bluuebunny/crossref_metadata_2025 huggingface dataset:
The pseudo‐βI‐turn
Authors: KESSLER H. , MATTER H. , GEMMECKER G. , DIEHL H.‐J. , ISERNIA C. , MRONGA S.
Published: August 2010

Synthesis and conformational analysis of three cyclic hexapeptides cyclo(‐Gly1‐Pro2‐Phe3‐Val4‐Xra5‐Phe6), Xaa= Phe (I), D‐Phe (II) and D‐Pro (III), were carried out to examine the influence of proline on the formation of reverse turns and the dynamics of hydrophobic peptide regions. Assignment of all 1H and 13C resonances was achieved by homo‐ and heteronuclear 2D‐NMR techniques (TOCSY, ROESY, HMQC, HMQC‐TOCSY and HMBCS‐270). The conformational analysis is based on interproton distances derived from ROESY spectra and homo‐ and heteronuclear coupling constants (E.COSY, HETLOC and HMBCS‐270). For structural refinements restrained molecular dynamics (MD) simulations in vacuo and in DMSO were performed.

Each peptide exhibits two conformations in DMSO solution due to cis‐trans isomerism about the Gly‐Pro peptide bond. Surprisingly the cis‐Gly‐Pro segment in the minor isomers is not involved in a βVI‐turn, but forms a turn structure with cis‐Gly‐Pro in the i and i+ 1 positions. Although no stabilizing hydrogen bond is found in this turn, the φ and ψ‐angles closely correspond to a βI‐turn [Pro2:φ(i+ 1) ‐60°, ψ(i+ 1) ‐30° Phe3: φ(i+ 2) ‐100°, ψ(i+ 2) ‐50°]. Hence we call this structural element a pseudo‐βI‐turn.

As expected, in the dominating all‐trans isomers proline occupies the i+ 1 position of a standard βI‐turn. Therefore, cis‐trans isomerization of the Gly1‐Pro2 amide bond only induces a local conformational rearrangement, with minor structural changes in other parts of the molecule. However, the geometry of the other regions is affected by the chirality of the i+ 1 amino acid for both isomers (βI for Phe5, βII′ for D‐Phe5 or D‐Prp5).
Binding of enkephalin/dextran conjugates to opioid receptors
Authors: SASAKI‐YAGI YOSHIKO , KIMURA SHUNSAKU , UEDA HIROSHI , IMANISHI YUKIO
Published: August 2010

[ala2]Enkephalin molecules were connected to dextran, and the affinities of the enkephalin/dextran conjugates for opioid receptors were studied. Two kinds of enkephalin derivatives, YaGFLGK‐NH2and YaGFLGS′S′PS′S′PS′KP‐OMe (S'represents a Sar residue) were prepared. They retained the high affinity of the enkephalin unit toward opioid receptors. On the other hand, receptor affinity of the enkephalin derivative dextran conjugates became lower than that of the enkephalin derivatives. Fluorescence from the Tyr residue of the conjugates in a buffer solution was less quenched by succinimide than that of the enkephalin derivatives. Therefore, in these conjugates, the binding of the enkephalin moieties to receptors should be hindered by a steric effect of the dextran matrix. However, the receptor affinity (as defined on the basis of an enkephalin unit) increased on increasing the amount of enkephalin units connected to the dextran matrix, especially in the case of the connection through a shorter spacer arm, suggesting simultaneous binding to a few receptors by the conjugate.
Conformational study of alanine and α‐aminoisobutyric Ψ[NHCO]‐retroamide peptide analogues
Authors: ALEMÁN CARLOS , PEREZ JUAN J.
Published: August 2010

The minimum‐energy conformations of N,N′‐dimethyl‐2‐methylmalondiamide (2mMA) and N,N′‐dimethyl‐2‐dimethylmalondiamide (2dmMA) have been computed using the AM1 method. The results show that molecules tend to form an intramolecular six‐membered ring hydrogen‐bond system. The same trend is observed in crystals of malonamide derivatives substituted in the central carbon atom. The results are also compared with previous molecular‐mechanics calculations. The conformational trends of 2mMA and 2dmMA are very similar to those showed by N,N′‐dimethylmalondiamide. Details of the computed conformational energy maps for 2mMA and 2dmMA compounds are given.
Conformations of arginine and lysine side chains in association with anions
Authors: CHAKRABARTI P.
Published: August 2010

The side chain conformations shown by arginine and lysine in amino‐acid and peptide crystal structures and bound to oxyanions in proteins have been analyzed in an attempt to understand the behaviour of these long‐chain amino acids in an ionic environment. Except for χ1, torsions have a preference for the trans conformation. However, for arginine in protein structures, χ3 and χ4 appear to be flexible and can be tuned for optimal anion binding. For χ4, values in the range –80 to 80° are excluded for steric reasons; the remaining region in conformational space is accessible. This orientational variety exhibited by χ4 has not been hitherto appreciated. Factors that can forbid a χ‐angle to be in the trans geometry are the simultaneous binding of the anion by the main‐ and side‐chain atoms, or the sharing of the anion between two different molecules in the crystal structure. Small molecules containing arginine have a distinct tendency to crystallize with two molecules in the asymmetric unit. This may be a general phenomenon for all extended molecules which have hydrogen‐bond donors (or acceptors) embedded in a rigid set‐up.
Side‐product formation during cyclization with HBTU on a solid support
Authors: STORY SANDRA C. , ALDRICH JANE V.
Published: August 2010

The coupling reagent 2‐(1H‐benzotriazol‐1‐yl)‐1,1,3,3‐tetramethyluronium hexafluorophosphate (HBTU) was used in an attempt to prepare a highly strained 10‐membered lactam ring on a solid support via side‐chain to side‐chain cyclization of the adjacent α, γ‐diaminobutyric (Dab) and d‐glutamic acid residues in [Dab2,d‐Glu3,Leu5]enkephalinamide. This attempted cyclization failed, however, and yielded linear products instead. Characterization by mass spectrometry, amino acid analysis, peptide sequencing and NMR indicated that the major products were the tetramethylguanidinium (Tmg) derivatives [Dab(Tmg)2,d‐Glu3,Leu5]‐enkephalinamide and the corresponding dimeric linear Tmg‐containing peptide which resulted from the transfer of the tetramethyluronium moiety from HBTU to the amino side chain of Dab. The formation of these tetramethylguanidinium side products during cyclization reactions limits HBTU's usefulness for the formation of lactams.
Synthesis and biological activity of some linear and cyclic kinin analogues
Authors: GOBBO MARINA , BIONDI LAURA , FILIRA FERNANDO , ROCCHI RANIERO , PIEK TOM
Published: August 2010

