Chiral Peptide Research Articles

Direct enantiomeric separation of N-aminoethylamino acids: determination of the enantiomeric excess of chiral peptide nucleic acids (PNAs) by GC

Direct chiral separation of N-aminoethylamino acids has been performed for the first time by gas chromatographic (GC) analysis with a Chirasil-Val column, after derivatisation with trifluoroacetic anhydride in dichloromethane, which led to the corresponding piperazin-2-one derivatives, as identified by NMR and GC/MS analysis. The method was used for the analysis of the enantiomeric excess of chiral peptide nucleic acid (PNA) monomers and oligomers after hydrolysis with 6N HCl.

Synthesis of New Chiral Peptide Nucleic Acid (PNA) Monomers by a Simplified Reductive Animation Method

The aim of this work was the preparation of four new peptide nucleic acid (PNA) monomer backbone by reductive animation of Nα-Boc-protected chiral amino aldehydes, derived from Leu, Phe, Tyr(Bzl), and Thr(Bzl), with methyl glycinate. To the crude 2-substituted methyl N-(2-Boc-aminoethyl)glycinates obtained, thymin-1-ylacetic acid was coupled using TBTU procedure in a one-pot reaction. PNA monomers were isolated and characterized.

Chiral Peptide Nucleic Acids (PNAs): Helix Handedness and DNA Recognition

Peptide Nucleic Acids (PNAs) are DNA mimics in which the deoxyribose phosphate backbone has been replaced by a pseudo-peptide skeleton composed of N-(2-aminoethyl)glycine units; they bind to complementary DNA strands with high affinity and selectivity. In order to study the effect of stereogenic centers within the backbone on PNA preorganization and DNA binding properties, chiral PNA decamers were synthesized which contained thymine monomers derived from L-Leu and D- or L-Lys inserted either at C-terminus and/or in the middle of an achiral PNA strand. PNAs containing three chiral thymine monomers derived from L-Leu, D- or L-Lys, L-Asp, or D-Glu were also synthesized. CD spectral analyses showed that a charged chiral monomer inserted in the middle of the strand is able to induce a strong preference in the helix handedness of a PNA-PNA duplex. The effect is increased by the presence of three chiral charged monomers. The L-Lys- and L-Asp-PNAs induced a preference for the left-handed and the D-Lys and D-Glu-PNAs for the right-handed conformation. As expected, the PNA-DNA duplexes are dominated by the DNA strand and thus are right-handed with both D- and L-PNAs. However, the D-PNAs, being inherently right-handed, lead to more stable PNA-DNA duplexes than the L-PNAs. The lysine-based PNAs form more stable complexes with the DNA at low ionic strength, due to the electrostatic interactions between the charged lysine side chain and DNA.

Chiral peptide nucleic acids: a new family of ligands for metal ions

The first studies on peptide nucleic acid co-ordination abilities towards Cu2+ ions indicated that when nucleobases were present in the amino acid residue side chain the interactions between the nucleic bases induced very effective metal-ion binding by the peptide backbone donor system.

Enantiomeric separation of small chiral peptides by capillary electrophoresis

Different approaches to the enantiomeric separation of sixteen derivatized di- and tripeptides, having one or two chiral centers, by means of capillary electrophoresis have been examined. The approaches were: direct separation using cyclodextrin (CD), vancomycin or teicoplanin and indirect separation. The highest plate numbers, 106 plates/m, were obtained with CD and the indirect method. The maximum resolution was 3 with CD and 11 when using the indirect method. The antibiotics gave somewhat lower plate numbers, 0.5·106 plates/m, but the resolution was high, up to 38. All examined peptides, except Leu–Ala, Leu–Leu and Arg–Gly, were fully resolved with the antibiotics as chiral selectors. The three remaining peptides were fully resolved when using the indirect method.

Hybridization Studies with Chiral Peptide Nucleic Acids

A novel class of chiral peptide nucleic acids has been synthesized in which the sugar-phosphate backbone of DNA has been replaced with the glycyl-proline backbone of both theL- and theD-configurations, nucleobases being attached through the 4-position of proline withcis- andtrans-stereochemistry. TheT10homopolymers withcis-stereochemistry in theL- andD-series bind strongly to poly(dA) withTmvalues of 69 and 70°C, respectively. They bind more strongly to poly(rA) withTmvalues of 73 and 72°C, respectively, and with apparent 1:1 stoichiometry. Using a mixed sequence decamer it was found that the thermal stability of the chiral peptide nucleic acid/oligonucleotide complex was comparable to that formed by Nielsen's polyamide nucleic acid.

2-Methyl-3-oxo-4-phenyl-2,3-dihydrofuran-2-yl acetate: a fluorogenic reagent for detection and analysis of primary amines.

