ISSN:1075-2617    

DOI:10.1002/psc.426

出版商:John Wiley&Sons, Ltd.    

年代:2003

数据来源: WILEY

摘要:

AbstractDiketopiperazines (DKPs), the smallest cyclic peptides, represent an important class of biologically active natural products and their research has been fundamental to many aspects of peptide chemistry. The advent of combinatorial chemistry has revived interest in DKPs for two reasons: firstly, they are simple heterocyclic scaffolds in which diversity can be introduced and stereochemically controlled at up to four positions; secondly, they can be prepared from readily available α‐amino acids using very robust chemistry. Here synthetic methods, conformation, as well as applications of DKPs are summarized and discussed critically. Copyright © 2003 European Peptide Society and John Wiley&Sons,

ISSN:1075-2617    

DOI:10.1002/psc.446

出版商:John Wiley&Sons, Ltd.    

年代:2003

数据来源: WILEY

摘要:

AbstractA variety of Asp β‐carboxy protecting groups, Hmb backbone protection and a range of Fmoc cleavage protocols have been employed in syntheses of the model hexapeptide H‐VKDGYI‐OH to investigate the aspartimide problem in more detail. The extent of formation of aspartimide and aspartimide‐related by‐products was determined by RP‐HPLC. This study included three new Fmoc‐Asp‐OH derivatives: the β‐(4‐pyridyl‐diphenylmethyl) and β‐(9‐phenyl‐fluoren‐9‐yl) esters and also the orthoester Fmoc‐β‐(4‐methyl‐2,6,7‐trioxabicyclo[2.2.2]‐oct‐1‐yl)‐alanine. 3‐Methylpent‐3‐yl protection of the Asp side chain resulted in significant improvements with respect to aspartimide formation. Complete suppression was achieved using the combination OtBu side chain protection and Hmb backbone protection for the preceding Gly residue. Copyrig

ISSN:1075-2617    

DOI:10.1002/psc.430

出版商:John Wiley&Sons, Ltd.    

年代:2003

数据来源: WILEY

摘要:

AbstractIn this paper HRMAS NMR was used to investigate whether peptides on a peptidyl resin swollen in aqueous solution can adopt an intramolecular β‐sheet structure. A model peptide YQNPDGSQA, that was previously shown to adopt such a secondary structure in solution, (Blancoet al., J. Am. Chem. Soc., 1993) was grafted onto three different solid supports that swell in aqueous solution to examine the influence of the resin on the structure. Both parameters of resin loading and pH inside the swollen peptidyl resin proved to be important for the physicochemical behaviour of the peptide on the support. Copyright © 2003 European Peptide Society and John Wiley&Sons,

ISSN:1075-2617    

DOI:10.1002/psc.431

出版商:John Wiley&Sons, Ltd.    

年代:2003

数据来源: WILEY

摘要:

AbstractThe peptide Boc‐Val1‐ΔPhe2‐Leu3‐Ala4‐ΔPhe5‐Ala6‐OMe has been examined for the structural consequence of placing a two‐residue segment between the ΔPhe residues. The peptide is stabilized by four consecutive β‐turns. The overall conformation of the molecule is a right‐handed 310‐helix, with average (ϕ, ψ) values (−67.7°, −22.7°), unwound at theC‐terminus. The1H NMR results also suggest that the peptide maintains its 310‐helical structure in solution as observed in the crystal state. The crystal structure is stabilized through head‐to‐tail hydrogen bonds and a repertoire of aromatic interactions laterally directed between adjacent helices, which are antiparallel to each other. The aromatic ring of ΔPhe5forms the hub of multicentred interactions, namely as a donor in aromatic C–H···π and aromatic C–H···OC interactions and as an acceptor in a CH3···π interaction. The present structure uniquely illustrates the unusual capability of a ΔPhe ring to host such concerted interactions and suggests its exploitation in introducing long‐range interactions in the folding of supersecondary structures. Copy

ISSN:1075-2617    

DOI:10.1002/psc.432

出版商:John Wiley&Sons, Ltd.    

年代:2003

数据来源: WILEY

摘要:

AbstractA series of three homologous dimethyldiamides Ac‐(Z)‐ΔPhe‐NMe2, Ac‐L‐Phe‐NMe2and Ac‐DL‐Phe‐NMe2have been synthesized and their structures determined from single‐crystal X‐ray diffraction data. To learn more about the conformational preferences of the compounds studied, the fully relaxed ϕ, ψ conformational energy maps on the free molecules of Ac‐ΔAla‐NMe2and Ac‐(Z)‐ΔPhe‐NMe2were obtained with the HF/3‐21G method and the calculated minima re‐optimized with the DFT/B3LYP/6‐31G**method. The crystal state results have been compared with the literature data. The studied dimethyldiamide Ac‐ΔXaa‐NMe2combines the double bond in positions α, β and theC‐terminal tertiary amide within one molecule. As the representative probe with ΔXaa = ΔAla, (Z)‐ΔLeu and (Z)‐ΔPhe shows, in the solid state they adopt the conservative conformation with ϕ, ψ∼ −45°, ∼130° and with a non‐planar tertiary amide bond, whatever the packing forces are. This conformation is located on the Ramachandran map in region H/F, which is of high‐energy for common amino acids, but not so readily accessible to them. The free molecule calculations on Ac‐ΔAla‐NMe2and Ac‐(Z)‐ΔPhe‐NMe2reveal that, in spite of dissimilar overall conformational profiles of these molecules, this structure is one of their low‐energy conformers and for Ac‐(Z)‐ΔPhe‐NMe2it constitutes the global minimum. So, the theoretical results corroborate those experimental results proving that this structure is robust enough to avoid conformational distortion due to packing forces. In contrast to Ac‐ΔXaa‐NMe2, the saturated Ac‐L/DL‐Xaa‐NMe2shows the constancy of the associative patterns but do not prefer any m

ISSN:1075-2617    

DOI:10.1002/psc.433

出版商:John Wiley&Sons, Ltd.    

年代:2003

数据来源: WILEY