bluuebunny/crossref_metadata_2025 huggingface dataset:
Proton, calcium, and magnesium binding by peptides containing γ‐carboxyglutamic acid
Authors: CABANISS STEVEN E. , PUGH KATHLEEN C. , PEDERSEN LEE G. , HISKEY RICHARD G.
Published: August 2010

γ‐Carboxyglutamic acid (Gla) is believed to bind Ca [II] ions and Mg [II] ions in prothrombin and other coagulation proteins. Binding constants for H +, Ca [II] ions, and Mg [II] ions to Gla‐containing peptides are determined using pH and ion selective electrode titrations. The binding constants for peptides containing a single Gla residue are similar to the constants for malonic acid. Peptides containing two Gla residues in sequence (di‐Gla peptides) bind Ca [II] ions and Mg [II] ions more strongly. KMgL for the di‐Gla peptides is similar to the site‐binding constant for Ca [II] ions in denatured BF1. These di‐Gla peptides may be useful analogs for metal binding by the disordered Gla domain in BF1.
Fully synthetic immunogens
Authors: WÜNSCH E. , MORODER L. , GÖHRING‐ROMANI S. , MUSIOL H.‐J. , GÖHRING W. , SCHARF R.
Published: August 2010

The bis‐cysteinyl hinge‐fragment 225–232 of human IgG1 has been extended at the N‐ or C‐terminus with Nle15‐desamido‐human‐little‐gastrin‐[5‐17] and Nle15‐human‐little‐gastrin‐[5‐17]‐NH2, respectively. Thermodynamically controlled air oxidation of the resulting bis‐cysteinyl‐peptides led to the predominant formation of the corresponding dimers in parallel alignment despite the incorporation of the immunoglobulin‐unrelated gastrin‐sequences. These surprising results confirm the high degree of structural information inherent in the hinge‐sequence and its intrinsic tendency to fold into the correct structure in terms of cysteine pairings. This protein subdomain‐the hinge‐peptide‐is therefore well suited as core molecule for the design of fully synthetic immunogens with multiple attachment of antigenic determinants.
Biological and conformational studies of [Val4]morphiceptin and [D‐Val4]morphiceptin analogs incorporating cis‐2‐aminocyclopentane carboxylic acid as a peptidomimetic for proline
Authors: YAMAZAKI TOSHIMASA , PRÖBSTL ALBERT , SCHILLER PETER W. , GOODMAN MURRAY
Published: August 2010

We report the synthesis, biological activity, and conformational analysis of tetrapeptide analogs related to [Val4] morphiceptin and [d‐Val4]morphiceptin in which the proline at the second position has been replaced with cw‐2‐aminocyclopentane carboxylic acid (cis‐2‐Ac5c). Since thecis‐2‐Ac5c residue contains a normal amide, only thetransform has been observed about the amide bond between the first and second residues. Thecis‐2‐Ac5c is a β amino acid with two chiral centers resulting in two possible configurational isomers, namely (1s, 2R) and (1R, 2S) forms. The analogs containing the (1s, 2R)‐Ac5c residue show activity at the μ‐receptor but are inactive at the δ‐receptor, resulting in a high selectivity for the μ‐receptor. The (1R, 2S)‐Ac5c containing analogs are completely inactive at both theμ‐ andδ‐receptors. The conformational analysis indicates that the separation of the aromatic rings of the tyrosine and phenylalanine residues, as expressed by the center‐to‐center distance, is 10.1‐12.7 Å for the preferred conformations of the bioactive analogs containing the (1S, 2R)‐Ac5c residue while a range of 4.8‐7.0 Å is observed for the preferred conformations of the inactive analogs with the (1R, 2S)‐Ac5c residue. A comparison of the findings from the conformational analysis and biological assays establishes the fact that a relatively large separation of the two aromatic side chains is required for theμ‐opioid receptor activity of these molecules. Since the tetrapeptide amides studied in this investigation show similar biological profiles to those of the morphiceptin‐related analogs, we have compared the preferred conformations estimated for thecis‐2‐Ac5c containing analogs with those of morphiceptin. One of the low energy conformations calculated for morphiceptin with thecisform about the tyrosine and proline residues has considerable topological similarity with the bioactive analogs containing the (1S, 2R)‐Ac5c residue, indicating that thecisfrom about these two residues is required for the biological activity of the morphiceptin‐related analogs containing the proline at the second position.
Guanidination of a peptide side chain amino group on a solid support*
Authors: TIAN ZHENPING , ROESKE ROGER W.
Published: August 2010

A novel guanidination method of converting a peptide side chain amino group to a guanidino group on a solid support is described. Four guanidinating reagents were evaluated using a model tetrapeptide attached to a polystyrene resin. Experimental data indicate that the two nitroguanidinating reagents, but not the two tosylguanidinating reagents, can be used effectively in solid phase peptide synthesis.
Direct electrophilic fluorination of tyrosine in dermorphin analogues and its effect on biological activity, receptor affinity and selectivity
Authors: LABROO VIRENDER M. , HEBEL DAVID , KIRK KENNETH L. , COHEN LOUIS A. , LEMIEUX CAROLE , SCHILLER PETER W.
Published: August 2010

In a preliminary communication we reported [(Tetrahedron Lett.31, 619 (1990)] that acetyl hypofluorite can be used efficiently to introduce fluorine regiospecifically (ortho to OH) into the phenolic ring of tyrosine‐containing peptides. This procedure has been applied to the fluorination of a number ofμ‐selective opioid peptides derived from dermorphin. While the procedure can be used even when the side chains of Arg, Lys, and Tyr are left unprotected, the sulfoxide of a Met(O)‐containing analogue was oxidized to sulfone faster than fluorination of the phenolic ring. This method can also be used when the peptide is attached to Merrifield resin. Thus, Tyr(3‐F)‐d‐Ala‐Phe‐Gly‐NH2and Tyr(3‐F)‐d‐Arg‐Phe‐Lys‐NH2(F‐DALDA) have been prepared, purified, and characterized. Affinities of these fluorinated peptides for bothμ‐andδ‐opioid receptors are reduced (two‐ to nine‐fold) relative to their nonfluorinated analogues, but their selectivity forμ‐opioid receptors is not significantly altered. Similarly, thein vitrobiological potencies (GPI and MVD assays) of the fluorinated analogues are reduced (two‐ to seven‐fold) relative to their nonfluorinated parent peptides. Thus, F‐DALDA, which has high affinity (K δ= 15.2nM) and selectivity (K δ/K δ= 5390) forμ‐opioid receptors, has potential use in biochemical studies which utilize19F or18F‐ labeled compounds.
Amatoxins bearing amino and carboxyl groups prepared by selective alteration of the aldehyde generated by periodate oxidation of methylated α‐amanitin1
Authors: MULLERSMAN J. E. , PRESTON J. F.
Published: August 2010