A new fluorogenic reagent, 2-methyl-3-oxo-4-phenyl-2,3-dihydrofuran-2-yl acetate, has been developed for the analysis of primary amines and aminated carbohydrates by means of HPLC, CE, and MALDI/MS. Peptides at 1 pmol (2 x 10(-7) M) levels were successfully labeled and analyzed through CE. The fluorescent derivatives have good stability in both acidic and basic solutions, making their further manipulation and structural analysis possible. The derivatives can be analyzed in reversed-phase HPLC due to the hydrophobic nature of this fluorescent tag. Characteristic elution intervals between the diastereomeric peaks of the chiral peptide derivatives may be used in structural verification. The labeled peptides and neutral oligosaccharides are also readily detectable through MALDI/MS in its positive mode.

Synthesis of a New Chiral Peptide Analogue of DNA Using Ornithine Subunits and Solid‐phase Peptide Synthesis Methodologies

AbstractIn this paper we describe the synthesis of chiral peptide nucleic acids (PNAs) 1–3 using SPPS methodologies. Starting material for the monomer units was the commercially available amino acid ornithine. l‐ or D‐ornithine and the nucleobase thymine were linked by a carboxymethylene spacer giving the chiral monomers l‐7 and D‐7. The SPPS was performed according to the Fmoc strategy.

A convenient synthesis of chiral peptide nucleic acid (PNA) monomers

Chiral peptide nucleic acid monomers containing amino acid side chains can be easily prepared from the BOC-protected amino acids.

HPLC Enantioseparation Of Dl-and Tripeptides on Cyclodextrin Bonded Stationary Phases After Derivatization with 6-Aminoquinolyl-N-hydroxysuccinimidyl Carbamate (AQC)

Abstract Enantiomeric separations were performed on a number of di- and tripeptides after their pre-column derivatization with the fluorescence derizatizing agent 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC). It has been demonstrated that the choice of a suitable cyclodextrin bonded phase in conjunction with nonaqueous polar mobile phases offers an effective means to resolve chiral peptides. It was found that the strength of interaction between the cyclodextrin and the solute, and therefore the retention and stereoselectivity, is extremely sensitive to small structural variations of the analyte.

A new chiral peptide analog: Synthesis and characterization of poly[4(S)-2-propyl-4-methoxycarbonyl-2-oxazoline

Synthese de poly (N-acyl-ethyleneimines racemique et optiquement actif. Formation competitive du monomere dehydroalanine correspondant

Capillary Gas Chromatographic Analysis of Amino Acids by Enantiomer Labeling

The optical isomers of amino acids can be easily separated by gas chromatography using capillary columns coated with the chiral polysiloxane peptide, Chirasil-Val. Quantitative trace amino acid analysis in complex mixtures such as biological fluids, sea water, or protein hydrolysates can be achieved by enantiomer labeling: The D-amino acid enantiomers, which do not occur naturally, are added to the sample prior to analysis as internal standards. Because the D-enantiomers show the same physical and chemical properties as the natural L-enantiomers, they are ideal standard references. In routine analysis, the derivatization is achieved with a new automated derivatization robot. The D-standard serves as overall internal standard for the whole analytical procedure from sample enrichment to derivatization, chromatography, and response of the detector.

Chirale Erkennung von Naturstoffen an optisch aktiven Polysiloxanen Chiral Recognition of Natural Products on Optically Active Polysiloxanes

Abstract Polysiloxanes with chiral peptide side chains have been synthesized and used as stationary phases in gas chromatography. With these phases amino acid enantiomers can be separated as N-acyl esters. Due to temperature stability up to 230 °C all protein amino acids can be separated and the racemization of synthetic biologically active peptides controlled. The phases can be used to assign the absolute configuration of amino acids. A variety of other classes of compounds can be separated into their enantiomers using the chiral polysiloxanes, like hydroxy acids, sulfoxides, phosphorous compounds, glycols, atrop isomers, amines and alcohols. Various applications of these phases are described including investigations of enantiomer selectivity in nature.

Non-racemic mixture model: a computational approach.

The behavior of a slight chiral bias in favor of l-amino acids over d-amino acids was studied in an evolutionary mathematical model generating mixed chiral peptide hexamers. The simulations aimed to reproduce a very generalized prebiotic scenario involving a specified couple of amino acid enantiomers and a possible asymmetric amplification through autocatalytic peptide self-replication while forming small multimers of a defined length. Our simplified model allowed the observation of a small ascending but not conclusive tendency in the l-amino acid over the d-amino acid profile for the resulting mixed chiral hexamers in computer simulations of 100 peptide generations. This simulation was carried out by changing the chiral bias from 1% to 3%, in three stages of 15, 50 and 100 generations to observe any alteration that could mean a drastic change in behavior. So far, our simulations lead to the assumption that under the exposure of very slight non-racemic conditions, a significant bias between l- and d-amino acids, as present in our biosphere, was unlikely generated under prebiotic conditions if autocatalytic peptide self-replication was the main or the only driving force of chiral auto-amplification.