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C Toniolo

Publications and source records attributed to C Toniolo.

At least 55 records · Page 3Linked to original sources
PubMed1999

Synthesis, conformational study, and spectroscopic characterization of the cyclic C alpha, alpha-disubstituted glycine 9-amino-9-fluorenecarboxylic acid.

A series of terminally blocked peptides (to the pentamer level) from L-Ala and the cyclic C alpha, alpha-disubstituted Gly residue Afc and one Gly/Afc dipeptide have been synthesized by solution method and fully characterized. The molecular structure of the amino acid derivative Boc-Afc-OMe and the dipeptide Boc-Afc-Gly-OMe were determined in the crystal state by X-ray diffraction. In addition, the preferred conformation of all of the model peptides was assessed in deuterochloroform solution by FT-IR absorption and 1H-NMR. The experimental data favour the conclusion that the Afc residue tends to adopt either the fully-extended (C5) or a folded/helical structure. In particular, the former conformation is highly populated in solution and is also that found in the crystal state in the two compounds investigated. A comparison with the structural propensities of the strictly related C alpha, alpha-disubstituted Gly residues Ac5c and D phi g is made and the implications for the use of the Afc residue in conformationally constrained analogues of bioactive peptides are briefly examined. A spectroscopic (UV absorption, fluorescence, CD) characterization of this novel aromatic C alpha, alpha-disubstituted Gly residue is also reported.

Amino Acids↗
PubMed1999

Total synthesis and membrane modifying properties of the lipopeptaibol trikoningin KB II and its analogues with acyl chains of different length at the N- and C-termini.

Trikoningin KB II, a ten-amino acid residue lipopeptaibol blocked at the N-terminus by the n-octanoyl group and at the C-terminus by the 1,2-amino alcohol L-leucinol, and extracted from the fungus Trichoderma koningii, exhibits membrane-modifying properties. We have synthesized by solution-phase methods trikoningin KB II and several analogues with acyl chains of different length at the N- and C-termini. Permeability measurements showed that an appropriate length of the linear acyl chain is a more important characteristic for the onset of significant membrane-modifying activity than its position in the peptide chain.

Amino Acid Sequence↗
PubMed1999

Preferred solution conformation of peptides rich in the lipophilic, chiral, C(alpha)-methylated alpha-amino acid (alpha Me)Aoc.

The lipophilic, chiral, C(alpha)-methylated alpha-amino acid L-(alphaMe)Aoc (2-methyl-2-amino-octanoic acid) was prepared using a chemo-enzymatic approach. Two series of terminally protected model peptides, from dimer through to hexamer, containing L-(alphaMe)Aoc in combination with either Gly or Aib, were synthesized by solution methods and were fully characterized. A solution conformational analysis, based on FT-IR absorption, 1H-NMR and circular dichroism (CD) techniques, was performed with the aim at determining the preferred conformation of this novel amino acid and the relationship between chirality at its alpha-carbon atom and screw sense of the helix that is formed. The results obtained strongly support the view that L-(alphaMe)Aoc favours the formation of the right-handed 3(10)-helical conformation.

Amino Acids↗
PubMed1999

Determining the occurrence of a 3(10)-helix and an alpha-helix in two different segments of a lipopeptaibol antibiotic using TOAC, a nitroxide spin-labeled C(alpha)-tetrasubstituted alpha-aminoacid.

Trichogin GA IV is a 11-residue lipopeptaibol antibiotic exhibiting membrane modifying properties. We synthesized step-by-step by solution methods three trichogin analogues, each with a double Aib (alpha-aminoisobutyric acid)-->TOAC (2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid) replacement. The strict similarity in the conformational propensities of Aib and TOAC allowed us to exploit these analogues in a detailed investigation of the conformation of this lipopeptaibol in different organic solvents and in a membrane-mimetic environment using in particular the double spin labeling ESR technique. We conclude that the secondary structure in solution remains essentially unchanged if compared to that previously found in the crystal state for trichogin. More specifically, the N-terminal region of the peptide folds in a 3(10)-helix, while the central and C-terminal regions are mainly alpha-helical. An additional, significant proof for the modest plasticity of the trichogin structure was obtained by an X-ray diffraction analysis of the nOct-[TOAC4,8, Leu-OMe11] analogue. For the three analogues permeability measurements revealed membrane-modifying properties comparable to those of natural trichogin.

