Synthesis of peptidomimetic, nonpeptidic and conformationally constrained analogues of acetyl-aspartyl-glutamic acid as inhibitors of NAALA dipeptidase

N-Acetylated {dollar} alpha{dollar}-linked acidic dipeptidase (NAALA dipeptidase) is a membrane bound, chloride activated, metallopeptidase which is mainly localized in the central nervous system (CNS). There is substantial evidence to suggests a neuronal role for this enzyme. Furthermore, NAALA dipeptidase has shown high specificity for the hydrolysis of Ac-Asp-Glu-OH (1), a brain peptide believed to be involved in synaptic processes. While the overall objective of this project was to gain some insight into the structural requirements for the inhibition of NAALA dipeptidase, it more specifically addresses two questions; (1) Is the N-acetamido group in Ac-Asp-Glu-OH involved in an important binding interaction within the active site of the enzyme? (2) What spatial arrangement does the aspartic acid carboxyl group take in relation to the glutamic acid residue?; The following structural and conformationally constrained analogues of Ac-Asp-Glu-OH were synthesized: A desacetamido analogue N-succinyl-L-glutamic acid (13) was synthesized in order to answer the first question. Conformationally constrained analogues were synthesized by substituting the aspartyl residue with maleyl, fumaryl and the Z- and E-dehydroaspartyl ({dollar} Deltasp{lcub}Z{rcub}{dollar} and {dollar} Deltasp{lcub}E{rcub}{dollar}Asp) residues. N-fumaryl-L-glutamic acid (15) and Ac-{dollar} Deltasp{lcub}Z{rcub}{dollar}Asp-Glu-OH (16) should mimic an extended conformation of the aspartyl carboxy residue in relation to the glutamyl carboxy groups, while N-maleyl-L-glutamic acid (14) and Ac-{dollar} Deltasp{lcub}E{rcub}{dollar}Asp-Glu-OH (17) should mimic a more folded conformation. A non-peptidic aromatic compound (18) was synthesized in order to mimic one low energy conformation of N-fumaryl-L-glutamic acid and a compound containing a trans olefin amide bond surrogate (19) was synthesized as a non-hydrolyzable analogue of Ac-Asp-Glu-OH.; Compounds 13-16 were evaluated for their ability to inhibit the hydrolysis of Ac-Asp- (3,4-{dollar} sp3{dollar}H) -Glu-OH by NAALA dipeptidase. Compound 14 was a very weak inhibitor of NAALA dipeptidase (K{dollar} sb{lcub}rm i{rcub}{dollar} = 41 {dollar} mu{dollar}M), while compounds 13, 15 and 16 were good inhibitors of NAALA dipeptidase with K{dollar} sb{lcub}rm i{rcub}{dollar} values 0.9, 0.4 and 1.4 {dollar} mu{dollar}M respectively. Compounds 18 and 19 were poor inhibitors of NAALA dipeptidase. These studies suggests that the acetamido moiety is not an important requirement for binding to the enzyme. They also indicate that the {dollar} chisb1{dollar} torsional angle for the aspartyl residue is in the vicinity of 0{dollar} spcirc{dollar}.