Heteroclitic properties of mixed alpha- and aza-beta3-peptides mimicking a supradominant CD4 T cell epitope presented by nucleosome.

Recent studies have revealed that peptide analogues containing modified peptide bonds might replace poorly stable natural peptides in therapeutic strategies. Using the model peptide 88-99 of histone H4, which contains a supradominant epitope recognized by Th cells induced to nucleosomes, we have generated twelve analogues containing aza-beta(3)-amino acid residue substitutions. The ability of this new class of peptidomimetics corresponding to the Psi[CONHNRCH(2)] modification to be recognized by T cells primed with the parent peptide was examined in BALB/c mice. An Ala-scan study revealed that residues 88 to 92 were essential for keeping antigenic activity of the nominal peptide. In good agreement, the six aza-beta(3)-analogues encompassing substitutions in the region 89-92 were antigenically inactive. Analogues PsiG94 and PsiG99 were both antigenic and immunogenic, though at levels that were slightly lower to that of the parent peptide. However, the remaining analogues PsiR95, PsiL97, PsiY98 and PsiL97-Y98 were strongly recognized by T cells generated to the homologous peptides. The PsiL97-Y98 analogue, in particular, strongly activated CD4(+) T cells as visualized in CFSE dilution assay. T cells primed to these four analogues and recalled with the nominal peptide secreted high levels of either IL-2 (PsiR95, PsiY98) or IFN-gamma (PsiL97, PsiL97-Y98). This result, supported by molecular modeling, suggests that TCRs of T cells primed to these four analogues recognized the parent peptide associated with the MHC I-A(d)/I-E(d) molecules. Since these T cells produce a distinct cytokine pattern when they are recalled with the parent sequence, this new class of analogues may have valuable applications in the context of self-tolerance and autoimmunity.

Solid-phase synthesis of "mixed" peptidomimetics using Fmoc-protected aza-beta3-amino acids and alpha-amino acids.

[structure: see text] A solid-phase fluorenylmethyloxycarbonyl (Fmoc)-based synthesis strategy is described for "mixed" aza-beta3-peptides as well as a convenient general approach for their required building blocks, the aza-beta3-amino acid residues (aza-beta3-aa). These monomers allow the synthesis of relatively large quantities of pure mixed aza-beta3-peptides. The required Fmoc-substituted aza-beta3-amino acids are accessible by convenient synthesis, and a number of monomers including those containing side chains with functional groups have been synthesized. The method was applied toward the solid-phase synthesis of aza-beta3-peptide mimetics of a biologically active histone H4 sequence.

Synthesis and evaluation of new omega-borono-alpha-amino acids as rat liver arginase inhibitors.

Recent studies have demonstrated that arginase plays important roles in pathologies such as asthma or erectile dysfunctions. We have synthesized new omega-borono-alpha-amino acids that are analogues of the previously known arginase inhibitors S-(2-boronoethyl)-l-cysteine (BEC) and 2-amino-6-boronohexanoic acid (ABH) and evaluated them as inhibitors of purified rat liver arginase (RLA). In addition to the distance between the B(OH)(2) and the alpha-amino acid functions, the position of the sulfur atom in the side chain also appears as a key determinant for the interaction with the active site of RLA. Furthermore, substitution of the alkyl side chain of BEC by methyl groups and conformational restriction of ABH by incorporation of its side chain in a phenyl ring led to inactive compounds. These results suggest that subtle interactions govern the affinity of inhibitors for the active site of RLA.