1,721,009 research outputs found
Synthesis of Protected Derivatives and Short Peptides of AntAib, a Novel Ca-Tetrasubstituted a-Amino Acid of the A5c Type Possessing a Fused Anthracene Fluorophore
No full textThe Nα-Boc and Nα-Fmoc protected derivatives of 2-amino-2,3-dihydro-1H-cyclopenta[b]anthracene-2-carboxylic acid (antAib), a novel fluorescent, achiral, α-amino acid, rigid analogue of the known 9-antAla and 2-antAla residues, and belonging to the class of Ciα→Ciα cyclized, Cα,α-disubstituted glycines (strong β-turn and helix inducers in peptides), were synthesized in seven steps from 1,2,4-trimethylbenzene. The UV absorption and fluorescence properties of Boc–antAib–OEt and Boc–antAib–OH are also described. Solution syntheses of the short peptides Boc–antAib–l-Ala–OMe, Fmoc–l-Ala–antAib–l-Ala–OMe, as well as Boc–Aib–antAib–l-Ala–OMe and the side product 2,5-dioxopiperazine cyclo-[antAib–l-Ala], are presented as examples of the coupling ability at both C- and N-termini of the antAib residue
First access to the spin-labelled beta-amino acid POAC in an enantiopure state by resolution through its binaphthyl esters
No full textResolution of trans 3-(9-fluorenylmethyloxycarbonylamino)-1-oxyl-2,2,5,5-tetramethylpyrrolidine-4-carboxylic acid (Fmoc-POAC-OH) was quickly achieved upon esterification with (aR)-1,1'-binaphthyl-2,2'-diol, chromatographic separation of the obtained diastereomers, and facile saponification of the aryl ester function with removal of the chiral auxiliary
EPR Distance Measurements in a Doubly Nitroxide-Labelled Helical β-Peptide.
No full textK. Rolka, P. Rekowski, and J. Silberring Eds., Kenes Int., Geneva, Switzerland, 2007, pp. 30-31
9-Amino-4,5-diazafluorene-9-carboxylic Acid (Daf), a New C-alpha,alpha-Disubstituted Glycine Containing a Spatially Constrained Bipyridine-Like Ligand for Transition Metals - Synthesis and Evaluation of Peptide-Coupling Conditions at its C- and N-Termini
No full textAcylation of the anion of N-benzyl-8,5-diazafluorene-9-methyleneamine with methyl or benzyl chloroformate, followed by acidic hydrolysis, resulted in 9-amino-4,5-diazafluorene-9-carboxylic acid methyl ester (H-Daf-OMe) and benzyl ester (H-Daf-OBz1), respectively N-alpha-protection with Boc(2)O at 60 degreesC gave Boc-Daf-OMe and Boc-Daf-OBz1, saponification or hydrogenolysis of which resulted in complete decarboxylation. However, hydrazinolysis of the ester function afforded Boc-Daf-NHNH2, which was efficiently coupled with H-Ala-OMe by the acylazide method. Coupling of Boc-Ala-OH at the N-terminus of Daf could also be performed by the mixed anhydride method. However, coupling of the crowded Aib residue required the use of Boc-Aib-NCA. Daf, a new C-alpha,C-alpha-disubstituted glycine, is the first alpha -amino acid containing a rigid bipyridine ligand in a totally controlled spatial disposition relative to the C-alpha atom
Synthesis, conformational study, and spectroscopic characterization of the cyclic C-alpha,alpha-disubstituted glycine 9-amino-9-fluorenecarboxylic acid
No full textA series of terminally blocked peptides (to the pentamer level) from L-Ala and the cyclic C-alpha,C-alpha-disubstituted Gly residue Afc and one Gly/Afc dipeptide have been synthesized by solution method and fully characterized. The molecular structure of the amino acid derivative Boc-Afc-OMe and the dipeptide Boc-Afc-Gly-OMe were determined in the crystal state by X-ray diffraction. In addition, the preferred conformation of all of the model peptides was assessed in deuterochloroform solution by FT-IR absorption and H-1-NMR. The experimental data favour the conclusion that the Afc residue tends to adopt either the fully-extended (C-5) or a folded/helical structure. In particular, the former conformation is highly populated in solution and is also that found in the crystal state in the two compounds investigated. A comparison with the structural propensities of the strictly related C-alpha,C-alpha-disubstituted Gly residues Ac(5)c and D Phi g is made and the implications for the use of the Afc residue in conformationally constrained analogues of bioactive peptides are briefly examined. A spectroscopic (UV absorption, fluorescence, CD) characterization of this novel aromatic C-alpha,C-alpha-disubstituted Gly residue is also reported
Afc can adopt either the fully extended or a turn conformation
No full textWe have synthesized by solution methods and fully characterized two sets of terminally protected peptides based on the tricyclic C-alpha,C-alpha-disubstituted glycine Afc. The conformational preferences of the Afc/Gly peptides were examined by FT-IR absorption and H-1 NMR techniques, while those of the Afc/TOAC peptides were primarily investigated by using fluorescence spectroscopy. The X-ray diffraction structure of an Afc derivative was also analyzed. The body of solution and crystal-state experimental data conclusively confirms previous findings that the Afc residue may either adopt the fully extended (C-5) or a turn conformation
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