Syntheses are described of some linear and cyclic kinin analogues. Cyclization, by the diphenyl‐phosphorazide method, of linear peptides prepared by the solid‐phase procedure based on Fmoc chemistry, was used for preparing cyclo‐bradykinin and cyclo‐kallidin (cyclo‐Lys‐bradykinin). Removal of the protecting group from the lysine side chain of cyclo‐kallidin followed by acylation with the N‐terminal sequence of vespulakinin 1 (VSK l), Fmoc‐Thr(tBu)‐Ala‐Thr(tBu)‐Thr(tBu)‐Arg(Pmc)‐Arg(Pmc)‐Arg(Pmc)‐Gly‐OH, by the Bop‐HOBt procedure, yielded the protected Nε‐(1‐8 VSK 1)‐cyclo‐Nα‐kallidin, which was deblocked by acid treatment and purified by semi‐preparative HPLC. The diglycosylated 1‐8 VSK 1 sequence Boc‐Thr(tBu)‐Ala‐ (Galβ)Thr‐(Galβ)Thr‐Arg(Pmc)‐Arg(Pmc)‐Arg(Pmc)‐Gly‐OH was also synthesized by the solid‐phase procedure and used to prepare the Nε‐[(Galβ)Thr3, (Galβ)Thr3, 1‐8 VSK 1]‐cyclo‐Nα‐kallidin. Peptides and glycopeptides were characterized by amino acid analysis, optical rotation, analytical HPLC and FAB‐MS. Preliminary pharmacological experiments showed that the cyclic kinin analogues are much less potent than bradykinin but still show specific bradykinin‐like actions that support the hypothesis of the presence of a pharmacophore in the centre of the (brady)kinin molecule.
Synthesis of peptides mediated by KOBt
Authors: SIVANANDAIAH K.M. , BABU V.V. SURESH , SHANKARAMMA S.C.
Published: August 2010

Coupling of Fmoc‐amino acid chlorides can be mediated by the potassium salt of 1‐hydroxybenzotriazole (KOBt), the reaction being carried out in an organic medium. The use of a base like NaHC03/Na2C03 or DIEA/NMM/pyridine is not necessary. Coupling is fast and racemization free; the work‐up, isolation of the product and scale‐up are easy. The pentapeptide sequence of Fmoc‐[Leu]enkephalin was thus synthesized in the solution phase on a 5 mmol scale without isolation of any intermediate. Acylation of C‐protected N‐methylamino acid esters by Fmoc‐N‐methylamino acid chlorides by this procedure is also feasible, as demonstrated by the synthesis of cyclosporin A fragments 4‐7 and 8‐11. The peptides obtained in high yields were crystalline solids, unlike earlier reports in which they were obtained mostly as oily or foamy intermediates. They showed spectral properties identical with those of the authentic compounds.
Use of a new sonically cleavable and acido‐labile handle for solid‐phase peptide amide synthesis
Authors: CALMES MONIQUE , DAUNIS JACQUES , DAVID DOMINIQUE , JACQUIER ROBERT
Published: August 2010

A new handle usable for solid‐phase peptide amide synthesis was designed. New releasing conditions of the peptide using sonication allowed much shorter reaction times at lower TFA concentrations.
Synthesis of the partially protected fragment 1–16 of salmon calcitonin by using the phenylhydrazide protecting group
Authors: SEMENOV ANATOLY N. , LOMONOSOVA IRINA V.
Published: August 2010

The partially protected fragment BOC‐Cys(Acm)‐Ser(But)‐Asn‐Leu‐Ser(But)‐Thr(But)‐Cys(Acm)‐Val‐Leu‐Gly‐Lys(&‐BOC)‐Leu‐Ser(But)‐Gln‐Glu(0But)‐Leu‐OH of salmon calcitonin was synthesized by segment condensation in solution. Segments were synthesized in solution by the DCC/HOBt method using the phenylhydrazide as a semipermanent protecting group for protection of the carboxyl function of the C‐terminal residue. The phenylhydrazide protecting group was removed by oxidation with air oxygen catalyzed by copper‐pyridine complexes. The segments were then condensed by the DCC/HOBt method according to the scheme (6 + 3) + (3 + 4). The proposed synthetic scheme permits production of gram amounts of the partially protected fragment 1–16 of salmon calcitonin.
Local structural differences between α and β‐elicitins shown by circular dichroism and ultraviolet difference spectroscopy
Authors: NESPOULOUS CLAUDE , PERNOLLET JEAN‐CLAUDE
Published: August 2010

In order to investigate differences in the conformation of elicitins exhibiting different levels of activity (toxicity to tobacco plants). the environment of the tyrosyl residues in four elicitins has been compared by different spectroscopic methods (difference absorption and circular dichroism). We compared two α‐elicitins (capsicein and parasiticein) and two β‐elicitins (β‐cryptogein and β‐cinnamomin), that are 50–100 times more toxic than the α‐ones. Thermal difference UV spectroscopy and titration experiments clearly showed the exposure of Tyr‐85 by comparison of parasiticein lacking Tyr‐85 and the accessibility of its hydroxyl group to the solvent. The adjacent Ty‐87 was also suggested to be located at the surface. In β‐cryptogein, β‐cinnamoniin and capsicein the pK was measured at between 10.5 and 10.8, while in parasiticein it is higher (11.5) owing to a difference in the local environment. Thermal difference UV spectroscopy showed one more exposed tyrosine in β‐elicitins than in α‐ones. This difference was attributed to Tyr‐12, considering the more hydrophilic characteristic of the sequence around residue 13 in β‐elicitins and the role of this region in the toxicity. However, no difference in titration behaviour was noted among elicitins concerning Tyr‐12. The other two tyrosines also presented an abnormal pK of titration (> 12). In all elicitins Tyr‐47 was probably exposed, while Tyr‐33 was probably buried and not titrated, except in β‐cinnamomin at very alkaline pH.
Simultaneous multiple synthesis and selective conjugation of cyclized peptides derived from a surface loop of a meningococcal class 1 outer membrane protein
Authors: BRUGGHE HUMPHREY F. , TIMMERMANS HANS A.M , VAN UNEN LEONTINE MA , TEN HOVE G. JAN , VAN DE WERKEN GERRIT , POOLMAN JAN T. , HOOGERHOUT PETER
Published: August 2010

Starting from the α‐(2,4‐diniethoxybcnzyl) ester of N‐(9‐fluorenylniethoxycarbonyl)aspartic acid [Fmoc‐Asp‐ODmb], side‐chain‐protected resin‐bound Fmoc‐peptides containing an Nc‐l‐(4,4‐dimethyl‐2,6‐dioxocyclohexylidenc)ethyl lysY1 [Lys(Dde)] residue were prepared. The C‐terminal dimethoxybenzyl esters of aspartic acid were removed with 1% trifluoroacetic acid and 10% anisole in dichloromethane, followed by Fmoc‐cleavage in the usual manner. The resin‐bound peptides were then cyclized using 1‐benzotriazolyloxy‐tris‐[N‐pyrrolidino]phosphonium hexafluorophosphate (PyBOP) in the presence of N‐methylmorpholine. The (dimethyldioxocyclohexylidene)ethyl groups of lysine were removed with 1% hydrazine hydrate in N,N‐dimethylacetarnide, and the liberated side‐chain amino functions were modified by reaction with pentafluorophenyl S‐acetylinercaptoacetate (SAMA‐OPfp). Finally, the peptides were side‐chain deprotected, with exception of the Lys(SAMA) residue. and cleaved from the solid support with trifluoroacetic acid/anisole/ water, 95/2.5/2.5. Cyclic peptides comprising 7–14 amino acid residues were obtained employing this procedure.

