Development of a synthetic cyclized peptide derived from α‐fetoprotein that prevents the growth of human breast cancer

Abstract: The peptide, EMTPVNPG, derived from alpha‐fetoprotein, inhibits estrogen‐stimulated growth of immature mouse uterus and estrogen‐dependent proliferation of human breast cancer cells. However, the biological activities of the peptide diminish over time in storage, even when in the lyophilized state, probably because of peptide aggregation through hydrophobic interaction among monomers. Two analogs of EMTPVNPG were designed with the intent of minimizing aggregation and retaining biological activity during prolonged storage. EMTOVNOG, where O is 4‐hydroxyproline, is a linear peptide generated by substituting 4‐hydroxyproline for the two prolines, thereby increasing peptide hydrophilicity. This analog exhibited a dose‐dependent inhibition of estrogen‐stimulated growth of immature mouse uterus similar to that of EMTPVNPG (maximal activity at 1 µg/mouse). A second analog, cyclo‐(EMTOVNOGQ), a hydrophilic, cyclic analog with increased conformational constraint, was as potent as the other peptides in its inhibition of estrogen‐dependent growth of immature mouse uterus, and had an expanded effective dose range. Both linear and cyclized hydroxyproline‐substituted analogs exhibited indefinite shelf‐life. Furthermore, both analogs inhibited the estrogen‐dependent growth of MCF‐7 human breast cancer growing as a xenograft in SCID mice. These analogs may become significant, novel agents for the treatment of breast cancer.     

Studies on a growth‐inhibitory peptide derived from alpha‐fetoprotein and some analogs

Abstract: A 34‐amino acid synthetic peptide was derived from the third domain of human alpha‐fetoprotein, and the peptide was shown to inhibit estrogen‐stimulated growth. Under certain conditions, however, the peptide lost growth‐inhibitory activity. A biophysical study of the peptide was undertaken with a goal of obtaining completely reliable preparations. The peptide was studied using gel‐filtration column chromatography as a function of peptide concentration and age of solution, and was found to exhibit complex aggregation behaviors. During the early period (0–3 h) after dissolving lyophilized peptide into pH 7.4 buffer, solutions were composed mostly of trimers. At higher peptide concentrations (≥ 3.0 g/L), the trimers aggregated extensively to a large aggregate (minimum size ≈ 102 peptides). At 5.0–8.0 g/L, these large aggregates increased in size (up to ≈ 146 peptides) until trimers were largely exhausted from solution. During the later times (> 3 h) after sample preparation, the trimeric oligomer of the peptide dissociated slowly to form dimers for samples at 0.10–3.0 g/L. After their build‐up, a very small number of dimers associated to form hexamers. Disulfide bonds stabilized the dimers as indicated by the conversion of dimers to trimers upon the addition of a reducing agent, and the failure of dimers to form in the presence of reducing agent. Reducing agent did not affect trimer or large aggregate formation. Trimers were found to be active in an assay monitoring inhibition of estrogen‐stimulated growth, whereas dimers and large aggregates were inactive. The two cysteines in the peptide were modified to either S‐methylcysteine or S‐(2‐aminoethyl)cysteine, and both derivatives showed significant growth‐inhibition activity. A serine analog in which both cysteines were replaced had very different aggregation behavior than the cysteine peptide and lacked its growth inhibitory ability. Peptide aggregation is critically important in establishing the ability of the peptide to inhibit growth and have anticancer activity, but the state of its two cysteines is of little influence.     

