Abstract
An improved synthesis of 3-β-D-ribofuranosylwybutine (2) has been achieved by the Wittig reaction between 4,6-dimethyl-9-oxo-3-[2,3,5-tris-O-(tert-butyldimethylsilyl)-β-D-ribofuranosyl]-4,9-dihydro-3H-imidazo[1,2-a]purine-7-carbaldehyde (8) and the phosphorane derived from (R)-2-[(methoxycarbonyl)amino]-3-(triphenylphosphonio)propanoate (9), followed successively by methylation, hydrogenation, and deprotection. On the other hand, the minor nucleoside wybutosine of yeast tRNAPhe was isolated on a scale of 80 μg by partial digestion of unfractionated tRNA (1 g) with nuclease P1, followed successively by reversed-phase column chromatography, complete digestion with nuclease P1/alkaline phosphatase, and reversed-phase HPLC. Comparison of this nucleoside with 2 has unambiguously established that the structure of wybutosine is (αS)-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 (2).