Amatoxins are cyclic peptides which can be purified from the carpophores of various mushroom species. Since they were first recognized as potent inhibitors of the nuclear RNA polymerases of most cukaryotes these peptides have served as important tools in the study of transcription. The presence of unusual amino acid residues in these peptides has provided opportunities to attempt a variety of semisynthetic modifications. We describe several new amatoxin derivatives that were prepared by selective modification of an aldehyde group which can be generated by periodate oxidation of 6’‐O‐methyl‐α‐amanitin. The derivatives which resulted from sodium cyanoborohydride‐mediated coupling to the toxin of ammonia, glycine, and l‐proline exhibited Ki values for calf thymus RNA polymerase II of 1.7 × 10−7m, 2.5 × 10−7m and 7.0 × 10−6m, respectively. Treatment of the aldehyde with sodium chlorite or hydroxylamine‐O‐sulfonic acid converted the amanitin aldehyde to the corresponding carboxyl or nitrile compounds with Ki values of 1.0 × 10−7m and 3.0 × 10−9m, respectively. Difficulties which were encountered in the preparation of these derivatives are discussed relative to peculiarities in the chemical behavior of the amanitin aldehyde.
Conformation and hydration of aspartame
Authors: KANG YOUNG KEE
Published: August 2010

Conformational free energy calculations using an empirical potential (ECEPP/2) and the hydration shell model were carried out on the neutral, acidic, zwitterionic, and basic forms of aspartame in the hydrated state. The results indicate that as the molecule becomes more charged, the number of low energy conformations becomes smaller and the molecule becomes less flexible. The calculated free energies of hydration of charged aspartames show that hydration has a significant effect on the conformation in solution. Only two feasible conformations were found for the zwitterionic form, and these are consistent with the conformations deduced from NMR and X‐ray diffraction experiments. The calculated free energy difference between these two conformations was 1.25 kcal/mol. The less favored of the two solvated conformations can be expected to be stabilized by hydrophobic interaction of the phenyl groups in the crystal.
Purification and primary structure of glucagon from ostrich pancreas splenic lobes
Authors: FERREIRA ALET , LITTHAUER DEREK , SAAYMAN HESTA , OELOFSEN WILLEM , CRABB JOHN , LAZURE CLAUDE
Published: August 2010

Glucagon is a highly conserved polypeptide hormone which appears to play a more important role in regulation of glycaemia in birds than insulin. Ostrich glucagon was isolated and purified from ostrich pancreas splenic lobes using an adapted acid ethanol extraction procedure, gel filtration, ion exchanges, and HPLC steps. The purified glucagon fraction appeared to contain small quantities of a more acidic contaminant (polyacrylamide gel isoelectric focussing, PAGE) but appeared homogeneous on SDS‐PAGE. Amino acid analysis and sequence analysis showed identity with the duck hormone. Identity with the duck hormone was confirmed by liquid phase as well as gas phase sequencing. The ostrich glucagon preparation seemed to have a higher Km than the porcine homologue in stimulating glycerol release from isolated chicken adipocytes.
Difficult couplings in stepwise solid phase peptide synthesis: predictable or just a guess?
Authors: Van WOERKOM W.J. , Van NISPEN J.W.
Published: August 2010

Stepwise solid phase peptide synthesis, Fmoc‐approach, of 88 peptides varying in length from 4 to 24 amino acid residues was performed using a uniform procedure for coupling, monitoring and deprotection steps. The data of 696 couplings have been incorporated into a computer programme in order to study whether the degree of coupling can be predicted. Parameters studied are the nature of the amino acid to be coupled, the amino acid to be acylated and the length of the growing peptide chain. Using this information, prediction of “good” or “difficult” sequences, that is, peptides that can be synthesized without appreciable repeated couplings or the opposite, seems possible.
Dimensional oscillation
Authors: SNOW MARK E. , CRIPPEN GORDON M.
Published: August 2010

The structure of the AMBER potential energy surface of the cyclic tetrapeptide cyclotetrasarcosyl is analyzed as a function of the dimensionality of coordinate space. It is found that the number of local energy minima decreases as the dimensionality of the space increases until some limit at which point equipotential subspaces appear. The applicability of energy embedding methods to finding global energy minima in this type of energy‐conformation space is explored. Dimensional oscillation, a computationally fast variant of energy embedding is introduced and found to sample conformation space widely and to do a good job of finding global and near‐global energy minima.
Application of carboxylic‐phosphinic mixed anhydrides in the fragment peptide synthesis of protected analogues of substance P
Authors: POULOS CONSTANTINE , PASALIMANIOTOU PAGONITSA , MANOLOPOULOU AMALIA , TSEGENIDIS THEODOROS
Published: August 2010

Mixed carboxylic‐phosphinic anhydrides derived from peptide acids and 1‐oxo‐1‐chlorophospholane have been applied in the synthesis of the protected [Leu11]‐SP1‐11 by the fragment coupling strategy. The yields from fragment couplings were ca. 75%, the products were of high purity while the conditions of formation and coupling of the corresponding mixed phosphinic anhydrides, for optimum yields, have been evaluated.
Binding to opioid receptors of enkephalin derivatives taking α‐helical conformation and its dimer
Authors: SASAKI‐YAGI YOSHIKO , KIMURA SHUNSAKU , IMANISHI YUKIO
Published: August 2010

