摘要:

With the objectives of developing new protecting groups for the β‐carboxyl group of aspartic acid that are resistant to base‐catalyzed aspartimide formation and of evaluating the importance of sterical factors in the design of such protecting groups, four new alkyl ester derivatives of aspartic acid were synthesized. The β‐3‐pentyl, β‐4‐heptyl, β‐2,6‐dimethyl‐4‐heptyl and the recently described β‐2,4‐dimethyl‐3‐pentyl esters of Boc‐aspartic acid were incorporated into model peptides, and the resin‐bound protected peptides were treated with 20% pipetidine for 10 h. The levels of aspartimide‐related side products were compared with the previously reported β‐cyclohexyl, β‐menthyl and β‐2‐adamantyl esters of aspartic acid. The results show that bulky, acyclic, aliphatic protecting groups (in particular the 2,4‐dimethyl‐3‐pentyl ester) are significantly more resistant to base‐catalyzed aspartimide formation than comparably rigid cyclic alkyl esters that under the same reaction conditions form several‐fold more aspartimide‐related side products. Using elevated temperatures to overcome difficult couplings leads to the formation of significant amounts of aspartimide when aspartic acid is protected with the cyclohexyl group, but the 2,4‐dimethyl‐3‐pentyl protecting group offers excellent protection under these conditions. The use of the 2,4‐dimethyl‐3‐pentyl protecting group will allow the use of orthogonally removable base‐labile protecting groups in Boc chemistry and suggests a design of protecting groups for other nucleophile‐sensitiv

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb00846.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Five stereochemically constrained analogs of the chemotactic tripeptide incorporating l‐aminocycloalkane‐l‐carboxylic acid (Acnc) and α, α‐dialkylglycines (Deg, diethylglycine; Dpg,N,N‐dipropylglycine and Dbg,N,N‐dibutylglycine) at position 2 have been synthesized. NMR studies of peptides For‐Met‐Xxx‐Phe‐OMe (Xxx = Ac7c. I: Ac8c. II: Deg, III; Dpg, IV and Dbg, V; For, formyl) establish that peptides with cycloalkyl residues, I and II, adopt folded β‐turn conformations in CDCl3, and (CD3)2SO. In contrast, analogs with linear alkyl sidechains, III‐V, favour fully extended (C5) conformations in solution. Peptides I‐V exhibit high activity in inducing β‐glucosaminidase release from rabbit neutrophils, with ED50values ranging from 1.4–8.0 × 10–11. M. In human neutrophils the Dxg peptides III‐V have ED50values ranging from 2.3 × 10−8to 5.9 × 10−10M, with the activity order being V>IV>III. While peptides I‐IV are less active than the parent. For‐Met‐Leu‐Phe‐OH, in stimulating histamine release from human basophils, the Dbg peptide V is appreciably more potent, suggesting its potential utility as a

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb00847.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Anti‐Sm antibodies are usually considered highly specific for systemic lupus erythematosus (SLE), while anti‐UI RNP antibodies are found in high titers in patients with mixed connective tissue disease (MCTD). The sequence P1‐P‐G‐M‐R‐P‐P7, present in three copies in the Sm (Ul‐U6 RNA‐protein complex) autoantigen, is an important functional domain of the antigenic determinants. The immunoreactivity of this proline‐rich repetitive epitope was investigated by testing sera with various autoantibody specificities for reactivity against this epitope, as well as its conformational properties by means of ID and 2D1HNMR spectroscopy. It was found that the P‐P‐G‐M‐R‐P‐P epitope is recognized mainly by anti‐UlRNP and/or anti‐Sm positive sera, but also by anti‐Ro(SSA) (hY1RNA‐protein complex) and anti‐La(SSB) (hY1RNA‐protein complex) positive sera, although these sera are negative for anti‐UlRNP and anti‐Sm. Conformational analysis of the proline‐rich epitope in DMSO‐d6solution obtained from lyophilized aqueous solution at pH 5 showed the presence of at least three conformers. The main conformer A (62%) is stabilized by an ionic interaction between the guanidinium and the C‐terminal carboxylate groups, and the Pro6‐Pro7peptide bond adopts thecisform. A type II β‐turn is also present in theN‐terminal sequence (Pro1‐Pro‐Gly‐Met4‐) of this conformer. Conformer B (21%) is also stabilized by a similar ionic interaction, as in conformer A, while the NMR data indicate the absence of a folded structure in theN‐terminal tetrapeptide of this conformer. Conformer C (17%) adopts a completely extended structure. The multiple conformers of the P‐P‐G‐M‐R‐P‐P may offer some explanation for the reactivity of

