bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxidation of L‐lysine derivatives to L‐α‐aminoadipamic acid (homoglutamine) derivatives with KMnO 4
Authors: LIBEREK BOGDAN , KASPRZYKOWSKA REGINA
Published: August 2010

A new route to L‐homoglutamine (L‐α‐aminoadipamic acid) derivatives is presented via preferential KMnO4 oxidation in acidic media of the e‐methylene group in H‐L‐Lys(Z)‐OH and Z‐L‐Lys(Z)‐OH. The main oxidation products are 5‐benzyloxy‐carbonylcarbamoyl‐2‐aminopentanoic acid (H‐L‐Aad(NHZ)‐OH) 2 and 5‐benzyl‐oxycarbonylcarbamoyl‐2‐benzyloxycarbonylaminopentanoic acid (Z‐L‐Aad(NHZ)‐OH) 10, respectively, in which the intact benzyloxycarbonyl protection is now attached to the nitrogen atom of the δ‐amide group. The accompanying hydrolysis of the labile N‐protected amide group and the continuing oxidation, however, diminish the quantity of 2 and 10 in the reacting mixture. Therefore, to obtain fair yields of these products, useful in peptide synthesis, involving homoglutamic acid and homoglutamine (H‐L‐Aad(NHZ)‐OH and Z‐L‐Aad(NHZ)‐OH contain carboxylic groups in differential form) a compromise must be reached and the oxidation process stopped at the right moment. Besides the desired oxidation product involving the transformation of the e‐methylene group into the carbonyl group, a number of side products formed by oxidation of the α‐carbon atom (derivatives of δ‐aminovaleric acid) and e, α‐carbon atoms (derivatives of glutaric acid) have been isolated and identified.
Synthesis, conformation, and biological activity of the carbohydrate‐free vespulakinin 1
Authors: ROCCHI R. , BIONDI L. , FILIRA F. , SCOLARO B.
Published: August 2010

Synthesis of the carbohydrate‐free heptadecapeptide corresponding to the amino acid sequence of vespulakinin 1 was achieved by the continuous flow solid phase procedure on 4‐hydroxymethyl‐phenoxyacetyl‐norleucyl derivatized Kieselguhr‐supported polydimethylacrylamide resin, as well as by a combination of solid phase and solution syntheses. Preformed Fmoc‐amino acid symmetrical anhydrides (Boc derivative for theN‐terminal residue) were used for amine acylation in the continuous flow method. Serine and threonine were side chain protected astert.‐butyl ethers and the 4‐methoxy‐2, 3, 6,‐trimethyl‐benzenesulfonyl group was used for masking the guanidino function of arginine residues. After cleavage from the resin the final peptide was purified by ion exchange chromatography and characterized by amino acid analysis, high voltage electrophoresis, and RP‐HPLC analysis. Alternatively, the protectedN‐terminal octapeptide, Fmoc‐Thr(But)‐Ala‐Thr(But)‐Thr(But)‐Arg(Mtr)‐Arg‐(Mtr)‐Arg(Mtr)‐Gly‐OH was prepared on 4‐hydroxymethyl‐3‐methoxyphenoxyacetyl‐norleucyl derivatized Kieselguhr‐supported polydimethylacrylamide resin and theC‐terminal nonapeptide H‐Arg(NO2)‐Pro‐Pro‐Gly‐Phe‐Ser‐Pro‐Phe‐Arg‐(NO2)‐OBzl was synthesized in solution through the fragment condensation method. The two fragments were coupled by the DCC‐HOBt procedure and the resulting heptadecapeptide was deblocked and purified. The conformational features of the synthesized peptides are reported. Preliminary pharmacological experiments indicated that carbohydrate‐free vespulakinin 1 is more potent than bradykinin in lowering rat blood pressure.
Chemical synthesis of phosphoseryl‐phosphoserine, a partial analogue of human salivary statherin, a protein inhibitor of calcium phosphate precipitation in human saliva
Authors: SCHLESINGER DAVID H. , BUKU ANGELIKI , WYSSBROD HERMAN R , HAY DONALD I.
Published: August 2010

Human salivary secretions are supersaturated with respect to basic calcium phosphates but spontaneous precipitation of these salts from saliva, or surface‐induced precipitation of calcium phosphates onto dental enamel, does not normally occur. This unexpected stability has been attributed to the inhibitory activities of two kinds of salivary phosphoproteins: statherin and the acidic, proline‐rich phosphoproteins (PRP). Investigation of the structure‐function relationships of statherin, the most potent inhibitor of primary (spontaneous) and secondary (seeded) precipitation of calcium phosphate salts in human saliva has been limited to studies of peptide segments obtained from the native peptide by specific proteolysis. Solid phase peptide synthesis (SPPS) is a useful and potentially more flexible alternative. Phosphoserine residues (positions 2 & 3) play critically important roles in the precipitation‐inhibition activities of statherin, but SPP synthesis of these phosphorylated peptides is precluded because of the instability of phosphoserine residues in the presence of HF. Thus, this peptide was synthesized by solution‐phase methods. The dipeptide possessed substantial inhibitory activity in assays for inhibition of both primary and secondary precipitation of calcium phosphate salts, but was not as active as either N‐terminal tryptic hexapeptide of statherin or intact statherin. Syntheses of other model phosphorylated peptides are underway to expand the structure‐function relationships.
Novel μ‐selective Met‐enkephalinamide analogs with antagonist activity.
Authors: JUDD AMRIT K. , LAWSON JOHN A. , OLSEN CRIS M. , TOLL LAWRENCE R. , POLGAR WILLMA E. , UYENO EDWARD T. , KEYS CHRISTOPHER J. , LOEW GILDA H.
Published: August 2010

