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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis and peptide bond orientation in tetrapeptides containing L-azetidine-2-carboxylic acid and L-proline (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 1039-1049 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The role of the amino acid proline in influencing the secondary and tertiary structure of proteins and polypeptides has been an area of active study for many years. We have investigated this problem by incorporating the four-membered ring amino acid, azetidine-2-carboxylic acid, into some proline polypeptides. An adjunct to the synthesis of the peptides was the synthesis of azetidine-2-carboxylic acid and its resolution. We developed an improved synthesis of N-benzhydryl-2-carbobenzyloxy azetidine, an essential intermediate required for the synthesis of Lazetidine-2-carboxylic acid. This amino acid was subsequently obtained via the partial hydrogenation of the N-benzhydryl compound, under mild conditions. Our ability to isolate the intermediate N-benzhydryl-2-carboxylic acid demonstrated that the rate of cleavage of the O-benzyl ester group in this molecule is faster than the cleavage of the N-benzhydryl group.The tetrapeptides, Boc-(LPro)3-LAze-Opcp, and Boc-(LAze-LPro)2-Opcp (Boc: t-butoxycarbonyl; Pro: praline; Aze: azetidine-2-carboxyl acid; Opcp: pentachlorophenyl), were prepared using traditional solution peptide synthesis. They were characterized by direct chemical ionization-mass spectrometry, CD spectra, and 13C- and 1H-nmr spectroscopy. The assessment of the secondary structure assessment of the two peptides using the methods noted above has led us to conclude that the compound Boc-(L-Aze-LPro)2-Opcp, in trifluoroethanol, has an all-cis peptide bond conformation with φ and ψ torsion angles compatible with a left-handed helix. The secondary structure assessment of the peptide Boc-(LPro)3-LAze-Opcp, in chloroform or trifluoroethanol, leads to an assignment of both cis and trans peptide bonds as being present in the peptide. We have interpreted this latter finding as indicating that the introduction of the azetidine group into a peptide containing three consecutive praline residues in a linear sequence perturbs the normal proline peptide secondary structure in this tetrapeptide.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360301105
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  • 2
    Electronic Resource
    Electronic Resource
    Calorimetric studies of the polynucleotide analog poly(-)2-[2-(thymin-1-yl) propanamido]propenoic acid (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 787-794 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermally elicited structural and conformational transitions of the polynucleotide analog, poly(-)-2-[2-(thymin-1-yl)propanamido]propenoic acid, P(-)TDHA, have been studied using differential scanning calorimetry (DSC), differential thermal analysis (DTA), and thermogravmetric analysis (TGA). The differential scanning calorimetry curves obtained on solid P(-)TDHA samples exhibited five distinct transitions. The transition occurring at 50°C is attributed to a disruption of interactions involving thymine-thymine stacking. In contrast the transition observed at 83°C is attributed to a hydrogen-bonding interaction involving the thymine residues, whereas the transition occurring at 110°C is assigned to hydrogen bonding of the carboxylic acid side-chain groups. The transitions observed at 50, 83, and 110°C are reversible if the heated and quenched sample is allowed to equilibrate in an atmosphere of high humidity. The transition occurring at 127°C is viewed as a structural rearrangement of the polymer backbone that does not involve the participation of water molecules. The transition observed at a temperature above 197°C is attributed to a structural modification of the polymer resulting from decomposition. Solutions of P(-)TDHA in 0.1M phosphate buffer at pH 7.05 showed only a single transition at 50°C, which is in accord with an observed transition in the solid state assigned to the disruption of base-stacking interactions. The average enthalpy for the transition at 50°C was 0.92 cal/g in the solid state and 1.08 cal/g for the solution, which provides additional support for the assignment.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250504
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  • 3
    Electronic Resource
    Electronic Resource
