A series of N- and C-protected, monodispersed homo-oligopeptides (to the dodecamer level) from the small-ring alicyclic C alpha, alpha-dialkylated glycine 1-aminocyclobutane-1-carboxylic acid (Ac4c) and two Ala/Ac4c tripeptides were synthesized by solution methods and fully characterized. The conformational preferences of all the model peptides were determined in deuterochloroform solution by FT-IR absorption and 1H-NMR. The molecular structures of the amino acid derivatives Z-Ac4c-OH and Z2-Ac4c-OH, the tripeptides Z-(Ac4c)3-OtBu, Z-Ac4c-(L-Ala)2-OMe and Z-L-Ala-Ac4c-L-Ala-OMe, and the tetrapeptide Z-(Ac4c)4-OtBu were determined in the crystal state by X-ray diffraction. The average geometry of the cyclobutyl moiety of the Ac4c residue was assessed and the tau(N-C alpha-C') bond angle was found to be significantly expanded from the regular tetrahedral value. The conformational data are strongly in favour of the conclusion that the Ac4c residue is an effective beta-turn and helix former. A comparison with the structural propensities of alpha-aminoisobutyric acid, the prototype of C alpha, alpha-dialkylated glycines, and the other extensively investigated members of the family of 1-aminocycloalkane-1-carboxylic acids (Acnc, with n = 3, 5-8) is made and the implications for the use of the Ac4c residue in conformationally constrained peptide analogues are briefly examined.

Amino Acids↗

PubMedDate not supplied

Conformational characterization of peptides rich in the cycloaliphatic C alpha,alpha-disubstituted glycine 1-aminocyclononane-1-carboxylic acid.

A series of N- and C-protected, monodispersed homo-oligopeptides (to the pentamer level) from the cycloaliphatic C alpha,alpha-dialkylated glycine 1-aminocyclononane-1-carboxylic acid (Ac9c) and two Ala/Ac9c tripeptides have been synthesized by solution methods and fully characterized. The conformational preferences of all the model peptides were determined in deuterochloroform solution by FT-IR absorption and 1H-NMR. The molecular structures of the amino acid derivatives mCIAc-Ac9c-OH and Z-Ac9c-OtBu, the dipeptide pBrBz-(Ac9c)2-OtBu, the tetrapeptide Z-(Ac9c)4-OtBu, and the pentapeptide Z-(Ac9c)5-OtBu were determined in the crystal state by X-ray diffraction. Based on this information, the average geometry and the preferred conformation for the cyclononyl moiety of the Ac9c residue have been assessed. The backbone conformational data are strongly in favour of the conclusion that the Ac9c residue is a strong beta-turn and helix former. A comparison with the structural propensity of alpha-aminoisobutyric acid, the prototype of C alpha,alpha-dialkylated glycines, and the other extensively investigated members of the family of 1-aminocycloalkane-1-carboxylic acids (Acnc, with n = 3-8) is made and the implications for the use of the Ac9c residue in conformationally constrained analogues of bioactive peptides are briefly examined.

Amino Acids, Cyclic↗

PubMedDate not supplied

Preferred conformation of peptides rich in Ac8c, a medium-ring alicyclic C (alpha,alpha)-disubstituted glycine.

A complete series of terminally blocked, monodispersed homo-oligopeptides (to the pentamer level) from the sterically demanding, medium-ring alicyclic C (alpha,alpha)-disubstituted glycine 1-aminocyclooctane-1-carboxylic acid (Ac8c), and two Ala/Ac8c tripeptides, were synthesized by solution methods and fully characterized. The preferred conformation of all the oligopeptides was determined in deuterochloroform solution by IR absorption and 1H-NMR. The molecular structures of the amino acid derivative Z-Ac8c-OH, the dipeptide pBrBz-(Ac8c)2-OH and the tripeptide pBrBz-(Ac8c)3-OtBu were assessed in the crystal state by X-ray diffraction. Conformational energy computations were performed on the monopeptide Ac-Ac8c-NHMe. Taken together, the results obtained strongly support the view that the Ac8c residue is an effective beta-turn and helix former. A comparison is also made with the conformational preferences of alpha-aminoisobutyric acid, the prototype of C (alpha,alpha)-disubstituted glycines, and of the other members of the family of 1-aminocycloalkane-1-carboxylic acids (Acnc with n = 3, 5-7) investigated so far. The implications for the use of the Ac8c residue in peptide conformational design are considered.

Amino Acids↗

PubMedDate not supplied

Synthetic formyl-methionyl chemoattractants: a conformation-activity study of oxidized tripeptides.

