Retro-inverso pseudopeptides

Another possibility to convert biologically active peptides into more stable molecules is the introduction of the retro-inverso amide bond modification lyfNHCO] (Fig. 7.17) [81,82], 

A totally retro-inverso peptide is an isomer of a linear peptide in which the direction of the amino acid sequence is reversed and the chirality at the C carbon of the residues is inverted. This modification has been widely applied [83]. Antigenicity and immunogenic-ity have been demonstrated by preparation of retro-inverso isomers of natural antigenic peptides [84], Retro-inverso forms derived from mellitin and cercropin A maintain antimicrobial activity [85]. A cyclic retro-enantiomeric D amino acid peptide has been designed and shown to be active as synthetic inhibitor of the interaction between immunoglobulin E (IgE) and its high-affinity receptor FceRl [86]. 

The properties of an active peptide can also be modified simply by inverting the direction of only one amide bond within the backbone. This has been demonstrated by Durr 

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The introduction of retro-, retro-inverso-, and PMRI-peptides with free and blocked C-and N-termini has been successful in numerous biological systems such as neurotransmitters, inhibitors of proteases and protein kinases, sweeteners, antimicrobial peptides, hormones, adhesion molecules, antigenic epitopes, immuno-modulators, and immunological probes. Table 1 provides an exhaustive list of retro-, retro-inverso-, PMRI-, and end-group-modified re/ro-mvmo-pseudopeptides derived from bioactive peptides. 

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