Comparative Study of the Synthesis and Structural and Physicochemical Properties of Diketopiperazines vs Aza-diketopiperazines

Aza-diketopiperazines (aza-DKPs) represent an underprivileged motif obtained by scaffold hopping of 2,5-diketopiperazines (2,5-DKPs). Herein, we compare the synthesis and the structural and physicochemical properties of aza-DKP 4 vs 2,5-DKP 7. Thus, X-ray and 1H NMR studies show that aza-DKP 4 is a rigid and nonflat scaffold like the 2,5-DKP 7. Moreover, the replacement of one Cα-stereogenic center by a nitrogen atom results in a significant improvement of both the water solubility and the microsomal stability.