The opioid receptor binding of [Leu]enkephalin derivatives with extended address segment to the C‐terminal was studied. The extension peptide is designed to take an amphiphilic helical structure in order to evaluate effects of helical conformation and membrane affinity of enkephalin moiety of the derivatives on receptor binding. In the σ‐receptor‐selective binding assay, Tyr‐Gly‐Gly‐Phe‐Leu‐Lys‐Aib‐Leu‐Aib‐OH (1) showed the same affinity as enkephalinamide, whereas in the μ‐receptor‐selective binding assay, a 7‐fold reduction in affinity was observed. On the other hand, Tyr‐GIy‐Gly‐Phe‐Leu‐(Lys‐Aib‐Leu‐Aib)2‐OH (2) showed 51‐and 96‐fold decreases in affinities for δ‐ and μ‐receptors, respectively, compared with enkephalinamide. The low receptor affinity of derivative 2 is considered due to α‐helical conformation, which might not be compatible with topological requirements of δ‐ and μ‐receptors. A dimer, Tyr‐Gly‐GIy‐Leu‐Phe‐(Lys‐Aib‐Leu‐Aib)2‐Lys(X)‐Aib‐OCH3 (X = Tyr‐Gly‐Gly‐Phe‐Leu‐, (4)), showed 2.5‐ and 3.0‐fold increases in affinities respectively for δ‐ and μ‐receptors compared with the monovalent derivative 2, possibly due to cross‐linking of neighboring receptors. The Hill plot of the binding of the dimer to bovine brain membranes was composed of two phases, although such a heterogeneity of receptors was not observed in the presence of naloxone or in the binding to NG108‐15 cell membranes. These findings indicate the presence of the bivalent‐ligand‐induced interactions between δ‐ and μ‐receptors in bovine brain membranes.
Synthesis, crystal structure and molecular conformation of N‐Ac‐dehydro‐Phe‐l‐Val‐OH
Authors: DEY S. , SHARMA P. , KHANDELWAL B. , SINGH T.P.
Published: August 2010

The peptide N‐Ac‐dehydro‐Phe‐l‐Val‐OH (C16H20N2O4) was synthesized by the usual workup procedure. The peptide crystallizes from its solution in acetonitrile at 4° in hexagonal space group P65 with a = b = 11.874(2)Å, c = 21.856(9)Å, V = 2668(1)Å3, Z = 6, dm = 1.151(3)g cm‐3, dc = 1.136(4)g cm‐3, CuKα= 1.5418Å, μ= 0.641mm‐1, F(000) = 972, T = 293K. The structure was solved by direct methods and refined by least‐squares procedure to an R value of 0.074 for 1922 observed reflections. In the dehydro‐residue, the Cx1‐Cβ1 distance is 1.35(1)Å while the bond angle Cx1‐Cβ1‐Cï1 is 131.2(9)°. The backbone torsion angles are: ω= 172(1)°, ø1= ‐60(2)°, Ψ1= ‐31(2)°, ω1, = ‐ 179(1)°, ø2= 59(2)°. These values suggest that the peptide tends to adopt an alternating right‐handed and left‐handed helical conformation. The side chain torsion angles are: χ11= ‐6(2)°, χ2,11= ‐ 1(2)°, χ2,21= ‐ 178(2)°, χ1,12= 63(2)° and χ1,22= ‐ 173(1)°. These values show that the side chain of dehydro‐Phe is planar whereas the valyl side chain adopts a sterically most preferred conformation. The molecules, linked by intermolecular hydrogen bonds and van der Waals forces, are arranged in helices along the c‐axis. The helices are held side‐by‐side by van der Waals contacts.
Neurophysin‐neurohypophyseal hormone interactions: studies using dansylated vasotocin analogue
Authors: HASSELBACHER C.A. , SCHWARTZ GERALD P. , GLASS JOHN D. , LAWS WILLIAM R.
Published: August 2010

We have synthesized a neurohypophyseal hormone analogue containing an extrinsic fluorescence probe by linking a dansyl (DNS) group to the ε‐amino group of the lysine at residue 8 of vasotocin. The fluorescence properties of this analogue have been characterized by steady‐state and time‐resolved spectroscopic methods and compared with those of ε‐DNS‐lysine and the dansylated carboxyl terminal tripeptide Pro‐Lys(DNS)‐GlyNH2. The binding of this hormone analogue to purified isoforms of bovine neurophysins, the natural carrier proteins of the neurohypophyseal hormones, results in changes in several fluorescence parameters of the dansyl probe. These changes include an increase in intensity and average lifetime, a shift of the emission band to higher energies, and an increase in the emission anisotropy. Anisotropy changes have been used to determine dissociation constants for binding to these neurophysin isoforms. Based on the changes in the fluorescence properties of the dansyl probe, the dansyl group itself interacts with the protein. The degree of the dansyl‐neurophysin interaction, however, appears to be different for the full sequence isoform of neurophysin I and the Val89isoform of neurophysin II.
Solid‐phase peptide synthesis without side‐chain hydroxyl protection of threonine
Authors: FISCHER PETER M. , RETSON KIM V. , TYLER MARGARET I. , HOWDEN MERLIN E.H.
Published: August 2010

A peptide containing four threonine residues was synthesised by the solid‐phase method using fluorenyl‐methoxycarbonylamino acid reactive esters or coupling by preactivation with 1‐hydroxybenzotriazole and Castro's reagent. In two separate experiments the synthesis was carried out with or without protection of the side‐chain hydroxyl group of threonine as the tert‐butyl ether. Comparison of the crude peptides after deprotection and detachment from the synthesis resin suggests that side‐chain protection of threonine is unnecessary under the synthetic conditions employed.
Synthesis of Nα‐Fmoc protected derivatives of S‐(2,3‐dihydroxypropyl)‐cysteine and their application in peptide synthesis
Authors: METZGER JÖRG W. , WIESMÜLLER KARL‐HEINZ , JUNG GÜNTHER
Published: August 2010