Four novel μ‐selective peptide antagonists have been synthesized and examined for receptor binding, analgesic agonist and antagonist activity and energy conformational properties. These peptides were designed by analogy to results of molecular modeling of 3‐phenyl piperidines which led to incorporating four modified tyrosine residues,m‐Tyr, β‐methyl‐m‐Tyr,N‐phenethyl‐m‐Tyr and α, β‐dimethyl‐m‐Tyr into D‐Ala2‐Met5‐enkephalinamide. Peptides were synthesized by stepwise solution synthesis using an active ester coupling procedure. Receptor binding assays were performed on rat brain homogenates and data were analyzed by a modified version of the program LIGAND. Analgesic agonist and antagonist activity was evaluated by the mouse tail‐flick test. Energy‐optimized conformations were obtained using a program called Molecule‐AIMS. The results demonstrate that relative ratios ofin vivoagonist and antagonist potencies in D‐Ala2‐Met5‐enkephalinamides can be modulated by chemical modification of the tyrosine residue. A shift in the phenolic‐OH position fromparatometasignificantly enhances relative antagonist versus agonist activity; addition of a β‐CH3group to them‐Tyr enhances μ‐selectivity and leads to nearly equal agonist/antagonist activity. Energy conformational studies indicate that all analogs with high μ‐receptor affinity examined have a common energy accessible B'II2–3 turn conformation similar to that previously identified for high μ‐affinity binding in peptides, lending further support to this candidate conformer. This conformer also has tyrosine side‐chain angles which allowed total overlap with the amine and phenolic groups of a known structure of 3‐(m‐OH phenyl)‐piperidine. This structural similarity together with the observation of mixed agonist antagonist activity in both types of opioids confirms the rationale upon which design of these peptides was based.
Analogs of oxytocin containing a modified peptide bond*
Authors: LEBL MICHAL , SUGG ELIZABETH E. , VAN BINST GEORGES , ELST PIERRE VANDER , TOURWÉ DIRK , SLANINOVÁ JIŘINA , HRUBY VICTOR J.
Published: August 2010

Analogs of deamino‐oxytocin and deamino‐oxypressin containing a CH2‐NH group instead of an amide bond between positions 8 and 9 were synthesized. All tested compounds exhibit significantly lowered biological activities.
Isolation and amino acid sequence of insulins and C‐peptides of European bison (Bison bonasus) and fox (Alopex lagopus)
Authors: MAJEWSKI TADEUSZ , THIM LARS , IZDEBSKI JAN , MARKUSSEN JAN
Published: August 2010

Insulins and C‐peptides were extracted and purified from bison and fox pancreatic glands. The insulins were reduced and pyridylethylated, and the derived A‐ and B‐chains separated by HPLC. Amino acid sequence determinations of the pyridylethylated A‐ and B‐chains proved bisontine insulin to be identical to bovine insulin and fox insulin to be identical to dog and porcine insulin. Bisontine C‐peptide proved to be identical to bovine C‐peptide. The isolated fox C‐peptide comprises 23 amino acid residues and probably represents a major tryptic fragment of a larger C‐peptide. The fox C‐peptide fragment is identical to the dog C‐peptide (9–31) except for residue 3 (residue 11 in the dog C‐peptide), which is aspartic acid as compared with glutamic acid in the dog C‐peptide.
Cyclization under mild conditions of anthraniloyl‐ and N‐methyl‐anthraniloyl dipeptides*
Authors: PINNEN FRANCESCO , DI MURO ALFREDO , ZANOTTI GIANCARLO , LUCENTE GINO
Published: August 2010

Anthraniloyl‐ and N‐methyl‐anthraniloyl dipeptides containing C‐terminal L and D proline residues have been synthesized and subjected to cyclization reaction under mild conditions. The influence of substituents and of the chirality of the residues on the output of the reaction is discussed.
Cystine peptides.
Authors: KISHORE R. , ISHIZAKI H. , TU ANTHONY T. , RAVI A. , BALARAM P.
Published: August 2010

NHCH3 (X = Gly 1, Ala 2, Aib 3, Leu 4 and D‐Ala 5), have been investigated by Raman and circular dichroism (CD) spectroscopy. Solid state Raman spectra are consistent with β‐turn conformations in all five peptides. These peptides exhibit similar conformations of the disulfide segment in the solid state with a characteristic disulfide stretching frequency at 519 ± 3 cm‐1, indicative of a trans‐gauche‐gauche arrangement about the Cα—Cβ—S—S—Cβ—Cα bonds. The results correlate well with the solid state conformations determined by X‐ray diffraction for peptides 3 and 4. CD studies in chloroform and dimethylsulfoxide establish solvent dependent conformational changes for peptides 1, 3 and 5. Disulfide chirality has been derived using the quadrant rule. CD results together with previously reported nuclear magnetic resonance (n.m.r.) data suggest a conformational coupling between the peptide backbone and the disulfide segment.
Slow O,N‐acyl shift in an actinomycin‐related peptide lactone
Authors: MAUGER ANTHONY B. , STUART OSWALD A.
Published: August 2010

The pentapeptide lactone Cbz‐(Thr‐D‐Val‐Pro‐Sar‐MeAla‐) was synthesized in order to observe the behavior of the unprotected lactone resulting from its hydrogenolytic deprotection. Closely related peptide lactones have been reported as intermediates in total syntheses of actinomycin D and its analogues, despite the fact that unprotected and unprotonated O‐peptides of serine and threonine are known to undergo rapid O,N‐acyl shift. In the present study the peptide lactone was seen to undergo a slow O,N‐acyl shift, in a matter of hours, to the known cyclic pentapeptide. This contrasted with the rapid rearrangement of a model O‐peptide, O‐hippuryl‐L‐threonine methyl ester. This slowness of an O,N‐acyl shift in a cyclic system presumably results from higher energy barriers of conformational origin. It explains the suitability of unprotected peptide lactones for the syntheses of actinomycins and other peptide lactone antibiotics which have appeared in the literature.
Rapid hydrolysis of proteins and peptides by means of microwave technology and its application to amino acid analysis
Authors: CHEN SHUI‐TEIN , CHIOU SHYH‐HORNG , CHU YEN‐HO , WANG KUNG‐TSUNG
Published: August 2010

A rapid heating method of hydrolysis by the use of microwave oven has been applied to amino acid analysis of proteins and peptides. This convenient method has been compared with the conventional 6 n HCl hydrolysis at 110° for 24 h. The advantages of this new method are its expedition and the accurate and comparable results as compared to the tedious conventional technique. The method provides a rapid processing of multiple samples within minutes instead of days and inexpensive access to the important data of amino acid compositions of proteins by the commonly used microwave oven. The necessary change in the design of hydrolysis vials and the safety precautions accompanying this novel use of microwave acid‐digestion method are also described.
Synthesis, receptor binding activity and fluorescence property of fluorescent enkephalin analogs containing L‐1‐pyrenylalanine
Authors: MIHARA HISAKAZU , LEE SANNAMU , SHIMOHIGASHI YASUYUKI , AOYAGI HARUHIKO , KATO TETSUO , IZUMIYA NOBUO , COSTA TOMMASO
Published: August 2010