The two diastereomeric sulphoxides and the sulphone derived from the formyl-methionyl tripeptide chemoattractant CHO-L-Met-L-Phe-OMe have been synthesized and fully characterized. The diastereomeric sulphoxide tripeptides have been separated at the stage of their N-tert-butyloxycarbonyl synthetic precursors. All of the oxidized sulphur derivatives induce secretion of granule enzymes with ED50s from 1-2 x 10(-9) M with no significant differences in activity among them. They are also active to the same relative extent in inducing chemotaxis. In parallel, a solution conformational analysis has been performed in solvents of widely different polarities and capabilities of H-bond formation using circular dichroism, infrared absorption and 1H nuclear magnetic resonance. No significant propensity for formation of intramolecularly (C = O...H-N) H-bonded folded forms has been detected in any of the four tripeptides. Intermolecular S = O...H-N interactions are postulated to tentatively explain the 1H nuclear magnetic resonance behavior of the Met and, particularly, Leu NH resonances of the two sulphoxide tripeptides in CDCl3 solution. The biological and conformational data agree with the recently proposed model of the chemotactic peptide receptor of rabbit neurotrophils, which involves the extended backbone of the integrity of the Met side-chain sulphide sulphur atom as a corollary point of ligand interaction.

Circular Dichroism↗

PubMedDate not supplied

Antisense activity of an anti-HIV oligonucleotide conjugated to linear and branched high molecular weight polyethylene glycols.

An anti-HIV 12mer oligonucleotide (ODN) conjugated to two different high molecular weight monomethoxy polyethylene glycols (MPEGs) has been tested for its antisense activity. The capacity of these conjugates to protect the MT-4 cells against HIV infection has been compared to the unmodified, native ODN, and the effect of the different structures of the supporting polymer has been discussed. It was found that only the ODN conjugated to the linear MPEG shows an anti-HIV activity in the investigated conditions. The same 12mer, when conjugated to a branched (MPEG)2, is fully inactive, as well as the native, unmodified ODN.

Anti-HIV Agents↗

PubMedDate not supplied

Triple, MPEG-conjugated, helix-forming oligonucleotides (TRIPEGXs): liquid-phase synthesis of natural and chimeric "all-purine" sequences linked to high molecular weight poly(ethylene glycols).

Long "all-purine" oligonucleotides, up to the 20mer, known to be active as antigene effectors, conjugated to high molecular weight monomethoxy poly(ethylene glycol)s (MPEG)s, were successfully synthesized. Through a liquid-phase, MPEG-supported process, both natural and chimeric sequences containing selected phosphorothioate backbone modifications were obtained, purified, and characterized. To follow their cellular trafficking, a fluorescent probe was linked by soluble supported organic reactions to the 5'-terminus, and the efficiency of the different synthetic procedures for the introduction of a fluorescein moiety was compared. The usefulness of the fluorescent marker was estimated by laser confocal microscopy that ascertains that the MPEG-conjugation enhances the oligonucleotide capacity to cross the cellular membranes and to be accumulated inside the nuclei.

Cell Membrane Permeability↗

PubMedDate not supplied

Synthesis and characterization of high-molecular mass polyethylene glycol-conjugated oligonucleotides.

The use of synthetic oligonucleotides as possible drugs for human therapy is usually hampered by their low in vivo stability and capacity to achieve high concentrations at their cellular targets. To overcome this, it has been suggested that they be modified chemically. Among the various options, conjugation with short- and long-chain polyethylene glycols (PEGs) has several advantages: PEG is nontoxic and very soluble, reduces immunogenic reactions, and increases the stability of the conjugated molecules. PEG is generally joined to oligonucleotides while bound to the insoluble solid-phase supports, after their synthesis, which does not allow for their being easy scaled up. The use of the liquid-phase approach as an alternative synthetic process, utilizing the PEG polymer both as a soluble, inert synthetic support and a stabilizing agent of the oligonucleotide, is proposed. A new protocol has been set up, characterized by a stable phosphate bond between the support and the oligonucleotide. This method has been tested on a 12mer previously investigated as an antisense agent against HIV. The PEG-conjugated 12mer was efficiently synthesized and purified. It was found that the high-molecular mass PEG chain results in enzymatic stability and does not interfere with the formation of the duplex with its nucleic acid target.

Anti-HIV Agents↗

PubMedDate not supplied

On the oxy analogues to the 4 leads to 1 intramolecularly hydrogen-bonded peptide conformations.

The occurrence of the oxy analogue to the type II' 4 leads to 1 intramolecularly hydrogen-bonded nonhelical peptide conformation, recently proposed for t-BOC-Gly-L-Pro-OH in the solid state by Deber on the basis of infrared absorption evidence, has been disproved by x-ray diffraction analysis. This type of folding is also absent in solvents of moderate or high polarity. The latter conclusion is in agreement with Deber's results. However, in solvents of low polarity this intramolecularly hydrogen-bonded form could account for the strong negative Cotton effect near 230 nm observed in the circular dichroism spectrum.

Binding Sites↗

PubMedDate not supplied

Solid-state and solution conformation of N-tert-butyloxycarbonyl-L-prolylglycine.

The occurrence of the oxy analogue in the trans-II 4 leads to 1 intramolecularly hydrogen-bonded nonhelical peptide conformation, recently proposed for t-BOC-L-Pro-Gly-OH in the solid state on the basis of infrared absorption evidence, has been disproved by x-ray diffraction analysis. This type of folding is also absent in polar solvents. However, in solvents of low polarity the presence of this folded form cannot be excluded.

Circular Dichroism↗