bluuebunny/crossref_metadata_2025 huggingface dataset:
Conformational behaviour of a synthetic peptide of the C‐terminus of villin that interacts with actin: an NMR, CD and simulated annealing study
Authors: SIMENEL CATHERINE , ROSE THIERRY , GOETHALS MARC , VANDEKERCKHOVE JOËL , FRIEDERICH EVELYNE , LOUVARD DANIEL , DELEPIERRE MURIEL
Published: August 2010

The solution structure of a synthetic 22‐amino acid peptide (P1) corresponding to the extreme C‐terminal end and one of the F‐actin binding sites of villin has been determined by 1H NMR and CD spectroscopy. The structure of this peptide was compared to that of a peptide in which lysine to glutamic acid substitutions were introduced at positions 17 and 19 (P11), abolishing F‐actin binding. Both peptides are largely unstructured in aqueous solution. Changes observed in the NMR and CD spectra of both peptides are consistent with α‐helix formation in trifluoroethanol/water mixtures. A set of 189 interproton distances derived from nuclear Overhauser enhancement (NOE) measurements, 17 φ‐angle constraints obtained from 3Jnhα coupling constants, as well as about 10 N···O distance restraints deduced from amide proton exchange kinetics with deuterium, were used for the structure determination. The three‐dimensional structure of P1 and P11 is characterized by two helical regions, one extending from residues 2 to 5 and a second covering residues 7 to 17. The central fragment, ranging from Leu‐7 to Leu‐15, is more stable. The C‐terminal residues are less structured, particularly within peptide P11. The significance of these structural results is discussed in relation to the biological activity of villin. © Munksgaard 1995.
Role of amino and carboxyl groups of cobrotoxin in the conformational stability and the interaction with acetylcholine receptor
Authors: KUO KOU‐WHA , CHANG LONG‐SEN , CHANG CHUN‐CHANG
Published: August 2010

To study the functional involvements of the common interaction of the Leu‐1 α‐amino group and Asp‐58 in cobrotoxin, the lysine ε‐amino groups of cobrotoxin were initially guanidinated with o‐methylisourea. The α‐amino group of Leu‐I was then modified with TNBS after the guanidination of cobrotoxin. Both modified derivatives displayed no significant changes in the secondary structure and antigenicity of cobrotoxin, whereas the binding affinity for nicotinic acetylcholine receptor (nAChR) was pronouncedly decreased when Leu‐1 was modified. Six out of seven free carboxyl groups and the remaining buried Glu‐21 carboxyl group of cobrotoxin were modified with glycine methyl ester in the absence and presence of guanidine HCl, respectively. Alternation in the β‐sheet secondary structure of cobrotoxin was observed with the carboxyl‐group modified derivatives, which caused a decrease in the binding activity of the toxin molecule to the antibody and nAChR. Moreover, modification of the Glu‐21 carboxyl group of cobrotoxin further reduced the nAChR binding activity, while the antigenicity remained unchange. Thus, our results conclude that the Glu‐21 residue and the common interaction of the terminal Leu‐1 α‐amino group and the Asp‐58 carboxyl group are related to the nAChR‐binding activity of cobrotoxin, and the free carboxyl groups in cobrotoxin are conformation‐essential. © Munksgaard 1995.
Efficient synthesis of metal binding peptides incorporating aminodiacetic acid based ligands
Authors: KAZMIERSKI WIESLAW M.
Published: August 2010

New Nx‐Fmoc/But protected amino acids bearing half‐EDTA side chains (CH2)nN(Ada‐O‐Bu1)2n= 1 (5), n= 2 (24), n= 3 (10), n= 4 (15) were prepared in satisfactory yields. These derivatives can be conveniently used in a solid‐phase peptide synthesis as they are devoid of serious shortcomings of Boc/Bzl based syntheses of metallopeptides, such as preliminary peptide capping as well as undesired lactamization of 5 during the peptide synthesis.
Simultaneous differential scanning calorimetry, X‐ray diffraction and FTIR spectrometry in studies of ovalbumin denaturation
Authors: GORINSTEIN S. , ZEMSER M. , FRIEDMAN M. , CHANG SH.‐M.
Published: August 2010

The new application of differential scanning calorimetry (DSC) and the susceptibility of ovalbumin to α‐chymotrypsin gave a quantitative estimation of protein denaturation in solid ovalbumin. Solid ovalbumin in granules with 11% of water was heated at 100 °C in closed and nonclosed ampules. In order to compare effects of size and crystal structure, two proteins (bovine albumin and γ‐globulin) were examined at similar conditions for the extent of denaturation. Ovalbumin and bovine albumin showed similar extents of denaturation, but γ‐globulin, with a very different molecular mass, showed the maximal conformational changes. The enthalpy of denaturation was measured to elucidate the conformational changes in solid proteins. Its value was used for calculation of the degree of denaturation. The thermodynamic data associated with transition were calculated and the number of bonds broken during denaturation was determined. Intrinsic fluorescence was utilized in order to compare these two methods. Moreover, X‐ray diffraction and FTIR spectrometry were applied to native and denatured proteins.
Synthesis of dipeptide 4‐nitroanilides containing non‐proteinogenic amino acids
Authors: SCHUTKOWSKI MIKE , MRESTANI‐KLAUS CARMEN , NEUBERT KLAUS
Published: August 2010

A series of tert‐butyloxycarbonyl amino acid 4‐nitroanilides, including N‐alkylated amino acids and (R)‐ thiazolidine‐4‐carboxylic acid, (S)‐oxazolidine‐4‐carboxylic acid. (4S,5S)‐5‐methyloxazolidine‐4‐carboxylic acid, (4S,5R)‐5‐methyloxazolidine‐4‐carboxylic acid, (S)‐azetidine‐2‐carboxylic acid, (S)‐pipecolic acid and (S)‐3,4‐dehydroproline, were prepared conveniently by the isocyanate method or the mixed anhydride procedure. The resulting amino acid 4‐nitroanilides were extended to corresponding dipeptide 4‐nitroanilides with tert‐butyloxycarbonyl‐(S)‐alanine. In the case of sterically hindered amino acid 4‐nitroanilides the mixed anhydride procedure with diphenylphosphinyl chloride was successful.
A novel oxidation‐labile linker for solid‐phase peptide synthesis
Authors: SEMENOV ANATOLY N. , GORDEEV KONSTANTIN YU.
Published: August 2010