Aminoisobutyric Acids↗
PubMed1999

The antimicrobial peptide trichogin and its interaction with phospholipid membranes.

The interaction of the antimicrobial peptide trichogin GA IV with phospholipid bilayers has been studied. A series of analogs of trichogin was synthesized in which the nitroxide spin label, 4-amino-4-carboxy-2,2,6,6-tetramethylpiperidino-1-oxyl (TOAC), replaced one of the three alpha-aminoisobutyric acid (Aib) residues in the sequence. These modified peptides were used to assess the location of different residues of the peptide in a phospholipid bilayer composed of egg phosphatidylcholine containing 0.4 mol% of a fluorescently labelled phospholipid. We demonstrate that the substitution of Aib residues with TOAC does not alter the manner in which the peptide affects membrane curvature or induces vesicle leakage. The proximity of the nitroxide group on the peptide to the 4,4-difluoro-4-bora-3a,4a-diaza-S-indacene (BODIPY) fluorophore attached to the phospholipid was estimated from the extent of quenching of the fluorescence. By this criterion it was concluded that the peptide penetrates into the bilayer and that Aib4 is the most deeply inserted of the Aib residues. The results suggest that the helix axis of the peptide is oriented along the plane of the membrane. All of the peptides were shown to raise the bilayer to the hexagonal phase transition temperature of dipalmitoleoylphosphatidylethanolamine, indicating that they promote positive membrane curvature. This is a property observed with peptides that do not penetrate deeply into the bilayer or are oriented along the bilayer normal. We also demonstrate trichogin-promoted leakage of the aqueous contents of liposomes. These results indicate that the peptides cause bilayer destabilization. The extent of leakage induced by trichogin is very sensitive to the peptide to lipid ratio over a narrow range.

Amino Acid Sequence↗
PubMed1998

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.

Bacterial Proteins↗
PubMed1998

Conformation and membrane activity of an analogue of the peptaibol antibiotic trichogin GA IV with a lipophilic amino acid at the N-terminus.

We have synthesized by solution-phase methods two analogues of the 11-residue lipopeptaibol antibiotic trichogin GA IV in which the N-terminal n-octanoyl group is replaced either by an N-acetylated 2-amino-2-methyl-L-undecanoic acid or by an N-acetylated alpha-aminoisobutyric acid. CD, FTIR absorption. and NMR analyses unequivocally show that the main structural features of trichogin GA IV are preserved in these analogues. Since only the peptide containing the lipophilic chain exhibits membrane-modifying properties, these results strongly support the view that moving the long acyl moiety from the Nalpha-blocking group to the side chain of the N-terminal extra-residue does not affect the conformational properties or the membrane activity of trichogin GA IV.

Amino Acid Sequence↗
PubMed1998

Solution conformational analysis of amphiphilic helical, synthetic analogs of the lipopeptaibol trichogin GA IV.

The step-by-step synthesis by solution methods of the [Ser2,5,6,9, Leu-OMe11] analog of trichogin GA IV is described. The four Ser residues have been incorporated into the sequence as replacements of the naturally occurring Gly residues to increase the amphiphilicity of the 3D-structure of the lipopeptaibol. A detailed solution conformational analysis has been performed on this undecapeptide and its prototypical [Leu-OMe11] trichogin GA IV analog using FTIR absorption and CD spectroscopies, and two-dimensional NMR under a variety of experimental conditions, including a membrane-mimetic environment. Both peptides adopt a mixed 3(10)/alpha-helical structure, which in the micellar system was found to be less flexible for the Ser-containing analog. For both analogs permeability measurements revealed membrane-modifying properties comparable to those of the natural lipopeptaibol.

Anti-Bacterial Agents↗
PubMed1997

Beta-turn induction by C60-based fulleroproline: synthesis and conformational characterization of Fpr/Pro small peptides.

We have recently described the preparation of Fpr (C60-based fulleroproline). In this paper the synthesis and a conformational characterization of heterochiral di- and tripeptides containing this new alpha-amino acid are reported. A folded structure, induced by the -L-Fpr-D-Ala-sequence in chloroform solution and detected by Fourier transform infrared absorption and 1H nuclear magnetic resonance, has been compared with the known propensity of the cognate -L-Pro-D-Ala-sequence to adopt a beta II-turn conformation, which has also been confirmed in this work. The beta II-turn structure is retained in the crystal state by the Pro-peptides, as shown by the X-ray diffraction structures of Ibu-L-Pro-D-Ala-NHtBu and Z-L-Pro-D-Ala-L-Ala-OtBu.

