Synthesis of imidazole phosphinic acids as I4AA analogues

Synthesis of α-carboxyphosphinopeptides derived from norleucine

In the present study, we describe in detail the synthesis of a relatively rare class of phosphorus compounds, α-carboxyphosphinopeptides. We prepared several norleucine-derived α-carboxyphosphinic pseudopeptides of the general formula Nle-Ψ[PO(OH)]-Gly. These compounds could have important applications as transition state-mimicking inhibitors for methionine or leucine aminopeptidases or other enzymes. For the preparation of the key α-carboxyphosphinate protected precursors, we investigated, compared and improved two different synthetic methods described in literature: the Arbuzov reaction of a silylated N-protected phosphinic acid with a bromoacetate ester and the nucleophilic addition of a mixed O-methyl S-phenyl N-protected phosphonic acid or a methyl N-protected phosphonochloridate with tert-butyl lithioacetate. We also prepared two N-Fmoc protected synthons, Fmoc-Nle-Ψ[PO(OH)]-Gly-COOH and Fmoc-Nle-Ψ[PO(OAd)]-Gly-COOH, and demonstrated that these precursors are suitable building blocks for the solid-phase synthesis of α-carboxyphosphinopeptides.

5-Substituted imidazole-4-acetic acid analogues: synthesis, modeling, and pharmacological characterization of a series of novel gamma-aminobutyric acid(C) receptor agonists

A series of ring-substituted analogues of imidazole-4-acetic acid (IAA, 4), a partial agonist at both GABAA and GABAC receptors (GABA = gamma-aminobutyric acid), have been synthesized. The synthesized compounds 8a-l have been evaluated as ligands for the alpha1beta2gamma2S GABAA receptors and the rho1 GABAC receptors using the FLIPR membrane potential (FMP) assay and by electrophysiology techniques. None of the tested compounds displayed activity at the GABAA receptors at concentrations up to 1000 microM. However, the 5-Me, 5-Ph, 5-p-Me-Ph, and 5-p-F-Ph IAA analogues, 8a,c,f,g, displayed full agonist activities at the rho1 receptors in the FMP assay (EC50 in the range 22-420 microM). Ligand-protein docking identified the Thr129 in the alpha1 subunit and the corresponding Ser168 residue in rho1 as determinants of the selectivity displayed by the 5-substituted IAA analogues. The fact that GABA, 4, and 8a displayed decreased agonist potencies at a rho1Ser168Thr mutant compared to the WT rho1 receptor strongly supported this hypothesis. However, in contrast to GABA and 4, which exhibited increased agonist potencies at a alpha1(Thr129Ser)beta2gamma2 mutant compared to WT GABAA receptor, the data obtained for 8a at the WT and mutant receptors were nonconclusive.