The use of an oxidation‐labile phenylhydrazide group as a linker for solid phase peptide synthesis (SPPS) is discussed.
Stereoselective synthesis of Xaaψ[CH2CH(OH)]Yaa dipeptidomimetics and their inclusion in HIV‐1 protease inhibitors
Authors: CHEN HUAI G. , TUSTIN JAMES M. , WUTS P.G.M. , SAWYER TOMI K. , SMITH CLARK W.
Published: August 2010

Two stereoselective syntheses of a new pseudodipeptide isostere, the right‐hand hydroxyethylene dipeptido‐mimetic (Xaaψ[CH2CH(OH)]Yaa), are presented. In one method readily available amino acids are used as starting materials for Evans chiral aldol condensation chemistry. The second method relies on the synthesis of an anti‐aldol product for the hydroxyethylene isostere via an E‐selective ethyl hydrocinnamate enolization, and thus allows for the synthesis of isosteres having side chains other than those available from amino acids. Both methods are illustrated by the chiral synthesis of Boc‐Pheψ[CH2CH(OH)]Phe. Two diastereomers, (S,S,R)and (S,R,R) are incorporated into an HIV‐1 protease inhibitor template which yields potent inhibitors of HIV‐1 protease when the pseudodipeptide isostere is Pheψ[CH(OH)CH2]Phe or Pheψ[CH(OH)CH(OH)]Phe. The resulting Pheψ[CH2CH(OH)]Phe‐containing inhibitors possess modest potency. © Munksgaard 1995.
Solution structure of the hydrophilic region of HIV‐1 encoded virus protein U (Vpu) by CD and lH NMR spectroscopy
Authors: WRAY VICTOR , FEDERAU TORSTEN , HENKLEIN PETER , KLABUNDE STEFAN , KUNERT OLAF , SCHOMBURG DIETMAR , SCHUBERT ULRICH
Published: August 2010

The HIV‐1 specific Vpu is a class I oligomeric membrane phosphoprotein of unknown structure and mechanism. The first experimental evidence for the position of secondary structural elements present in the hydrophilic C‐terminal region of Vpu under various solution regimes is reported. CD data for nine overlapping 15 amino‐acid fragments and 3 longer fragments indicate the presence of only transitory amounts of stable structure in aqueous solution alone, while with increasing trifluoroethanol content limiting structures were found indicating two helical segments in the hydrophilic region of Vpu. These limiting structures were more precisely defined from a detailed study of Vpu63–81, Vpu52–74 and Vpu63–81, by a combination of 2D 2H NMR spectroscopy, distance geometry, and restrained molecular dynamics and energy minimization calculations. Sets of low‐energy conformations compatible with the quantitative NOE data indicate that Vpu41–58 has an α‐helix from residues 42 to 50 while a second helix is found for VPU52–74 from residues 57 to 69. Vpu63–81 shows only the presence of a single reverse turn at residues 74 to 77, without any evidence of helix, under the same conditions. From CD measurements the first helix extends back to residue 30 and is connected to the N‐terminal anchor of Vpu. Thus the hydrophilic region of Vpu consists of two α‐helices joined by a flexible region of 6 or 7 residues, which contains the phosphoacceptor sites of Vpu at positions 52 and 56. The second helix is followed by a single reverse turn and a flexible C‐terminus. © Munksgaard 1995.
A new approach to phosphoserine, phosphothreonine and phosphotyrosine synthons and to thiophospho analogs
Authors: MORA NATHALIE , LACOMBE J.M. , PAVIA ANDRÉ A.
Published: August 2010

Several phosphoserine, phosphothreonine and phosphotyrosine synthons suitable for the stepwise synthesis of phosphopeptides were prepared. Treatment of methylthiomethyl (MTM) esters of either Z‐, Boc‐, Alloc‐serine and threonine with phosphochloridate in pyridine followed by MgBr2 cleavage of MTM in diethyl ether afforded the title compounds in good yield. Thiophosphoserine and phosphotyrosine synthons were also obtained by the phosphoramidite method using di‐(2,2,2‐trichloroethyl) ‐N.N‐diisopropylphosphoramidite and MCPBA as oxidizing reagent. Trichloroethyl proved valuable as phosphate protecting group especially in phosphotyrosine derivatives owing to its stability in acidic conditions. These synthons were involved in the liquid‐phase synthesis of several phospho and/or thiophosphopeptides related to either src‐protein kinase or rat liver pyruvate kinase.
Coupling in the absence of tertiary amines. V Removal of the 2‐nitrobenzenesulfenyl (NPS) group with 1‐hydroxybenzotriazole in the presence of aniline or N‐methylaniline
Authors: BEDNAREK MARIA A. , BODANSZKY MIKLOS
Published: August 2010

In a search for conditions of acidolytic removal of amine protecting groups leading to salts of the deblocked amine that can be acylated without addition of a tertiary amine, cleavage of the 2‐nitrobenzenesulfenyl (Nps) group with hydroxybenzotriazole (HOBt) in 2,2,2‐trifluoroethanol was attempted. The Nps group was smoothly removed, but the resulting salt of the amine component could not be acylated unless deprotonated with a tertiary base. A rationale is now proposed for this unsatisfactory outcome of the cleavage reaction and for the concomitant surprising reduction of HOBt to benzotriazole.

Based on the proposed mechanism, a new approach was designed for the removal of the Nps group. It was cleaved with HOBt in the presence of weakly basic nucleophiles such as aniline, N‐methylaniline or 8‐aminoquinoline. The protecting group was transferred smoothly to the amino group of the nucleophilic acceptor leaving the deblocked amine component in the form of its HOBt salt. This was then readily acylated without addition of a tertiary amine. © Munksgaard 1995.
High‐throughput purity estimation and characterisation of synthetic peptides by electrospray mass spectrometry
Authors: SMART SWEE S. , MASON TOM J. , BENNELL PAUL S. , MAEIJ N. JOE , GEYSEN H. MARIO
Published: August 2010

High‐throughput analysis for purity and molecular weight determination of synthetic peptides including characterisation of any peptidic byproducts arising from synthesis is described. The data from electrospray mass spectrometry are processed with an algorithm that calculates the contribution of the target peptide and each of the identifiable contaminants to the total ionizable material in a sample of synthetic peptide. All essential data are obtained by one instrumental technique in <3 min per sample. The technique has distinct advantages in the rapid analysis of the many hundreds of peptides/peptidomimetics required in systematic quantitative structure‐activity relationship and other investigations. ©Munksgaard 1996.
Sensitive fluorometric assay for the activity of chymosin
Authors: YONEZAWA HIROO , UCHIKOBA TETSUYA , KXNEDA MAKOTO , IZUMIYA NOBUO
Published: August 2010

