Unexpected stability of the urea cis-trans isomer in urea-containing model pseudopeptides.

In contrast to the situation observed in the crystal state, the urea moiety in N-Boc-N'-carbamoyl-gem-diaminoalkyl derivatives (single-residue ureidopeptides) 1-4 exclusively assumes a cis-trans conformation in solution. When R(3) = H, the resulting structure can be further stabilized by an intramolecular hydrogen bond that closes an eight-membered pseudocycle. The root-mean-square deviation calculated for heavy atoms between a peptide gamma-turn and the folded conformation that we propose to call urea turn is 0.60 A. [structure: see text]

The bare skin and the nose as non-invasive routes for administering peptide vaccines.

Among the different technologies currently tested for the development of novel vaccines, synthetic peptides represent a promising option, since they are chemically pure and induce immune responses of predetermined specificity. Furthermore, they can be replaced with pseudopeptides or peptide mimetics that contain changes in the amide bond, resulting in more stable and immunogenic molecules. Administration of peptide vaccines via non-invasive routes, such as the nose or the bare skin, allows the efficient uptake of antigen by antigen-presenting cells, which are abundant in the associated lymphoid tissues, ensuring the induction of effective systemic and mucosal immune responses. Using non-invasive routes could be advantageous for vaccination programs in third-world countries, since vaccine administration is simple, painless and economical. In this review, we discuss and present some preliminary data on the advantages of synthetic peptides and peptidomimetics as candidate vaccines, and their potential for administration via the skin and the nose.