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Conversion of single-chain or disulfide-bridged dimeric collagenous peptides into Cys(Npys) derivatives as activated species for subsequent regioselective thiol/disulfide exchange reactions leads to side products whose origin and nature was determined by HPLC and ESI-MS. In both cases the high tendency of the educts to self-associate into triple-helical homotrimers, as assessed by their dichroic properties in the reaction media, is responsible for the failure of this well established cysteine chemistry. Only by optimizing the synthetic strategy or by exploiting a kinetic control of the reaction, could these conformation-dependent limitations be more or less efficiently bypassed for the regioselective assembly of heterotrimeric collagen model peptides crosslinked with artificial cystine knots. Copyright © 2002 European Peptide Society and John Wiley & Sons, Ltd.

Conversion of single‐chain or disulfide‐bridged dimeric collagenous peptides into Cys(Npys) derivatives as activated species for subsequent regioselective thiol/disulfide exchange reactions leads to side products whose origin and nature was determined by HPLC and ESI‐MS. In both cases the high tendency of the educts to self‐associate into triple‐helical homotrimers, as assessed by their dichroic properties in the reaction media, is responsible for the failure of this well established cysteine chemistry. Only by optimizing the synthetic strategy or by exploiting a kinetic control of the reaction, could these conformation‐dependent limitations be more or less efficiently bypassed for the regioselective assembly of heterotrimeric collagen model peptides crosslinked with artificial cystine knots. Copyright © 2002 European Peptide Society and John Wiley & Sons, Ltd.

Acetyl-β-(1-azulenyl)-D,L-alanine has been synthesized in high overall yield by the malonic ester condensation procedure, and the racemate has been enzymatically resolved with acylase I from Aspergillus melleus. The enantiomerically pure L-amino acid is of interest as a blue-colored fluorescent tryptophan analog. The bioactivity data of a heptagastrin analog containing it suggests that the planar aromatic azulene moiety may indeed mimic the tryptophan side chain to some extent, and the spectral properties of the azulene moiety makes β-(1-azulenyl)-L-alanine of potential value as a UV and fluorescence probe in synthetic peptides, and possibly even in proteins if bioincorporation succeeds with chemically misacylated tRNAs. Copyright © 2000 European Peptide Society and John Wiley & Sons, Ltd.

Acetyl‐β‐(1‐azulenyl)‐D,L‐alanine has been synthesized in high overall yield by the malonic ester condensation procedure, and the racemate has been enzymatically resolved with acylase I from Aspergillus melleus. The enantiomerically pure L‐amino acid is of interest as a blue‐colored fluorescent tryptophan analog. The bioactivity data of a heptagastrin analog containing it suggests that the planar aromatic azulene moiety may indeed mimic the tryptophan side chain to some extent, and the spectral properties of the azulene moiety makes β‐(1‐azulenyl)‐L‐alanine of potential value as a UV and fluorescence probe in synthetic peptides, and possibly even in proteins if bioincorporation succeeds with chemically misacylated tRNAs. Copyright © 2000 European Peptide Society and John Wiley & Sons, Ltd.

Based on the peculiar spatial array of the active sites in the internal chamber of the multicatalytic proteasome, as derived from the X-ray structure of yeast proteasome, homo- and heterobivalent inhibitors were designed and synthesized to exploit the principle of multivalency for enhancing inhibition potency. Peptidic bis-aldehyde compounds of the octapeptide size were synthesized to address adjacent active sites, whilst a PEG spacer with a statistical length distribution of 19–25 monomers was used to link two identical or different tripeptide aldehydes as binding heads. These bis-aldehyde compounds were synthesized applying both methods in solution and solid phase peptide synthesis. Bivalent binding was observed only for the PEG-spaced inhibitors suggesting that binding from the primed side prevents hemiacetal formation with the active site threonine residue. Copyright © 2000 European Peptide Society and John Wiley & Sons, Ltd.

Based on the peculiar spatial array of the active sites in the internal chamber of the multicatalytic proteasome, as derived from the X‐ray structure of yeast proteasome, homo‐ and heterobivalent inhibitors were designed and synthesized to exploit the principle of multivalency for enhancing inhibition potency. Peptidic bis‐aldehyde compounds of the octapeptide size were synthesized to address adjacent active sites, whilst a PEG spacer with a statistical length distribution of 19–25 monomers was used to link two identical or different tripeptide aldehydes as binding heads. These bis‐aldehyde compounds were synthesized applying both methods in solution and solid phase peptide synthesis. Bivalent binding was observed only for the PEG‐spaced inhibitors suggesting that binding from the primed side prevents hemiacetal formation with the active site threonine residue. Copyright © 2000 European Peptide Society and John Wiley & Sons, Ltd.

