1. Department of Chemistry, WestChem, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ, Scotland, U.K., Institute of Organic Chemistry and Biochemistry and Gilead Sciences Research Center & IOCB, Academy of Sciences of the Czech Republic, Flemingovo náměstí 2, 16610 Prague 6, Czech Republic, and Department of Organic Chemistry, Charles University, Hlavova 2030, 12840, Prague 2, Czech Republic