Stereoselective aminoacylation of a dinucleoside monophosphate by the imidazolides ofDl-alanine and N-(tert-butoxycarbonyl)-Dl-alanine

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Abstract
The aminoacylation of diinosine monophosphate (IpI) was studied. When the acylating agent was the imidazolide of N-(tert-butoxycarbonyl)-Dl-alanine, a 40% enantiomeric excess of thel isomer was incorporated at the internal 2′ site and the positions of equilibrium for the 2′⇆3′ migration reaction differed for theD andl enantiomers. The reactivity of the nucleoside hydroxyl groups decreased in the order 2′(3′)>internal 2′>5′, and the extent of reaction was affected by the concentration of the imidazole buffer (pH 7.1). In contrast, reaction of IpI with the imidazolide of unprotectedDl-alanine led to an excess of theD isomer at the internal 2′ site, while reaction with the N-carboxy anhydride ofDl-alanine proceeded without detectable stereoselection. The relevance of these results to the evolution of optical activity and the origin of genetically directed protein synthesis is discussed.