The novel fluorescent amino acid,l‐1‐pyrenylalanine (l‐Pya), was prepared by the asymmetric hydrogenation of cyclic dehydrodipeptide. Fluorescent enkephalins containing one or two Pya residues at position 1, 4 or 5 of [d‐Ala2, Leu5]enkephalin were synthesized by the solution method. Mono‐Pya‐enkephalins showed strong fluorescence intensities and potent binding affinities with specificity and selectivity for opiate receptors. However, di‐Pya‐enkephalins showed markedly decreased receptor binding affinities. These results indicate that the incorporation of two Pya residues into enkephalin makes the peptide unable to interact with the opiate receptors, although introduction of one Pya residue is effective to elicit a specific receptor interaction. Di‐Pya‐enkephalins showed intramolecular excimer spectra, indicating that the peptides are able to take possible folded conformations.
Synthesis and enzymic hydrolysis of cyclic peptides containing an anthranilic acid residue
Authors: MAZALEYRAT JEAN‐PAUL , REBOUD‐RAVAUX MICHÈLE , WAKSELMAN MICHEL
Published: August 2010

Two cyclic peptides cyclo (Phe‐MeAnt‐Glyn) with MeAnt = 5‐methyl‐anthranilic acid residue, n = 4 (3b) and n = 6 (4b), have been synthesized in solution and their reaction with α‐chymotrypsin analyzed. The polyglycyl chain was prepared by the phosphazo method; cyclization at the Gly‐Phe site occurred in good yield using the azide method. Catalysis of the hydrolysis of peptides 3b and 4b by α‐chymotrypsin was characterized at 37° by the apparent second‐order rate constants kcat/Km 0.12 and 1.15 m‐1 s‐1, respectively, in agreement with the usual acceleration observed upon enlargement of the size of the peptidic ring in cyclic peptides. α‐Chymotrypsin specifically split the Phe‐MeAnt amide bond in cyclopeptide 4b. This specific orientation suggests that analogous structures with a functionalized methylene group instead of the methyl substituent can be used in the design of suicide substrates for serine proteases.
Amino acids and peptides. XVIII. Dipeptide formation during the synthesis of Z‐Asp(OBzl)‐OH
Authors: IGUCHI SHIN , KAWASAKI KOICHI , OKADA YOSHIO
Published: August 2010

During the benzyloxycarbonylation of H‐Asp(OBzl)‐OH by the Schotten‐Bauman reaction with benzyloxycarbonyl chloride in the presence of NaHCO3 or Na2CO3, besides Z‐Asp(OBzl)‐OH, Z‐Asp(OBzl)‐Asp(OBzl)‐OH was formed as side product, although the extent of the dipeptide formation differed depending on the base used (10% and 20% respectively). It was found that melting point, rotation value and Rf values upon thin‐layer chromatography of Z‐Asp(OBzl)‐Asp(OBzl)‐OH were quite similar to those of Z‐Asp(OBzl)‐OH.
Stereochemistry of collagen*
Authors: RAMACHANDRAN G.N.
Published: August 2010

This review article, based on a lecture delivered in Madras in 1985, is an account of the author's experience in the working out of the molecular structure and conformation of the collagen triple‐helix over the years 1952–78. It starts with the first proposal of the correct triple‐helix in 1954, but with three residues per turn, which was later refined in 1955 into a coiled‐coil structure with approximately 3.3 residues per turn. The structure readily fitted proline and hydroxyproline residues and required glycine as every third residue in each of the three chains. The controversy regarding the number of hydrogen bonds per tripeptide could not be resolved by X‐ray diffraction or energy minimization, but physicochemical data, obtained in other laboratories during 1961–65, strongly pointed to two hydrogen bonds, as suggested by the author. However, it was felt that the structure with one straight NH … O bond was better. A reconciliation of the two was obtained in Chicago in 1968, by showing that the second hydrogen bond is via a water molecule, which makes it weaker, as found in the physicochemical studies mentioned above. This water molecule was also shown, in 1973, to take part in further cross‐linking hydrogen bonds with the OH group of hydroxyproline, which occurred always in the location previous to glycine, and is at the right distance from the water. Thus, almost all features of the primary structure, X‐ray pattern, optical and hydrodynamic data, and the role of hydroxyproline in stabilising the triple helical structure, have been satisfactorily accounted for. These also lead to a confirmation of Pauling's theory that vitamin C improves immunity to diseases, as explained in the last section.
Study of the conformation of cyclosporine in aqueous medium by means of monoclonal antibodies
Authors: QUESNIAUX VALÉRIE F.J. , WENGER ROLAND M. , SCHMITTER DORIS , VAN REGENMORTEL MARC H.V.
Published: August 2010

The three‐dimensional structure of the immunosuppressive cyclic peptide cyclosporine (Cs), determined in crystal by X‐ray analysis and in solution in aprotic solvents by n.m.r., differs mainly by the orientation of the 7 carbon side chain of residue 1. Because of its poor solubility in water, the conformation of Cs in aqueous medium cannot be studied by n.m.r. methods, which require concentrations of the substance of the order of milligram/mL but can be analyzed by immunochemical methods in which concentrations in the nanogram/mL range are detected. In the present study, the ability of a series of monoclonal antibodies (McAbs) raised against Cs to recognize different parts of residue 1 of Cs was determined from the cross‐reactivity of different Cs‐analogues modified in residue 1. The results show that when Cs is dissolved in aqueous buffer, the terminal atoms of residue 1 side chain are not available for binding to antibodies recognizing the face of the molecule defined by residues 1, 2, 3, 10, 11, suggesting that the chain is probably folded back under the molecule, as observed in the crystal structure. Binding of McAbs to Cs was also affected by conformational modifications of the peptide ring that occur in some Cs‐analogues. The results illustrate the potential of McAbs for probing the conformation of Cs‐derivatives for which no structural data are available.
Isolation and characterization of growth hormone from blue fox pituitary glands
Authors: LI CHOH HAO , CHUNG DAVID , IZDEBSKI JAN , MAJEWSKI TADEUSZ , MOWLES THOMAS F.
Published: August 2010