As a model conjugation. cyclo[Thr‐Asn‐Asn‐Asn‐Leu‐Lys(SAMA)‐Thr‐Lys‐Asp] was coupled with bromoacetamide. The same peptide was also coupled with a bromoacetylpeptide to give a well defined peptide1 peptide conjugate. All peptides were conjugated to bromoacetylated tetanus toxoid for immunization purposes.
Solid‐phase synthesis of cionin, a protochordate‐derived octapeptide related to the gastrin/cholecystokinin family of peptides, and its mono‐tyrosine‐sulfate‐containing derivatives
Authors: KITAGAWAI KOUKI , FCTAKI SHIROH , YAGAMI TAKESHI , SUMI SHOICHIRO , INOUE KAZUTOMO
Published: August 2010

Cionin, a protochordate‐derived octapeptide amide related to the gastrin/cholecystokinin family of peptides, contains two consecutive tyrosine sulfate residues. In order to gain insight into the role of the respective tyrosine sulfate residue in biological activity, cionin and its derivatives in which one of the two tyrosine sulfate residues was replaced by tyrosine, were prepared by two Fmoc‐based solid‐phase approaches. In approach (1) Fmoc‐Tyr(SO3Na)‐OH was employed as a building block to assemble the Tyr(SO3Na)‐containing peptide‐resin, and a global deprotection cleavage was conducted with 90% aqueous TFA in the presence of m‐cresol and 2‐methylindole at 4°C. In approach (2) the Tyr(Msib) [Msib =p‐(methylsulfinyl)benzyl] derivative was used for the peptide‐chain assembly to achieve sulfation on the selective Tyr residue. Partially protected peptide with the Msib Msz protecting groups [Msz =p‐(methylsulfinyl)benzyloxycarbonyl], obtained after peptide‐resin cleavage, was treated with DMF‐SO3 complex in the presence of ethanedithiol to achieve the sulfation of free Tyr residue and the reduction of the Msib/Msz groups to TFA‐labile Mtb/Mtz groups [Mtb =p‐(methyithio)benzyl, Mtz =p‐(methylthio)benzyloxycarbonyl]. Final deprotection of the Mtb/ Mtz groups with 90° aqueous TFA in the presence of m‐cresol and 2‐methylindole gave the desired cionin derivative, which contains the tyrosine sulfate residue at the selective position. Yields obtained with approach (2) were considerably higher than those obtained with approach (1). Cionin and mono‐Tyr(SO3H)‐containing derivatives were assayed on exocrine pancreas in dogs.
Experimental studies and potential‐energy calculations of the blocked tetrapeptide Ac‐Lys‐Gln‐Gly‐Ile‐NMA from the third loop of a short‐chain snake venom neurotoxin
Authors: ROOS H. MARITA , ROOYEN PETRUS H. VAN , WESSELS PHILIPPUS L.
Published: August 2010

The conformational space of the tetrapeptide Ac‐Lys‐Gin‐Gly‐Ile‐NMA from the β‐bend in the third loop of a short‐chain snake venom neurotoxin was investigated with the aid of energy calculations. It was shown that this peptide has a preference for an α‐helical conformation. This result was compared with the experimentally determined conformations, as observed using NMR and CD spectroscopy. With NMR spectroscopy a random‐coil conformation of the peptide is indicated in H2O, DMSO and TFE. The results from the CD experiments suggest that the peptide exists as a random coil in water, but a small population of 3‐helical conformations is present in TFE. These results indicate that additional long‐range interactions also play a role in the conformation of this tetrapeptide in the protein.
Preparation of an aspartic acid‐containing protected peptide
Authors: ROBLES JORDI , PEDROSO ENRIQUE , GRANDAS ANNA
Published: August 2010

Treatment of the peptide‐resin Ac‐Asn‐Ser(Bzl)‐Gly‐Asp(OFm)‐pMeBHA with HF/anisole cleaves the peptide‐resin bond and removes the benzyl group, as expected, but also yields an impurity (ca. 25%) in which the benzyl group is linked to the fluorenylmethyl protecting group. Separation of the desired peptide from the impurity can be accomplished by reversed‐phase medium‐pressure liquid chromatography. The side reaction does not take place when the γ‐carboxyl of aspartic acid is protected with the 2‐(4‐acetyl‐2‐nitrophenyl)ethyl group.
Synthesis of disulfide‐bridged fragments of ω‐conotoxins GVIA and MVIIA
Authors: SIMMONDS ROBIN G. , TUPPER DAVID E. , HARRIS JOHN R.
Published: August 2010

The 3‐nitro‐2‐pyridinesulphenyl (Npys) moiety is finding increasing utility as a protecting‐activating group for cysteine, particularly in the synthesis of cyclic and unsymmetrical disulfides using the Boc strategy. This chemistry has been extended to peptides assembled by the Fmoc strategy. N‐Terminal Cys(Npys) is introduced via Boc‐Cys(Npys)‐OPfp. Non‐N‐terminal Cys(Npys) is incorporated by reacting a resin‐bound, fully protected Cys(Acm) peptide with NpysCl. This approach has been applied to the synthesis of four disulfide‐bridged fragments of ω‐conotoxins GVIA and MVIIA.
Solid‐phase synthesis of human osteocalcin by using a γ‐carboxyglutamic acid derivative
Authors: KURIHARA TAKASHI , TANIYAMA EIJI , HANE MOTOMU , SAITO TAKAO , HIROSE SACHIO , OHASHI SHINICHI
Published: August 2010

