| 1. |
- Buttner, Frank, et al.
(författare)
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Cyclic B-Tetra- and Pentapeptides: Synthesis through On-Resin Cyclization and Confomrational Studies by X-Ray, NMR and CD Spectroscopy and Theoretical Calculations
- 2005
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Ingår i: Chem. Eur. J.. - : Wiley. ; 11, s. 6145-6158
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Tidskriftsartikel (refereegranskat)abstract
- The solution-phase synthesis of the simplest cyclic B-tetrapeptide, cyclo(B-Ala)4 (4), as well as the solidphase syntheses through side chain anchoring and on-resin cyclization of the cyclic B3-tetrapeptide cyclo-(B3hPhe-B3hLeu-B3hLys-B3hGln-) (14) and the first cyclic B3-pentapeptide cyclo- (B3hVal-B3hPhe-B3Leu- B3hLys-B3hLys-) (19) are reported. Extensive computational as well as spectroscopic studies, including X-ray and NMR spectroscopy, were undertaken to determine the preferred conformations of these unnatural oligomers in solution and in the solid state. cyclo(B-Ala)4 (4) with no chiral side chains is shown to exist as a mixture of rapidly interchanging conformers in solution, whereas inclusion of chiral side chains in the cyclo-B3-tetrapetpride causes stabilizaton of one dominating conformer. The cyclic B3-pentapeptide on the other hand shows larger conformational freedom. The X-ray structure of achiral cyclo(B-Ala)4 (4) displays a Ci-symmetrical 16-membered ring with adjacent C=O and N-H atoms pointing pair wise up and down with respect to the ring plane. CD spectorscopic examinations of all cyclic B-peptides were undertaken and revealed results valuable as starting point for further structural investigations of these entities.
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| 2. |
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| 3. |
- Hossain, M. Akhter, et al.
(författare)
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Solid phase synthesis and structural analysis of novel A-chain dicarba analogs of human relaxin-3 (INSL7) that exhibit full biological activity
- 2009
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Ingår i: Organic and biomolecular chemistry. - : Royal Society of Chemistry (RSC). - 1477-0520 .- 1477-0539. ; 7:8, s. 1547-1553
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Tidskriftsartikel (refereegranskat)abstract
- Replacement of disulfide bonds with non-reducible isosteres can be a useful means of increasing the in vivo stability of a protein. We describe the replacement of the A-chain intramolecular disulfide bond of human relaxin-3 (H3 relaxin, INSL7), an insulin-like peptide that has potential applications in the treatment of stress and obesity, with the physiologically stable dicarba bond. Solid phase peptide synthesis was used to prepare an A-chain analogue in which the two cysteine residues that form the intramolecular bond were replaced with allylglycine. On-resin microwave-mediated ring closing metathesis was then employed to generate the dicarba bridge. Subsequent cleavage of the peptide from the solid support, purification of two isomers and their combination with the B-chain via two intermolecular disulfide bonds, then furnished two isomers of dicarba-H3 relaxin. These were characterized by CD spectroscopy, which suggested a structural similarity to the native peptide. Additional analysis by solution NMR spectroscopy also identified the likely cis/trans form of the analogs. Both peptides demonstrated binding affinities that were equivalent to native H3 relaxin on RXFP1 and RXFP3 expressing cells. However, although the cAMP activity of the analogs on RXFP3 expressing cells was similar to the native peptide, the potency on RXFP1 expressing cells was slightly lower. The data confirmed the use of a dicarba bond as a useful isosteric replacement of the disulfide bond.
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| 4. |
- Hossain, M. Akhter, et al.
(författare)
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Synthesis, conformation, and activity of human insulin-like peptide 5 (INSL5)
- 2008
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Ingår i: ChemBioChem. - : Wiley. - 1439-4227 .- 1439-7633. ; 9:11, s. 1816-1822
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Tidskriftsartikel (refereegranskat)abstract
- Insulin-like peptide 5 (INSL5) was first identified through searches of the expressed sequence tags (EST) databases. Primary sequence analysis showed it to be a prepropeptide that was predicted to be processed in vivo to yield a two-chain sequence (A and B) that contained the insulin-like disulfide cross-links. The high affinity interaction between INSL5 and the receptor RXFP4 (GPCR142) coupled with their apparent coevolution and partially overlapping tissue expression patterns strongly suggest that INSL5 is an endogenous ligand for RXFP4. Given that the primary function of the INSL5–RXFP4 pair remains unknown, an effective means of producing sufficient quantities of this peptide and its analogues is needed to systematically investigate its structural and biological properties. A combination of solid-phase peptide synthesis methods together with regioselective disulfide bond formation were used to obtain INSL5. Both chains were unusually resistant to standard synthesis protocols and required highly optimized conditions for their acquisition. In particular, the use of a strong tertiary amidine, DBU, as Nα-deprotection base was required for the successful assembly of the B chain; this highlights the need to consider incomplete deprotection rather than acylation as a cause of failed synthesis. Following sequential disulfide bond formation and chain combination, the resulting synthetic INSL5, which was obtained in good overall yield, was shown to possess a similar secondary structure to human relaxin-3 (H3 relaxin). The peptide was able to inhibit cAMP activity in SK-N-MC cells that expressed the human RXFP4 receptor with a similar activity to H3 relaxin. In contrast, it had no activity on the human RXFP3 receptor. Synthetic INSL5 demonstrates equivalent activity to the recombinant-derived peptide, and will be an important tool for the determination of its biological function.
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| 5. |
- Hossain, M. Akhter, et al.
(författare)
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The A-chain of the human relaxin family peptides has distinct roles in the binding and activation of the different relaxin family peptide receptors
- 2008
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 283:25, s. 17287-17297
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Tidskriftsartikel (refereegranskat)abstract
- The relaxin peptides are a family of hormones that share a structural fold characterized by two chains, A and B, that are cross-braced by three disulfide bonds. Relaxins signal through two different classes of G-protein-coupled receptors (GPCRs), leucine-rich repeat-containing GPCRs LGR7 and LGR8 together with GPCR135 and GPCR142, now referred to as the relaxin family peptide (RXFP) receptors 1-4, respectively. Although key binding residues have been identified in the B-chain of the relaxin peptides, the role of the A-chain in their activity is currently unknown. A recent study showed that INSL3 can be truncated at the N terminus of its A-chain by up to 9 residues without affecting the binding affinity to its receptor RXFP2 while becoming a high affinity antagonist. This suggests that the N terminus of the INSL3 A-chain contains residues essential for RXFP2 activation. In this study, we have synthesized A-chain truncated human relaxin-2 and -3 (H2 and H3) relaxin peptides, characterized their structure by both CD and NMR spectroscopy, and tested their binding and cAMP activities on RXFP1, RXFP2, and RXFP3. In stark contrast to INSL3, A-chain-truncated H2 relaxin peptides lost RXFP1 and RXFP2 binding affinity and concurrently cAMP-stimulatory activity. H3 relaxin A-chain-truncated peptides displayed similar properties on RXFP1, highlighting a similar binding mechanism for H2 and H3 relaxin. In contrast, A-chain-truncated H3 relaxin peptides showed identical activity on RXFP3, highlighting that the B-chain is the sole determinant of the H3 relaxin-RXFP3 interaction. Our results provide new insights into the action of relaxins and demonstrate that the role of the A-chain for relaxin activity is both peptide- and receptor-dependent.
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| 6. |
- Hossain, M. Akhter, et al.
(författare)
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The structural and functional role of the B-chain C-terminal arginine in the relaxin-3 peptide antagonist, R3(B Delta 23-27)R/I5.
- 2009
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Ingår i: Chemical Biology and Drug Design. - : Wiley. - 1747-0277 .- 1747-0285. ; 73:1, s. 46-52
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Tidskriftsartikel (refereegranskat)abstract
- Relaxin-3, a member of the insulin superfamily, is involved in regulating stress and feeding behavior. It is highly expressed in the brain and is the endogenous ligand for the receptor RXFP3. As relaxin-3 also interacts with the relaxin receptor RXFP1, selective agonists and antagonists are crucial for studying the physiological function(s) of the relaxin-3/RXFP3 pair. The analog R3(B Delta 23-27)R/I5, in which a C-terminally truncated human relaxin-3 (H3) B-chain is combined with the INSL5 A-chain, is a potent selective RXFP3 antagonist and has an Arg residue remaining on the B-chain C-terminus as a consequence of the recombinant protein production process. To investigate the role of this residue in the RXFP3 receptor binding and activation, the analogs R3(B Delta 23-27)R/I5 and R3(B Delta 23-27)R containing the B-chain C-terminal Arg as well as R3(B Delta 23-27)/I5 and R3(B Delta 23-27), both lacking the Arg, were chemically assembled and their secondary structure and receptor activity assessed. The peptides generally had a similar conformation but those with the extra Arg residue displayed a significantly increased affinity for the RXFP3. Interestingly, in contrast to R3(B Delta 23-27)R and R3(B Delta 23-27)R/I5, the peptide R3(B Delta 23-27) is a weak agonist. This suggests that the C-terminal Arg, although increasing the affinity, alters the manner in which the peptide binds to the receptor and thereby prevents activation, giving R3(B Delta 23-27)R/I5 its potent antagonistic activity.
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| 7. |
- Norgren, Anna, et al.
(författare)
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Synthesis and circular dichroism spectroscopic investigations of oligomeric β-peptoids with α-chiral side chains
- 2006
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Ingår i: Organic Letters. - : American Chemical Society (ACS). - 1523-7060 .- 1523-7052. ; 8:20, s. 4533-4536
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Tidskriftsartikel (refereegranskat)abstract
- Biomimetic oligomers are of large interest both as targets for combinatorial and parallel synthetic efforts and as foldamers. For example, shorter peptoid derivatives of beta-peptides, i.e., oligo-N-substituted beta-Ala, have been described as potential lead structures. Herein, we describe a solid-phase synthetic route to beta-peptoids with alpha-chiral aromatic N-substituents up to 11 residues long. Furthermore, the folding propensities of these oligomers were investigated by circular dichroism (CD) spectroscopy.
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| 8. |
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| 9. |
- Zhang, Suode, et al.
(författare)
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Facile synthesis of N-protected amino acid assisted by microwave irradiation
- 2008
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Ingår i: International journal of peptide research and therapeutics. - : Springer Science and Business Media LLC. - 1573-3149 .- 1573-3904. ; 14:3, s. 219-222
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Tidskriftsartikel (refereegranskat)abstract
- A highly efficient and safe methodology for synthesis of various N-protected amino acid ethyl esters have been established in this study. This methodology employs orthoesters as both esterification reagent and solvent for protected amino acids. The reactions were carried out under microwave irradiation in neutral conditions for only 2 min, resulting in highly pure crude products in most cases. This strategy works with a variety of N-protecting groups, such as acid labile protecting group: BOC and tBu, base labile protecting group: Fmoc, hydrogenation labile protecting group: Z and Na/NH3 labile protecting group: Tos, thus providing facile access to numerous valuable building blocks for solid phase synthesis. Further reduction of the crude protected amino acid ethyl ester by sodium borohydride under mild conditions led to the corresponding protected beta-amino alcohols with excellent yield, as demonstrated by three examples.
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