Growth hormone has been purified to homogeneity from blue fox pituitary glands. It has 191 amino acids with two disulfide bridges and a single tryptophan residue. The somatotropin activity is only 8% when compared with the bovine hormone in the receptor‐binding assay. From radioimmunoassay data using baboon antisera to porcine or bovine growth hormone, the fox hormone has 14–17% immunoreactivity of bovine or porcine hormone.
Solid‐phase synthesis of a nonadecapeptide coded for by the v‐myb oncogene
Authors: KRCHŇÁK VIKTOR , MALÝ ANTONÍN , FLEGEL MARTIN
Published: August 2010

A nonadecapeptide comprising a predicted B‐cell determinant from the v‐myb oncoprotein was synthesized by Merrifield's solid‐phase method. Hydrogen chloride in dichloromethane was used for protective t‐butyloxycarbonyl group removal; the deprotection was monitored using a new qualitative deprotection test. The nonadecapeptide coupled to a carrier elicited a high titre of protein‐reactive antipeptide antibodies.
Configuration and conformation of a cyclopropane peptide
Authors: VARUGHESE K.I. , WANG C.H. , KIMURA H. , STAMMER C.H.
Published: August 2010

The absolute configuration of the cyclopropane phenylalanine moiety in N‐benzyloxycarbonyl‐(+)‐E‐cyclopropane‐phenylalanyl‐l‐leucine methyl ester (Z‐(+)‐▿EPhe‐Leu‐OMe) has been determined by X‐ray crystallographic methods. The conformation of the cyclopropane amino acid and its effect on the peptide is also discussed. The peptide crystallizes in the monoclinic space group P2, and the structure was solved using MULTAN and refined by block diagonal least‐squares to a present R value of 11 %. The absolute configuration of the (+)‐▿EPhe residue is seen to be 2R, 3S.
Chain reversals in model peptides: studies of cystine‐containing cyclic peptides II. Effects of valyl residues and possible i‐to‐(i + 3) attractive ionic interactions on cyclization of [Cys1], [Cys6] hexapeptides
Authors: MILBURN P.J. , MEINWALD Y.C. , TAKAHASHI S. , OOI T. , SCHERAGA H.A.
Published: August 2010

The synthesis of four N‐acetyl N′‐methylamide cystine‐containing hexapeptides, CVPGVC, CGVVGC, CKPGEC, and CEPGKC, is described. These were used in disulfide‐exchange reactions with the peptide CVPGGC as the formal oxidant. The relative propensities for peptide cyclization were thus deduced, and the tendency toward the formation of chain‐reversal conformations was established quantitatively. An additional peptide, CVVVVC, was prepared but was never obtained as the cyclic monomer, demonstrating that the formation of chain‐reversals in this peptide was of very low probability. Incorporation of pairs of valyl residues decreased the ease of cyclization, but it appeared that conformational flexibility in the cystine‐containing hexapeptides may have compensated for substitutions which would have been expected to hinder the adoption of certain β‐turn conformations. The peptides containing ionic residues were cyclized more readily than expected, and this process was relatively insensitive to salt concentration. This observation is discussed with regard to the stabilization of β‐turns by i‐to‐(i + 3) ionic interactions in peptides and proteins. A method for blocking thiols was introduced as an improvement in the analysis of the equilibrium mixtures.
Novel method for monitoring the coupling efficiency in solid phase peptide synthesis*
Authors: REDDY M.P. , VOELKER P.J.
Published: August 2010

The method reported here involves tritylation of the uncoupled amino groups with an active tritylating agent generated in situ from 4,4′‐dimethoxytrityl chloride and tetra‐n‐butylammonium perchlorate, and subsequent release of the trityl cation under mild acid treatment. Spectrophotometric measurement of the trityl color determines the coupling yield. This approach has been successfully tested by synthesizing an octapeptide. Some of the advantages of this method are pointed out.
Polypeptide fluoroacetate derivatives Synthesis and 19F n.m.r.
Authors: KURTH MARK J. , GREEN CARTER B. , MOUNT MICHAEL E. , JACKSON DAVID Y.
Published: August 2010

The synthesis and characterization of monofluoroacetyl (MFAc) functionalized haptens are described. These were covalently bound to polypeptide carriers (bovine serum albumin and poly‐d‐lysine) by primary amine/succinimide ester or primary amine/acid chloride coupling. Epitopic densities of the resulting antigens were determined by both 19F n.m.r. and picryl sulfonic acid assays. 19F n.m.r. experiments defining the stability of MFAc ester and amide linkages as a function of media (including in vitro), time, and temperature are presented. These results indicate that MFAc functionalized antigens are well suited for further immunologic studies.
Racemization of acylamino acids and the carboxy‐terminal residue of peptides
Authors: CHEN FRANCIS M.F. , BENOITON N. LEO
Published: August 2010

Enantiomeric N‐acetyl‐, N‐benzoyl‐. and N‐benzyloxycarbonylglycyl‐amino acids have been transformed into their racemates by conversion of the acids into their 2.4‐dialkyl‐5(4H)‐oxazolones through the mixed anhydrides in tetrahydrofuran followed by N‐methylpiperidine‐catalyzed racemization of the oxuzolone and subsequent hydrolysis by aqueous acid, all at room temperature.
Proline‐containing β‐turns
Authors: ANANTHANARAYANAN V.S. , CAMERON T.S.
Published: August 2010

