Uracils, 1-alkylation thiouracils

Although the first aim of the use of a water-soluble palladium catalyst in allylic alkylation in a two-phase system was the recycling of the catalyst, this methodology finds quite interesting applications in the deprotection of peptides as well as in the selective alkylation of uracils and thiouracils. More recently, the effective use of supported aqueous-phase catalysis as well as asymmetric alkylation in water in the presence of surfactants or amphiphilic resin-supported phosphines open new applications and developments for the future. 

Finally, the most complex synthetic reaction clearly catalysed by RNA molecules generated by in vitro selection is the formation of the C-N bond of a nucleoside (Scheme 7), from 4-thiouracil and most of the natural substrate for the natural (uracil phos-phoribotransferase) reaction.1461. (Thiouracil was used because it is easily tagged by alkylation on sulfur.) The catalytic RNAs produced by 11 rounds of selection required Mg++ cations and had kcat as high as 0.13 min-1,with kcaJKM at least 107 times greater than the (undetectable) uncatalyzed reaction. Once again these systems are convincing, rather efficient enzyme mimics. 

---