    Nucleic acid base grafted poly(ethylenimine): Polynucleotide analog and therapeutic agent (1985)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 13 (1985), S. 13-32 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Poly(N-acyl ethylenimine) of various molecular weights was synthesized by the cationic ring-opening polymerization of 2-H-2-oxazoline and 2-methyl-2-oxazoline. Acid hydrolysis afforded the linear poly(ethylenimine) which was used in the following grafting reactions. Vapor pressure osmometry, gel permeation chromatography and viscosity measurements were used to characterize the polymers synthesized. Potassium 2-(cytos-l-yl) propanoate and potassium 3-(cytos-l-yl) butanoate were synthesized in good yield from thenucleic acid base. These cytosyl pendant groups were grafted onto the poly(ethylenimine) using 4-chloro-1-(4-chlorobenzenesulfonyl) benzotriazole, 90% graft, and norborn-5-ene-2,3-carboximido diphenyl phosphate, 70% graft. Grafting of the t-butoxycarbonyl and n-butoxycarbonyl protected cytosyl pendant groups resulted in a 47% graft. Hypochromicity studies indicated an ordered structure at the local level. The secondary structure is a base-stacked conformation. Light scattering results gave insight into the tertiary structure of the macromolecule. The polymer exists in solution as stiff chains, rod-like in nature. Continuous mixing experiments were carried out with polyribonucleotides. The Job plots indicated increased level of ordered conformation with either an increase in the molecular weight or an increase of the base to base distance in the analog. Enhancement in the base-stacked conformation was higher in the polyinosinic acid complex than that of the polyguanylic acid complex.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1985.020131985103
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  • 4
    Electronic Resource
    Electronic Resource
    Potentiometric and viscosimetric titration of poly(N-acyldehydroalanines) containing asymmetric nucleic acid base derivatives as pendant groups (1986)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 24 (1986), S. 2815-2821 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The potentiometric and viscosimetric titration curves of poly(N-acetyldehydroalanine) (PNAcDHA) were compared with those of the nucleic acid base-containing dehydroalanine backbone polymers poly{(+ -) and (-)- [2-(thymin-1-yl]{propanoamido}propenoic acid} (PTDHA and P(-)TDHA)). The behavior of PNAcDHA was similar to polyacids such as poly(acrylic acid), but PTDHA and P(-)TDHA displayed very strong nearest neighbor interactions, since the pH curves had an additional inflection at half neutralization that was sensitive to the ionic strength of the medium and the viscosity curves showed little expansion of the polymer coil with increasing ionization. NAcDHA-TDHA copolymers were prepared which showed similar behavior. These results suggested that PTDHA and P(-)TDHA were extended and conformationally restricted in aqueous solution compared to PNAcDHA, findings that agreed with the results of spectroscopic studies of these polymers.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1986.080241110
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  • 5
    Electronic Resource
    Electronic Resource
    Synthesis of copoly(vinylamine-vinylalcohol) containing two kinds of asymmetric nucleic acid base derivatives as grafted pendants (1987)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 1523-1543 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preparation of new model polymers of polynucleotides with poly(vinylamine-vinylalcohol) [P(Vam-Val)] backbones and different kinds of nucleic acid base derivatives as grafted pendants is described. At first, the grafting of (-) and (±)-2-(thymin-1-yl)propionic acid [(-) and (±)TPA] onto linear P(Vam-Val) at the amino group via an amide bond was carried out in a mixed solvent of ethanol-dimethylformamide by selective N-acylation of the active ester of N-hydroxy-5-norbornene-2,3-dicarboximide (HONB) or N-hydroxysuccinimide (HOSu). This procedure gave the corresponding hydroxyl polymers P[Vam(-)T-Val] and P[Vam(±)T-Val]. In addition, direct, low temperature esterification was used to graft (-), (±)TPA, and (±)-2-(uracil-1-yl)propionic acid, [(±)UPA], onto the hydroxyl polymer at the hydroxyl group via an ester bond. This process gave the corresponding copoly(Vam-Val) with different or the same kinds of nucleic acid base derivatives. P[Vam(-)-Ve(-)T], P[Vam(±)T-Ve(±)T], P[Vam(-)T-Ve(±)U], and P[Vam(±)T-Ve(±)U] are representative examples. The related monomer and segmental model compounds were also prepared by this method; 3-aminopentane, 3-pentanol, 3-amino-1-propanol, and threo-2-amino-4-pentanol were employed in the syntheses. The segment models were separated and purified using HPLC techniques.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1987.080250607
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  • 6
    Electronic Resource
    Electronic Resource
    Polymerization and conformational studies of poly(trans-3-ethyl-D and L-proline) (1987)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 2941-2952 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Poly(L-trans-3-ethylproline), L-PT3EP, and poly(D-trans-3-ethylproline), D-PT3EP, were prepared by ring opening polymerization of the corresponding N-carboxyanhydrides (NCA) using triethylamine as an initiator. Using circular dichroism spectroscopy, it was shown that the incorporation of an ethyl group at the 3 position of the pyrrolidine ring caused a noticeable change in the conformational behavior of the polymer in solution. The ethyl group limited to some extent rotation of the polymer chain around the C——CO bond and prevented the mutarotation between the two forms found in poly-L-proline polymers.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1987.080251102
