Alberto Bianco

A Helical Peptide Receptor for [60]Fullerene

Two terminally blocked nonapeptides, each made up of six Aib residues, a Gly spacer and two L-Tyr residues in positions 2 and 8 (these are substituted in the side chain with either ferrocenoyl or methyl moieties), have been synthesized by solution methods and fully characterized. FT-IR absorption and two-dimensional NMR analyses indicate that a 3(10)-helical conformation is adopted by these rigid peptides in structure-supporting solvents. An X-ray diffraction investigation shows that the bis-L-Tyr(Me) nonapeptide in the crystal state is folded in a regular right-handed 3(10)-helical structure. As five amino acid units separate the two substituted L-Tyr residues in the peptide sequence, the two side chain moieties will-in solution-face each other after two complete turns of the ternary helix. By carrying out a detailed photophysical analysis, we have demonstrated that the electron-rich, hydrophobic and wide cavity generated by the nonapeptide template with two ferrocenoyloxybenzyl walls is able to host [60]fullerene. Further evidence for this superstructure has been provided in the gas phase by a mass spectrometric investigation.

Trans‐cis amide bond isomerization in fulleroprolines

The 1H NMR study of fulleroproline derivative Ac‐Fpr‐OtBu and its Pro analogue Ac‐l‐Pro‐OtBu over a range of temperatures in toluene‐d8 solution has enabled the comparison of their equilibrium and activation parameters for the trans/cis interconversion around the amide partial double bond.

The polypeptide 310-helix as a template for molecular recognition studies. Structural characterization of a sidechain functionalized octapeptide

A Nα-blocked, Aib-rich octapeptide methylamide containing two Nω-benzoylated l-Lys residues at positions 3 and 6 was synthesized by solution methods and fully characterized. A solution and crystal-state conformational analysis, performed by using FT-IR, 1H NMR, CD, and X-ray diffraction techniques, showed that the peptide is folded into a regular, right-handed 310-helix stabilized by seven consecutive Nue5f8H…Oue5fbC intramolecular H-bonds of the β-turn III type. The two benzamidobutyl l-Lys side chains, located on the same side of the helix after one complete turn, generate a cleft the minimal width of which was found to be 3.47 A.

The polypeptide 310-helix as a template and a spacer

X-ray diffraction analyses have provided detailed structural information on the 310-helices of (i) pBrBz-d-(αMe)Phe-(Aib)2-d-(αMe)Phe-Aib-OtBu and Ac-(Aib)2-l-Lys(Bz)-(Aib)2-l-Lys(Bz)-(Aib)2-NHMe as suitable templates for molecular recognition studies, and (ii) pBrBz-TOAC-(l-Ala)2-TOAC-l-Ala-NHtBu as an appropriate spacer for an ESR study of side chain to side chain interactions. In addition, in Ac-TOAC-(Aib)2-l-Trp-Aib-OMe, forming a 310-helix, the TOAC residue plays the role of an effective quencher of the fluorescence of the tryptophan residue located one turn apart.

Tryptophan-Containing Polypeptide 310-Helices

A proper understanding of the mechanisms of side-chain interactions and molecular recognition depends heavily upon the ability to design and build conformationally constrained structures whose intercomponent geometry is well defined. As appropriate temxadplates, we chose to focus on structurally restricted 310-helical oligopeptides, which fold to bring into close proximity two partners positioned one turn apart.