Acylated derivatives of S‐(2,3‐dihydroxypropyl)‐cysteine (S‐glycerylcysteine) form the N‐terminus of structural and functional proteins of bacterial origin. Synthetic lipopeptides containing tripalmitoyl‐S‐glycerylcysteine are derived from bacterial lipoprotein and constitute potent immunoadjuvants activating both B‐lymphocytes and macrophages. There is increasingly interest in conjugates consisting of tripalmitoyl‐S‐glycerylcysteine linked to appropriate viral and bacterial antigens, because of their capability of inducing antigen specific antibodies and T‐helper and T‐killer cell specific immune responses. A new convenient synthetic pathway for the preparation of these tripalmitoyl‐S‐glycerylcysteinyl peptides is described. The use of Nα‐Fmoc‐protected S‐(2,3‐dihydroxypropyl)‐cysteine and its O,O′‐bis acylated derivatives for the synthesis of triacyl‐S‐glycerylcysteinyl, O,O′‐bis‐acyl‐5‐glycerylcysteinyl and S‐glycerylcysteinyl peptides of high diastereomeric purity by solid phase peptide synthesis or synthesis in solution is demonstrated.
N‐Alkoxycarbonyl‐glutamic and aspartic acids
Authors: CHEN FRANCIS M.F. , BENOITON N. LEO
Published: August 2010

N‐Alkoxycarbonylaminodicarboxylic acids were reacted in dichloromethane with N‐ethyl‐N′‐(dimethylaminopropyl)carbodiimide hydrochloride, and with methyl chloroformate in the presence of N‐methylmorpholine. Removal of secondary products by washing the mixtures with aqueous solutions gave good yields of the pure crystalline internal anhydrides. Anhydrides of N‐benzyloxycarbonyl‐ (Z) and N‐9‐fluorenylmethoxycarbonyl‐(Fmoc) L‐glutamic and L‐aspartic acids and of N‐tert.‐butoxycarbonyl‐L‐aspartic acid were prepared in this way. The compounds were shown to be amenable to normal phase high‐performance liquid chromatography (NP‐HPLC) on a CN‐column using tert.‐butanol‐hexane as solvent. The products of the reactions of Z‐ and Fmoc‐glutamic acid with hot acetic anhydride were examined by nuclear magnetic resonance and NP‐HPLC before and after methanolysis in an attempt to establish if any of the corresponding pyroglutamates were formed. The reaction of Fmoc‐chloride with Fmoc‐glutamate was examined for the same reason. It is concluded that the side product generated during the reaction of Fmoc‐chloride with glutamic acid which is used for analysis of the latter is the N‐protected internal anhydride and not the pyroglutamate as reported in the literature.
Conformational studies of N‐Tyr‐MIF‐1 in aqueous solution by 1H nuclear magnetic resonance spectroscopy
Authors: PETERSHEIM M. , MOLDOW R.L. , HALLADAY H.N. , KASTIN A.J. , FISCHMAN A.J.
Published: August 2010

N‐Tyr‐MIF‐1 (Tyr‐Pro‐Leu‐Gly‐NH2) is an endogenous brain peptide with multiple effects on animal behavior. However, there have been no studies on the conformation of this tetrapeptide. In this report, we studied the conformation of N‐Tyr‐MIF‐1 in aqueous solution by conventional one‐dimensional and two‐dimensional (COSY and NOESY) 1H nuclear magnetic resonance spectroscopy at 300 MHz. A complete set of assignments for the resolved resonances and approximate assignments for the overlapping resonances were made. The results demonstrate that N‐Tyr‐MIF‐1 is in slow exchange between two conformers, most likely determined by the cis and trans states of the proline residue. The minor conformation represents 30 ± 3% of the population over the temperature range from 3° to 73°. In the major conformation, the tyrosine aromatic ring appears to be close enough to interact directly with the proline pyrrolidine ring, as indicated by a strong temperature dependence of the proline CβH, CδH and CδH′ chemical shifts. In contrast, this interaction of the tyrosine and proline rings is not present in the minor conformation.
Survey of conformational role of ester bonds in a cyclic depsipeptide
Authors: KATO TAMAKI , MIZUNO HIROSHIGE , LEE SANNAMU , AOYAGI HARUHIKO , KODAMA HIROAKI , GO NOBUHIRO , KATO TETSUO
Published: August 2010

The effect of ester bond on the conformation of peptide molecule was studied by designing and synthesizing a model tetradepsipeptide cyclo(‐l‐Ala‐l‐Hmb‐)z and by analyzing the conformation both theoretically and experimentally. Theoretical analysis showed that both ester and peptide bonds in the calculated low‐energy conformations within 3 kcal/mol of the global minimum take a trans but distorted configuration. The distortion is larger in ester bonds than in peptide bonds. Further, the four carbonyls project from one side of the plane of the cyclic backbone, whereas the side chains project from the other side. These results are consistent with the experimental results obtained by NMR measurement; first, the coupling constant deduced from 1H‐NMR species in DMSO‐d6 is consistent with the dihedral angles of the calculated low‐energy conformations; second, results of NOE measurement can reproduce the calculated configuration of the carbonyls and side chains. From the consistency between theoretical and experimental results, it is concluded that this model tetradepsipeptide takes an all‐trans backbone conformation in solution and this backbone conformation is stabilized by large distortion in the ester bond, which compensates the strain resulted from the 12‐membered cyclic backbone structure consisting only of L‐residues.
Solid‐phase synthesis of bovine pancreatic trypsin inhibitor BPTI) and two analogues
Authors: FERRER MARC , WOODWARD CLARE , BARANY GEORGE
Published: August 2010

The linear sequence of bovine pancreatic trypsin inhibitor (BPTI) has been assembled by stepwise Fmoc solid‐phase peptide synthesis on a polyethylene glycol‐polystyrene (PEG‐PS) graft support with p‐alkoxybenzyl ester anchoring. Similar methods were used to prepare two analogues, the first with all six half‐cystine (Cys) residues replaced by α‐amino‐n‐butyric acid (Abu), and the second with replacement of Abu at four Cys positions while retaining the native pairing between positions 14 and 38. Following cleavage from the sup‐port, the linear molecules (reduced form) were purified by semipreparative reversed‐phase high performance liquid chromatography (HPLC). The native structure of BPTI was then formed by oxidation of a dilute solution of the protein at pH 8.7 in the presence of oxidized glutathione. The BPTI analogue with one disulfide bridge was obtained following treatment with dimethyl sulfoxide (DMSO)‐pH 6 buffer (1:9). Overall yields of homogeneous proteins were 2–4%, and further characterization was provided by amino acid analysis, sequencing, ion electrospray mass spectrometry, analytical HPLC, and capillary zone electrophoresis (CZE). Purified synthetic BPTI with the native sequence was indistinguishable from natural material by the analytical and biophysical criteria applied, including circular dichroism (CD) spectra and inhibition of trypsin action. Studies are in progress to evaluate conformational features of the analogues which respectively lack two, or all three, of the native disulfide bridges.
Constrained phenylalanine analogues
Authors: VALLE G. , KAZMIERSKI W.M. , CRISMA M. , BONORA G.M. , TONIOLO C. , HRUBY V.J.
Published: August 2010