The conformations of the dipeptide t‐Boc‐Pro‐dAla‐OH and the tripeptide tBoc‐Pro‐dAla‐Ala‐OH have been determined in the crystalline state by X‐ray diffraction and in solution by CD, n.m.r. and i.r. techniques. The unit cell of the dipeptide crystal contains two independent molecules connected by intermolecular hydrogen bonds. The urethane‐proline peptide bond is in the cis orientation in both the molecular forms while the peptide bond between Pro and dAla is in the trans orientation. The single dipeptide molecule exhibits a “bent” structure which approximates to a partial β‐turn. The tripeptide adopts the 4 → 1 hydrogen‐bonded type II β‐turn with all trans peptide bonds. In solution, the CD and i.r. data on the dipeptide indicate an ordered conformation with an intramolecular hydrogen bond. N.m.r. data indicate a significant proportion of the conformer with a trans orientation at the urethane‐proline peptide bond. The temperature coefficient of the amide proton of this conformer in DMSO‐d6 points to a 3 → 1 intramolecular hydrogen bond. Taken together, the data on the dipeptide in solution indicate the presence (in addition to the cis conformer) of a C7 conformation which is absent in the crystalline state. The spectral data on the tripeptide indicate the presence of the type II β‐turn in solution in addition to the nonhydrogen‐bonded conformer with the cis peptide bond between the urethane and proline residues. The relevance of these data to studies on the substrate specificity of collagen prolylhydroxylase is pointed out.
Synthesis of somatostatin analogs resistant to the action of trypsin
Authors: ALLEN MARK C. , WADE ROY
Published: August 2010

The synthesis of a series of octapeptides based on the somatostatin analog cyclo(‐Asn‐Phe‐Phe‐d‐Trp‐Lys‐Thr‐Phe‐Gaba‐) containing the substitutions [Aap9], [d‐Lys9], [l‐Trp8, d‐Lys9], [l‐Orn9] and [d‐aThr10] is reported. The analogs were designed and have been shown to inhibit proteolysis at the proposed (1) primary cleavage site between Lys9‐Thr10 and thereby increase their stability to enzymic attack.
Conformational modification of the PRP‐hexapeptide by a direct covalent attachment of aromatic side chain groups
Authors: SZEWCZUK ZBIGNIEW , KUBIK ALEKSANDRA , SIEMION IGNACY Z. , WIECZOREK ZBIGNIEW , SPIEGEL KRYSTYNA , ZIMECKI MICHAL , JANUSZ MARIA , LISOWSKI† JÓZEF
Published: August 2010

PRP‐hexapeptide possessing the azo‐bridge between Tyr1 and Phe5 residues, called azo‐PRP‐hexapeptide: Tyr‐Val‐Pro‐Leu‐Phe‐Pro, was synthesized and tested for immunoregulatory activity. High biological activity of the synthesized azo‐PRP‐hexapeptide suggests that the biologically active conformation of PRP‐hexapeptide must be such that both aromatic rings (Tyr and Phe) are apparently close to each other.
Malaria invasion of human erythrocytes
Authors: LACOMBE J.M. , FERRARI B. , ANDRIAMANANPISOA R. , PAVIA A.A.
Published: August 2010

The objective of this study was to determine whether a nonglycosylated portion of glycophorin A (GPA), the main erythrocyte membrane glycoprotein, was involved in the process of invasion of red blood cells (RBC) by merozoites of Plasmodium falciparum, a parasite responsible for the most severe form of malaria. A series of peptides covering the sequence 55‐76 situated upstream from the intramembraneous hydrophobic region of GPA was synthesized by an active ester coupling strategy and assessed for invasion‐blocking capacity by using an in vitro assay system. Tests showed peptide 65‐69, Ala‐His‐His‐Phe‐Ser, to be a good inhibitor of the invasion of RBC. Results presented here provide a confirmation of the existence of parasite binding sites on the peptide domain of GPA. Furthermore, comparison of inhibitory activity with peptide composition allowed us to rule out any contribution of a toxic parameter related to hydrophobicity as reported earlier.
N.m.r. analyses of the histidine microenvironments in a human salivary proline‐rich glycoprotein
Authors: LOOMIS RONALD E. , TSENG CHING‐CHUNG , LEVINE MICHAEL J.
Published: August 2010

The pKa's of the three histidine residues in a proline‐rich glycoprotein from human parotid saliva (PRG) were determined by 360 MHz proton n.m.r. spectroscopy. The addition of calcium (0.64 mm) caused drops in the pKa's of all three histidines by ∼0.25 units. When imidazole and cyclo(l‐histidine‐l‐proline) were used as model compounds, corresponding concentrations of calcium had no effect on their pKa's. Also, the model compounds gave absolute pKa values in good agreement with similar chemical species reported in the literature. Exchange lifetime data and previously reported hydrogen → deuterium exchange experiments suggest that the PRG histidine NtH protons are not involved in hydrogen‐bonds. Collectively, these data imply that changes in PRG conformation occur upon the addition of calcium.
New N‐terminal modified proctolin analogues
Authors: KONOPIŃSKA DANUTA , ROSIŃSKI GRZEGORZ , LESICKI ANDRZEJ , SUJAK PRZEMYSŁAW , SOBÓTKA WIESŁAW , BARTOSZ‐BECHOWSKI HUBERT
Published: August 2010

Five proctolin analogues modified in position 1 of the peptide chain by Cit (I), Lys (II), His (III), Phe(p‐NH2) (IV) and γ‐Abu (V) were synthesized by conventional liquid phase method. Biological activity of the obtained peptides was investigated by the cardioexcitatory test on two insect species, cockroach, Periplaneta americana L. and yellow mealworm, Tenebrio molitor L.
[d‐Met2, Pro5] enkephalin [N1.5‐β‐d‐glucopyranosyl] amide: a glycosylpeptide with high antinociceptive activity
Authors: TORRES JOSEP L. , REIG FRANCESCA , VALENCIA GREGORIO , RODRÍGUEZ RAQUEL E. , GARCÍA‐ANTÓN JOSÉ M.
Published: August 2010

Different synthetic strategies have been attempted for the synthesis of a glycosylpeptide resulting from the covalent bonding of a sugar residue to the C‐terminal carboxyl group of an enkephalin related pentapeptide. The final structure is: Tyr‐d‐Met‐Gly‐Phe‐Pro [N15‐β‐d‐glucopyranosyl] amide. The in vitro potency on the GPI test of this analogue was IC50= 64.0 nm. However, its antinociceptive activity by tail immersion tests, after intraperitoneal administration, was 2000 and 200 times higher than morphine in rats and mice, respectively.
1H‐n.m.r. studies on the specificity of the interaction between bovine pancreatic ribonuclease A and dideoxynucleoside monophosphates
Authors: ALONSO JULI , PAOLILLO LIVIO , D'AURIA GABRIELLA , NOGUÉS M. VICTÒRIA , CUCHILLO CLAUDI M.
Published: August 2010

