Synthesis and properties of peptides containing beta-turn mimetics based on alpha-alkylproline derivatives
Synthesis and properties of peptides containing beta-turn mimetics based on alpha-alkylproline derivatives
Peptides containing alpha-methyl amino acid residues exhibit a restricted backbone flexibility when compared to those comprised of the normal proteinogenic amino acids. In order to investigate its effect on the flexibility of peptides, (2S) 2-methylproline was synthesised using the methodology of Seebach et.al. (J. Am. Chem. Soc. 1983, 105, 5390). The (2S) 2-methylproline was protected using the 9-fluorenylmethoxycarbonyl (Fmoc) group for use in solid phase peptide synthesis. The peptide YPYDVPVYA was shown by Dyson et.al. (Nature 1985, 318, 480) to have a preference, in water, for a type II β-turn at the residues YPYD. Two analogues of this peptide were synthesised using (2S)-2-methylproline (= P^Me) (YP^MeYDVPDYA and Ac-YP^MeYDVPDYA). NMR studies on these peptides indicate that the (2S)-2-methylproline considerably stabilises a reverse turn conformation. Previously two monoclonal antibodies were isolated which specifically recognise an epitope at the β-turn formed by YPYD (D. Brennand, personal communication). The dissociation constants of these antibodies and the analogues were lower than for the original peptide. These effects may be due to the conformational restrictions imposed by the 2-methylproline residue. Three more analogues were synthesised (Ac-Y-[1'-13C]PMe-[15N]FDVPDYA, Ac-FPMeFDVPDYA and Ac-[2-13C]F- [1'-13C]PMe-[15N]F- [15N]DVPDYA) to facilitate the development of a new triple resonance isotope edited ROESY experiment, which will be used to investigate the conformation of the peptide when bound to the antibodies. To establish whether the same stabilisation of conformation could be observed in other peptides, two analogues of the hormone bradykinin (BK = RPPGFSPFR) were synthesised with (2S) 2-methylproline in either the 3- or 7-position. In contrast to BK, which appears largely disordered by NMR, both BK analogues show a network of ROE connectivities, which is consistent with an ordered structure due to two reverse turns whose formation appears to be cooperative. The IC50 values for these analogues indicate that they are much less active than BK. The reasons for the difference in relative activities are discussed. An investigation into ways of improving the synthesis of the β-turn mimetic (5'R,2S) 3-(4-hydroxyphenyl)-2-(6-oxo-1.7-diaxa-spiro[4,4]non-7-yl)-proprionic acid was carried out, this included the preparation of the (5'S,2S) diastereomer. The [4,5]-spirocyclic compound could not be easily synthesised.
University of Southampton
1992
Welsh, John Hamilton
(1992)
Synthesis and properties of peptides containing beta-turn mimetics based on alpha-alkylproline derivatives.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Peptides containing alpha-methyl amino acid residues exhibit a restricted backbone flexibility when compared to those comprised of the normal proteinogenic amino acids. In order to investigate its effect on the flexibility of peptides, (2S) 2-methylproline was synthesised using the methodology of Seebach et.al. (J. Am. Chem. Soc. 1983, 105, 5390). The (2S) 2-methylproline was protected using the 9-fluorenylmethoxycarbonyl (Fmoc) group for use in solid phase peptide synthesis. The peptide YPYDVPVYA was shown by Dyson et.al. (Nature 1985, 318, 480) to have a preference, in water, for a type II β-turn at the residues YPYD. Two analogues of this peptide were synthesised using (2S)-2-methylproline (= P^Me) (YP^MeYDVPDYA and Ac-YP^MeYDVPDYA). NMR studies on these peptides indicate that the (2S)-2-methylproline considerably stabilises a reverse turn conformation. Previously two monoclonal antibodies were isolated which specifically recognise an epitope at the β-turn formed by YPYD (D. Brennand, personal communication). The dissociation constants of these antibodies and the analogues were lower than for the original peptide. These effects may be due to the conformational restrictions imposed by the 2-methylproline residue. Three more analogues were synthesised (Ac-Y-[1'-13C]PMe-[15N]FDVPDYA, Ac-FPMeFDVPDYA and Ac-[2-13C]F- [1'-13C]PMe-[15N]F- [15N]DVPDYA) to facilitate the development of a new triple resonance isotope edited ROESY experiment, which will be used to investigate the conformation of the peptide when bound to the antibodies. To establish whether the same stabilisation of conformation could be observed in other peptides, two analogues of the hormone bradykinin (BK = RPPGFSPFR) were synthesised with (2S) 2-methylproline in either the 3- or 7-position. In contrast to BK, which appears largely disordered by NMR, both BK analogues show a network of ROE connectivities, which is consistent with an ordered structure due to two reverse turns whose formation appears to be cooperative. The IC50 values for these analogues indicate that they are much less active than BK. The reasons for the difference in relative activities are discussed. An investigation into ways of improving the synthesis of the β-turn mimetic (5'R,2S) 3-(4-hydroxyphenyl)-2-(6-oxo-1.7-diaxa-spiro[4,4]non-7-yl)-proprionic acid was carried out, this included the preparation of the (5'S,2S) diastereomer. The [4,5]-spirocyclic compound could not be easily synthesised.
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Published date: 1992
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Local EPrints ID: 461985
URI: http://eprints.soton.ac.uk/id/eprint/461985
PURE UUID: 4addab83-7fc5-4905-97be-224a5a0f3d28
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Date deposited: 04 Jul 2022 18:59
Last modified: 04 Jul 2022 18:59
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Author:
John Hamilton Welsh
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