Protective effects of β‐sheet breaker α/β‐hybrid peptide against amyloid β‐induced neuronal apoptosis in vitro

Alzheimer's disease is most common neurodegenerative disorder and is characterized by increased production of soluble amyloid‐β oligomers, the main toxic species predominantly formed from aggregation of monomeric amyloid‐β (Aβ). Increased production of Aβ invokes a cascade of oxidative damages to neurons and eventually leads to neuronal death. This study was aimed to investigate the neuroprotective effects of a β‐sheet breaker α/β‐hybrid peptide (BSBHp) and the underlying mechanisms against Aβ₄₀‐induced neurotoxicity in human neuroblastoma SH‐SY5Y cells. Cells were pretreated with the peptide Aβ₄₀ to induce neurotoxicity. Assays for cell viability, cell membrane damage, cellular apoptosis, generation of reactive oxygen species (ROS), intracellular free Ca²⁺, and key apoptotic protein levels were performed in vitro. Our results showed that pretreatment with BSBHp significantly attenuates Aβ₄₀‐induced toxicity by retaining cell viability, suppressing generation of ROS, Ca²⁺ levels, and effectively protects neuronal apoptosis by suppressing pro‐apoptotic protein Bax and up‐regulating antiapoptotic protein Bcl‐2. These results suggest that α/β‐hybrid peptide has neuroprotective effects against Aβ₄₀‐induced oxidative stress, which might be a potential therapeutic agent for treating or preventing neurodegenerative diseases.     

New tools for the control of peptide conformation: the helicogenic Cα‐methyl,Cα‐cyclohexylglycine*

Abstract: The novel C^α‐tetrasubstituted α‐amino acid C^α‐methyl, C^α‐cyclohexylglycine was prepared by hydrogenation of its C^α‐methyl, C^α‐phenylglycine precursor. Terminally protected homodi‐, homotri‐, and homotetrapeptides from C^α‐methyl, C^α‐cyclohexylglycine and co‐oligopeptides to the pentamer level in combination with Gly or α‐aminoisobutyric acid residues were prepared by solution methods and fully characterized. The results of a conformational analysis, performed by use of Fourier transform infrared (FT‐IR) spectrophotomet absorption, ¹H NMR, and X‐ray diffraction techniques, support the contention that this C^α‐methylated, C^β‐trisubstituted aliphatic α‐amino acid is an effective β‐turn and 3₁₀‐helix inducer in tri‐ and longer peptides as its C^α‐methyl valine parent compound, but partially divergent from the corresponding aromatic C^α‐methyl, C^α‐diphenylmethylglycine residue, known to promote folded and fully extended structures to a significant extent in these oligomers.     

Improved solid‐phase synthesis of α,α‐dialkylated amino acid‐rich peptides with antimicrobial activity*

Abstract: A homologous series of nonapeptides and their acetylated versions were successfully prepared using solid‐phase synthetic techniques. Each nonapeptide was rich in α,α‐dialkylated amino acids [one 4‐aminopiperidine‐4‐carboxylic acid (Api) and six α‐aminoisobutyric acid (Aib) residues] and also included lysines or lysine analogs (two residues). The incorporation of the protected dipeptide 9‐fluorenylmethyloxycarbonyl (Fmoc)‐Aib‐Aib‐OH improved the purity and overall yields of these de novo designed peptides. The helix preference of each nonapeptide was investigated in six different solvent environments, and each peptide's antimicrobial activity and cytotoxicity were studied. The 3₁₀‐helical, amphipathic design of these peptides was born out most prominently in the N‐terminally acetylated peptides. Most of the peptides exhibited modest activity against Escherichia coli and no activity against Staphylococcus aureus. The nonacetylated peptides (concentrations ≤100 μm ) and the acetylated peptides (concentrations ≤200 μm ) did not exhibit any significant cytotoxicity with normal (nonactivated) murine macrophages.     

Conformational investigation of α, β-dehydropeptides

The crystal structure of Ac-Pro-ΔVal-NHCH₃ was examined to determine the influence of the α,β-dehydrovaline residue on the nature of peptide conformation. The peptide crystallizes from methanol-diethyl ether solution at 4° in needle-shaped form in orthorhombic space group P2₁2₁2₁ with a= 11.384(2) Å, b = 13.277(2) Å, c = 9.942(1) Å. V = 1502.7(4) ų Z = 4, D_m= 1.17 g cm^?3 and D_c=1.18 g cm^?3 The structure was solved by direct methods using SHELXS-86 and refined to an R value of 0.057 for 1922 observed reflections. The peptide is found to adopt a β-bend between the type I and the type III conformation with φ₁=?68.3(4)°, ψ₁=? 20.1(4)°, φ₂=?73.5(4)°= and Ψ₂=?14.1(4)°=. An intramolecular hydrogen bond between the carbonyl oxygen of ith residue and the NH of (i+ 3)th residue stabilizes the β-bend. An additional intermolecular N.,.O hydrogen bond joins molecules into infinite chains. In the literature described crystal structures of peptides having a single α,β-dehydroamino acid residue in the (i+ 2) position and forming a β-bend reveal a type II conformation.     

‘100 years of peptide synthesis’: ligation methods for peptide and protein synthesis with applications to β‐peptide assemblies*

Abstract: A brief survey of the history of peptide chemistry from Theodore Curtius to Emil Fischer to Bruce Merrifield is first presented. The discovery and development of peptide ligation, i.e. of actual chemical synthesis of proteins are described. In the main chapter, ‘ Synthesis of Proteins by Chemical Ligation ’ a detailed discussion of the principles, reactivities and mechanisms involved in the various coupling strategies now applied (ligation, chemical ligation, native chemical ligation) is given. These include coupling sites with cysteine and methionine (as well as the seleno analogs), histidine, glycine and pseudo‐prolines, ‘unrestricted’ amino‐acid residues (using the Staudinger reaction), as well as solid‐phase segment coupling by thioligation of unprotected peptides. In another section, ‘ Synthesis of β‐peptides by Thioligation ’, couplings involving β²‐ and β³‐peptides are described (with experimental details).     

Facile synthesis of Nα‐protected‐l‐α,γ‐diaminobutyric acids mediated by polymer‐supported hypervalent iodine reagent in water

Abstract: Hofmann rearrangement of N^α‐Boc‐l ‐Gln‐OH mediated by a polymer‐supported hypervalent iodine reagent poly[(4‐diacetoxyiodo)styrene] (PSDIB) in water afforded N^α‐Boc‐l ‐α,γ‐diaminobutyric acid (Boc‐Dab‐OH, 1 ) in 87% yield. N^α‐Z‐derivative (Z‐Dab‐OH, 2 ) was prepared with PSDIB in 83% yield. Since the reaction of N^α‐Fmoc‐Gln‐OH by this procedure did not proceed because of the insolubility of Fmoc‐Gln‐OH in aqueous media, we synthesized Fmoc‐Dab(Boc)‐OH ( 5 ) from 2 in 54% yield. Polymyxin B heptapeptide (PMBH) which contains four Dab residues was successfully synthesized in a solution‐phase synthesis.     

The Proteolytic Stability and Cytotoxicity Studies of l‐Aspartic Acid and l‐Diaminopropionic Acid derived β‐Peptides and a Mixed α/β‐Peptide

The use of peptides as drugs in pharmaceutical applications is hindered by their susceptibility to proteolysis and therefore low bioavailability. β‐Peptides that contain an additional methylene group in the backbone, are gaining recognition from a pharmaceutical stand point as they are considerably more resilient to proteolysis and metabolism. Recently, we reported two new classes of β ‐peptides, β ³‐ and β²‐peptides derived from l ‐aspartic acid and l ‐diaminopropionic acid, respectively. Here, we report the proteolytic stability of these β‐peptidic compounds and a mixed α /β‐peptide against three enzymes (pronase, trypsin and elastase), as well as, human serum. The stability of these peptides was compared to an α‐peptide. Peptides containing β‐linkages were resistant to all conditions. The mixed α /β‐peptide, however, exhibited proteolysis in the presence of trypsin and pronase but not elastase. The rate of degradation of the mixed α /β‐peptide was slower than that would be expected for an α‐peptide. In addition, these β‐peptides were not toxic to HeLa and COS‐1 cell lines as observed by MTT cytotoxicity assay. These results expand the scope of mixed α /β‐peptides containing β‐amino acids or small β‐peptide fragments as therapeutic peptides.     