Three Tic‐containing (Tic = 1,2,3,4‐tetrahydroisoquinoline‐3‐carboxylic acid) model peptides were synthesized to assess the tendency of this constrained Phe analogue to fold into a β‐bend and a helical structure, and to adopt a preferred side‐chain disposition. The results of the solution conformational analysis, performed by using Fourier transform infrared absorption and 1H nuclear magnetic resonance, indicate that in chloroform the ‐Aib‐D‐Tic‐Aib‐, ‐(Aib)2‐D‐Tic‐(Aib)2‐, and ‐l‐Pro‐D‐Tic‐ sequences fold into intramolecularly H‐bonded forms to a great extent. An X‐ray diffraction analysis on p‐BrBz‐(Aib)2‐dl‐Tic‐(Aib)2‐OMe monohydrate and p‐BrBz‐l‐Pro‐D‐Tic‐NHMe allows us to conclude that, while the pentapeptide methylester forms an incipient (distorted) 310‐helix, the dipeptide methylamide adopts a type‐II β‐bend conformation. In both cases, the d‐Tic side‐chain conformation is d, gauche(‐). The implications for the use of the Tic residue in designing conformationally restricted analogues of bioactive peptides are briefly discussed.
Novel approach to the design of synthetic radioiodinated linear V1A receptor antagonists of vasopressin
Authors: MANNING M. , BANKOWSKI K. , BARBERIS C. , JARD S. , ELANDS JACK , CHAN W.Y.
Published: August 2010

We report the solid phase synthesis of six analogs of the potent and selective linear AVP vasopressor (V1a receptor)antagonist: Phaa1‐d‐Tyr(Et)2‐Phe3‐Gln4‐Asn5‐Lys6‐Pro7‐Arg‐NH28(A) (where Phaa = phenylacetyl) in which the Phaa1 residue is replaced by hydroxyphenylacetyl (HO‐Phaa), hydroxyphenylpropionyl (HO‐Phpa) and phenylpropionyl (Phpa) and the d‐Tyr(Et)2 and Lys6 residues by d‐Tyr(Me)2 and Arg6 substituents. The phenolic‐containing peptides were synthesized to test the feasibility of using this approach for the design of high affinity selective ligands for AVP V1a receptors. The following analogs of A were synthesized: 1. [(HO)Phaa1]; 2. [(HOPhpa1,d‐Tyr(Me)2]; 3. [(HO)Phaa1,d‐Tyr(Me)2,Arg6]; 4. [(HO)Phaa1,Arg6]; 5. [Phpa1]; 6. [(HO)Phpa1]. All six peptides were examined for agonistic and antagonistic potencies in vasopressor (V1a‐receptor) and antidiuretic (V2‐receptor) and in vitro oxytocic assays in rats. The affinities of the phenolic‐containing peptides for hepatic V1a and uterine receptors were also determined. The phenolic‐containing peptides all exhibit potent V1a antagonism. Their anti‐V1a pA2 values range from 8.23 to 8.63 (the anti‐V1a pA2 value of A = 8.69). Their inhibition constants (Ki in nm) range from 0.4 to 1.0. They are weak antidiuretic agonists with activities ranging from 0.022 U/mg to 0.13 U/mg (A = 0.033 U/mg). They all exhibit OT antagonism in vitro. Their anti‐OT pA2 values range from 7.28 to 7.71 (A = 7.62). All five phenolic compounds were iodinated using iodine chloride and tested in the same in vivo and in vitro assay systems. The iodinated derivatives all exhibited potent V1a antagonism and OT antagonism. With Ki values in the liver of 0.1 nM the affinities of the iodinated derivatives of peptides 3 and 6 are particularly impressive. These two peptides are very promising candidates for radioiodination as potential high affinity, selective ligands for Vla receptors. Thus this approach which complements the traditional approach of utilizing tyrosine substitutions, offers promise for the design of high affinity radioligands for AVP V1a receptors, AVP pituitary (V1b) receptors, AVP V2 receptors and OT uterine receptors. It may also have application for the design of radioligands for other biologically active peptides.
Synthesis of specific peptide substrates for HIV‐1 proteinase
Authors: HANDA BALRAJ K. , KAY CORINNE
Published: August 2010

Two small peptide substrates for HIV‐1 proteinase were synthesised. The sequences chosen were basically from that of the gag‐pol protein, which is the natural substrate for the proteinase. To protect these peptides from the attack of exopeptidases, the N‐ and C‐termini were suitably protected, which also makes these substrates specific to HIV‐proteinase and eliminates the requirement for highly purified enzyme.
Hydrogen bond connectivity patterns and hydrophobic interactions in crystal structures of small, acyclic peptides
Authors: GÖRBITZ CARL HENRIK , ETTER MARGARET C.
Published: August 2010

Crystal structures of all available unblocked linear peptides with two to five residues were retrieved from the Cambridge Structural Database and their intermolecular contacts and packing modes studied using molecular graphics. This survey reveals that interactions between hydrophobic portions of the molecules are critically important in determining the overall features of their crystal packing patterns. Distinct hydrophobic columns or layers are observed in almost all crystal structures. Analyses of the relationships between these interactions and crystal growth properties of small peptides are given. It is suggested that needle growth is promoted by hydrophobic packing, usually along a short crystallographic axis (4.6‐6.0 Å). Also contributing to these morphologic characteristics are entropic factors associated with hydrophobic aggregation as well as tightly bound water molecules on hydrophobic faces. The paper also provides a comprehensive overview of hydrogen bond patterns in acyclic peptide crystals. It is demonstrated that one of their primary roles is to provide a scaffolding within which hydrophobic groups can aggregate. Even though there is a high density of hydrogen bonds in the crystals, often with complex patterns and networks, certain motifs are found to recur in a number of structures indicating specific hydrogen bond preferences. Water, for example, is an integral part of the hydrogen bond networks in these crystals, usually acting as the primary donor for main‐chain carboxylate groups in peptide hydrates.
1H‐NMR conformational study of a synthetic peptide derived from the consensus sequence of Annexins
Authors: MACQUAIRE FRANÇOIS , BALEUX FRANÇOISE , HUYNH‐DINH TAM , NEUMANN JEAN MICHEL , SANSON ALAIN
Published: August 2010