The titration curves of the C‐2 histidine protons of bovine pancreatic ribonuclease A in the presence of several dideoxynucleoside monophosphates (dNpdN) were studied by means of proton nuclear magnetic resonance at 270 MHz in order to obtain information on the ligand — RNase A interaction. The changes in the chemical shift and pKs of the C‐2 proton resonances of His‐12, ‐48, ‐119 in the complexes RNase A — dNpdN were smaller than those previously found when the enzyme interacted with mononucleotides. The pK2of His‐12 was not affected by the interaction of the enzyme with these ligands, whereas, the perturbation of the pK2of His‐119 was clearly dependent on the nature of the ligand. If there is a pyrimidine nucleoside at the 3′ side of the dideoxynucleoside monophosphates, as in TpdA and TpT, an enhancement due to the well known interaction of the phosphate in p1, the catalytic site, was found. However, when there is a purine nucleoside, as in dApT and dApdA, a decrease in the pK2value was observed and we propose that in such cases the phosphate group interacts in a secondary phosphate binding site, p2. The results obtained suggest the existence of different specific interactions depending on the structure of the dideoxynucleoside monophosphate studied.
Synthesis of 17O isotope labeled Leu‐enkephalin and 17O n.m.r.*
Authors: PONNUSAMY E. , ECKERT H. , FIAT D.
Published: August 2010

Oxygen‐17 isotope was introduced into the α‐carboxyl group of glycine, 1‐phenylalanine, 1‐leucine and 1‐tyrosine by acid catalyzed exchange of 17O from H217O or by acid hydrolysis of respective amino acid methyl esters in H217O. Quantitative enrichment of glycine was achieved by acid hydrolysis of amino acetonitrile in H217O. For α‐amino protection in amino acids t‐butoxycarbonyl (Boc) group was employed for 17O labeled enkephalin synthesis. Five analogues of Leu‐enkephalins (I–V) labeled with 17O at different amino acid residues were synthesized by solid phase method. 17O n.m.r. spectra were measured at 24.4 and 67.8 MHz for Leu‐enkephalins 17O labeled at Gly2 and Phe4 positions. A downfield shift was observed for 17O labeled Gly2 Leu‐enkephalin upon heating. This shift is indicative of the rupture of intramolecular hydrogen bonds. The preliminary results confirm the hypothesis that an intramolecular hydrogen bond exists between the carbonyl group of Gly2 and NH group of Leu5.
Continuous fluorogenic substrates for atrial dipeptidyl carboxyhydrolase
Authors: SOLER DULCE F. , HARRIS ROBERT B.
Published: August 2010

Several N‐acyltetrapeptides of the general structure 2‐aminobenzoyl‐Gly‐X‐Phe(4‐nitro)‐Arg were synthesized and tested as substrates for atrial dipeptidyl carboxyhydrolase, an enzyme associated with atrial granules that converts one active atrial natriuretic peptide, atriopeptin II, to another, atriopeptin I. Hydrolysis of the X‐Phe(4‐nitro) bond generates the 2‐aminobenzoyl fluorophore and the increasing fluorescence can be monitored in a continuous assay. Based on the ratio of Vmax/Km as an indication of substrate specificity, peptides containing X = Ser > Ala ≅ Lys‐ > Asn ≫ Thr ≅ Asp. With the exception of the Asn substrate, the Km determined for all the substrates was about the same. Thus, the effect of the P1 residue substitution shows up almost exclusively in Vmax.
Controlled peptide‐protein conjugation by means of 3‐nitro‐2‐pyridinesulfenyl protection‐activation
Authors: DRIJFHOUT J.W. , PERDIJK E.W. , WEIJER W.J. , BLOEMHOFF W.
Published: August 2010

The disulfide bond in S‐3‐nitro‐2‐pyridinesulfenyl (S‐Npys) compounds is stable towards the acid treatment used in solid‐phase peptide synthesis, yet the lability of S‐Npys‐peptides towards nucleophiles enables the conjugation to proteins to proceed under mild conditions. Thus Boc‐Cys(Npys)‐OH was coupled as N‐terminal residue to a resin‐linked peptide chain. After deprotection and cleavage from the resin the Npys‐cysteinylpeptide was attached to a properly functionalized protein by reaction with a mercapto group. The amount of peptide conjugated to the protein was determined by measuring the amount of 3‐nitro‐2‐thiopyridone liberated. The cysteinylpeptide which was detached from the protein by reduction of the disulfide bond was shown to be identical with the product obtained by reduction of the Npys‐cysteinylpeptide.
Crystal molecular structures of two tripeptides related to the sequence coding for N‐glycosylation
Authors: PICHON‐PESME VIRGINIE , AUBRY ANDRÉ , ABBADI ABDELILAH , BOUSSARD GUY , MARRAUD MICHEL
Published: August 2010

The crystal structures of two tripeptides related to the sequence coding for N‐glycosylation of peptides have been solved: Boc‐Asn(Me)‐Ala‐Ser‐OMe, 1, and Boc‐Asn(Me)‐Pro‐Ser‐NHMe, 2. Both molecules contain an “Asx‐turn” characterized by a hydrogen bond between the Ser‐NH and Asn‐CγOγ sites. Moreover, the Pro‐Ser sequence is βI‐folded in 2. The Ser hydroxyl group is also intramolecularly hydrogen‐bonded in both molecules, but two different hydrogen bondings are observed. In 1, the Ser‐Oγ H bond interacts with the Asn‐CγOγ carbonyl, in good agreement with one of the mechanisms which have been proposed for the N‐glycosylation of peptides. In 2, the Ser‐OγH bond turns out to be involved in an intra‐residue interaction with Ser‐C'O, and this conformational change is essentially the consequence of chemically different C‐terminus functions.
Secondary structure prediction of 11 mammalian growth hormones
Authors: ERMÁCORA M.R. , RIVERO J.L.
Published: August 2010

The secondary structure of 11 mammalian growth hormones has been predicted by combining five different methods. Three long helical regions located around residues 20, 120, and 170 constitute the most prominent common feature in the species studied. The strong amphiphilic character of these helices suggests that they can play an important role in protein folding or stability.
Synthesis and conformational study in solution and in solid state of oligopeptides containing l‐leucine and glycine
Authors: D'ALAGNI MARIA , MANIGRASSO MAURIZIO
Published: August 2010