Transforming growth factor β‐activated kinase 1 inhibitor suppresses the proliferation in triple‐negative breast cancer through TGF‐β/TGFR pathway

Breast cancer is one of the most invasive cancer types in female population. The functional activity of Transforming growth factor β‐activated kinase 1 (TAK1) in breast cancer progression increasingly attracts attention as it provides a potential target for antibreast cancer drug development. However, the fundamental role of TAK1 for triple‐negative breast cancer (TNBC) progression and the effect of potential anti‐TAK1 drug candidate needs to be further evaluated. Herein, we focused on the role of TAK1 in human breast cancer cells, and we hypothesized that the inhibition of TAK1 activation can repress the growth of human TNBC cells. We found that the TAK1 is robustly activated within cancer cell population of clinic‐derived TNBC samples and the human breast cancer cell lines in culture. Furthermore, we determined the effect of 5Z‐7‐oxozeaenol (5Z‐O), a TAK1‐specific small molecule inhibitor, on proliferation of human TNBC cell line. 5Z‐O treatment significantly suppressed the proliferation of human TNBC cells. Collectively, these demonstrate the role of TAK1 in human breast cancer and the antiproliferate effect of TAK1 inhibitor. Our study sets the stage for further research on TAK1 as a promising target for development of anti‐TNBC drugs and therapeutic strategies.     

Studies on analogs of a peptide derived from alpha‐fetoprotein having antigrowth properties

Abstract: A 34‐amino acid portion of the third domain of alpha‐fetoprotein possesses antigrowth and anticancer activities. Three analogs of this sequence were chemically synthesized, in which the two cysteines of the original sequence were replaced by alanines, glycines or serines. The original cysteine and alanine peptides formed trimers at 0.20 g/L in pH 7.4 phosphate buffer, and the glycine and serine peptides formed dimers. Trimer preparations were more potent in inhibiting estrogen‐induced growth in the mouse uterine assays than the two dimeric oligomers. Of salient importance is that the alanine peptide retained its trimeric form in solution much longer than the cysteine peptide. Antigrowth assays were performed starting with stock solutions at a peptide concentration of 0.20 g/L, because at very high peptide concentration (8.0 g/L) the peptides aggregated extensively. All the peptides, although differing in biological activity, had almost identical secondary structures. Unlike alpha‐fetoprotein, the three peptides have low amounts of α‐helix. Trifluoroethanol has the ability to convert peptides into a helical conformation when they have a propensity for that structure. At trifluoroethanol concentrations of 20% and higher, the alanine and glycine peptides were changed into highly helical structures.     

Synthetic peptides derived from the β2−β3 loop of Raphanus sativus antifungal protein 2 that mimic the active site

Abstract: Rs‐AFPs are antifungal proteins, isolated from radish (Raphanus sativus) seed or leaves, which consist of 50 or 51 amino acids and belong to the plant defensin family of proteins. Four highly homologous Rs‐AFPs have been isolated (Rs‐AFP1–4). The structure of Rs‐AFP1 consists of three β‐strands and an α‐helix, and is stabilized by four cystine bridges. Small peptides deduced from the native sequence, still having biological activity, are not only important tools to study structure?function relationships, but may also constitute a commercially interesting target. In an earlier study, we showed that the antifungal activity of Rs‐AFP2 is concentrated mainly in the β2?β3 loop. In this study, we synthesized linear 19‐mer peptides, spanning the entire β2?β3 loop, that were found to be almost as potent as Rs‐AFP2. Cysteines, highly conserved in the native protein, are essential for maintaining the secondary structure of the protein. Surprisingly, in the 19‐mer loop peptides, cysteines can be replaced by α‐aminobutyric acid, which even improves the antifungal potency of the peptides. Analogous cyclic 19‐mer peptides, forced to adopt a hairpin structure by the introduction of one or two non‐native disulfide bridges, were also found to possess high antifungal activity. The synthetic 19‐mer peptides, like Rs‐AFP2 itself, cause increased Ca²⁺ influx in pregerminated fungal hyphae.     

