Solid-supported synthesis of 5′-mRNA CAP-4 from trypanosomatids

The unique structure of 5′ mRNA cap from Trypanosomatids is the most modified cap found in nature. Here we present the synthesis of cap-4 (m ⁷ Gpppm₃^6,6,2′ Apm^2′ Apm^2′ Cpm₂^3,2′ Up) on a disulfide-tethered solid support. This approach allows obtaining cap-4 more efficiently then previously described. Moreover such modified resin could be a useful tool for affinity purification of Leishmania proteins interacting with cap-4. For the final step of synthesis, namely coupling of phosphorylated tetranucleotide with activated 7-methylguanosine 5′-diphosphate two systems were compared. Surprisingly, the coupling in water with Mn²⁺ as a catalyst, gave better results than usually more effective coupling in DMF with ZnCl₂.