Human osteocalcin, also called bone Gla protein (BGP), consisting of 49 amino acids with two to three γ‐carboxyglutamate residues, was chemically synthesized for the first time by a novel solid‐phase peptide synthesis. An l‐enantiomer of N‐tert‐butyloxycarbonyl‐γ,γ′‐dicyclohexyl‐γ‐carboxyglutaniic acid was designed, prepared and utilized as a monomeric compound and proven to be useful for the solid‐phase peptide synthesis of human osteocalcin. The synthesis and optical resolution of the γ‐carboxyglutamic acid (Gla) derivative are first described, followed by the synthesis and characterization of Gla17‐human osteocalcin.
Acetylated glucopyranosyl esters of enkephalins
Authors: SKCRIĆ M. , HORVAT J. , HORVAT Š. , CHUNG N.N. , SCHILLER P.W.
Published: August 2010

Acetylated d‐glucopyranosyl esters of enkephalins were prepared by two different fragment condensation procedures involving direct participation of imidazole in the ester linkage formation. By both methods anomeric mixtures of d‐glucosyl esters were obtained and resolved by column chromatography. Depending on coupling conditions, racemization of either the C‐terminal or the penultimate amino acid residue of the enkephalin molecule occurred. The glucoconjugates with inverted stereochemistry were quantitated and separated from the main product by reversed‐phase high‐performance liquid chromatography. The opioid agonist potencies of the synthesized glucopyranosyl esters of enkephalins on electrically stimulated guinea pig ileum and mouse vas deferens preparations were determined in comparison with [Leu5]enkephalin.
Novel ψ‐S‐CH2 peptide‐bond replacement and its utilization in the synthesis of nonpeptidic surrogates of the Leu‐Asp‐Val sequence that exhibit specific inhibitory activities on CD4+ T cell binding to fibronectin
Authors: GREENSPOON NOAM , HERSHKOVIZ RAMI , ALON RONEN , GERSHONOV EYTAN , LAVIE BARAK , LIDER OFER
Published: August 2010

The Leu‐Asp‐Val‐(LDV)‐containing amino acid sequence, derived from the alternatively spliced first connecting segment region of fibronectin (FN), was shown to be recognized primarily by the α4β1‐integrin receptor expressed on the surface of various cell types. This adhesion epitope may therefore inhibit integrin‐mediated cell interactions with the extracellular matrix glycoprotein, including adhesion, migration, activation and differentiation. To probe the structural requirements for LDV recognition by integrins and examine the feasibility of inhibition of LDV‐dependent cell‐FN interactions, we have designed and constructed a novel ψ‐S—CH2 peptide bond surrogate that was employed in the formation of LDV surrogates. The synthesis of the ψ‐S–CH2 surrogates reported herein is based on Michael addition of 4‐methylpentane thiol to an itaconic acid diester to form an S–CH2 bond. We have found that the LDV surrogates comprises of 4‐methylpentanoate‐Asp‐i‐butyl amide and 8‐methyl‐3‐(2‐methylpropylaminocarbonyl)‐5‐thianonanoic acid interfered with CD4+ human T‐cell adhesion to FN in vitro, with an ED50 of 280 μg/mL. A control structural mimetic of the Leu‐Glu‐Val (LEV) peptide did not interfere with the T‐cell‐FN interaction. The specificity of the reaction was substantiated by the finding that the LDV mimetics did not interfere with T‐cell adhesion to laminin, another major cell‐adhesive glycoprotein of the extracellular matrix. That the nonpeptidic mimetics of LDV interfered markedly with T‐cell‐FN adhesive interactions indicate that the peptide bond and the amine and carboxyl end groups of the tripeptide makes only a minor contribution to the integrin binding affinity. Thus, consistent with our recent report on the production of Arg‐Gly‐Asp surrogates, we suggest that these constructs could provide novel insights into the fundamental mechanisms of integrin‐ligand interactions, and serve as competitive antagonists of conceivable therapeutic value.
Solvent effects on the conformation of cyclo(‐D‐Trp‐D‐Asp‐Pro‐D‐val‐Leu‐) An NMR spectroscopy and molecular modeling study
Authors: GONNELLA NINA C. , ZHANG XIAOLU , JIN YONG , PRAKASH OM , PARIS C. GREGORY , KOLOSSVÁRY ISTVAN , GUIDA WAYNE C. , BOHACEK REGINE S. , VLATTAS ISIDOROS , SYTWU TERRI
Published: August 2010

The conformations of cyclo(‐D‐Trp‐D‐Asp‐Pro‐D‐val‐Leu‐) in dimethyl sulfoxide‐d6 (DMSO‐d6) and water were determined using two‐dimensional nuclear magnetic resonance spectroscopy and restrained molecular dynamics. Comparisons were made between conformations of the cyclic pentapeptide in both solvents. The NMR study revealed that, while the backbone remained relatively unchanged in both solvents, the side‐chains adopted distinctly different orientations in DMSO‐d6 vs. H2O. A modeling study, minus NOE constraints, produced a set of low‐energy conformers possessing agreement in backbone conformation with the NMR‐derived structures; however, lowest‐energy conformers did not have this agreement. These results show that different solvents can significantly affect the preferred side‐chain conformation of small cyclic peptides in solution. This finding will impact the selection of solvent when determining structures for use as templates in rational drug design.
A new general solid‐phase method for the synthesis of backbone‐to‐backbone cyclized peptides
Authors: KALJUSTE KALLE , UNDÉN ANDERS
Published: August 2010

A model peptide with the sequences Ala‐Pro‐Lys(2ClZ)‐Tyr(2BrZ) was synthesized on a 4‐methylbenzhydryl amine (MBHA) polystyrene resin using conventional Boc/benzyl protective group strategy. The amino acid aldehyde Boc‐valinal was coupled by reductive alkylation with NaCNBH3 in acidified DMF for 1 h. The secondary amine in the peptide‐resin Boc‐Valψ[CH2NH]Ala‐Pro‐Lys(2CIZ)‐Tyr(2BrZ)‐MBHA was reductively alkylated by 3(4‐methylbenzylthio)‐propanal at 40 °C for 6 h, resulting the peptide‐resin Boc‐Valψ[CH2N(CH2CH2CH2‐S‐pMeBzl)]Ala‐Pro‐Lys(2ClZ)‐Tyr(2BrZ)‐MBHA. After the removal of the Boc group the synthesis was continued employing the above‐mentioned methods, which led to the resin‐bound peptide Leuψ[CH2N(CH2CH2CH2S‐pMeBzl)]Ser‐Pro‐Gly‐Lys(2ClZ)‐Valψ[CH2N(CH2CH2CH2‐S‐pMeBzl)]Ala‐Pro‐Lys(2ClZ)‐Tyr(2BrZ)‐MBHA. The peptide was cleaved from the resin with hydrogen fluoride. Reversed‐phase HPLC and plasma desorbtion mass spectrometry analysis showed that the expected peptide Leuψ[CHIN(CH2CH2CH2SH)ISer‐Pro‐Gly‐Lys‐Valψ[CH2N(CH2CH2CH2‐SH)]Ala‐Pro‐Lys‐Tyr‐NH2 was obtained as the major product with low levels of side products. Intramolecular oxidation of the thiols gave the backbone to backbone cyclized peptide Leuψ[CH2N(CH2CH2CH2S)]Ser‐Pro‐Gly‐Lys‐Valψ[CH2N(CH2CH2CH2‐S)]A1a‐Pro‐Lys‐Tyr‐NH2.
Molecular structures of CPF‐dipeptides, inhibitors for the binding of CD4 with gp120
Authors: VENKATRAMANI LALITHA , HOSSAIN M. BILAYET , HELM DICK VAN DER
Published: August 2010