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb00848.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The structural stabilizing property of 2,2,2‐trifluoroethanol (TFE) in peptides has been widely demon strated. More recently, TFE has been shown to enhance secondary structure content in globular proteins, and to influence quaternary interactions in protein multimers. The molecular mechanisms by which TFE exerts its influence on peptide and protein structures remain poorly understood. The present analysis integrates the known physical properties of TFE with a variety of experimental observations on the interaction of TFE with peptides and proteins and on the properties of fluorocarbons. Two features of TFE, namely the hydrophobicity of the trifluoromethyl group and the hydrogen bonding character (strong donor and poor acceptor), emerge as the most important factors for rationalising the observed effects of TFE. A model is proposed for TFE interaction with peptides which involves an initial replacement of the hydration shell by fluoroalcohol molecules, a process driven by apolar interactions and favourable entropy of dehydration. Subsequent bifurcated hydrogen‐bond formation with peptide carbonyl groups, which leave intramolecular interactions unaffected, promotes secondary structure formation. © Munksgaard

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb00849.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Nine low molecular weight nerve growth factor (NGF)‐like peptides have been designed to mimic the putative receptor‐binding epitope of NGF defined by two β‐hairpin loops. Eight different spacers were used as variable links between the β‐loop amino acid residues, which from mutagenesis experiments were found to play an important role in the biological activity of NGF. These spacers were amino acids, natural or non‐natural, differing in length (5–13 Å) and polarity. The peptides were synthesized via the Fmoc solid‐phase peptide synthesis and purified by reversed‐phase HPLC. Their primary sequences were analyzed by a combination of automated Edman degradation and mass spectrometry. The peptides were tested using two different biological assays, the fibre outgrowth from chick embryonic sympathetic ganglia and the PC 12 cell differentiation assay. Weak antagonistic effects could be observed for some peptides.

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb00850.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The crystal structure and solution conformation of Ac‐Pro‐ΔAla‐NHCH3and the solution conformation of Ac‐Pro‐(E)‐ΔAbu‐NHCH3were investigated by X‐ray diffraction method and NMR, FTIR and CD spectroscopies. Ac‐Pro‐ΔAla‐NHCH, adopts an extended‐coil conformation in the crystalline state, withall‐transpeptide bonds and the ΔAla residue being in a C5form, φ1=– 71.4(4), ψ1=– 16.8(4), φ2=– 178.4(3) and ψ2= 172.4(3)°. In inert solvents the peptide also assumes the C5conformation, but a γ‐turn on the Pro residue cannot be ruled out. In these solvents Ac‐Pro‐(E)‐ ΔAbu‐NHCH3accommodates a βII‐turn, but a minor conformer with a nearly planar disposition of the CO—NH and C=C bonds (φ2∼0°) is also present. Previous spectroscopic studies of the (Z)‐substituted dehydropeptides Ac‐Pro‐(Z)‐ ΔAbu‐NHCH, and Ac‐Pro‐ΔVal‐NHCH3reveal that both peptides prefer a βII‐turn in solution. Comparison of conformations in the family of four Ac‐Pro‐ΔXaa‐NHCH3peptides let us formulate the following order of their tendency to adopt a β‐turn in solution: (Z)‐ ΔAbu>(E)‐ δAbu>ΔVal; ΔAla does not. None of the fol

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb00851.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The antimicrobial peptide, lactoferricin, is generated upon the gastric pepsin cleavage of lactoferrin and has many basic and hydrophobic amino acid residues essential for its biological activity. To investigate the structure‐antimicrobial activity relationships, the basic amino acid‐rich region of bovine lactoferricin (BLFC), RRWQWRMKKLG, was selected. Using chemically synthesized BLFC and its substituted peptides, the antimicrobial activities of the peptides were tested by determining the minimal inhibitory concentration (MIC) ofEscherichia coliandBacillus subtilisand the disruption of the outer cell membrane ofE. coli, and the peptide's toxicities were assayed by hemolysis. The short peptide (B3) composed of only 11 residues had similar antimicrobial activities while losing most of the hemolytic activities as compared with the 25 residue‐long ones (B1 and B2). The short peptides (B3, B5 and B7) with double arginines at theN‐termini had more potent antimicrobial activity than those (B4 and B6) with lysine. However, no antimicrobial and hemolytic activities were found in B8, in which all basic amino acids were substituted with glutamic acid, and in B9, in which all hydrophobic amino acids were substituted with alanine. The circular dichroism (CD) spectra of the short peptides in 30 MM SDS were correlated with their antimicrobial activities. These results suggested that the 11‐residue peptide of BLFC is involved in the interaction with bacterial phospholipid membranes and plays an important role in antimicrobial activity with little or no hemolytic activity. © Munks

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb00852.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

