Synthesis and Structure of the Hypermodified Nucleoside of Rat Liver Phenylalanine Transfer Ribonucleic Acid

Abstract

The first synthesis of (αS,βS)-β-hydroxy-α-[(methoxycarbonyl)amino]-4,6-dimethyl-9-oxo-3-β-D-ribofuranosyl-4,9-dihydro-3H-imidazo[1,2-a]purine-7-butanoic acid methyl ester [(αS,βS)-11] has been achieved by OsO₄ oxidation of [S-(E)]-4-[4,6-dimethyl-9-oxo-3-[2,3,5-tris-O-(tert-butyldimethylsilyl)-β-D-ribofuranosyl]-4,9-dihydro-3H-imidazo[1,2-a]purin-7-yl]-2-[(methoxycarbonyl)amino]-3-butenoic acid methyl ester (13) followed by successive γ-deoxygenation through the cyclocarbonates, separation from the (αS,βR)-isomer by means of flash chromatography, and deprotection. On the other hand, the minor nucleoside of rat liver tRNA^Phe was isolated on a scale of 100 μg by partial digestion of unfractionated tRNA (1 g) with nuclease P₁, followed by reverse-phase column chromatography, complete digestion with nuclease P₁/alkaline phosphatase, and reverse-phase HPLC. Comparison of this nucleoside with the synthetic one has unambiguously established its structure to be (αS,βS)-11.