Aminoacyl ethyl phosphates are functional analogues of aminoacyl adenylates, the activated intermediates formed by ribosomal enzymes from the reaction of amino acids with ATP. The aminoacyl ethyl phosphates are prepared by DCC-mediated coupling of a tetraalkylammonium salt of ethyl phosphate and an N-t-Boc-amino acid, followed by deprotection. The efficiency of the synthesis and the solubility properties of the product depend on the alkyl group in the ammonium counterion of the phosphate. N-Protected and free aminoacyl ethyl phosphates hydrolyze slowly ([Formula: see text] in neutral solution, 25 °C, ~100 h). These materials are potentially useful in biomimetic peptide synthesis, protein modification, and aminoacylation of RNA. Key words: amino acids, acyl phosphates, aminoacyl phosphates, biomimetic aminoacylation.