Synthetic collagen peptides containing larger numbers of Gly‐Pro‐Hyp repeats are difficult to purify by standard chromatographic procedures. Therefore, efficient strategies are required for the synthesis of higher molecular weight collagen‐type peptides. Applying the Fmoc/tBu chemistry, a comparative analysis of the standard stepwise chain elongation procedure on solid support with the procedure based on the use of the synthons Fmoc‐Gly‐Pro‐Hyp(tBu)‐OH and Fmoc‐Pro‐Hyp‐Gly‐OH was performed. The crude products resulting from the stepwise elongation procedure and from the use of Fmoc‐Gly‐Pro‐Hyp(tBu)‐OH clearly revealed large amounts of microheterogeneities that result from incomplete imino acid acylation as well as from diketopiperazine formation with cleavage of Gly‐Pro units from the growing peptide chain. Conversely, by the use of the Fmoc‐Pro‐Hyp‐Gly‐OH synthon, the quality of the crude products was significantly improved; moreover, protection of the Hyp side chain hydroxyl function is not required using the Fmoc/tBu strategy. With this optimized synthetic procedure, relatively large collagen‐type peptides were obtained in satisfactory yields as highly homogeneous compounds. Copyright © 1999 European Peptide Society and John Wiley & Sons, Ltd.

The search for photoresponsive conformational transitions accompanied by changes in physicochemical and biological properties led us to the design of small cyclic peptides containing azobenzene moieties in the backbone. For this purpose, (4‐aminomethyl)phenylazobenzoic acid (H‐AMPB‐OH) and (4‐amino)phenylazobenzoic acid (H‐APB‐OH) were synthesized and used to cyclize a bis‐cysteinyl‐octapeptide giving monocyclic derivatives in which additional conformational restriction could be introduced by conversion to bicyclic structures with a disulphide bridge. While synthesis with H‐AMPB‐OH proceeded smoothly on a chlorotrityl‐resin with Fmoc/tBu chemistry, the poor nucleophilicity of the arylamino group of H‐APB‐OH required special chemistry for satisfactory incorporation into the peptide chain. Additional difficulties were encountered in the reductive cleavage of the S‐tert‐butylthio group from the cysteine residues since concomitant reduction of the azobenzene moiety took place at competing rates. This difficulty was eventually bypassed by using the S‐trityl protection. Side‐chain cyclization of the APB‐peptide proved to be difficult, suggesting that restricted conformational freedom was already present in the monocyclic form, a fact that was fully confirmed by NMR structural analysis. Conversely, the methylene spacer in the AMPB moiety introduced sufficient flexibility for facile and quantitative side‐chain cyclization to the bicyclic form. Both of the monocyclic peptides and both of the bicyclic peptides are photoresponsive molecules which undergo cis/transisomerization reversibly. Copyright © 1999 European Peptide Society and John Wiley & Sons, Ltd.

Synthetic collagen peptides containing larger numbers of Gly-Pro-Hyp repeats are difficult to purify by standard chromatographic procedures. Therefore, efficient strategies are required for the synthesis of higher molecular weight collagen-type peptides. Applying the Fmoc/tBu chemistry, a comparative analysis of the standard stepwise chain elongation procedure on solid support with the procedure based on the use of the synthons Fmoc-Gly-Pro-Hyp(tBu)-OH and Fmoc-Pro-Hyp-Gly-OH was performed. The crude products resulting from the stepwise elongation procedure and from the use of Fmoc-Gly-Pro-Hyp(tBu)-OH clearly revealed large amounts of microheterogeneities that result from incomplete imino acid acylation as well as from diketopiperazine formation with cleavage of Gly-Pro units from the growing peptide chain. Conversely, by the use of the Fmoc-Pro-Hyp-Gly-OH synthon, the quality of the crude products was significantly improved; moreover, protection of the Hyp side chain hydroxyl function is not required using the Fmoc/tBu strategy. With this optimized synthetic procedure, relatively large collagen-type peptides were obtained in satisfactory yields as highly homogeneous compounds. Copyright © 1999 European Peptide Society and John Wiley & Sons, Ltd.

The search for photoresponsive conformational transitions accompanied by changes in physicochemical and biological properties led us to the design of small cyclic peptides containing azobenzene moieties in the backbone. For this purpose, (4-aminomethyl)phenylazobenzoic acid (H-AMPB-OH) and (4-amino)phenylazobenzoic acid (H-APB-OH) were synthesized and used to cyclize a bis-cysteinyl-octapeptide giving monocyclic derivatives in which additional conformational restriction could be introduced by conversion to bicyclic structures with a disulphide bridge. While synthesis with H-AMPB-OH proceeded smoothly on a chlorotrityl-resin with Fmoc/tBu chemistry, the poor nucleophilicity of the arylamino group of H-APB-OH required special chemistry for satisfactory incorporation into the peptide chain. Additional difficulties were encountered in the reductive cleavage of the S-tert-butylthio group from the cysteine residues since concomitant reduction of the azobenzene moiety took place at competing rates. This difficulty was eventually bypassed by using the S-trityl protection. Side-chain cyclization of the APB-peptide proved to be difficult, suggesting that restricted conformational freedom was already present in the monocyclic form, a fact that was fully confirmed by NMR structural analysis. Conversely, the methylene spacer in the AMPB moiety introduced sufficient flexibility for facile and quantitative side-chain cyclization to the bicyclic form. Both of the monocyclic peptides and both of the bicyclic peptides are photoresponsive molecules which undergo cis/trans isomerization reversibly. Copyright © 1999 European Peptide Society and John Wiley & Sons, Ltd.