Bacterial Proteins↗
PubMed1996

Crystallographic structure of a multiple beta-turn containing, glycine-rich heptapeptide: a synthetic precursor of the lipopeptaibol antibiotic trichodecenin I.

In continuation of our studies on the structure and function of peptaibol antibiotics, the conformational properties of a sequence analogous to that of Trichodecenin I (Z-Gly-Gly-D-Leu-Aib-Gly-D-Ile-D-Leu-OMe, where Z = benzyloxycarbonyl, Aib = alpha-aminoisobutyric acid, and OMe = methyl ester) have been investigated crystallographically. This sequence is the mirror image of the naturally occurring molecule and also of the C-terminal heptapeptide of the related lipopeptaibol Trichogin A IV (where, however, the Leu-OMe residue has replaced the original Leuol residue). The molecule crystallized in the monoclinic system, space group P21, Z = 4, and cell parameters a = 11.610(5), b = 33.342(8), c = 11.735(4) A, beta = 110.42(1) degrees, V = 4257(3) A3. The crystallographic refinement converges at residual values of R = 0.047 and wR2 = 0.134 on F2. In the 1-5 segment the molecular conformation is virtually identical to that one reported from solution nmr studies of a similarly protected sequence [Biopolymers (1995), Vol. 35. pp. 21-29)] and is characterized by beta-turns of type I at Gly1-Gly2, II' at Leu3-Aib4, and I at Aib4-Gly5. In the crystal structure, a beta-sheet-like arrangement is seen at the C-terminus.

Anti-Bacterial Agents↗
PubMed1996

Structural versatility of peptides from C alpha, alpha-disubstituted glycines: crystal-state conformational analysis of peptides from C alpha-methylhomophenylalanine, (alpha Me) Hph.

The molecular and crystal structures of the C alpha-tetrasubstituted, delta-branched alpha-amino acid C alpha-methylhomophenylalanine, H-D-(alpha Me)Hph-OH, and three peptides (to the pentamer level), including the homotripeptide, have been determined by X-ray diffraction. The peptides are Z-L-(alpha Me)Hph-(L-Ala)2-OMe pBrBz-[D-(alpha Me)Hph]3-OtBu and Ac-(Aib)2-L-(alpha Me)Hph-(Aib)2-OtBu. All the (alpha Me)Hph residues prefer phi, psi torsion angles in the helical region of the conformational map. The two terminally blocked tripeptides adopt a beta-bend conformation stabilized by a 1<--4 C = O... H-N intramolecular H-bond. The terminally blocked pentapeptide is folded in a regular 3(10)-helix. In general, the relationship between (alpha Me)Hph alpha-carbon chirality and helix handedness is the same as that exhibited by protein amino acids. A comparison is also made with the conclusions extracted from published work on peptides from other types of C alpha-alkylated aromatic alpha-amino acids.

Aminobutyrates↗
PubMed1996

Crystallographic characterization of geometry and conformation of TOAC, a nitroxide spin-labelled C alpha,alpha-disubstituted glycine, in simple derivatives and model peptides.

The molecular and crystal structures of one derivative and two oligopeptides of TOAC, a nitroxide spin-labelled C alpha, alpha-disubstituted glycine, have been determined by X-ray diffraction. The derivative is the 5(4H)-oxazolone from Piv-TOAC-OH; the oligopeptides are Z-TOAC-(L-Ala)2-NHtBu sesquihydrate and pBrBz-TOAC-(L-Ala)2-TOAC-L-Ala-NHtBu hemihydrate. Incipient and fully developed right-handed 3(10)-helical conformations are formed by both independent molecules in the asymmetric unit of the terminally blocked tripeptide amide and the terminally blocked pentapeptide amide, respectively. The average geometry and preferred conformation for the piperidine ring of the TOAC residues are also discussed in detail.

Cyclic N-Oxides↗
PubMed1995

beta-turn conformations in crystal structures of model peptides containing alpha,alpha-di-n-propylglycine and alpha,alpha-di-n-butylglycine.

