**3. Results and discussions**

#### **3.1 Synthesis of GZK-111**

*N*-Phenylacetyl-glycyl-L-proline ethyl ester was prepared according to **Figure 1** by the mixed anhydride method under Anderson conditions [28] using isobutyl chloroformate. *N*-phenylacetylglycine obtained from glycine and phenylacetic acid chloride according to Schotten-Baumann procedure [29] was used as carboxylic component, and proline ethyl ester obtained with thionyl chloride in absolute ethanol according to Brenner method [30] was used as amine component. The Denantiomer of GZK-111 (GZK-121) was prepared by the same procedure.
