- Water-solubilized, cap-stabilized, helical polyalanines: Calibration standards for NMR and CD analyses
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NMR and CD studies are reported for two length series of solubilized, spaced, highly helical polyalanines that are N-capped by the optimal helix stabilizer βAsp-Hel and C-capped by β-aminoalanine beta and that are studied in water at 2°C, pH 1 -8. NMR analysis yields a structural characterization of the peptide AcβAspHelAla 8betaNH2 and selected members of one βAspHelAlanbeta series. At pH > 4.5 the βASpHel cap provides a preorganized triad of carboxylate anion and two amide residues that is complementary to the helical polyalanine N-terminus. The C-terminal β-aminoalanine assumes a helix-stabilizing conformation consistent with literature precedents. H(N)CO NMR experiments applied to capped, uniformly 13C- and 15N-labeled Ala 8 and Ala12 peptides define Alan hydrogen bonding signatures as α-helical without detectable 310 character. Relative NH→ND exchange rates yield site protection factors PFi that define uniquely high fractional helicities FH for the peptide Alan regions. These Alan calibration series, studied in water and lacking helix-stabilizing tertiary structure, yield the first 13C NMR chemical shifts, 3JHNHα coupling constants, and CD ellipticities [θMolar] λ,n characteristic of a fully helical alanine within an Alan context. CD data are used to assign parameters X and [θ]λ,∞, required for rigorous calculation of FH values from CD ellipticities.
- Heitmann, Bjoern,Job, Gabriel E.,Kennedy, Robert J.,Walker, Sharon M.,Kemp, Daniel S.
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- Opioid deltorphin C analogues containing cis- or trans-2- or 3- or 4- aminocyclohexanecarboxylic acid residues
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The solid phase synthesis, based on the Fmoc chemical protocol, was used to prepare ten deltorphin C (Del-C; H-Tyr-D-Ala-Phe-Asp-Val-Val-Gly-NH2) analogues containing cis- and trans- 2 or 3- or 4- aminocyclohexanecarboxylic acid (ACCA) residues at position 2, ACCA-peptides showed high resistance to degradation by plasma or brain enzymes, negligible affinity for the κ- binding site and modest δ- and/or μ-receptor affinities. Both [cis-3- ACCA2]Del-C analogues and one trans isomer are the only deltorphin analogues of this series exhibiting an appreciable δ-affinity and selectivity. These data suggest that the presence of a conformationally constrained ACCA residue in position 2 of the 'message' sequence of deltorphin C is slightly tolerated.
- Marastoni, Mauro,Guerrini, Remo,Balboni, Gianfranco,Salvadori, Severo,Fantin, Giancarlo,Fogagnolo, Marco,Lazarus, Lawrence H.,Tomatis, Roberto
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- Synthesis and Opioid Activity of Dynorphin A-(1-13)NH2 Analogues Containing cis- and trans-4-Aminocyclohexanecarboxylic acid
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It has been proposed that the "message" sequence of dynorphin A (Dyn A) exists in an extended conformation in aqueous solution (Schiller, P.W.Int.J.Pept.Protein Res. 1983, 21 307-312).Molecular modeling suggested that trans-4-aminocyclohexanecarboxylic acid (trans-ACCA) might function as a conformationally constrained replacement for Gly2-Gly3 of Dyn A in such an extended conformation.ACCA was synthesized by catalytic hydrogenation of p-aminobenzoic acid, and the cis and trans isomers were separated by fractional recrystallization.Analogues ofDyn A-(1-13)-NH2 containing cis- and trans-ACCA were prepared by solid-phase peptide synthesis using the Fmoc chemical protocol.Results from radioligand binding assays indicated that the peptides have modest affinity for κ opioid receptors (Ki's = 9.1 and 13.4 nM for 2-3>- and 2-3>Dyn A-(1-13)NH2, respectively) and modest κ-receptor selectivity (Ki ratio (κ/μ/δ) = 1/13/210 and 1/21/103, respectively) 2-3>- and 2-3>Dyn A-(1-13)-NH2 are the first reported Dyn A analogues constrained in the "message" sequence that are selective for κ receptors.The cis-ACCA analogue showed very weak opioid activity (IC50 = 4.0 μM) in the guinea pig ileum.
- Snyder, Kristin R.,Murray, Thomas F.,DeLander, Gary E.,Aldrich, Jane V.
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p. 1100 - 1103
(2007/10/02)
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