We report here a study of photoaffinity labeling of the V1a‐vasopressin receptor with high‐affinity, V1‐specific radioiodinated antagonist ligands: one containing an azidophenylalanine residue ([β, β‐dimethyl‐β‐mercaptopropionyl1,p‐azido‐Phe2, Val4, Lys8,d‐Tyr9] vasopressin), two others containing nitrophenyl‐alanine, and one, highly similar but without a photosensitive function, as control. All analogues competed in the dark for the same binding site with vasopressin. Long‐wavelength UV irradiation of rat liver membranes incubated in presence of the radio‐iodinated azido photolabel produced a specifically labeled protein band at 53 kDa in SDS‐PAGE. Identical experiments with the nitrophenylalanyl peptides produced only non‐specific labeling and control experiments with the non‐photosensitive analogue produced no labeling at all. Chemical cross linking of3H‐VP to the same membrane preparation produced a result identical to that of the azido photolabel, confirming the receptor nature of the labeled protein. Deglycosylation of the labeled receptor with endoglycosidase F reduced the observed molecular weight of 53 kDa to 43 kDa. The molecular parameters reported herein of the presumed hepatic vasopressin receptor confirm the values deduced from the molecular cloning of the

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb00853.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Dimethylformamide containing strong acids (CF3COOH, HBF4. TosOH, etc.) and an excess of tertiary base withpK≤6is an effective solvent system for the dissolution of amino acids and their derivatives. The preferable base is pyridine, which forms a system with an apparent pH of 5.3. Amino acids dissolved in this solvent system readily interact with acylating reagents (BOC2O, ZOSu, Fmoc‐OSu and activated derivatives ofN‐protected amino acids). A number of BOC‐, Z‐, Fmoc‐amino acids, as well as several dipeptides, were synthesized using this solvent system with 80‐99%) yields. © M

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb00854.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The synthesis, biological activities and conformational behaviour of a variety of analogues of the mating pheromones of the basidomyceteUstilago maydisare reported. The pheromone analogues derived from the two allelic forms H‐G‐R‐D‐N‐G‐S‐P‐I‐G‐Y‐S‐S‐Xaa‐Z (a1) and H‐N‐R‐G‐Q‐P‐G‐Y‐Y‐Xaa‐Z (a2), with Xaa‐Z being an unidentified lipophilic cysteine derivative, all differ in theC‐terminal residue and include ‐Cys(farnesyl)‐OMe, ‐Cys(farnesyl)‐OH, ‐Cys(prenyl)‐OMe,‐Cys‐OMe, ‐Cys(n‐dodecyl)‐OMeand the unnatural residues ‐Ahds‐OMe(Ahds =α‐aminohexadecanoic acid), ‐Ahds‐OH, ‐Ads‐OMe(Ads =α‐aminodecanoic acid) and ‐N‐Hdg‐OMe(N‐Hdg=N‐hexadecylglycine). The synthesis of the unnatural methyl ester analogues was carried out by condensation of the fully protected fragmentsFmoc‐G‐R(Pmc)‐D(tBu)‐N(Trt)‐G‐S(tBu)‐P‐I‐G‐Y(tBu)‐S(tBu)‐S(tBu)‐OH (a1′) and Fmoc‐N(Trt)‐R(Pmc)‐G‐Q(Trt)‐P‐G‐Y(tBu)‐Y(tBu)‐OH (a2′) respectively, prepared by Fmoc‐SPPS, with the appropriate methylester compounds and subsequent deprotection with TFA/scavenger and piperidine. Synthesis and physicochemical properties of the unnatural lipophilic amino acid methylesters are described. The preparation of the cysteine analogues was performed by condensation of a1′ or a2′ withH‐Cys(Trt)‐OMeand subsequent deprotection with TFA/scavenger. Alkylation of the thiol function and Fmoc‐deprotection was achieved in a novel one‐pot reaction by treatment with alkyl bromide and DIPEA, quenching with EDT and Fmoc removal by addition of 20% piperidine (v/v). Hydrolysis of the methyl esters was carried out by treatment with NaOH in MeOH/H2O. The results of the biological assay reveal an increase in activity with increasing chain length of the lipophilic anchor, with alkyl being better than prenyl and sulfur being not essential, while the position of the anchor is optimal atCαand the methyl ester moiety is important. NMR studies of two chosen analogues in DMSO and SDS/water demonstrate that the lipophilicC‐terminal residue has no influence on the structural behaviour of the peptides. Chemical‐shift and NOE patterns indicate a mainall‐transconformation of the peptide backbone and a weakly populatedcisconformation around the Xaa‐Pro peptide bond in all eight cases without formation of a defined folded structure. No evidence is seen that the membrane‐simulating system SDS/water has a structure‐inducing effect on the bound peptide. We therefore conclude that the lipomodification in mating pheromones ofU.

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1996.tb00855.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY