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  • 1
    Electronic Resource
    Electronic Resource
    Evaluation of two new coupling agents for incorporation of α,α-dialkylamino acids, such as α-methylalanine, in solid-phase peptide synthesis (1995)
    Springer
    International journal of peptide research and therapeutics 1 (1995), S. 283-290 
    Details
    ISSN: 1573-3904
    Keywords: α,α-Dialkylamino acids ; α-Methylalanine ; Aminoisobutyric acid ; Coupling reagents ; HATU ; Amino acid fluoride ; Peptaibol ; Emerimicin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The introduction of solid-phase peptide synthesis (SPPS) has greatly facilitated the preparation of peptides containing proteinaceous amino acids. Less common, sterically hindered α,α-dialkylamino acids, such as α-methylalanine (MeA, aminoisobutyric acid, Aib), have proven a synthetic challenge for incorporation by this approach, especially when present in contiguous sequences. Solution protocols, utilizing highly reactive intermediates such as oxazalones, are generally used during the preparation of peptaibol antibiotics such as alamethicin, emerimicin, etc. which contain such contiguous sequences. Two recently developed coupling strategies (O-(7-azabenzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate, HATU, and Fmoc-protected amino acid fluorides) allow peptides comprising contiguous sequences of α,α-dialkylamino acids to be prepared using SPPS. The present study evaluates the relative merits of these two methods on a set of difficult peptides containing oligo-MeA sequences.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00119769
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  • 2
    Electronic Resource
    Electronic Resource
    Facilitated synthesis of peptaibols: Alamethicin via enzymatic segment condensation (1992)
    New York : Wiley-Blackwell
    Biopolymers 32 (1992), S. 1461-1470 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have used a combined chemical-enzymatic approach to facilitate the total synthesis of the 20-residue peptaibol, alamethicin. The 1-11 segment of alamethicin, having a C-terminal Gly, and the 12-20 segment, having an N-terminal Leu, were prepared by well-established chemical methods, and then coupled using papain to afford a 54% yield of alamethicin in straightforward fashion. In contrast to the reported chemical syntheses of alamethicin requiring side-chain protection at Glu, 18 the papain-catalyzed coupling proceeded readily and selectively using a C-terminal segment having a free γ-carboxyl group at this position. Several alamethicin partial sequences were obtained via enzymatic formation of the Gly 11-Leu12 bond. The high efficiency of this route is illustrated by the enzymatic assembly of the 1-17 alamethicin fragment on a 400-mg scale in 62% yield. An alternative route to alamethicin through enzymatic formation of the Ala6-Gln7 bond was less successful because of a low yield in the final coupling. © 1992 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360321106
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  • 3
    Electronic Resource
    Electronic Resource
    Nonspecific protease-catalyzed hydrolysis/synthesis of a mixture of peptides: Product diversity and ligand amplification by a molecular trap (1996)
    New York : Wiley-Blackwell
    Biopolymers 40 (1996), S. 617-625 
    Details
    ISSN: 0006-3525
    Keywords: nonspecific protease-catalyzed hydrolysis/synthesis ; product diversity ; ligand amplification ; molecular trap ; peptide library ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We sought to develop a peptide library in solution and dynamically screen this library for peptides that would bind to macromolecules of interest. Peptide diversity was achieved in an initial stock solution of peptides by using proteases under conditions in which both hydrolysis and synthesis occurred. As an example, a simple reaction containing YGG, FL, and thermolysin resulted in the synthesis of YGGFL as well as many other undefined products. When low molecular weight products of a reaction containing VA, AL, and thermolysin were subsequently exposed to dipeptidase, 7 out of 9 potential dipeptides were observed. Incubation of protease with an hydrolysate of albumin and a radiolabeled peptide resulted in the radiolabel participating in reactions other than simple hydrolysis and, after 24 h, the specific activity of radiolabel was shown by high performance liquid chromatography to disperse to a level that would be necessary in the event of maximum theoretical diversity. When a binding macromolecule was exposed to this system, ligand production was amplified relative to reactions run in the absence of binding macromolecule. This protease-based peptide scrambling and binding system was utilized for the discovery of novel peptides that bind to fibrinogen. © 1997 John Wiley & Sons, Inc. Biopoly 40: 617-625, 1997
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Conformational mimicry: Synthesis and solution conformation of a cyclic somatostatin hexapeptide containing a tetrazole cis amide bond surrogateThe first two authors (DDB and JZ) contributed equally to the experimental work. This is the fourth in a series of articles32,35,37 detailing the conformational mimicry of the 1,5-disubstituted tetrazole. (1995)
    New York : Wiley-Blackwell
    Biopolymers 36 (1995), S. 181-200 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Potent, cyclic hexapeptide analogues of somatostatin are generally believed to adopt some common secondary structural features: a II′ β turn at one end of the cycle, and a type VI turn with a cis amide bond at the other. A proposed cis amide surrogate, the 1,5-disubstituted tetrazole, has been placed into a cyclic hexapeptide analog of somatostatin in order to constrain the putative cis amide bond. The final cyclization was done by either chemical or enzymatic means. The product, cyclo(Ala6-Tyr7-D-Trp8-Lys9-Val10-Phe11-Ψ[CN4]), was found to have 83% of the activity of somatostatin. Solution nmr analysis in DMSO/water revealed that the backbone as well as side chain χ1 and χ2 were well ordered. Relaxation matrix methods were used to extract distance restraints from the nuclear Overhauser effect spectroscopy data set, and these were used in a systematic search of torsional space to identify structures consistent with the nmr data. Restrained minimizations of these structures using a number of different force fields produced structures having the expected βII′ turn at D-Trp8-Lys9 and αβVIa turn in the Phe11-Ψ[CN4]-Ala6 portion of the molecule. The similarity of the minimized structures to those previously reported for cyclic hexapeptide analogues of somatostatin confirms the similarity of the tetrazole geometry to that of the cis amide in solution. © 1995 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360360207
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