Fluorogenic substrates for chymosin [Dns‐Leu‐Ser‐Phe‐Trp‐Ala‐Leu‐OCH2Py (I), Dns‐Leu‐Ser‐Phe‐Met‐Trp‐Leu‐OCH2Py (II), Dns‐Leu‐Ser‐Leu‐Trp‐Ala‐Leu‐OCH2Py (III), Dns‐Leu‐Ala‐Phe‐Trp‐Ala‐Leu‐OCH2Py (IV), Dns‐Leu‐Ser‐Phe‐Leu‐Ala‐Leu‐OCH2Py (V) and Dns‐Leu‐Ser‐Phe‐Phe‐Ala‐Leu‐OCH2Py (VI)] were synthesized by a solution method. The obtained substrates I‐VI were cleaved specifically (between the Phe and Trp residues for substrates I and IV, the Phe and Met residues for substrate II, the Leu and Trp residues for substrate III, the Phe and Leu residues for substrate V, and the Phe and Phe residues for substrate VI) by chymosin. The fluorescence of substrates I‐IV (345 nm) increased with their hydrolysis, and hydrolysis rates were obtained by measuring the increase in fluorescence. The minimum detectable chymosin concentrations for substrates I and IV were about 1 nM; those for substrates II and III were about 4 and 2 nM. This assay method is very sensitive, and it is possible to determine the chymosin activity rapidly and easily. Substrates I and IV‐VI were hydrolyzed by chymosin two times faster than substrates II and III. The effect of the amino‐acid residues of the substrates on the hydrolysis rate is discussed. ©Munksgaard 1996.
Effect on protein phosphatase activity of peptide backbone modification and truncation of the autoinhibitory domain peptide of calcineurin
Authors: BANNOW CAROL A. , STAPLES DOUGLAS J. , SMITH CLARK W. , CHAPMAN DARRYL L. , LEACH KAREN L.
Published: August 2010

Solid‐phase synthesis of the autoinhibitory domain of calcineurin, CaN A467–491, also produced [aspartimide477]CaN A467–491 and [iso‐Asp477]CaNA467–491 when Boc‐based chemistry was employed. In addition, the truncated peptide CaN A467‐488 was obtained when Fmoc‐based chemistry was employed. All four peptides proved to be effective inhibitors of protein phosphatase activity of calcineurin. The full‐length peptide and the C‐terminally truncated peptide (CaN467‐488) were indistinguishable, with Ki values of 28 ± 3 and 31 ± 5 μM respectively. The internally modified peptides, [iso‐Asp477]CaN A467–491 and [aspartimide477]‐CaN A467–491, possessed lower inhibitory potencies (Ki values of 87 ± 10 and 55 ±3 μM, respectively).©Munksgaard 1996.
Design of peptides: synthesis, crystal structure and molecular conformation of N‐Boc‐L‐Val‐δPhe‐L‐Ile‐OCH3
Authors: DEY SHARMISTHA , MITRA SHOME NATH , SINGH TEJ. P.
Published: August 2010

The dehydro‐peptide Boc‐L‐Val‐δPhe‐L‐Ile‐OCH3 was synthesized by the azlactone method in the solution phase. The peptide crystallized from a methanol/dimethyl sulfoxide (95:5) mixture in space group P61, with a=b= 15.312(1), c= 22.164(5) Å. The structure was determined by direct methods and refined to an R value of 0.098 for 1589 observed reflections [I≥ 1.5 σ(I)]. The peptide adopts an S‐shaped conformation with torsion angles: ø1=‐127(1), ψ1= ‐44(1), ø2, = 67(1), ψ2, = 37(1), ø3,=‐82(1)°. The side‐chain torsion angles in δPhe of X12= 1(2), X2.12= 7(2) and X2.22 = 177(1)° indicate that the δPhe residue is essentially planar. In valyl residue the two side‐chain torsion angles are X11= ‐65(1) and X21= 177(1), whereas the torsion angles in Ile are X1,13= 72(2), X1,23= ‐159(2), X23= 150(2)°. This is the first peptide which does not adopt a folded conformation for a sequence with a δPhe at the (i+ 2) position. The molecular packing in the crystals is stabilized by several hydrogen bonds: N1‐H1⋯O1’= 2.77(1) Å, N2‐H2⋯O1’= 2.95(1) Å, N3‐H3⋯O2=2.85(1) Å and a possible weak interaction N2‐H2⋯O1’3.29(1) Å‐ within the columns of molecules along the c‐axis and van der Waals forces between the columns. © Munksgaard 1996.
Synthesis of lipidic amino acid and dipeptide inhibitors of human platelet phospholipase A2
Authors: KOKOTOS GEORGE , CONSTANTINOU‐KOKOTOU VIOLETTA , NOULA CATERINA , NICOLAOU ANNA , GIBBONS WILLIAM A.
Published: August 2010

Phospholipases A2 (PLA2s) catalyze the hydrolysis of glycerophospholipids at the sn‐2 position, and their inhibition is considered a rational approach for the prevention and treatment of inflammation. A number of amides and esters of α‐amino acids with saturated linear side chains, esters of α‐amino alcohols and derivatives of lipidic peptides were prepared and tested against secreted humal platelet phospholipase A2. Among the compounds tested the amides of free amino acids with long‐chain amines presented the highest in vitro inhibitory activity. © Munksgaard 1996.
Purification and characterization of ostrich pancreatic secretory trypsin inhibitor
Authors: ZHAO MING , NAUDÉ RYNO J , MURAMOTO KOJl , OELOFSEN WILLEM
Published: August 2010

Ostrich pancreatic secretory trypsin inhibitor was isolated and purified using acid extraction, salt fractionation, SP‐Sephadex C‐50 and QAE‐Sephadex A‐25 chromatography and RP‐HPLC. The amino acid sequence of ostrich PSTI showed it is a single peptide chain containing 69 amino acid residues with the highest homology between ostrich and chicken PSTI. The molecular weight, as determined by electronspray mass spectrometry and from amino acid sequence data, is 7650 Da. The isoelectric point of ostrich PSTI was found to be 5.7. Ostrich PSTI specifically inhibited ostrich and commercial bovine trypsin with Ki values of 8.0 × 10−9 and 2.4 × 10−7M, respectively, while no inhibitory effects were observed with other serine proteases. © Munksgaard 1996.
Synthesis of phospho‐urodilatin by combination of global phosphorylation with the segment coupling approach
Authors: MOSTAFAVI HOSSEIN , AUSTERMANN SABINE , FORSSMANN WOLF‐GEORG , ADERMANN KNUT
Published: August 2010