The solution conformation of a synthetic 18 amino acid peptide derived from a consensus sequence of Annexins has been investigated by 1HNMR. Full sequential assignment has been achieved. Conformational properties of the peptide were deduced from the analysis of J(NH–CHα) coupling constants, amide proton exchange, 2D NOESY connectivities and computer modeling.
Cyclo(l‐propyl‐l‐N‐methylphenylalanyl) Conformation in solution and in the crystal
Authors: BUDĚŠÍNSKÝ M. , SYMERSKÝ J. , JEČNÝ J. , VAN HECKE J. , HOSTEN N. , ANTEUNIS M. , BORREMANS F.
Published: August 2010

Detailed analysis of the proton and carbon‐13 NMR spectra of cyclo(l‐prolyl‐l‐N‐methylphenylalanyl) in chloroform and methanol in relation to its nonmethylated analog provided information on the conformation of the title compound in solution as well as on the effect of N‐methylation and solvation. The N‐ray structure of the title compound in the crystalline state showed the same conformational features as the solution structure. The phenyl group folds over the diketopiperazine ring which resembles a flattened half‐chair. Both amide bonds are considerably nonplanar. The pyrrolidine ring of proline shows a strong pucker at the ring junction with the largest χ5 value hitherto observed.
14‐Membered cyclic opioids related to dermorphin and their partially retro‐inverso modified analogues
Authors: SAID‐NEJAD ODILE E. , FELDER EDUARD R. , MIERKE DALE F. , YAMAZAKI TOSHTMASA , SCHILLER PETER W. , GOODMAN MURRAY
Published: August 2010

As a continuation of our program to study structure‐activity relationships of opiate peptides, we report the syntheses and biological activities of a series of 14‐membered cyclic dermorphin analogues closely related to enkephalin analogue Tyr‐c[d‐A2bu‐Gly‐Phe‐Leu] incorporating a phenylalanine at the third position in place of glycine. In addition to two parent dermorphin analogues Tyr‐c[d‐A2bu‐Phe‐Phe‐(l and D)‐Leu], four stereoisomeric retro‐inverso modified analogues Tyr‐c[D‐A2bu‐Phe‐gPhe‐(S and R)‐mLeu] with a reversed amide bond between residues four and five, and Tyr‐c[d‐Glu‐Phe‐gPhe‐(L and D)‐rLeu] with two reversed amide bonds between residues four and five, and between residue five and the side chain of residue two have been synthesized. The results from the guinea pig ileum (GPI) and mouse vas deferens (MVD) assays show that all analogues are superactive at either one or both opiate receptors and in general display higher activities as compared to the corresponding enkephalin analogues with a glycine at the third position. Results from the in vitro biological assays and conformational analysis using 1H‐NMR spectroscopy (adjoining paper) will provide useful information to understand the role of the Phe3 aromatic side chain in dermorphin, and that of the Phe4 aromatic side chain in enkephalin, on opiate activity since these cyclic dermorphin analogues contain two Phe residues at both the third and fourth positions.
Crystal structure and conformation of a highly constrained linear tetrapeptide Boc‐Leu‐dehydro Phe‐Ala‐Leu‐OCH3
Authors: CHAUHAN V. S. , BHANDARY KRISHNA K.
Published: August 2010

The conformation of a tetrapeptide containing a dehydro amino acid, ΔzPhe, in its sequence has been determined in the crystalline state using X‐ray crystallographic techniques. The tetrapeptide, Boc‐Leu‐ΔzPhe‐Ala‐Leu‐OCH3, crystallizes in the orthorhombic space group P212121 with four molecules in a unit cell of dimensions a = 11.655(1) Å, b = 15.698(6) Å and c = 18.651(3) Å V = 3414.9 Å and Dcalc =1.12 g/cm −3. The asymmetric unit contains one tetrapeptide molecule, C30H46N4O7, a total of 41 nonhydrogen atoms. The structure was determined using the direct methods program SHELXS86 and refined to an R‐factor of 0.049 for 3347 reflections (13.0(I). The linear tetrapeptide in the crystal exhibits a double bend of the Type III‐I, with Leu1 (<φ=−54.1°, Ψ=−34.5°) and ΔzPhe2 (φ=−59.9°, Ψ=−17.1°) as the corner residues of Type III turn and ΔzPhe2 (φ=−59.9°, Ψ=−17.1°) and Ala3 (φ=−80.4°, Ψ= 0.5°) residues occupying the corners of Type I turn, with ΔzPhe as the common residue in the double bend. The turn structures are further stabilized by two intramolecular 4→1 type hydrogen bonds.
Design and inhibitory properties of synthetic Bowman‐Birk loops
Authors: MAEDER DENNIS L. , SUNDE MARGARET , BOTES DAWIE P.
Published: August 2010

A cyclic tridecapeptide based on the sequence of an anti‐tryptic loop of a Bowman‐Birk inhibitor was synthesized, and demonstrated to be active as an inhibitor of trypsin. Molecular modeling of this sequence suggested an improved sequence which demonstrated an order of magnitude improvement in the inhibitory constant.
Insect peptide hormones, an overview of the present literature
Authors: KONOPIŃSKA DANUTA , ROSIŃSKI GRZEGORZ , SOBÓTKA WIESIAW
Published: August 2010

