Mixed anhydrides (phosphoric-carboxyl) are also formed in the esterification of 5'-AMP with N-acetylaminoacyl imidazolides: implications regarding the origin of protein synthesis.

Procedures for the formation of aminoacyl esters of monoribonucleotides with aminoacyl imidazolides were first reported by Gottikh et al. and summarized in 1970. This reaction has been widely used by us and numbers of other workers as a convenient means of preparing aminoacyl esters of nucleotides. We have previously reported that, under conditions of excess imidazolide, large amounts of bis 2', 3' esters are formed in addition to the monoesters, (Lacey et al., 1991). However, to our knowledge, no one has reported that in addition to the esters, relatively large amounts of the mixed anhydride, with the amino acid carboxyl attached to the phosphate, are also formed at short reaction times. We report here on the relative amounts of anhydride and esters formed in this reaction of racemic mixtures of eleven N-acetyl amino acid imidazolides with 5'-AMP and discuss the relevance of the findings to the origin of protein synthesis.