The chemical synthesis of biologically active phosphorylated urodilatin (CDD/ANP‐95‐126) was achieved by using a strategy of coupling protected peptide segments in solution. Three protected peptide segments corresponding to urodilatin (1‐14) with side chain‐unprotected Ser10, (15‐24) and (25‐32) were prepared manually using Fmoc chemistry on an aminopropyl polystyrene resin with the super acid‐labile HMPB linker. For the coupling of segments, the carboxy group of the C‐terminal segment (25‐32) was converted into the tert‐butyl ester by treatment with TBTA. The protected peptide segments were coupled in the presence of EDC/HOOBt or TBTU/HOBt to yield fully protected urodilatin with a free hydroxy function at Ser10. Introduction of the phosphate was performed with Et2NP(OtBu)2 and tetrazole followed by oxidation of the phosphite. Alternatively, a prephosphorylated protected segment (1‐14) was used in the segment condensation. Our investigations indicate that both pathways, phosphorylation of protected urodilatin in solution and use of a prephosphorylated building block, are suitable methods to obtain a large phosphopeptide of high purity without formation of H‐phosphonates or other by‐products. © Munksgaard 1996.
Anomalous mobility of sulfitolysed proteins in SDS‐PAGE. Analysis and applications
Authors: MALHOTRA M. , SAHAL D.
Published: August 2010

Some cysteine‐containing proteins upon sulfitolysis have been found to show anomalously retarded SDS‐PAGE mobilities in non‐reducing gels. These proteins include bovine serum albumin, ovalbumin, aldolase, ribonuclease and a recombinant fusion protein (XA) consisting of a portion of γ‐interferon linked to the A chain of human insulin. This mobility shift has been employed to determine the stability of the sulfonated products and to study the kinetics of the sulfitolysis reaction. Partially sulfonated products of intermediate shifts were observed at 0.01%β‐ME, while 0.05%β‐ME gave a shift characteristic of the completely reduced protein. The undiluted sulfitolysis reagent reacted with XA to give within 1 min a gel shift characteristic of the fully sulfitolysed protein. Its transition stages could be visualized at 15, 30 and 60 min when the reagent was diluted four‐fold. In the presence of 8 M urea, the sulfitolysis of BSA was nearly complete at 30 min when the sulfitolysis reagent was used at a dilution of 1:5. However, under the same conditions BSA was predominantly unsulfitolysed in the absence of urea. In order to elucidate the mechanism of sulfonation shift. several derivatives of XA, e.g. performic acid oxidized, alkylated with (a) iodoacetamide and (b) iodoacetate, have been prepared. While the mobility of XASSO−3 was sensitive to the presence of β‐ME, all other derivatives moved in a β‐ME‐insensitive fashion. Furthermore, while the nonreducing mobilities of the acidic derivatives (‐SSO‐3, ‐SO‐3 and ‐SCH‐2CO‐2) were anomalously retarded and identical, the mobility of the iodoacetamide derivative was intermediate between the retarded acidic derivatives above and XA below. These studies have suggested a role of the extended conformation of the A chain of insulin in causing a mobility shift of the acidic derivatives in this series. Similar results were observed in an analogous series of derivatives prepared from BSA. Non‐denaturing gel filtration analyses of native vs. sulfitolysed samples of serum albumin. ovalbumin and ribonuclease have indicated that the sulfitolysed proteins elute earlier than their native counterparts and appear to be significantly larger than their true molecular weights. Circular dichroism analysis has indicated significant loss in helicity of sulfitolysed BSA. This suggests that the retarded mobility of sulfitolysed proteins seen on SDS‐PAGE is likely to be due to an expansion in the hydrodynamic volumes of these proteins, a phenomenon triggered by cleavage of disulfide bonds and further accentuated by the introduction of strongly negatively charged sulfonates. © Munksgaard 1996.
Backbone—side‐chain interactions in serine Synthesis, crystal structure and solution conformation of a linear model peptide N‐Boc‐l‐Ser‐l‐Phe‐OCH3
Authors: DEY SHARMISTHA , KAUR PUNIT , SINGH TEJ P.
Published: August 2010

The peptide Boc‐Ser‐Phe‐OCH3 was synthesised by a solution‐phase method using the usual workup procedure. The peptide was crystallized from a 70:30 (v/v) methanol‐water mixture. The crystals are monoclinic, space group P21 with a= 5.128(2), b=17.873(2), c=11.386(2) Å, and β=98.03(3)°. The structure was determined by direct methods and refined by a structure factor least‐squares procedure. The final R‐value for 1499 observed reflections was 0.041. The structure contains one peptide and one solvent water molecule. The peptide adopts a β‐strand‐like conformation with φ1=‐ 100.3(5), ψl= 99.9(5), φ2= ‐ 122.2(5), ψT2= ‐172.5(6)°. The Ser side‐chain assumes an extended conformation with χ11= ‐ 177.0(4)°. The OγH group of serine acts as a proton donor in an intramolecular weak hydrogen bond with (Ser) O′1; [Oγ1;‐Hγ1⋯O′1= 3.253(6) Å]. The Phe side‐chain adopts a staggered conformation with χ12= ‐70.9(6), χ22,1= 88.4(7)°, χ2,22= ‐89.2(6)°. The water molecule generates a loop through two hydrogen bonds with Oγ1 [OW⋯Oγ1= 2.893(5) Å] and O′2 [OW‐O′2= 2.962(7) Å] atoms. The unit‐translated peptide molecules along the α‐axis are held by hydrogen bonds: N1‐H1⋯O2 (x‐1, y, z) = 2.954(4) Å and N2‐H2⋯O′1 (x+1, y, z) = 2.897(6) Å in a manner similar to those observed in parallel β‐pleated sheet structures. There is an additional interaction involving Oγ1 and the water molecule [OW⋯Oγ1 (x= 1, y, z) = 2.789(4) Å]. The strong NOE peak of Ci(H)⋯Ni+1 (H) and a simultaneous weak NOE peak of Ni(H)⋯Ni+l (H) in the ROESY spectra of two‐dimensional NMR in dimethyl sulfoxide indicate a β‐strand‐like conformation for the peptide in solution. © Munksgaard 1996.
Conformation—activity correlations for chemotactic tripeptide analogs incorporating dialkyl residues with linear and cyclic alkyl sidechains at position 2
Authors: PRASAD SUDHANAND , RAO R. BALAJI , BERGSTRAND HAKAN , LUNDQUIST BRITTA , BECKER ELMER L. , BALARAM P.
Published: August 2010

