One-step, regioselective synthesis of up to 50-mers of RNA oligomers by montmorillonite catalysis.

5‘-Nucleotides of A and U with the phosphate activated with 1-methyladenine generate RNA oligomers containing 40−50 monomers in 1 day in reactions catalyzed by montmorillonite. The corresponding monomers of C give oligomers that are 20−25-mers in length after a 9-day reaction. It was not possible to determine the chain lengths of the oligomers of G since they did not give well-defined bands on gel electrophoresis. Co-oligomers of A and U as well as A, U, G, and C were also prepared. The oligo(A)s formed were separated by gel electrophoresis, and the bands of the 7−39-mers were isolated, the 3‘,5‘-phosphodiester bonds were cleaved by RNase T2, and the terminal phosphate groups were cleaved with alkaline phosphatase. HPLC analysis revealed that the proportions of A5‘pp5‘A, A, A2‘pA, and A2‘pA2‘pA formed were almost the same for the long and shorter oligomers. A similar structure analysis performed on the oligo(U)s established that the proportions of U5‘pp5‘U, U, U2‘pU, U2‘pU2‘pU, U2‘pU2‘pU2‘pU, and U2‘pU2‘p...