The synthesis and conformational studies of the oligopeptide N‐tert.‐butyloxycarbonyl‐l‐Leu‐(l‐Leu‐Gly)n‐OBzl (n = 1, 3, 5) and N‐tert.‐butyloxycarbonyl‐(l‐Leu‐Gly)2‐OBzl are described. The peptides were synthesized by stepwise and fragment condensation techniques using dicyclohexylcarbodiimide as the condensing agent in solution. The conformational study of the oligopeptides was carried out using CD, u.v. and i.r. spectra. The conformation in solution was examined in trifluoroethanol, hexafluoroisopropanol. hexafluoroacetone trihydrate, and methanol. CD spectra in trifluoroethanol exhibited a gradual variation with increasing peptide chain length. This can be interpreted as a formation of an ordered structure which is already present in the heptapeptide and, to a greater extent, in the undecapeptide. The results obtained from the CD profiles and i.r. spectra showed the presence of β structure with antiparallel chains in the heptapeptide and undecapeptide. Finally, CD spectra revealed in trifluoroethanol‐water solution the binding of Ca2+ to heptapeptide and undecapeptide together with a contemporaneous conformational change. This change is probably due to the formation of β‐turns. No change in the CD profiles was obtained by using Mg2+, K+, Na+, and Li+ ions instead of Ca2+.
Amino acid side chain parameters for correlation studies in biology and pharmacology
Authors: FAUCHÈRE JEAN‐LUC , CHARTON MARVIN , KIER LEMONT B. , VERLOOP ARIE , PLISKA VLADIMIR
Published: August 2010

Fifteen physicochemical descriptors of side chains of the 20 natural and of 26 non‐coded amino acids are compiled and simple methods for their evaluation described. The relevance of these parameters to account for hydrophobic, steric, and electric properties of the side chains is assessed and their intercorrelation analyzed. It is shown that three principal components, one steric, one bulk, and one electric (electronic), account for 66% of the total variance in the available set. These parameters may prove to be useful for correlation studies in series of bioactive peptide analogues.
Conformationally stabilized gramicidin S analog containing dehydrophenylalanine in place of d‐phenylalanine4,4′
Authors: IMAZU SACHIKO , SHIMOHIGASHI YASUYUKI , KODAMA HIROAKI , SAKAGUCHI KAZUYASU , WAKI MICHINORI , KATO TETSUO , IZUMIYA NOBUO
Published: August 2010

Unsaturated gramicidin S analog, [ΔPhe4,4′]gramicidin S, was synthesized by conventional solution method in order to evaluate the role of the dehydrophenylalanine residues replacing d‐phenylalanine4,4′ in stabilizing the bioactive β‐shect conformation. The dehydrophenylalanine (ΔPhe) moiety was introduced by dehydroazlactonization of the β‐phenylserine residue. The [ΔPhe4,4′]gramicidin S prepared by this method showed very strong antimicrobial activities against Gram‐positive bacteria, but not against Gram‐negative ones. Several lines of spectroscopic evidence indicated that [ΔPhe4,4′] gramicidin S has a reinforced β‐sheet backbone conformation necessary for a full biological activity of gramicidin S. These results suggested that :α,β‐dehydrogenation of the amino acid residue in a cyclic peptide can stabilize the turn structure.
Synthesis of the bis‐cystinyl‐fragment 225‐232/225′‐232’ of the human IgGl hinge region
Authors: WÜNSCH E. , MORODER L. , GÖHRING‐ROMANI S. , MUSIOL H.‐J. , GÖHRING W. , BOVERMANN G.
Published: August 2010

In human IgGl the two heavy chains are crosslinked in the central portion of the molecule by two disulfide bridges forming a double chain bis‐cystinyl cyclic peptide in parallel alignment. For our synthetic studies we have chosen the sequence portion 225–232/225′‐232′. i.e. [H‐Thr‐Cys‐Pro‐Pro‐Cys‐Pro‐Ala‐Pro‐OH]2. By the use of a combination of the S‐tert.‐butylthio and the S‐acetamidomethyl groups selective cysteine pairings in two successive steps produced the hinge hexadecapeptide in parallel and antiparallel alignment as homogeneous and well characterized compounds. Thiol disulfide interchange experiments on the antiparallel dimer led to over 90% conversion to the parallel isomer. Similarly random air‐oxidation was found to generate again mainly the parallel dimer, thus strongly suggesting that this sequence portion contains sufficient structural information for a correct assembly of the two heavy chains of immunoglobulins without decisive contribution of a protein disulfide isomerase.
New antagonists of LHRH II. Inhibition and potentiation of LHRH by closely related analogues
Authors: BAJUSZ SANDOR , CSERNUS VALER J. , JANAKY TAMAS , BOKSER LAZARO , FEKETE MATYAS , SCHALLY ANDREW V.
Published: August 2010

Modifications of the previously described LHRH antagonists, [Ac‐d‐Nal(2)1,d‐Phe(4Cl)2,d‐Trp3,d‐Cit6,d‐Ala10]LHRH and the correspondingd‐Hci6analogue, have been made to alter the hydrophobicity of theN‐terminal acetyl‐tripeptide portion. Substitution ofd‐Trp3with the less hydrophobicd‐Pal(3) had only marginal effects on the antagonistic activities and receptor binding potencies of thed‐Cit/d‐Hci6analogues, but it appeared to further improve the toxicity lowering effect ofd‐Cit/d‐Hci6substitution. Antagonists containingd‐Pal(3)3andd‐Cit/d‐Hci6residues, i.e. [Ac‐d‐Nal(2)1,d‐Phe(4Cl)2,d‐Pal(3)3d‐Cit6,d‐Ala10]LHRH (SB‐75) and [Ac‐d‐Nal(2)1,d‐Phe(4Cl)2,d‐Pal(3)3,d‐Hci6,d‐Ala10]LHRH (SB‐88), were completely free of the toxic effects, such as cyanosis and respiratory depression leading to death, which have been observed in rats with thed‐Trp3,d‐Arg6antagonist and related antagonists. Replacement of theN‐acetyl group with the hydrophilic carbamoyl group caused a slight decrease in antagonistic activities, particularlyin vitro.Introduction of urethane type acyl group such as methoxycarbonyl (Moc) or t‐butoxycarbonyl (Boc) led to analogues that showed LHRH‐potentiating effect. The increase in potency induced by these analogues, e.g. [Moc‐d‐Nal(2)1,d‐Phe(4Cl)2,d‐Trp3,d‐Cit6,d‐Ala10]LHRH and [Boc‐d‐Phe1,d‐Phe(4Cl)2,d‐Pal(3)3,d‐Cit6,d‐Ala10]LHRH, was 170‐260% and persisted for more than 2 h when studied in a superfused rat pituitary system.
Importance of the C‐terminal α‐helical structure for glucagon's biological activity
Authors: KRSTENANSKY JOHN L. , ZECHEL CHRISTIAN , TRIVEDI DEV , HRUBY VICTOR J.
Published: August 2010