The dipeptides N‐carbomethoxycarbonyl‐phenylalanyl‐benzyl esters (CPFs) play a significant role in the prevention of HIV‐I virus infection by interacting with the glycoprotein gp120, one of the envelope proteins of the HIV‐1 virus. Of the four possible isomers of CPF. (L‐pro‐L‐phe), (L‐pro‐D‐phe), (D‐pro‐L‐phe) and (D‐pro‐D‐phe). herein denoted LL etc., the crystal structures of LL, stereoisomeric LD and the racemic mixture of LD DL have been determined. All three peptides crystallize in the orthorhombic system and they all have similar cell dimensions: (i) LL. P212121, (a= 13.699(2), b= 25.893(5), c= 6.155(1) Å, Z = 4, Deale= 1.333 g cm‐3, R= 0.070 for 1247 observed reflections: (ii) LD. P212121, a = 11.663(2), b= 26.557(2), c = 7.281(1) A. Z = 4. Deale= 1.290 g cm−3R= 0.054 for 1918 observed reflections; (iii) LD/DL, Pbc21, a= 11.953(2), b = 24.208(8), c= 7.782(2) A, Z = 4, Deale= 1.292 g cm−3, R= 0.080 for 894 observed reflections. Both the enantiomeric LD and the LD in racemic LD DL have a similar conformation, an extended peptide chain with φ1= ‐ 76, ‐73; ψ1= 160, 158°.φ2= 123, 131° and Ψ2= ‐ 172, ‐167°, while peptide LL adopts a bent conformation at the Phe residue. φ1= ‐69°. Ψ1= 158°,Ψ2=‐ 60° and Ψ2=−34°. Despite their conformational differences. all three dipeptides pack very similarly in the crystal. The molecules associate by a single intermolecular N‐H…O hydrogen bond to form a column along the short crystallographic c‐axis. In each structure, the column is made tip of a hydrophilic core with hydrophobic groups, primarily phenyl rings, projecting outward.
Fmoe SPPS using Perloza™ beaded cellulose
Authors: ENGLEBRETSEN DARREN R. , HARDING DAVID R.K.
Published: August 2010

Perloza™ beaded cellulose was functionalised by a cyanoethylation reduction procedure to give aminopropyl Perloza. Fmoc‐amino acids were anchored to aminopropyl Perloza beaded cellulose via the TFA labile 4‐oxymethylphenoxyacetyl (HMPA) linker. Using Fmoc‐aminoacyl‐4‐oxymethylphenoxyacetyl‐2,4‐dichloro‐phenyl esters, all 20 amino acids were anchored at substitution levels ranging from 0.37 to 0.65 mmol/g. Fmoc‐amino acids were also anchored using the peptide‐amide linker 4‐[(R,S)‐1‐[1‐(9H‐fluoren‐9‐yl)‐methoxycarbonylamino]‐(2′,4′dimethoxy‐benzyl]phenoxyacetic acid. The Fmoc‐aminoacyl resins were used for SPPS using Fmoc chemistry. SPPS was carried out using either an LKB Biolynx 4175 low‐pressure pumped column continuous‐flow peptide synthesiser or an ABI 430A automated vortexing batchwise instrument. Comparison of peptides made using each synthesiser showed little difference in quality of the crude peptides. Different Fmoc‐amino acid activation methods (DIC/HOBt/DMF, HBTU, DIC/HOBt/DCM) were found to be equally useful with Perloza. Peptides were cleaved using TFA plus scavengers; however, the TFA‐swollen resin was not readily separated from the TFA peptide solution by simple filtration. Therefore alternative cleavage workup procedures were used with Perloza. Peptides were purified by HPLC and characterised by HPLC and amino acid analysis, and in some cases by FAB‐MS. Successful syntheses ranged from 5 to 34 amino acids in length. Some of the peptides were also synthesized using a polystyrene support and standardised (ABI Fastmoc™) SPPS protocols. The crude cleaved peptides from each synthesis were compared by HPLC analysis. The overall aim of our work with Perloza is synthesis of resin‐bound peptide ligands for affinity chromatography and antibody generation. HPLC analysis of crude peptides showed that peptides up to 20 amino acids in length were of reasonable purity when synthesised using Perloza, thus encouraging us to continue with investigations of SPPS of resin‐bound ligands.
Multiple peptide synthesis on acid‐labile handle derivatized polyethylene supports
Authors: VALERIO ROBERT M. , BRAY ANDREW M. , MAEJI N. JOE
Published: August 2010

Using the multipin peptide synthesis approach, a range of peptides with native amide and carboxylate C‐termini were generated using an acid‐labile approach. Polyethylene crowns grafted with hydroxyethyl‐methacrylate (HEMA) polymer were functionalized with either 4‐hydroxymethylphenoxyacetic acid for the generation of peptide‐carboxylate or p‐[(R,S)‐α‐[1‐(9H‐fluoren‐9‐yl)methoxyformamido]‐2,4‐dimethoxy‐benzyl]phenoxyacetic acid for peptide‐amide. A range of known peptide hormone sequences and other peptides with native C‐termini were assembled by sequential incorporation of Nα‐Fmoc protected amino acids. Peptides were sidechain deprotected and cleaved from crowns with TFA/scavengers within 2 mL centrifuge tubes, and isolated by a series of ether petrol wash and centrifugation steps. In this way it was possible to avoid a cleavage and isolation botteneck, allowing rapid processing of large numbers of peptides.
Preparation and evaluation of peptidic aspartyl hemiacetals as reversible inhibitors of interleukin‐l β converting enzyme (ICE)
Authors: GRAYBILL TODD L. , DOLLE ROLAND E. , HELASZEK CARLA T. , MILLER ROBERT E. , ATOR MARK A.
Published: August 2010