Five stereochemically constrained analogs of the chemotactic tripeptide incorporating l‐aminocycloalkane‐l‐carboxylic acid (Acnc) and α, α‐dialkylglycines (Deg, diethylglycine; Dpg, N, N‐dipropylglycine and Dbg, N, N‐dibutylglycine) at position 2 have been synthesized. NMR studies of peptides For‐Met‐Xxx‐Phe‐OMe (Xxx = Ac7c. I: Ac8c. II: Deg, III; Dpg, IV and Dbg, V; For, formyl) establish that peptides with cycloalkyl residues, I and II, adopt folded β‐turn conformations in CDCl3, and (CD3)2SO. In contrast, analogs with linear alkyl sidechains, III‐V, favour fully extended (C5) conformations in solution. Peptides I‐V exhibit high activity in inducing β‐glucosaminidase release from rabbit neutrophils, with ED50 values ranging from 1.4–8.0 × 10–11. M. In human neutrophils the Dxg peptides III‐V have ED50 values ranging from 2.3 × 10−8 to 5.9 × 10−10 M, with the activity order being V>IV>III. While peptides I‐IV are less active than the parent. For‐Met‐Leu‐Phe‐OH, in stimulating histamine release from human basophils, the Dbg peptide V is appreciably more potent, suggesting its potential utility as a probe for formyl peptide receptors. © Munksgaard 1996.
Immunoreactivity and conformation of the P‐P‐G‐M‐R‐P‐P repetitive epitope of the Sm autoantigen
Authors: TSIKARIS VASSILIOS , VLACHOYIANNOPOULOS PANAYIOTIS G. , PANOU‐POMONIS EUGENIA , MARRAUD MICHEL , SAKARELLOS CONSTANTINOS , MOUTSOPOULOS HARALAMPOS M. , SAKARELLOS‐DAITSIOTIS MARIA
Published: August 2010

Anti‐Sm antibodies are usually considered highly specific for systemic lupus erythematosus (SLE), while anti‐UI RNP antibodies are found in high titers in patients with mixed connective tissue disease (MCTD). The sequence P1‐P‐G‐M‐R‐P‐P7, present in three copies in the Sm (Ul‐U6 RNA‐protein complex) autoantigen, is an important functional domain of the antigenic determinants. The immunoreactivity of this proline‐rich repetitive epitope was investigated by testing sera with various autoantibody specificities for reactivity against this epitope, as well as its conformational properties by means of ID and 2D 1HNMR spectroscopy. It was found that the P‐P‐G‐M‐R‐P‐P epitope is recognized mainly by anti‐UlRNP and/or anti‐Sm positive sera, but also by anti‐Ro(SSA) (hY1RNA‐protein complex) and anti‐La(SSB) (hY1RNA‐protein complex) positive sera, although these sera are negative for anti‐UlRNP and anti‐Sm. Conformational analysis of the proline‐rich epitope in DMSO‐d6 solution obtained from lyophilized aqueous solution at pH 5 showed the presence of at least three conformers. The main conformer A (62%) is stabilized by an ionic interaction between the guanidinium and the C‐terminal carboxylate groups, and the Pro6‐Pro7 peptide bond adopts the cis form. A type II β‐turn is also present in the N‐terminal sequence (Pro1‐Pro‐Gly‐Met4‐) of this conformer. Conformer B (21%) is also stabilized by a similar ionic interaction, as in conformer A, while the NMR data indicate the absence of a folded structure in the N‐terminal tetrapeptide of this conformer. Conformer C (17%) adopts a completely extended structure. The multiple conformers of the P‐P‐G‐M‐R‐P‐P may offer some explanation for the reactivity of sera with various autoantibody specificities against this epitope. © Munksgaard 1996.
A model for the interaction of trifluoroethanol with peptides and proteins
Authors: RAJAN RAHUL , BALARAM P.
Published: August 2010

The structural stabilizing property of 2,2,2‐trifluoroethanol (TFE) in peptides has been widely demon strated. More recently, TFE has been shown to enhance secondary structure content in globular proteins, and to influence quaternary interactions in protein multimers. The molecular mechanisms by which TFE exerts its influence on peptide and protein structures remain poorly understood. The present analysis integrates the known physical properties of TFE with a variety of experimental observations on the interaction of TFE with peptides and proteins and on the properties of fluorocarbons. Two features of TFE, namely the hydrophobicity of the trifluoromethyl group and the hydrogen bonding character (strong donor and poor acceptor), emerge as the most important factors for rationalising the observed effects of TFE. A model is proposed for TFE interaction with peptides which involves an initial replacement of the hydration shell by fluoroalcohol molecules, a process driven by apolar interactions and favourable entropy of dehydration. Subsequent bifurcated hydrogen‐bond formation with peptide carbonyl groups, which leave intramolecular interactions unaffected, promotes secondary structure formation. © Munksgaard 1996.
Design, synthesis, tandem mass spectrometric sequencing and biological activity of NGF mimetics
Authors: ESTENNE‐BOUHTOU GENEVIÈVE , KULLANDER KLAS , KARLSSON MAGNUS , EBENDAL TED , HACKSELL ULI , LUTHMAN KRISTINA
Published: August 2010

Nine low molecular weight nerve growth factor (NGF)‐like peptides have been designed to mimic the putative receptor‐binding epitope of NGF defined by two β‐hairpin loops. Eight different spacers were used as variable links between the β‐loop amino acid residues, which from mutagenesis experiments were found to play an important role in the biological activity of NGF. These spacers were amino acids, natural or non‐natural, differing in length (5–13 Å) and polarity. The peptides were synthesized via the Fmoc solid‐phase peptide synthesis and purified by reversed‐phase HPLC. Their primary sequences were analyzed by a combination of automated Edman degradation and mass spectrometry. The peptides were tested using two different biological assays, the fibre outgrowth from chick embryonic sympathetic ganglia and the PC 12 cell differentiation assay. Weak antagonistic effects could be observed for some peptides. © Munksgaard 1996.
Several polyhydroxymonoamide renin inhibitors assume similar conformations n the unbound and renin‐bound states
Authors: LAPLANTE STEVEN R. , TONG LIANG , AUBRY NORMAN , PAV SUSAN , JUNG GRACE , ANDERSON PAUL C.
Published: August 2010

