Crystal structures of two retropeptides related to the Gly-Gly and Ala-Ala sequencesLarbi El Masdouri, André Aubry, Emmanuel José Gomez, Bernard Vitoux and Michel MarraudJ. Chim. Phys., 85 (1988) 583-588DOI: https://doi.org/10.1051/jcp/1988850583