Aspartyl aldehyde, Ac‐Tyr‐Val‐Ala‐Asp‐H 1 (L–709,049), has been reported to be a potent, reversible inhibitor of interleukin‐1β converting enzyme (ICE) [Thornberry, N.A. et al. (1992) Nature (London)356, 768–774], In the context of our own work, we have developed a general synthetic approach to peptidic aspartyl aldehydes. Semicarbazone derivative, H‐Asp(Ot‐Bu)‐Sc 4, was identified as a stable, masked aspartyl aldehyde equivalent. We have used 4 to synthesize a series of mono‐, di‐ and tripeptide aldehydes, and multigram quantities of Ac‐Tyr‐Val‐Ala‐Asp‐H 1, Ac‐Tyr‐Val‐Lys‐Asp‐Sc 21 and Ac‐Tyr‐Val‐Lys‐Asp‐H 2. Biological evaluation of these aspartyl aldehydes and derivatives suggests that the tripeptide scaffold, Z‐Val‐Ala‐Asp, is a peptide scaffold that retains good potency and selectivity for ICE.
Conformational investigation of α,β‐dehydropeptides Part VI. Molecular and crystal structure of benzyloxycarbonylglycyl‐(Z)‐dehydrophenylalanine
Authors: RZESZOTARSKA BARBARA , KAROLAK‐WOJCIECHOWSKA JANINA , BRODA MALGORZATA A. , GALDECKI ZDZISLAW , TRZEŹWINSKA BARBARA , KOZIOL ANNA E.
Published: August 2010

The structure of a peptide containing C‐terminal dehydrophenylalanine, Z‐Gly‐(Z)‐δPhe (C19H18N2O5, MW = 354) was determined from single‐crystal X‐ray diffraction data. Needle‐shaped crystals were grown from a 1:1 mixture of methanol‐acetone in the monoclinic space group P21 with a= 14.717(4), b= 4.941(2), c= 12.073(4) Å, β= 103.72(4)˚; V= 852.86(8) Å3, Z= 2 and Dc= 1.32 g cm −3. The structure was solved by direct methods using SHELXS‐86 and refined to a final R‐index of 0.032 for 1714 observed reflections. The peptide adopts a conformation folded at the glycine residue, and principal torsion angles are ω0= 167.6(2)˚, pHGR;1= ‐71.8(3)˚, ψ1= ‐31.6(4)˚, ωl= ‐ 165.7(3)˚, pHGR;2= 65.6(4)˚, ψ1/2 = ‐174.4(3)˚ and ψ2/2 = 5.2(4)˚. Two intermolecular hydrogen bonds, N1—H…Oo and O2—H…O′1, join the folded molecules into columns and link columns to each other, respectively. FTIR spectroscopy shows the presence of three hydrogen bonds. This third one has been interpreted as an intramolecular hydrogen bond of the N2—H…N1 type. © Munksgaard 1994.
Methylation in positions 1 and 7 of angiotensin II A structure‐activity relationship study
Authors: CORDOPATIS PAUL , MANESSI‐ZOUPA EVY , THEODOROPOULOS DIMITRIOS , BOSSÉ ROGER , BOULEY RICHARD , GAGNON SYLVAIN , ESCHER EMANUEL
Published: August 2010

Six analogues of angiotensin II (Ang) were synthesized with modifications in positions 1 and 7. The study was undertaken in order to learn more about the influence of alkylations in positions 1 and 7 and their interdependence. Previous studies have shown thatx,x‐dimethylation of Gly (aminoisobutyric acid, Aib) in position 1 produces quite potent analogues, as doesN‐methylation of Gly (sarcosine). Combination of bothCx‐ andNx‐methylations toN‐Me‐Aib1, however, did not produce an affinity increase. Decyclisation of the Pro7‐residue produced moderately active analogues with position 7N‐methylation and inactive analogues if theN‐alkylation was suppressed. In order to investigate a possible stereochemical interdependence of positions 1 and 7, a group of peptides with combinations of position 1 and 7 alkylations were investigated. The following analogues were prepared: [Sar1, Aib7]Ang, [Sar1,Aib7,Leu8]Ang, [Aib1,7]Ang, [Aib1,7, Leu8]Ang, [N‐Me‐Aib1,Aib7]Ang, [N‐Me‐Aib1,Aib7,Leu8]Ang. They were synthesized by classical solid phase synthesis using the BOC‐TFA‐HF scheme. The biological properties of these peptides were assessed on the rabbit aorta preparation and their binding potencies were measured on bovine adrenal membranes. Both on agonistic and antagonistic [Leu8]Ang analogues single Aib substitutions in position 1 or 7 induced affinity reduction in both bioassays. Simultaneous Aib modifications in positions 1 and 7 induced more important affinity loss in a synergic manner in both bioassays and as well for agonists and antagonists. The N‐Me‐Aib1modifications induce similar affinity loss with or without concomitant Aib7modification. Agonistic (Phe8) analogues containing Aib in position 7 all have reduced intrinsic activity, indicating for the first time an influence of this position on the activation mechanism of the Ang receptor of the Type AT1. © Munksgaard 1994.
Synthesis and characterization of a new labeled gastrin ligand,125I‐BH‐[Leu15]‐gastrin‐(5‐17), on binding to canine fundic mucosal cells and Jurkat cells
Authors: GALLEYRAND J.C. , LIMA‐LEITE A.C. , LALLEMENT J.C. , LIGNON M.F. , BERNAD N. , FULCRAND P. , MARTINEZ J.
Published: August 2010

