Scheme 1. The reactions performed in this work from racemic mixtures of the 5(4H)-oxazolone enantiomers (l-2a and d-2a) with nucleophiles (NuH = H-l-Leu-NH₂, H-l-Ala-NH₂, H-Gly-NH₂, or H-l-Leu-OH) in aqueous media, leading to the corresponding dipeptides as mixtures of enantiomers (Ac-l-Tyr(Me)-Gly-NH₂ and Ac-d-Tyr(Me)-Gly-NH₂) or diastereomers (Ac-l-Tyr(Me)-l-Leu-NH₂ and Ac-d-Tyr(Me)-l-Leu-NH₂, Ac-l-Tyr(Me)-l-Ala-NH₂ and Ac-d-Tyr(Me)-l-Ala-NH₂, or Ac-l-Tyr(Me)-l-Leu-OH and Ac-d-Tyr(Me)-l-Leu-OH). Although prepared from chiral Ac-l-Tyr(Me)-OH (l-1a), the oxazolone was present in a racemic state due to its chiral instability.36.