A comprehensive overview of the recent state of the art of insect peptide hormones with chemical structures is presented. An increased interest in insect neuropeptides and dynamic development of that research area has been influenced by a rapid improvement of instrumentation necessary for isolation and structural characterization. Several research teams have studied the relationships between biological properties of insect and vertebrate peptide hormones (96‐98). Thus hormones from the AKH family can be considered glucagon counterparts, whereas the myotropic hormones such as proctolin and Lem‐PK (LPK) are a substance P equivalent. Insect melanization hormones Bom‐MRCH in their structural characteristics and properties resemble those of mammal MSH, and leucosulfakinins Lem‐SK‐I and ‐II show some similarities with gastrin II and cholecystokinin. Bombyxin‐II (Bom‐PTTH‐II) reveals a structural homology with human insulin and similar biological properties to adenocorticotropic mammal hormone. Allatostatin (Dip‐JHS‐I) may be compared to somatostatin as it can be inferred from the observations (99) that this peptide modulates JH secretion in cockroach, Blattella germanica. Determination of the primary structure of eclosion hormones Mas‐EH and Bom‐EH‐II as well as the amino acid sequence of allatotropin and allatostatin is a significant contribution to the understanding of the molecular mechanisms of metamorphosis and insect development.
Ionization of tyrosine residues in human serum albumin and in it complexes with bilirubin and laurate
Authors: HONORÉ BENT , BRODERSEN ROLF
Published: August 2010

Spectrophotometric titration of human serum albumin indicates that ionization of the 18 tyrosine residues takes place between pH 9 and 12.7. A Hill plot indicates that protons dissociate co‐operatively from tyrosine residues, in pure albumin between pH 11.0 and 11.4 with a Hill coefficient 1.7, and in the bilirubin‐albumin complex between pH 11.2 and 11.7 with a Hill coefficient 1.6. With a stopped‐flow technique it is shown that about seven of the tyrosines ionize fast, with rate constants well above 102 s−1, when pH is suddenly changed from near neutral to pH 11.76. Further residues ionize slowly, with rate constants around 102 s−1 or less. The N‐form of albumin (pH 6) contains one more fast ionizing tyrosine than the B‐form of albumin (pH 10). Binding of bilirubin or laurate to the albumin molecule (molar ratio 1:1) transforms one to three of the fast ionizing tyrosines to slowly ionizing.
Crystal structure of valinomycin‐monohydrate cage complexes crystallized from dioxane
Authors: LANGS DAVID A. , BLESSING ROBERT H. , DUAX WILLIAM L.
Published: August 2010

Valinomycin, cyclo‐[(l‐Val‐d‐Hyv‐d‐Val‐l‐Lac)3‐], was crystallized from aqueous dioxane solvent as a mono‐hydrate complex in which water molecules were found within the ion‐binding cavity of the ionophore: monoclinic P21 a = 14.377 (3), b = 41.554 (14), c = 14.080 (3) Å, β= 118.27 (2)c, Z = 4. There are two non‐equivalent valinomycin‐water complexes and three dioxane molecules in the asymmetric unit. The ionophore molecules adopt two similar but non‐identical, octahedral, bracelet, cage conformations that are a consequence of two distinct ways in which the complexed water molecules can deform the normal octahedral coordinate geometry of the metal binding site. In the first complex the water molecule forms hydrogen donor bonds to the carbonyl oxygens of two l‐valine residues on one facial side of the cavity, while in the second complex the water molecule is trigonal‐planar coordinate and binds to two l‐valine residues on one entrant face of the cavity plus a third d‐valine residue from the opposite side of the cavity.
Geometry of proline‐containing alpha‐helices in proteins
Authors: SANKARARAMAKRISHNAN R. , VISHVESHWARA SARASWATHI
Published: August 2010

Crystal structure analysis of proline‐containing α‐helices in proteins has been carried out. High resolution crystal structures were selected from the Protein Data Bank. Apart from the standard internal parameters, some parameters which are specifically related to the bend in the helix due to proline have been developed and analyzed. Finally the position and nature of these helices and their interactions with the rest of the protein have been analyzed.
Novel class of silicon‐based protective groups for the side chain of tyrosine
Authors: FOTOUHI NADER , KEMP DANIEL S.
Published: August 2010

A novel class of silyl‐based protective groups compatible with the Bpoc/t‐Bu strategy has been developed for the side chain of tyrosine. Carbobenzyloxy (CBZ) and biphenylisopropyloxy (Bpoc)‐O‐β‐trimethylsilylethyl‐tyrosine (10 and 12) and CBZ‐O‐β‐dimethylphenylsilylethyl‐tyrosine 14 were prepared in reasonable yields and in very high purity. The trimethylsilylethyl (TMSE) group proved to be 3–4 times more stable than the tert‐butyl ether group towards 0.5% TFA. The latter is removed up to 4% during the acidolysis of the Bpoc group. As expected, the dimethylphenylsilylethyl (DMPSE) group was even more resistant towards 0.5% TFA (five time greater than the TMSE analog). Both silyl protective groups were found to be resistant towards a variety of reagents used in peptide synthesis, such as trialkylamines, hydroxybenzotriazole, trialkylphosphine and nucleophiles. They are readily removed in neat TFA in 5–20 min in the absence of cation scavengers, without any detectable alkylation of the phenolic ring. The application of the new silyl‐based protective group was demonstrated by the synthesis of the C‐terminal 29 amino acid peptide of the basic pancreatic trypsin inhibitor by the prior thiol capture methodology. The protected octapeptide Boc‐C(Acm)QT(tBu)FW(TMSE)GG‐PO‐dibenzofuranthiol was synthesized by solid‐phase peptide synthesis using Bpoc‐(O‐TMSE)‐Tyr‐OH in greater than 90% yield and coupled to an unprotected 21‐mer. The partially blocked, purified peptide was deprotected quantitatively in neat TFA in 1 h.
Synthesis of a tritiated human growth hormone releasing peptide
Authors: SHU ARTHUR Y.L. , HEYS J. RICHARD
Published: August 2010

