Nucleic Acid Related Compounds. 14. 3′-O-Aminoacyl-2′-O-methyladenosines and 2′-O-Aminoacyl-3′-O-methyladenosines Related to Charged tRNA Termini

Aminoacyl nucleosides derived from 2′-O-methyladenosine and 3′-O-methyladenosine have been isolated as pure solids and completely characterized for the first time. Coupling of 5′-O-(mono-p-methoxytrityl)-2′-O-methyl- (and 3′-O-methyl-) adenosines (1 and 6, respectively) with N-tert-butyloxycarbonyl(N-tBOC)-amino acid anhydrides (2a–c) (generated insitu from the corresponding N-tBOC-amino acids and N,N′-dicyclohexylcarbodiimide) in the presence of 4-N,N-dimethylaminopyridine gave the 3′-O-(N-tBOC-aminoacyl)-5′-O-(mono-p-methoxytrityl-2′-O-methyladenosines (3a–c) and 2′-O-(N-tBOC-aminoacyl)-5′-O-(mono-p-methoxytrityl-3′-O-methyladenosines (7a–c), respectively, in good yields. The L-leucine (a), L-phenylalanine (b), and L-methionine (c) compounds were prepared in each series. Complete deblocking was effected using 98% formic acid since usual procedures had disadvantages with these molecules. The 3′-O-(L-aminoacyl)-2′-O-methyladenosines (4a–c) and 2′-O-(L-aminoacyl)-3′-O-methyladenosines (8a–c) were obtained in high yields with no detectable hydrolysis of the aminoacyl or glycosidic bonds under these conditions.N-Formylmethionyl and N-acetylphenylalanyl derivatives were prepared in each series by acylation of the deblocked products with acetic formic anhydride and p-nitrophenyl acetate, respectively. Biochemical rationale for the use of these compounds in the study of protein biosynthesis and initiation processes are discussed. The puromycin-like activity of 3′-O-phenylalanyl-2′-O-methyl-adenosine (4b) was confirmed.