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  • 7
    Electronic Resource
    Electronic Resource
    Synthesis and esterolytic reactions of linear and cross-linked asymmetric imidazole-containing polymers (1987)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 2963-2985 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Asymmetric linear and cross-linked imidazole-containing polymers were prepared from 1-[2(S)-methylbutyl]-4-vinylimidazole and 1-[2(S)-methylbutyl]-5-vinylimidazole. The esterolytic reactions of these linear and cross-linked asymmetric polymers with the enantiomeric substrates (R)- and (S)-4-(3-methylpentadecanoyl)-3-nitrobenzoic acid, (R)- and (S)-S-3Me15, were studied by measuring the pseudo-first order kinetics of the solvolysis of these enantiomeric substrates in the presence of these asymmetric polymers. The linear homopolymers and copolymers of 1-[2(S)-methylbutyl]-4- and 5-vinylimidazole showed hydrophobic and electrostatic effects in the solvolysis of the enantiomeric substrates with these linear asymmetric polymers. Cross-links were introduced into these asymmetric polymers to increase the rigidity and reduce the number of conformations available to the polymer. The reduced conformational mobility was expected to enhance any enantioselectivity in the solvolysis of the enantiomeric substrates with these polymers. Using these cross-linked polymers, hydrophobic interactions were observed in the solvolysis of a series of substrates with increasing alkyl chain length. Also, on changing the polarity of the solvent, a bell-shaped rate profile was observed in the solvolysis of the long chain substrate S-3Me15. This effect was attributed to a combination of the coiling of the cross-linked polymer chains and hydrophobic interactions with the substrate on changing solvent polarity. Even with the increased rigidity of these cross-linked polymers, no significant enantioselectivity in the solvolysis of the enantiomeric substrates was observed. So, neither the linear nor the cross-linked asymmetric polyvinylimidazoles showed enantioselectivity in the solvolysis of these enantiomeric substrates. In this case, the hydrophobic interactions and the reduced conformational mobility through crosslinking were not strong enough to bring about enantioselectivity in the solvolysis of these enantiomeric substrates.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1987.080251104
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  • 8
    Electronic Resource
    Electronic Resource
    Synthesis, separation, and resolution of cis- and trans-3-ethylproline (1987)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 3437-3458 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis, separation, and optical resolution of cis- and trans-3-ethylproline are described. Two different approaches were employed: (1) The Michael addition reaction of 2-pentenal with diethyl-N-carbobenzyloxyaminomalonate gave the intermediate 3-ethyl-5-hydroxy-N-benzyloxypyrrolidine. Hydrogenolysis of this intermediate followed by acid hydrolysis gave a mixture of cis- and trans-3-ethylproline. Separation of the isomers was accomplished by selective saponification of N-(p-toluenesulfonyl)-cis- and trans-3-ethylproline methyl esters using 0.25N methanolic sodium hydroxide. (2) The Michael condensation of diethyl acetamidomalonate with 2-pentenoic acid ethyl ether produced the intermediate 5,5-bis(ethoxycarbonyl)-4-ethylpyrrolidine. Partial saponification followed by decarboxylation afforded a mixture of cis- and trans-isomers of ethyl-3-ethylpyroglutamate. The diastereoisomers were separated using low temperature fractional crystallization. Reduction of these isomers and tosylation in situ afforded the corresponding N-(p-toluenesulfonyl)-cis- and trans-3-ethylprolinols. Chromic acid oxidation gave N-(p-toluenesulfonyl)-cis- and trans-3-ethylproline. Reaction of these tosylates with 30% hydrogen bromide in acetic acid gave cis- and trans-3-ethylproline. Both optically active isomers of D(+)-and L(-)-trans-3-ethylproline were successfully resolved using (+)-dibenzoyl-D-tartaric acid and (-)-dibenzoyl-L-tartaric acid as resolving agents. The absolute configurations of the optically active isomers were determined by circular dichroism spectroscopy.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1987.080251224
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  • 9
    Electronic Resource
    Electronic Resource
    Solid state suspension polymerization of N-vinyl-t-butylcarbamate (1986)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Letters Edition 24 (1986), S. 627-630 
    Details
    ISSN: 0887-6258
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1986.140241202
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  • 10
    Electronic Resource
    Electronic Resource
    Synthesis of bis and tris (dehydroalanine) crosslinking agents and their use in the preparation of hydrophilic nucleic acid base resins (1986)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Letters Edition 24 (1986), S. 199-206 
    Details
    ISSN: 0887-6258
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1986.140240501
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