Modification of amino acids is an important strategy in organic and bioorganic chemistry. In contrast to common side‐chain functionalization, backbone modification is much less explored. Especially glycine units seem to be attractive and versatile since a wide range of functionality can be potentially introduced. We report here oxidative modification of glycinates that are stable and enable further functionalization. Selective glycinate enolate oxidation by TEMPO or a FeCp2PF6/TEMPO reagent combination provides stable alkoxyamines in good to excellent yields. The methodology is expanded to glycine‐containing dipeptides demonstrating selective oxygenation at the glycine unit. The orthogonal reactivity potential of oxygenated glycines for transformation to other amino acid derivatives is explored.

Keywords:Oxazole/1,2,3-triazole isosteric replacement Ynamide CuACC Click chemistry VEGFR2 tyrosine kinase inhibition Cytotoxic activity in Huh-7 and Mahlavu hepatocellular carcinoma cell lines PI3K/Akt pathway a b s t r a c t Structure novelty, chemical stability and synthetic feasibility attracted us to design 1,2,3-triazole compounds as potential inhibitors of VEGFR2 tyrosine kinase. Novel triazoles T1eT7 were proposed by oxazole (AAZ from PDB: 1Y6A)/1,2,3-triazole isosteric replacement, molecular modelling and docking. In order to enable synthesis of T1eT7 we developed a methodology for preparation of ynamide 22. Compound 22 was used for all Click chemistry reactions leading to triazoles T1eT3 and T6eT7. Among the obtained products, T1, T3 and T7 specifically bind VEGFR2 TK and modulate its activity by concentration dependent manner. Moreover predicted binding poses of T1eT7 in VEGFR2 TK were similar to the one known for the oxazole inhibitor AAZ (PDB: 1Y6A). Unfortunately the VEGFR2 inhibition by triazoles e.g. T3 and T7 is lower than that determined for their oxazole bioisosters T3-ox and AAZ, resp. Different electronic properties of 1,2,3-triazole/oxazole heterocyclic rings were proposed to be the main reason for the diminished affinity of T1eT3, T6 and T7 to an oxazole AAZ inhibitor binding site in VEGFR2 TK (PDB: 1Y6A or 1Y6B). Moreover T1eT3 and T6 were screened on cytotoxic activity against two human hepatocellular carcinoma cell lines. Selective cytotoxic activity of T2 against aggressive Mahlavu cells has been discovered indicating possible affinity of T2 to Mahlavu constitutionally active PI3K/Akt pathway.

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