova 8, 12843 Praha 2, Czech Republic, Fax: +420‐221‐951‐326
2. Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, v.v.i., Flemingovo nám. 2, 166 10 Praha 6, Czech Republic