Synthesis and biological evaluation of 4-hydroxy-4-(4-methoxyphenyl)-substituted proline and pyrrolidin-2-ylacetic acid derivatives as GABA uptake inhibitors

A series of enantiomerically pure 4-hydroxy-4-(4-methoxyphenyl)-substituted proline and pyrrolidin-2-ylacetic acid derivatives have been synthesized starting from the respective N-protected 4-hydroxy derivatives via oxidation to the corresponding 4-oxo compounds, subsequent addition of organometallic reagents, final hydrolysis and deprotection. The major diastereoisomers obtained by the addition of the Grignard reagents were found to have opposite stereoconfigurations depending on whether cerium trichloride was present or absent as an additive. The final compounds were evaluated for their capability to inhibit the GABA transport proteins GAT1 and GAT3. 4-Hydroxyproline derivatives substituted with a tris(4-methoxyphenyl)methyloxyethyl residue at the nitrogen and a 4-methoxyphenyl group in 4-position showed, with the exception of the (2R,4R)-diastereomer, an improved inhibition at GAT3 compared to the derivatives missing the 4-methoxyphenyl group in 4-position. This may imply that an appropriate lipophilic group at the C-4 position of the proline moiety is beneficial for potent inhibition at GAT3.

Synthesis and biological evaluation of new GABA-uptake inhibitors derived from proline and from pyrrolidine-2-acetic acid

Several synthetic approaches to N-alkylated derivatives of 4-hydroxypyrrolidine-2-carboxylic acid and 4-hydroxypyrrolidine-2-acetic acid are described. The final compounds have been evaluated as potential inhibitors of the GABA transport proteins GAT-1 and GAT-3. The biological assays used were based on bovine material or porcine brain. As compared to the corresponding 4-unsubstituted compounds, the 4-hydroxypyrrolidine-2-carboxylic acid and 4-hydroxypyrrolidine-2-acetic acid derivatives showed a significant decrease in the inhibitory potency at both GAT-1 and GAT-3 with only four compounds having reasonable affinity to GAT-1 (IC(50): 5.1, 6.6 and 9.4 microM) or GAT-3 (IC(50): 19.9 microM), respectively. The biological data of the 4-hydroxypyrrolidine-2-acetic acid derivatives indicates that (2S)-configuration at the C-2 position for potent inhibition of GAT-1 and (4R)-configuration at the C-4 position for potent inhibition of GAT-3 may be crucial.

Assembly of binding loops on aromatic templates as VCAM-1 mimetics

The design and synthesis of cyclic mimetics of VCAM-1 protein that reproduce the integrin-binding domain are presented. The unprotected peptide precursor 37-43, Thr-Gln-Ile-Asp-Ser-Pro-Leu, was grafted onto functional templates of type naphthalene, biphenyl and benzyl through the chemoselective formation of C- and N-terminal oximes resulting in a mixture of four isomeric forms due to syn-anti isomerism of the oxime bonds. Some isomers could be monitored by HPLC and identified by NMR. The molecule containing a naphthalene-derived template was found to inhibit the VCAM-1/VLA-4 interaction more efficiently than previously reported for sulfur-bridged cyclic peptides containing similar sequences. The finding confirms the importance of incorporating conformational constraints between the terminal ends of the peptide loop 37-43 in the design of synthetic inhibitors of the VCAM-1/integrin interaction.