In the course of our study concerning gastrin and cholecystokinin (CCK) receptors, we have synthesized and characterized a new labeled gastrin ligand,125I‐BH‐[Leu15]‐gastrin‐(5‐17) [(3‐[125I]iodo‐4‐hydroxyphenyl)‐propionyl‐[Leu15]‐gastrin‐(5‐17)]. Binding of125I‐BH‐[Leu15]‐gastrin‐(5‐17) to isolated canine fundic mucosal cells was specific, saturable and of high affinity.125I‐BH‐[Leu15]‐gastrin‐(5‐17) and125I‐BH‐CCK‐8 [(3‐[125I]iodo‐4‐hydroxyphenyl)‐propionyl‐CCK‐8] interact with isolated canine fundic mucosal cells with small differences in maximal binding capacities and affinities, 3800 ± 900 binding sites/cell (Kd = 0.52 ± 0.23 nM) and 6200 ± 1100 binding sites/cell (Kd= 0.31 ± 0.18 nM), respectively. The relative order of potencies for gastrin and CCK analogs in displacing125I‐BH‐[Leu15]‐gastrin‐(5‐17) binding correlated well with those obtained using125I‐BH‐CCK‐8. Selective CCK/gastrin antagonists L‐364,718 (MK‐329) and L‐365,260 also inhibited125I‐BH‐[Leu15]‐gastrin‐(5‐17) binding. These results indicate that125I‐BH‐[Leu15]‐gastrin‐(5‐17) binds to gastrin receptors in isolated canine fundic mucosal cells. We have also characterized125I‐BH‐[Leu15]‐gastrin‐(5‐17) binding to the human Jurkat lymphoblastic cell line (Jurkat cells) known to express the CCK‐B/gastrin receptor. Saturation experiments have shown that both125I‐BH‐[Leu15]‐gastrin‐(5‐17) and125I‐BH‐CCK‐8 interact with a single class of high‐affinity binding sites in the Jurkat cell line. Binding characteristics of125I‐BH‐[Leu15]‐Gastrin‐(5‐17) and125I‐BH‐CCK‐8 were estimated to be about 2500 ± 400 binding sites/cell (Kd= 0.19 ± 0.09 nM) and 2400 ± 350 binding sites/cell (Kd= 0.06 ± 0.02 nM), respectively. Furthermore, the apparent affinities of CCK analogs and selective antagonists MK‐329 and L‐365,260 for the sites labeled by both probes were identical. The biological activity of cold125I‐BH‐[Leu15]‐gastrin‐(5‐17) and [Leu15]‐gastrin‐(5‐17) was demonstrated by their ability to increase intracellular calcium concentration in Jurkat cells. All these experiments showed that125I‐BH‐[Leu15]‐gastrin‐(5‐17) provides a convenient ligand for gastrin receptor binding studies. © Munksgaard 1994.
The critical C‐terminus of the small subunit of herpes simplex virus ribonucleotide reductase is mobile and conformationally similar to C‐terminal peptides
Authors: LAPLANTE STEVEN R. , AUBRY NORMAN , LIUZZI MICHEL , THELANDER LARS , INGEMARSON ROLF , MOSS NEIL
Published: August 2010

The C‐terminus of the small subunit of class I ribonucleotide reductases is essential for subunit association and enzymatic activity. 1H NMR analysis of the small subunit (2 × 38 kDa as a homodimer) of herpes simplex virus ribonucleotide reductase shows that this critical binding site is mobile and exposed in relation to the rest of the protein. Assignments of six C‐terminal amino acids are made by comparing the TOCSY and NOESY spectra of the small subunit with the spectra of an identical protein truncated by seven amino acids at the C‐terminus and the spectra of an analogous 15 amino acid peptide. The mobility of the C‐terminus may be important for subunit recognition and could be general for other ribonucleotide reductases. The spectral comparisons also suggest that the six C‐terminal amino acids of the small subunit and peptide are confor‐mationally similar. This observation may be important for the design of inhibitors of ribonucleotide reductase subunit association. © Munksgaard 1994.
Solution conformation of c‐[Gln‐Trp‐Phe‐Gly‐Leu‐Met], a NK‐2 tachykinin antagonist
Authors: AMODEO P. , ROVERO P. , SAVIANO G. , TEMUSSI P.A.
Published: August 2010

The conformation of cyclo‐[Gln‐Trp‐Phe‐Gly‐Leu‐Met], a potent tachykinin antagonist selective for the NK‐2 receptor, has been studied by 1H NMR spectroscopy in DMSO‐d6 and in a DMSO‐d6/H2O cryo‐protective mixture in the temperature range 280‐320 K. The NMR data cannot be interpreted on the basis of a single ordered conformation. An exhaustive search, based mainly on missing NOES among skeleton protons, yields a description of the conformational state in solution consisting of a few interconverting structures that can explain all observed NMR parameters. The relative position of the side chains of key residues may be interpreted in terms of bioactive conformations. © Munksgaard 1994.
Potential‐energy calculations of terminally blocked tetrapeptides from the third loop of short‐chain snake venom neurotoxins
Authors: ROOS H. MARITA , ROOYEN PETRUS H. VAN
Published: August 2010

The conformational space of six tetrapeptides from the β‐bends in the third loop of short‐chain snake venom neurotoxins was investigated with the aid of energy calculations. It was shown that these peptides can be divided into two groups: those with a specific preference for an α‐helix and those that exist as an ensemble of β‐turn conformations. © Munksgaard 1994.
Chiral recognition of Nα‐protected amino acids and derivatives in non‐covalently molecularly imprinted polymers
Authors: KEMPE MARIA , MOSBACH KLAUS
Published: August 2010

Highly crosslinked synthetic polymers, selective for various Nα‐protected amino acids and derivatives, were prepared by non‐covalent molecular imprinting. Methacrylic acid and ethylene glycol dimethacrylate were copolymerized in the presence of the print molecules, which were subsequently extracted from the polymers. The recognition of the polymers for the print molecules and molecules of similar structures was investigated by using the polymers as stationary phases in HPLC. The functional groups of the print molecules interact via hydrogen bonds with the positioned carboxyls of the polymer. It was shown that the Nα‐protecting group, the Cα‐protecting group and the amino acid side chain are also recognized by the binding sites in the polymer. © Munksgaard 1994.
NMR studies on the structure of some cyclic and linear antagonists of luteinizing hormone‐releasing hormone (LHRH)
Authors: REDDY D.V. , JAGANNADH B. , DUTTA ANAND S. , KUNWAR A.C.
Published: August 2010

The structure of cyclic antagonists of luteinizing hormone‐releasing hormone (LHRH), Ac‐D‐Phe(p‐Cl)1‐D‐Phe(p‐C1)2‐Trp3‐Ser4‐c(Asp5‐D‐Arg6‐Leu7‐Lys8)‐Pro9‐D‐Ala10‐NH2 (I), Ac‐D‐Phe(p‐Cl)l‐D‐Phe(p‐Cl)2‐D‐Trp3‐Ser4‐c(Glu5‐Arg6‐Leu7‐Lys8)‐Pro9‐D‐Ala10‐NH2 (II) and their linear analogues, Ac‐D‐Phe(p‐Cl)1‐Phe(p‐C1)2‐Trp3‐Ser4‐Asp5‐D‐Arg6‐Leu7‐Lys8‐Pro9‐D‐Ala10‐NH2 (III) and Ac‐D‐Phe(p‐Cl)1‐D‐Phe(p‐C1)2‐Trp3‐Ser4‐Glu5‐D‐Arg6‐Leu7‐Lys8‐Pro9‐D‐Ala10‐NH2 (IV), have been studied by NMR spectroscopy. The cyclic peptides I and II are more potent antagonists than the corresponding linear peptides in an in vivo assay. All the peptides show propensity of an unusual type II′β‐turn involving residues 3–6. Cyclic analogues also show some additional structure around residues 7 and 8 which is absent in the linear peptides. This additional structure in the cyclic peptides may be due to a minor conformation with a β‐turn between residues 5 and 8. © Munksgaurd 1995.
The delineation of hydrogen‐bonding patterns in supramolecular self‐assembly of several core oxalo retro‐peptides and crystal structure of MeO‐Ser‐Leu‐COCO‐Leu‐Ser‐OMe
Authors: KARLE ISABELLA L. , RANGANATHAN DARSHAN
Published: August 2010