Tritium‐labeled growth hormone releasing peptide His‐D‐Trp‐Ah‐Trp‐D‐Phe‐Lys‐NH2 was synthesized by tritium‐halogen exchange on the precursor His‐5,7‐Br2‐D‐Trp‐Ala‐Trp‐D‐Phe‐Lys‐NH2, The radiolabeled peptide had a specific activity of 29 Ci/mmol and a radiochemical purity of 95 %. The tritium label was shown by 3H NMR to be located mostly at the expected 5, 7‐positions of the indole nucleus in the D‐Trp residue. The dibromopeptide was prepared by solid‐phase peptide synthesis, employing racemic 5,7‐Br2‐Trp as a building block and separation of the resulting epimeric mixture by HPLC. 5,7‐Br2‐Trp was prepared by a five‐step sequence beginning with 2,4‐dibromoaniline, The use of anisole as an additive in the HF resin/peptide cleavage was rejected because anisolc was found to undergo electrophilic substitution of the dibromoindole nucleus; a modified HF deprotection/cleavage procedure was developed and used instead.
Preparation of 2‐alkoxy‐4‐alkyl‐5(4H)‐oxazolones from mixed anhydrides of N‐alkoxycarbonylamino acids
Authors: BENOITON N. LEO , CHEN FRANCIS M.F.
Published: August 2010

A general procedure for the preparation of 2‐alkoxy‐4‐alkyl‐5(4H)‐oxazolones (AlkOx's) from N‐tert‐butoxy‐N‐benzyloxy‐ and N‐(9‐fluorenylmethoxy)‐carbonylamino acids has been devised. Purified mixed anhydrides are prepared from the parent acid and isopropenyl chloroformate and left in chloroform (Boc) for 24 h or dimethylformamide (Z, Fmoc) for 0.5–2 h. Symmetrical anhydride that may originate from disproportionation or reaction of AlkOx with hydrolyzed product is partially removed by extracting the AlkOx into petroleum ether. The products contain 0.5–30% of symmetrical anhydride.
Conformational versatility of the Nα‐acylated tripeptide amide tail of oxytocin
Authors: FABIANO N. , VALLE G. , CRISMA M. , TONIOLO C. , SAVIANO M. , LOMBARDI A. , ISERNIA C. , PAVONE V. , DI BLASIO B. , PEDONE C. , BENEDETTI E.
Published: August 2010

The synthesis, physical and analytical characterization, and crystal‐state structural analysis by X‐ray diffraction of three analogues of the Nα‐acylated tripeptide amide tail of oxytocin, each containing a cyclic Cα, α‐ disubstituted glycine at position 2, have been performed. The peptides arc Boc‐L‐Pro‐Ac3c‐Gly‐NH2, Z‐L‐Pro‐Ac5c‐Gly‐NH2 and Z‐L‐Pro‐Ac5c‐Gly‐NH2. While the former is folded in a type‐II β‐turn conformation at the ‐L‐Pro‐Ac3c‐ sequence, the two latter tripeptides form two consecutive (type‐II, type‐I′) β‐turns. The Ac5c‐ and Ac6c‐tripeptides are the first examples of such a highly folded structural combination in a position‐2 analogue of the Nα‐acylated ‐L‐Pro‐L‐Leu‐GIy‐NH2 sequence.
Spontaneous chemical degradation of substance P in the solid phase and in solution
Authors: KERTSCHER UWE , BIENERT MICHAEL , KRAUSE EBERHARD , SEPETOV NIKOLAI F. , MEHLIS BURKHARD
Published: August 2010

The instability of the undecapeptide substance P (SP), a neuropeptide implicated in several physiological processes, was occasionally observed when the peptide was stored in the solid state or in solution. The aim of the present study was to identify the decomposition products of SP stored as lyophilized peptide or in aqueous neutral solution. The main pathway of the decomposition of SP acetate consists of the subsequent release of N‐terminal dipeptides via their diketopiperazines. cyclo(Arg‐Pro) and cyclo(Lyys‐Pro). In contrast to the decomposition of the acetate of SP, the hydrochloride and trifluoroacetate salts were found to be considerably more stable. Under the studied conditions the release of N‐terminal dipeptides dominates over other possible routes of spontaneous modifications, such as S‐oxidation and deamidation.
Diaminomethane dihydrochloride, a novel reagent for the synthesis of primary amides of amino acids and peptides from active esters
Authors: GALAVERNA GIANNI , CORRADINI ROBERTO , DOSSENA ARNALDO , MARCHELLI ROSANGELA
Published: August 2010

Amide formation from acids, N‐protected amino acids and peptides was achieved in an easy and convenient way by treating “active esters” such as succinimidyl or 4‐nitrophenyl esters or acyl chlorides with diami–nomethane dihydrochloride in dioxane in the presence of EtsN. Diaminomethane dihydrochloride behaves as a slow ammonia‐releasing agent. The method is a good alternative to the use of concentrated aqueous ammonia; it avoids solubility problems and allows better control of the stoichiometry of the reaction and of the pH. It gives good yields and does not induce racemization. The mechanism of the reaction is discussed.
Nine‐membered cyclodepsitripeptides containing the retroisomeric sequence of ergot peptides
Authors: CALCAGNI A. , KAJTAR‐PEREDY M. , LUCENTE G. , LUIS G. , PINNEN F. , RADICS L. , ROSSI D.
Published: August 2010

In order to examine factors influencing cyclodepsitripeptide formation and stability, three cyclic peptide models containing the α‐hydroxyacyl‐α‐aminoacylprolyl sequence, corresponding to the peptide lactone cyclo(‐Xha‐Pro‐Xaa‐) (Xha = Hiv, Lac; Xaa = Phe, dPhe, dAla), retroisomeric with respect to the ergot oxa‐cyclolic peptide moiety, have been considered. Starting from 2,5‐dioxomorpholines, aminoacyl incorporation reaction led, through intermediate tetrahedral adducts (aza‐cyclols), to the corresponding nine‐ membered cyclodepsitripeptides cycle(‐Hiv‐Pro‐dPhe‐) 4a, cycle(‐Lac‐Pro‐dPhe‐) 4b, and cyclo (‐Hiv‐Pro‐ dAla‐) 4c. Compounds 4a‐c contain a CONH peptide bond in the nine‐membered ring and are stable on standing. Solution conformations of 4a‐c, as inferred by NMR spectra and NOE experiments, have been studied. A cis‐cis‐trans backbone conformation, analogous to that observed in the case of previously stud‐ ied nine‐membered cyclodepsitripeptides containing two proline residues in the ring, is proposed for 4a‐c.