摘要:

Two isomeric, acyclic tetrapeptides containing a Z‐dehydrophenylalanine residue (Δz‐Phe) at position 2 or 3, Boc‐Leu‐Ala‐Δz‐Phe‐Leu‐OMe (1) and Boc‐Leu‐Δz‐Phe‐Ala‐Leu‐OMe (2), have been synthesized and their solution conformations investigated by 270MHz1H n.m.r. spectroscopy. In peptide 1 the Leu(4) NH group appears to be partially shielded from solvent, while in peptide 2 both Ala(3) and Leu(4) NH groups show limited solvent accessibility. Extensive difference nuclear Overhauser effect (n.O.e.) studies establish the occurrence of several diagnostic inter‐residue n.O.e.s (CαjH ⇆ Ni+1H and NiH ⇆ Ni+1H) between backbone protons. The simultaneous observation of “mutually exclusive” n.O.e.s suggests the presence of multiple solution conformations for both peptides. In peptide 1 the n.O.e. data are consistent with a dynamic equilibrium between an ‐Ala‐Δz‐Phe‐ Type II β‐turn structure and a second species with Δz‐Phe adopting a partially extended conformation with Ψ values of ± 100° to ± 150°. In peptide 2 the results are compatible with an equilibrium between a highly folded consecutive β‐turn structure for the ‐Leu

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00044.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Reproducible preparations are given for salts of the following L‐amino acid derivatives: Bpoc‐Ala‐OH, Bpoc‐Arg(Mtr)‐OH, Bpoc‐Asn‐OH, Bpoc‐Asp(OtBu)‐OH, Bpoc‐Cys(Acm)‐OH, Bpoc‐Cys(S‐tBu)‐OH, Bpoc‐Gln‐OH, Bpoc‐Glu(OtBu)‐OH, Bpoc‐Gly‐OH, Bpoc‐Ile‐OH, Bpoc‐Leu‐OH, N‐α‐Bpoc‐Lys(ε‐Boc)‐OH, Bpoc‐Met‐OH, Bpoc‐Phe‐OH, Bpoc‐Pro‐OH, Bpoc‐Ser(OtBu)‐OH, Bpoc‐Thr(OtBu)‐OH, Bpoc‐Tyr‐OH, Bpoc‐Val‐OH. A study of the deblocking ofN‐α‐Bpoc peptides in dichloromethane containing 0.5% trifluoroacetic acid revealed that a rapid equilb‐rium is established between the first‐formed monomeric alkene 2‐p‐biphenylylpropene and the hindered dimer 2,4‐bis(p‐biphenylyl)‐4‐methyl‐l‐pentene. Thioethers were found to be inefficient carbocation scavengers for the deblocking reaction. The most efficient scavengers were found to be thiophenol and benzyl mercaptan, and the following approximate reactivity order was established: benzyl mercaptan

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00045.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

N.m.r. studies on the conformations of cyclo(‐l‐Trp‐l‐His) in acidic and basic D2O and DMSO solutions are presented here. The detailed conformational analysis of the cyclodipeptide molecule is based on1H chemical shifts, spin‐spin coupling constants and NOE measurements. The conformational analysis consists of the following steps: 1) Calculations of the allowed {χn} states of the peptide molecule, (an allowed {χn} state is characterized by defining the two torsional angles χ1and χ2for each amino acid residue, which does not violate the excluded volume criteria). 2) Calculations of the induced chemical shifts of the His H5and Hβ resonances arising from the indole and imidazole ring current effects, in the various allowed {χn} states and the comparison of the calculated and measured chemical shifts of the above resonances. 3) The conformation of the DKP ring and the distribution of the relative populations among the three rotational isomers of each of the side chains were estimated from the measured coupling constants. Finally, the NOE measurements enabled us to determine the various pairs of protons which are spatially in close proximit

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00046.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The synthesis and characterization of monofluoroacetyl (MFAc) functionalized haptens are described. These were covalently bound to polypeptide carriers (bovine serum albumin and poly‐d‐lysine) by primary amine/succinimide ester or primary amine/acid chloride coupling. Epitopic densities of the resulting antigens were determined by both19F n.m.r. and picryl sulfonic acid assays.19F n.m.r. experiments defining the stability of MFAc ester and amide linkages as a function of media (includingin vitro), time, and temperature are presented. These results indicate that MFAc functionalized antigens are well suited for further immunologic stud

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00047.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

EnantiomericN‐acetyl‐,N‐benzoyl‐. andN‐benzyloxycarbonylglycyl‐amino acids have been transformed into their racemates by conversion of the acids into their 2.4‐dialkyl‐5(4H)‐oxazolones through the mixed anhydrides in tetrahydrofuran followed byN‐methylpiperidine‐catalyzed racemization of the oxuzolone and subsequent hydrolysis by aqueous acid, al

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00048.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The conformations of the dipeptide t‐Boc‐Pro‐dAla‐OH and the tripeptide tBoc‐Pro‐dAla‐Ala‐OH have been determined in the crystalline state by X‐ray diffraction and in solution by CD, n.m.r. and i.r. techniques. The unit cell of the dipeptide crystal contains two independent molecules connected by intermolecular hydrogen bonds. The urethane‐proline peptide bond is in thecisorientation in both the molecular forms while the peptide bond between Pro anddAla is in thetransorientation. The single dipeptide molecule exhibits a “bent” structure which approximates to a partial β‐turn. The tripeptide adopts the 4 → 1 hydrogen‐bonded type II β‐turn with alltranspeptide bonds. In solution, the CD and i.r. data on the dipeptide indicate an ordered conformation with anintramolecular hydrogen bond. N.m.r. data indicate a significant proportion of the conformer with atransorientation at the urethane‐proline peptide bond. The temperature coefficient of the amide proton of this conformer in DMSO‐d6points to a 3 → 1intramolecular hydrogen bond. Taken together, the data on the dipeptide in solution indicate the presence (in addition to thecisconformer) of a C7conformation which is absent in the crystalline state. The spectral data on the tripeptide indicate the presence of the type II β‐turn in solution in addition to the nonhydrogen‐bonded conformer with thecispeptide bond between the urethane and proline residues. The relevance of these data to studies on the substrate specificity

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00049.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

(d‐Trp)6‐LHRH:pGlu‐His‐Trp‐Ser‐Tyr‐d‐Trp‐Leu‐Arg‐Pro‐GlyNH2was prepared by solid‐phase peptide synthesis using the nitro group to protect the guanidine side chain of the arginyl residue. Removal of the side‐chain protecting groups was carried out by catalytic transfer hydrogenation (CTH) using palladium acetate/ammonium formate or palladium on charcoal/formic acid. We show in this paper that this deprotection method induces i) reduction of the tryptophan residue and ii) epimerization at the histidine level (with palladium acetate/ammonium formate). Despite the formation of significant amounts of reduced peptide. CTH enabled us to obtain (d‐Trp)6

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00050.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The conformational properties of the “reduced” dipeptides tBuCO‐Pro‐GlyΨ[CH2‐NH]NRR′(R = H, R = Et; R = R′= Me) greatly depend upon the neutral or protonated state of the “reduced” amide bond. Due to protonation, the quite flexible neutral molecule turns into a very stable conformation resembling a β‐turn in both the solid and solute states. The existence of a strong N+—H…O=C interaction closing a 10‐membered cycle illustrates the possible specific properties induced by a chemical modificati

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00051.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY