Novel ψ-S-CH2 peptide-bond replacement and its utilization in the synthesis of nonpeptidic surrogates of the Leu-Asp-Val sequence that exhibit specific inhibitory activities on CD4+ T cell binding to fibronectin

The Leu-Asp-Val-(LDV)-containing amino acid sequence, derived from the alternatively spliced first connecting segment region of fibronectin (FN), was shown to be recognized primarily by the α₄β₁-integrin receptor expressed on the surface of various cell types. This adhesion epitope may therefore inhibit integrin-mediated cell interactions with the extracellular matrix glycoprotein, including adhesion, migration, activation and differentiation. To probe the structural requirements for LDV recognition by integrins and examine the feasibility of inhibition of LDV-dependent cell-FN interactions, we have designed and constructed a novel ψ-S—CH₂ peptide bond surrogate that was employed in the formation of LDV surrogates. The synthesis of the ψ-S–CH₂ surrogates reported herein is based on Michael addition of 4-methylpentane thiol to an itaconic acid diester to form an S–CH₂ bond. We have found that the LDV surrogates comprises of 4-methylpentanoate-Asp-i-butyl amide and 8-methyl-3-(2-methylpropylaminocarbonyl)-5-thianonanoic acid interfered with CD4⁺ human T-cell adhesion to FN in vitro, with an ED₅₀ of 280 μg/mL. A control structural mimetic of the Leu-Glu-Val (LEV) peptide did not interfere with the T-cell-FN interaction. The specificity of the reaction was substantiated by the finding that the LDV mimetics did not interfere with T-cell adhesion to laminin, another major cell-adhesive glycoprotein of the extracellular matrix. That the nonpeptidic mimetics of LDV interfered markedly with T-cell-FN adhesive interactions indicate that the peptide bond and the amine and carboxyl end groups of the tripeptide makes only a minor contribution to the integrin binding affinity. Thus, consistent with our recent report on the production of Arg-Gly-Asp surrogates, we suggest that these constructs could provide novel insights into the fundamental mechanisms of integrin-ligand interactions, and serve as competitive antagonists of conceivable therapeutic value.