Porphyrin-based peptide receptors: syntheses and NMR analysis.
The synthesis and purification of a water-soluble host compound that contains three pyridinium units and one spacer-connected benzocrown ether unit in the meso-positions of porphyrin and of its Zn(II) or Cu(II) complexes is described. Metalation leads to small (compared to the apo-derivative) changes of selectivities with different peptides, with complexation constants in water of above 10(5)M(-1). One complex containing the tripeptide Gly-Gly-Phe is analyzed in detail by COSY, HSQC, HMBC, and NOESY NMR experiments. Temperature-dependent spectra show activation energies for a intramolecular hydrogen exchange of amide protons with valence isomerization of the porphyrin ring, in accordance with the literature. Sharp signals for the spin system are only found at elevated temperature. Vicinal coupling constants within the crown ether moiety indicate stronger puckering than that reported for benzocrowns. All NMR signals of the complexed peptide are shielded, in particular those of the terminal phenylalanine unit, in line with its stacking on the porphyrin surface. A corresponding structural model, obtained by CHARMm simulation, is also in line with the observed intermolecular NOE cross peaks.
Sirish
Mallena
M
FR 11.2 Organische Chemie, Universität des Saarlandes, 66041 Saarbrücken, Germany. ch12hs@rz.uni-sb.de
Chertkov
Vyacheslav A
VA
Schneider
Hans-Jörg
HJ
D055598:Chemical Phenomena; D002627:Chemistry, Physical; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D011166:Porphyrins / Q000138:chemical synthesis / Q000737:chemistry*; D012995:Solubility
D007202:Indicators and Reagents; D009842:Oligopeptides; D010455:Peptides; D011166:Porphyrins