Synthesis of Acyclic and Dehydroaspartic Acid Analogues of Ac-Asp-Glu-OH and Their Inhibition of Rat Brain N-Acetylated α-Linked Acidic Dipeptidase (NAALA Dipeptidase)

The following structural and conformationally constrained analogues of Ac-Asp-Glu-OH (1) were synthesized: Ac-Glu-Glu-OH (2), Ac-D-Asp-Glu-OH (3), Ac-Glu-Asp-OH (4), Ac-Asp-Asp-OH (5), Ac-Asp-3-aminohexanedioic acid (6), Ac-3-amino-3-(carboxymethyl)propanoyl-Glu-OH (7), N-succinyl-Glu-OH (8), iV-maleyl-Glu-OH (9), N-fumaryl-Glu-OH (10), and Ac-Δ^zAsp-Glu-OH (11). These analogues were evaluated for their ability to inhibit the hydrolysis of Ac-Asp-[3,4-³H]-Glu-OH by N-acetylated α-linked acidic dipeptidase (NAALA dipeptidase) in order to gain some insight into the structural requirements for the inhibition of this enzyme. Analogues 4-6 and 9 were very weak inhibitors of NAALA dipeptidase (K_i> 40 μM), while 2, 3, and 7 with K_ivalues ranging from 3.2-8.5 μM showed intermediate inhibitory activity. The most active inhibitors of NAALA dipeptidase were compounds 8, 10, and 11 with K_ivalues of 0.9, 0.4, and 1.4 μM, respectively. These results suggest that the relative spacing between the side chain carboxyl and the α-carboxyl group of the C-terminal residue may be important for binding to the active site of the enzyme. They also indicate that the x₁torsional angle for the aspartyl residue is in the vicinity of 0°.