The synthetic glucagon analogues [Glu21]glucagon, 2, and [Lys17.18.Glu21]glucagon, 3, were designed using Chou‐Fasman calculations for the purpose of enhancing the probability for the formation of a C‐terminal amphipathic α‐helical conformation. Circular dichroism indicates increased α‐helical content for these analogues in solution relative to glucagon. Analogues 2 and 3 also exhibit a 3‐fold and 5‐fold increase in receptor binding potency, respectively. The adenylate cyclase stimulating potencies of 2 and 3 relative to glucagon are 2.1 and 7 times greater, respectively. Attempts were made at further α‐helical enhancement by further substitutions in the 10–13 region of glucagon. as represented by the glucagon analogues [Phe13,Lys17.18 Glu21]glucagon, 4, and [Phe10.13, Lys17.18,Glu21]glucagon. 5. These latter substitutions resulted in lowered receptor binding and adenylate cyclase potencies for 4 and 5 relative to 3 despite increased α‐helical content in solution as observed by circular dichroism spectroscopy.
Synthesis and biological evaluation of pNPY fragments
Authors: DANHO WALEED , TRISCARI JOSEPH , VINCENT GEORGE , NAKAJIMA TOHRU , TAYLOR JOHN , KAISER E.T.
Published: August 2010

Peptide fragments of pNPY corresponding to the C'‐terminal segments (13‐36) and (25‐36). the N‐terminal segments (1‐12) and (1‐24), the segments (6‐14) and (7‐20), which contain a putative β‐turn, and the internal segments (13‐24) and (20‐30) were synthesized using solid phase methodology. These fragments were assayed for NPY receptor binding activity in the rat hypothalamus membrane preparation, enhancement of food intake in the rat following ivt administration and inhibition of electrically stimulated muscle contraction in the rat vas deferens. Only the C‐terminal fragment (13‐36) retained some of the activities of pNPY, appearing to act as a weak agonist, having an additive effect with pNPY on the inhibition of muscle contraction and prolonging the duration of action of pNPY in the feeding assay. It also had considerable α‐helical character, as did pNPY. None of the other peptide fragments had any agonist or antagonist activity. These results suggest that the expression of full biological NPY activity requires both the C‐ and the N‐terminal segments as well as a putative amphiphilic α‐helical segment (14‐31).
Synthesis and disulfide structure determination of porcine endothelin: an endothelium‐derived vasoconstricting peptide
Authors: KUMAGAYE SHIN‐ICHIROH , KURODA HISAYA , NAKAJIMA KIICHIRO , WATANABE TAKUSHI X. , KIMURA TERUTOSHI , MASAKI TOMOH , SAKAKIBARA SHUMPEI
Published: August 2010

All disulfide analogs (types A, B and C) of porcine or human endothelin, a 21‐amino acid peptide having two intramolecular disulfide bonds, were synthesized and their retention times on HPLC were compared with that of natural endothelin. One of the analogs (type A) having disulfide bonds between positions 1 and 15 and between 3 and 11 was found to be identical with natural endothelin. Random oxidation of fully reduced endothelin formed a mixture of type A and B in a ratio of 3:1, with almost none of type C, which has disulfide bonds between positions 1 and 3 and between 11 and 15. Type A endothelin was also synthesized by the segment condensation procedure in solution applying our maximum protection strategy. This product was found to have full vasoconstricting activity in rat pulmonary artery ring preparations; the potency was as high as that of the natural product.
Conformational effects of chiral α,α‐dialkyl amino acids I.C‐Terminal tetrapeptides of emerimicin containing α‐ethylalanine
Authors: MARSHALL GARLAND R. , CLARK JOHN D. , DUNBAR JAMES B. , SMITH G. DAVID , ZABROCKI JANUSZ , REDLINSKI ADAM S. , LEPLAWY MIROSLAW T.
Published: August 2010

The syntheses and the crystal structures of theC‐terminal tetrapeptide fragments of emerimicin IV and III, Boc‐r‐EtA‐Hyp(Bzl)‐Ala‐Phol and Boc‐r‐EtA‐Hyp(Bzl)‐MeA‐Phol, containing the chiral α,α‐dialkyl amino acid,r‐α‐ethylalanine (r‐EtA) are reported. The two peptides are isomorphous and assume a 310‐helical conformation in the crystal. A comparison of the crystal data on α,α‐dialkyl amino acids indicates that alkyl substituents larger than a methyl group do not preclude peptides containing these amino acids from assuming the conformations associated with minima which have been well characterized for α‐methylalanine.
Macrocyclic peptides II. Synthesis and structure of a novel dipeptide, (2S,3′S)‐2‐(2′‐oxo‐3′‐methylpiperazin‐1′‐yl)‐propanoic acid, and its use as the unit of cyclic peptides
Authors: YAMASHITA TETSUSHI , KOJIMA YOSHITANE , HIROTSU KEN , OHSUKA AKIO
Published: August 2010

A new cyclic compound [(2S,3′S)‐2‐(2′‐oxo‐3′‐methylpiperazin‐1′‐yl)‐propanoic acid] obtained using (2S,7S)‐2,7‐dimethyl‐3,6‐diazaoctanedioic acid as a starting material was derived from N‐t‐butyloxycarbonyl‐(2S,3′S)‐2‐(2′‐oxo‐3′‐methylpiperazin‐1′‐yl)‐propanoic acid in order to determine the molecular structure by X‐ray crystal analysis. Two new macrocyclic peptides were prepared using the above cyclic compound and sarcosine as peptide units.