The early days: although considered a species to be avoided in peptide chemistry, the intermediacy of 5(4H)-oxazolones is demonstrated to be essential for the formation of peptides through cyanamide and carbodiimide activation in aqueous solution.

We are indebted to the interdisciplinary program of the CNRS Planetary Environments and Origins of Life (EPOV) for support, and to the COST Action CM0703 "Systems chemistry" for providing the possibility of fruitful scientific exchanges during the realization of this work.Supporting information for this article is available on the WWW under http://dx.