The solution conformations of three polyhydroxymonoamide renin inhibitors which differ in the relative configuration and position of the hydroxyl groups at the P3, position were investigated by NMR spectroscopy. The NMR data are consistent with a predominant conformation in DMSO with the exception that two inhibitors exhibit conformational averaging about a torsion angle along P3 Comparisons with the renin‐bound structures determined by X‐ray crystallography [Tong et al., (1995) J. Mol. Biol.250, 211] show that the unbound and renin‐bound conformations are similar (with exceptions in the P3, position). This similarity suggests that gross conformational changes of the inhibitor are not a prerequisite for binding to renin. Apart from being able to tolerate different dihydroxylated structures at P3, renin can also accommodate different conformations at P3. Differences were observed at the P3, position between the inhibitors in the unbound state, between the unbound and renin‐bound states, and between the renin‐bound states. © Munksgaard 1996.
Application of the allyloxycarbonyl protecting group for the indole of Trp in solid‐phase peptide synthesis*
Authors: VORHERR THOMAS , TRZECIAK ARNOLD , BANNWARTH WILLI
Published: August 2010

The synthesis and stability of allyloxycarbonyl (Aloe) indole‐protected Trp derivatives and their application in solid‐phase peptide synthesis are reported. The study shows that the Aloe protection on the indole moiety is suitable for orthogonal protection in the Fmoc/tBu strategy if the Fmoc group is cleaved with DBU. Several tryptophan‐containing peptides have been synthesized including dynorphin A‐(1‐13), which has been intensively studied with respect to side reactions during the final TFA cleavage procedure. The results demonstrate the protective function of the Aloe group on the Trp during final deprotection. Furthermore, it could be demonstrated that Trp(Aloe)‐containing peptides can be isolated and that the Aloe group can then be removed in a second step. The synthesis of phosphorylated delta sleep inducing peptide (P‐DSIP) using the global phosphorylation approach provides another example in which Trp indole protection by Aloe prevents the formation of oxidative side products.
Conformation of a water‐soluble β‐sheet model peptide. A circular dichroism and Fourier‐transform infrared spectroscopie study of double D‐amino acid replacements
Authors: KRAUSE EBERHARD , BEYERMANN MICHAEL , FABIAN HEINZ , DATHE MARGITTA , ROTHEMUND SVEN , BIENERT MICHAEL
Published: August 2010

Among peptide secondary structures β‐sheet domains have been much less intensively studied than α‐helical conformations, mainly because of the lack of well characterized model peptides. In the present paper the secondary structure of a water‐soluble de novo peptide consisting of 26 amino acids (DPKGDPKGVTVTVTVTVTGKGDPKPD‐NH2) and the corresponding double D‐amino acid replacement set have been studied by circular dichroism and Fourier‐transform infrared spectroscopy. The model peptide was found to be unstructured in aqueous solution at peptide concentrations < 10−3 mol/L but to adopt a predominantly β‐sheet structure in the presence of 15 mM sodium dodecyl sulfate or at apolar/water interfaces. Although the peptide is composed of amino acids with low helical propensity, it formed a single‐stranded helical structure in aqueous trifluoroethanol. The D‐amino acid replacement set was synthesized in order to study the conformational stability of the model peptide selectively in distinct regions. The data show that both the α‐helix present in 50% trifluoroethanol as well as the β‐sheet domain formed in the presence of sodium dodecyl sulfate or at apolar/water interfaces, are located in the region between Val9 and Thr18. Pairwise substitution of adjacent amino acids by their corresponding D‐amino acids provides a pronounced β‐sheet disturbance. These findings demonstrate that double D‐amino acid replacements may be used to locate β‐sheet domains in peptides.
Structure‐activity relationship of the ring portion in backbone‐cyclic C‐terminal hexapeptide analogs of substance P. NMR and molecular dynamics
Authors: BEHRENS STEFAN , MATHÄ BARBARA , BITAN GAL , GILON CHAIM , KESSLER HORST
Published: August 2010

The conformations of two backbone‐cyclized substance P analogs were derived from homo‐ and heteronuclear NMR measurements and molecular dynamics simulations carried out in DMSO. The analogs contain subtle variations in the ring chemistry and are compared with biologically active analogs previously examined. The correlation between conformation and activity is used to gain insight into the conformational requirements from the pharmacophore.
Peptide boronic acids Versatile synthetic ligands for affinity chromatography of serine proteinases*
Authors: ZEMBOWER DAVID E. , NEUDAUER CHERYL L. , WICK MYRA J. , AMES MATTHEW M.
Published: August 2010

Peptide boronic acids are potent transition‐state analogue inhibitors of serine proteinases. We prepared the peptide boronic acids Ala‐Ala‐boroPhe (AAbF), targeted at chymotrypsin‐like proteinases, and Ala‐Ala‐boroVal (AAbV), targeted at elastolytic enzymes. Analogues protected on the N‐terminus with the carbonylbenzyloxy (Cbz) group were powerful inhibitors of human neutrophil elastase (HNE) and human cathepsin G (CatG), as well as the non‐human counterparts, porcine pancreatic elastase (PPE) and bovine α‐chymotrypsin (ChT). Removal of N‐Cbz protecting groups and immobilization with Sepharose 6B provided affinity matrices. Columns consisting of the AAbF or AAbV affinity matrix separated a mixture of PPE and ChT. PPE was specifically retained by the AAbV column and ChT was specifically retained by the AAbF column. HNE and CatG were not separated using the AAbF matrix, but were separated with the AAbV matrix. To demonstrate the practical utility of these affinity ligands, HNE was isolated from crude human neutrophil extracts, resulting in an 18‐fold purification in one chromatographic step, with a 41% recovery of elastolytic activity. Because peptide boronic acids can be synthesized having specificity for a wide range of target enzymes, this method is readily adaptable as a general procedure for isolation and purification of serine proteinases.
Solution structure of a biologically active cyclic LDV peptide analogue containing a type II′β‐turn mimetic
Authors: DOYLE PAUL M. , HARRIS JOHN C. , MOODY CLAIRE M. , SADLER PETER J. , SIMS MARTIN , THORNTON JANET M. , UPPENBRINK JULIA , VILES JOHN H.
Published: August 2010

