N-(Trifluoroacetyl)dehydrodipeptides 2-3 were coupled to aminomethylene dimethylacetal derivatives 4 5. The resulting pseudo-tripeptides 6 were stepwise deprotected (carbonyl function (7) then amine function) and in situ cyclized into imidazolopyrazines 1. (C) 2002 Elsevier Science Ltd. All rights reserved.
Devillers, I., Arrault, A., Olive, G., & Marchand-Brynaert, J. (2002). A biomimetic synthesis of coelenterazine analogs. Tetrahedron Letters, 43(17), 3161-3164. https://doi.org/10.1016/S0040-4039(02)00462-8 (Original work published 2002)