The crystal state conformations of three peptides containing the alpha,alpha-dialkylated residues, alpha,alpha-di-n-propylglycine (Dpg) and alpha,alpha-di-n-butylglycine (Dbg), have been established by x-ray diffraction. Boc-Ala-Dpg-Ala-OMe (I) and Boc-Ala-Dbg-Ala-OMe (II) adopt distorted type II beta-turn conformations with Ala (1) and Dpg/Dbg (2) as the corner residues. In both peptides the conformational angles at the Dxg residue (I: phi = 66.2 degrees, psi = 19.3 degrees; III: phi = 66.5 degrees, psi = 21.1 degrees) deviate appreciably from ideal values for the i + 2 residue in a type II beta-turn. In both peptides the observed (N...O) distances between the Boc CO and Ala (3) NH groups are far too long (I: 3.44 A; III: 3.63 A) for an intramolecular 4-->1 hydrogen bond. Boc-Ala-Dpg-Ala-NHMe (II) crystallizes with two independent molecules in the asymmetric unit. Both molecules IIA and IIB adopt consecutive beta-turn (type III-III in IIA and type III-I in IIB) or incipient 3(10)-helical structures, stabilized by two intramolecular 4-->1 hydrogen bonds. In all four molecules the bond angle N-C alpha-C' (tau) at the Dxg residues are > or = 110 degrees. The observation of conformational angles in the helical region of phi,psi space at these residues is consistent with theoretical predictions.

Amino Acid Sequence↗
PubMed1995

Characterization of beta-bend ribbon spiral forming peptides using electronic and vibrational CD.

Terminally blocked (L-Pro-Aib)n and Aib-(L-Pro-Aib)n sequential oligopeptides are known to form right-handed beta-bend ribbon spirals under a variety of experimental conditions. Here we describe the results of a complete CD and ir characterization of this subtype of 3(10)-helical structure. The electronic CD spectra were obtained in solvents of different polarity in the 260-180 nm region. The vibrational CD and Fourier transform ir (FTIR) spectra were measured in deuterochloroform solution in the amide I and amide II (1750-1500 cm-1) regions. The critical chain length for full development of the beta-bend ribbon spiral structure is found to be five to six residues. Spectral effects related to concentration-induced stabilization of the structures of the longer peptides were seen in the resolution-enhanced FTIR spectra. Comparison to previous studies of (Aib)n and (Pro)n oligomers indicate that the low frequency of the amide I mode is due to the interaction of secondary and tertiary amide bonds and not to a strong difference in conformation from a regular 3(10)-helix.

Amino Acid Sequence↗
PubMed1995

The polypeptide 3(10)-helix as a template for molecular recognition studies. Structural characterization of a side-chain functionalized octapeptide.

A N alpha-blocked, Aib-rich octapeptide methylamide containing two N omega-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 3(10)-helix stabilized by seven consecutive N-H...O=C intramolecular H-bonds of the beta-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.

Amino Acid Sequence↗
PubMed1995

The preferred solid-state conformation of (alpha Me)Trp peptides.

The two Z-L-Ala-DL-(alpha Me)Trp-NH2 diastereomeric dipeptides were synthesized from (Z-L-Ala)2(O) and H-DL-(alpha Me)Trp-NH2. The latter racemate, prepared by phase-transfer catalyzed alkylation of the N alpha-benzylidene derivative of alanine amide followed by acidic hydrolysis of the resulting Schiff base, was characterized by X-ray diffraction. The molecular and crystal structure of Z-L-Ala-L-(alpha Me)Trp-NH2, separated from its diastereomer by silica-gel column chromatography, was determined by X-ray diffraction analysis. Both independent molecules in the asymmetric unit of the dipeptide adopt a type-II beta-bend conformation. However, only the more regularly folded conformation of molecule B is stabilized by a 1<--4 C = O...H--N intramolecular H bond. The present results indicate that: (i) the C alpha-methylated (alpha Me)Trp residue is a strong beta-bend and helix former, and (ii) the relationship between (alpha Me)Trp chirality and helix screw sense tends to be opposite to that of protein amino acids. The implications for the use of the (alpha Me)Trp residue in designing conformationally restricted analogs of bioactive peptides are briefly discussed.

Amino Acid Sequence↗