The solution structure of cyclo‐[Gly‐Leu‐Asp‐Val‐BTD] (BTD=β‐turn dipeptide) has been determined by two‐dimensional 1H‐NMR (nuclear magnetic resonance) spectroscopy and systematic conformational searching combined with molecular dynamics studies. The structure contains two hydrogen bonds between the Gly and Val residues, and a type I β‐turn with Leu and Asp at the (i+ 1) and (i+ 2) positions of the turn. The cyclic compound shows activity in a scintillation proximity assay (SPA) for the inhibition of the interaction between the integrin α4β1 and vascular cell adhesion molecule‐1 (VCAM‐1). The structure‐activity relationship of the LDV sequence is discussed. © Munksgaard 1996.
Force‐field dependence of Boltzmann weighting factors on predicted π‐π*circular dichroic spectra of cyclo(Gly‐Pro‐Gly)2
Authors: MAcFARLANE K.J. , HUMBERT M.M. , THOMASSON K.A.
Published: August 2010

Semi‐empirical energy calculations were performed for published conformations of cyclo(Gly‐Pro‐Gly)2 using different force fields (DISCOVER cvff and cff91, AMBER, and CHARMM). The resulting potential energies were then used to create Boltzmann weighting factors for an ensemble of cyclo(Gly‐Pro‐Gly)2 structures. The dipole interaction model was used to predict π‐π* circular dichroic spectra (CD) for the individual structures of cyclo(Gly‐Pro‐Gly)2. The Boltzmann weighting factors were applied to the individual spectra so that a composite spectrum was constructed to represent a CD arising from a collection of different structures in solution. Weighting factors determined from different force fields were compared. Boltzmann‐weighted spectra better resembled the experimental CD than any calculated spectrum using only a single conformation of cyclo(Gly‐Pro‐Gly)2. The structures most heavily weighted contained at least one type I β‐turn.
Alkaline unfolding and salt‐induced folding of yeast alcohol dehydrogenase under high pH conditions
Authors: LE WEI‐PING , YAN SI‐XU , LI SEN , ZHONG HAI‐NING , ZHOU HAI‐MENG
Published: August 2010

The conformational changes of yeast alcohol dehydrogenase during unfolding at alkaline pH have been followed by fluorescence emission and circular dichroism spectra. A result of comparison of inactivation and conformational changes shows that much lower values of alkaline pH are required to bring about inactivation than significant conformational change of the enzyme molecule. At pH 9.5, although the enzyme has been completely inactivated, no marked conformational changes can be observed. Even at pH 12, the apparently fully unfolded enzyme retains some ordered secondary structure. After removal of Zn2+ from the enzyme molecule, the conformational stability decreased. At pH 12 by adding the salt, the relatively unfolded state of denatured enzyme changes into a compact conformational state by hydrophobic collapsing. Folded states induced by salt bound ANS strongly, indicating the existence of increased hydrophobic surface. More extensive studies showed that although apo‐YADH and holo‐YADH exhibited similar behavior, the folding cooperative ability of apo‐enzyme was lower than that of holo‐enzyme. The above results suggest that the zinc ion plays an important role in helping the folding of YADH and in stabilizing its native conformation. © Munksgaard 1996.
Chemical synthesis and purification of proteins: a methodology
Authors: BALL HAYDN L. , MASCAGNI PAOLO
Published: August 2010

Classical stepwise solid‐phase peptide synthesis (SPPS) has been used successfully for the synthesis of proteins up to 150 residues in length, although usually with poor yields and homogeneity. The major limitation has been the inability to separate chromatographically similar deletion and truncated impurities from the target sequence. We have developed a highly effective protocol for stepwise SPPS and‘one‐step’purification of small proteins. To demonstrate the effectiveness of the methodology we synthesised the 101 residue chaperonin 10 protein from Rattus norvegicus (Rat Cpnl0) using three different chemical protocols. Highly homogeneous Rat Cpnl0 was obtained using an optimised synthetic strategy and one‐step purification procedure (method C), involving (i) HBTU/HOBt activation, (ii) N‐(2‐chlorobenzyloxy‐carbonyloxy)succinimide as capping agent and (iii) the incorporation of a reversible Fmoc‐based chromatographic probe, derivatised with a lipophilic group for fast one‐step RP purification, to give an overall yield of 9.6%. Analysis by ESI‐MS indicated that the product was virtually free of deletion impurities, while RP‐HPLC under four different conditions and CZE indicated that the protein was 100 and 84% pure, respectively. The spontaneous folding of Rat Cpnl0 into its biologically active form was found to correlate well with the degree of purity as assessed by chromatography, ESI‐MS and sequencing, since 29 (A), 55 (B) and 81% (C) of correctly folded heptameric structure was obtained. The degree of homogeneity was also reflected in the ability of purified Rat Cpnl0 to facilitate the refolding of yeast enolase. © Munksgaard 1996.
Side reactions in the pyroglutamic acid‐7‐amino‐4‐methylcoumarin synthesis
Authors: ZICANE DANA , PETROVA MARINA , TETERE ZENTA , KREISHMAN GEORGE , BROOKS ELWOOD , KARLSON JAMES , KALEJS UDO
Published: August 2010

N‐Formylpyroglutamic acid‐7‐amido‐4‐methylcoumarine and pyroglutamyl‐pyroglutamic acid‐7‐amido‐4‐methylcoumarin are the major products in the synthesis of pyroglutamic acid‐7‐amido‐4‐methylcoumarin by phosphorus pentachloride in dimethylformamide and dicyclohexylcarbodiimide under pyridine activation. © Munksgaard 1996.
S‐ and C‐glycopeptide derivatives of an LH‐RH agonist
Authors: MICHAEL KATJA , WITTMANN VALENTIN , KÖNIG WOLFGANG , SANDOW JURGEN , KESSLER HORST
Published: August 2010