Pseudo‐C5‐type intramolecular hydrogen bonding, arising from the C2 disposition of the core NH‐CO‐CO‐NH unit in oxalo retro‐peptides, is formed in addition to extended hydrogen bonding with neighbors forming sheets in MeO‐Aib‐COCO‐Aib‐OMe (1), helices in MeO‐Leu‐COCO‐Leu‐OMe (2) and ribbons in MeO‐Ser‐Leu‐COCO‐Leu‐Ser‐OMe (3). In 3 the OH in the Ser side‐chains form hydrogen bonds with the backbone carbonyl of Leu groups from neighboring molecules. Crystal parameters for 3 are: C22H38N4O10, monoclinic, space group P21, a = 7.374(1), b = 18.218(4), c = 10.661(3) Å, β= 95.72(2) ˚, R = 0.063 for 1738 observed reflections with ‖Fo‖> 3σ(F).
Solution conformational dynamics of the C‐terminal residues in endothelin‐1 and some analogues: a time‐resolved fluorescence study
Authors: COWLEY DAVID J. , PELTON JOHN T.
Published: August 2010

The rotational relaxation times of the single tryptophan residues in endotherlin‐1, [Ala1,3,11,15]endothelin‐l, human pro‐endothelin‐1, the linear hexapeptide Ac‐His‐Leu‐Asp‐Ile‐Ile‐Trp which corresponds to the C‐terminal residues 16–21 in endothelin‐1, the cyclic pentapeptide BQ123, and several di‐ and tri‐peptides possessing C‐terminal tryptophan residues have been determined from time‐resolved fluorescence anisotropy decays obtained by phase/modulation techniques. Fluorescence lifetime distribution widths have also been examined as predictors of conformational heterogeneity/restriction.

A significant contribution from a slow rotational component supports either the persistence, on the nanosecond timescale at least, of a non‐flexible α‐helical structure for the C‐terminal tail residues of endothelin‐1 in water as solvent, as seen in the X‐ray crystallographic structure, or the interaction of the C‐terminal tail residues 16–21 with the constrained disulfide‐bridged core residues 1–15. This slow rotational contribution is less evident in the linear, acyclic tetraalanine analogue but greatly increased in pro‐endothelin‐1.

In BQ123 the fluorescence characteristics support the occurrence of a dominant rotameric form involving the indole sidechain of the d‐tryptophan residue (Cα‐Cβ torsion angle χ1of 60°, as previously determined by NMR).
Primary structure of a cytotoxin‐like basic protein from Naja naja naja (Indian Cobra) venom
Authors: BABU A.S. , PURI K.D. , GOWDA T.V.
Published: August 2010

The complete amino acid sequence of a cytotoxin‐like basic protein (CLBP) from the venom of Naja naja naja (Indian Cobra) was determined by manual degradation using a 4‐dimethylaminoazobenzene‐4′‐isothiocyanate double‐coupling method. Peptide fragments obtained by chemical cleavage with cyanogen bromide and enzymic cleavages with trypsin and Staphylococcus aureus proteases for sequence analysis were purified by reversed‐phase chromatography. The total number of amino acid residues was 61, with leucine as the C‐terminal residue.
CoMFA investigations on two series of artificial peptide inhibitors of the serine protease thermitase Synthesis of an inhibitor of predicted greater potency
Authors: BRANDT W. , LEHMANN T. , WILLKOMM C. , FITTKAU S. , BARTH A.
Published: August 2010

Comparative molecular field analysis (CoMFA) is shown to be a very useful tool in treating two series of artificial substrate analogue inhibitors, peptide methyl ketones and chloromethyl ketones, of the serine protease thermitase. The backbone structure of the native polypeptide eglin c found in the X‐ray structure of its complex with the enzyme served as a template for the alignment of the inhibitors, which could be shown to be the key for success. Restricted only by the relatively small number of different amino acids representing the peptide sequence we were able to determine the regions of the compounds that are important for the value of the inhibitor constant Ki. On the basis of these results we have suggested some new structures with possibly increased inhibitory activity. One such structure was synthesized and is shown to be the most active compound tested up to now, with an experimental Ki‐value in the predicted range.
Structure‐function relationships of des‐(B26‐B30)‐insulin
Authors: SPODEN MARTIN , GATTNER HANS‐GREGOR , ZAHN HELMUT , BRANDENBURG DIETRICH
Published: August 2010

In order to study the role of the amino acid in position B25 and its environment in shortened insulins, a series of analogues was prepared with the following modifications; 1, Stepwise shortening of the B‐chain including replacements of TyrB26 and ThrB27 by glycine; 2, substitutions at the carboxamide nitrogen of des‐(B26‐B30)‐insulin‐B25‐amide by apolar, polar or charged residues of various chain lengths; 3, replacement of PheB25 by asparagine‐amide, phenylalaninol or a series of alkyl and aralkyl residues. Trypsin‐catalyzed semisyntheses were performed with Boc‐protected or unprotected des‐octapeptide‐(B23‐B30)‐insulin and synthetic peptides. Relative receptor binding and in vitro bioactivity of [AsnB25]‐des‐(B26‐B30)‐insuIin‐B25‐amide was 227 and 292% (on insulin), other activities ranged between 1 and ca. 200%.

We make the following conclusions. An l‐amino acid is essential in position B25. The B25‐carbonyl and NH groups favour high binding and “superpotency”, but are not indispensible for receptor contacts. For high affinity receptor interaction, the planarity at the C2‐atom and the distance of B25‐side‐chain branching in position B25 are important, but an aromatic ring is not necessary.
Structural contribution of the A‐chain loop in relaxin
Authors: BÜLLESBACH E. E. , SCHWABE C.
Published: August 2010

Site‐directed sequential disulfide bond formation has been used to synthesize relaxin analogs with modifications in the A chain loop (AlO‐A15). In the four different derivatives either the amino acid residues between the cysteines (A12‐A14) were replaced or the intrachain disulfide bond (A10‐A15) was eliminated. The substitution of the human relaxin 11 sequence (His‐Val‐Gly; A12‐14) by the corresponding insulin sequence (Thr‐Ser‐Ile) or the hydrocarbon chain of ω‐aminooctanoic acid (Aoc) caused significant loss of biological activity. Similar observations were made when the pair of cysteines (A10‐A15) was replaced by either alanine or serine, whereby serine disturbs more than alanine. It is suggested that the structural features of the A chain loop not only make important contributions to the active conformation of relaxin but also that the structural requirements of insulin and relaxin are different.