The S‐ and C‐glycosylated nonapeptides 1 and 2 were synthesized as analogs of the non‐glycosylated LH‐RH agonist buserelin (pGlu‐His‐Trp‐Ser‐Tyr‐D‐Ser(tBu)‐Leu‐Arg‐Pro‐NHEt) by segment condensation in solution. 1 and 2 differ from this peptide in the amino acid in position 6. In the first case (l), D‐serine (tBu) is substituted by D‐CySteine carrying a rhamnosyl residue, in the second case (2) D‐alanine carrying a galactosyl moiety bound as C‐glycoside is incorporated. The bioactivity of both glycopeptides as fertility drugs was determined from the dose dependent LH release in male rats. Additionally, in female rats the ovulation rate was assessed. As a result the analog 1 exhibits a similar biological activity as buserelin while analog 2 shows about 25% of this potency. Compared to buserelin the solubility of the analogs 1 and 2 in aqueous buffer is improved by more than two orders of magnitude due to the carbohydrate moieties. © Munksgaard 1996.
Turn conformations in peptides containing the ‐Xaa‐Ser‐ sequence
Authors: SHAW R.A. , PERCZEL A. , FASMAN G.D. , MANTSCH H.H.
Published: August 2010

The conformations of the protected dipeptides Boc‐L‐Pro‐L‐Ser‐NHMe, Boc‐L‐Pro‐D‐Ser‐NHMe, Boc‐L‐val‐L‐Ser‐NHMe and Boc‐L‐Val‐D‐Ser‐NHMe have been explored through interpretation of their infrared spectra in CH2Cl2, DMSO and D2O solution. In CH2Cl2 solution the formation of a ten‐membered ring (β‐turn) for each compound is signaled by characteristic shifts in both the urethane C=O and the terminal NH stretching frequencies. For each peptide, differences in the amide I absorption patterns for LL and LD isomers are consistent with the formation of type I and type II β‐turns respectively in CH2C12 solution. The amide I absorptions suggest substantial disruption of intramolecular hydrogen bonding in DMSO, and no intermolecular hydrogen bonding whatsoever in aqueous solution. In CH2C12 solution the OH stretching vibration is consistent with the formation of a hydrogen bond to the C=O of the serine group; however, two additional absorptions at frequencies characteristic of‘free’OH groups also appear in all spectra. Implications regarding the serine in stabilizing the β‐turn are discussed. © Munksgaard 1996.
Synthesis, structure and stability of novel dimeric peptide‐disulfides
Authors: LEBAN JOHANN J. , SPALTENSTEIN ANDREW , LANDAVAZO ANTONIO , CHESTNUT WILLIAM , AULABAUGH ANN , TAYLOR LESTER C.E. , DANIELS ALEJANDRO J.
Published: August 2010

Oxidation of nonapeptide dithiol (2) with K3Fe(CN)6 leads to either monomeric disulfide (4) or antiparallel and parallel dimeric disulfides (3a and 3b) depending upon reaction conditions. When exposed to small amounts of thiols or cyanide in aqueous solution, these three species interconvert to an equilibrium mixture of 2:1:8 (3a: 3b: 4). © Munksgaard 1996. © Munksgaard 1996.
Generation of soluble and active subtilisin and α‐chymotrypsin in organic solvents via hydrophobic ion pairing
Authors: MEYER JEFFREY D. , KENDRICK BRENT S. , MATSUURA JAMES E. , RUTH JAMES A. , BRYAN PHILIP N. , MANNING MARK C.
Published: August 2010

With very low concentrations of anionic detergents, such as sodium dodecyl sulfate (SDS) and Aerosol OT (AOT), it is possible to solubilize proteases in organic solvents, while retaining enzymatic activity. For example, the SDS–subtilisin BPN′ complex catalyzes transesterification of Ac‐Phe‐OMe in ethanol with a kcat/Km of 36 M−1 S−1 for mutant M1 and 39 M−1 S−1 for the wild type. By comparison, M1 suspended in ethanol is approximately 1000‐fold less active, with a kcat/Km of 0.03 M−1 s−1. Similarly, AOT complexes of α‐chymotrypsin were found to be approximately 1000 times more active (kcat/Km= 100‐350 M−1 s−1) than the suspended enzyme. © Munksgaard 1996.
Amino monothio acids in solid‐phase synthesis of peptide thioamides
Authors: HOEG‐JENSEN THOMAS , SPATOLA ARNO F. , HOLM ARNE
Published: August 2010

Peptides containing backbone thioamides (endothiopeptides) have been synthesized utilizing thioacylation under solid‐phase conditions. The thioacylations were performed by activating N‐protected amino monothio acids with the phosphorus‐containing coupling reagent 6‐nitrobenzotriazol‐1‐yloxytris(pyrrolidino)phosphonium hexafluorophosphate (PyNOP). This method avoids the use of P4S10‐based O/S‐exchange reagents, and it is thus amendable to amino acids with side‐chain amides. Synthesis of endothio analogs of biologically active peptide such as pGlu‐ψ[CSNH]‐His‐Pro‐NH2 (TRH) and Leu‐Gln‐ψ[CSNH]‐Leu‐Lys demonstrated this feature. Proton and carbon NMR spectra of the TRH analog verified the sequential position of its thioamide function. Compatibility of endothiopeptides with allyl‐protecting groups was studied, and 1,8‐diazabicyclo[5,4,0]undec‐7‐ene (DBU) was evaluated as a substitute for piperidine. © Munksgaard 1996.
Protection of asparagine and glutamine during Nα‐Bpoc‐based solid‐phase peptide synthesis
Authors: CAREY ROBERT I. , HUANG HAIHONG , WADSWORTH JAMES L. , BURRELL C. SCOTT
Published: August 2010

In this paper we describe the synthesis and properties of Bpoc‐Asn(Trt)‐OH, Bpoc‐Asn(Trt)‐OPfp, Bpoc‐Gln(Trt)‐OH and Bpoc‐Gln(Trt)‐OPfp. These derivatives are highly soluble in CH2Cl2 and can be coupled efficiently in solid‐phase peptide synthesis. The peptides, acetyl‐Ala‐Phe‐Asn(Trt)‐Gly‐Leu‐Ala‐O‐Dbf‐SH and Boc‐Cys(Acm)‐Ala‐Phe‐Gln(Trt)‐Gly‐Leu‐Ala‐O‐Dbf‐SH (where O‐Dbf‐SH is the peptide ester of 4‐mercapto‐6‐hydroxydibenzofuran) were synthesized by stepwise solid‐phase peptide synthesis using Nα‐Bpoc amino acids. We have observed that less than 0.1% of the trityl group is removed from the carboxamide of Gln and Asn during a standard 15 min Nα‐Bpoc deprotection in 0.5% TFA in CH2Cl2. © Munksgaard 1996.