Agonist function of the recombinant α4β3δ GABAA receptor is dependent on the human and rat variants of the α4‐subunit

1. It is known that the α₄‐subunit is likely to occur in the brain predominantly in α₄β₃δ receptors at extrasynaptic sites. Recent studies have revealed that the α₁‐, α₄‐, γ₂‐ and δ‐subunits may colocalize extrasynaptically in dentate granule cells of the hippocampus. In the present study, we characterized a series of recombinant GABA_A receptors containing human (H) and rat (R) α₁/α₄‐, β₂/β₃‐ and γ_2S/δ‐subunits in Xenopus oocytes using the two‐electrode voltage‐clamp technique. 2. Both Hα₁β₃δ and Hα₄β₃γ_2S receptors were sensitive to activation by GABA and pentobarbital. Contrary to earlier findings that the α₄β₃δ combination was more sensitive to agonist action than the α₄β₃γ_2S receptor, we observed extremely small GABA‐ and pentobarbital‐activated currents at the wild‐type Hα₄β₃δ receptor. However, GABA and pentobarbital activated the wild‐type Rα₄β₃δ receptor with high potency (EC₅₀ = 0.5 ± 0.7 and 294 ± 5 μmol/L, respectively). 3. Substituting the Hα₄ subunit with Rα₄ conferred a significant increase in activation on the GABA and pentobarbital site in terms of reduced EC₅₀ and increased I_max. When the Hα₄ subunit was combined with the Rβ₃ and Rδ subunit in a heteropentameric form, the amplitude of GABA‐ and pentobarbital‐activated currents increased significantly compared with the wild‐type Hα₄β₃δ receptor. 4. Thus, the results indicate that the Rα₄β₃δ, Hα₁β₃δ and Hα₄β₃γ_2S combinations may contribute to functions of extrasynaptic GABA_A receptors. The presence of the Rα₄ subunit at recombinant GABA_A receptors containing the δ‐subunit is a strong determinant of agonist action. The recombinant Hα₄β₃δ receptor is a less sensitive subunit composition in terms of agonist activation.     

Conformational properties of hybrid peptides containing α‐ and ω‐amino acids*

Abstract: This review briefly surveys the conformational properties of guest ω‐amino acid residues when incorporated into host α‐peptide sequences. The results presented focus primarily on the use of β‐ and γ‐residues in αω sequences. The insertion of additional methylene groups into peptide backbones enhances the range of accessible conformations, introducing additional torsional variables. A nomenclature system, which permits ready comparisons between α‐peptides and hybrid sequences, is defined. Crystal structure determination of hybrid peptides, which adopt helical and β‐hairpin conformations permits the characterization of backbone conformational parameters for β‐ and γ‐residues inserted into regular α‐polypeptide structures. Substituted β‐ and γ‐residues are more limited in the range of accessible conformation than their unsubstituted counterparts. The achiral β,β‐disubstituted γ‐amino acid, gabapentin, is an example of a stereochemically constrained residue in which the torsion angles about the C^β–C^γ (θ₁) and C^α–C^β (θ₂) bonds are restricted to the gauche conformation. Hybrid sequences permit the design of novel hydrogen bonded rings in peptide structures.     

Peroxisome proliferator‐activated receptor‐γ coactivator‐1α in muscle links metabolism to inflammation

1. In higher eukaryotes, metabolism and immunity are tightly coupled. However, whereas in evolutionary terms a compromised immune response due to undernourishment has been the predominant problem, the inflammatory response to obesity and other lifestyle‐associated diseases has increased in relevance in Western societies in the past 100 years. 2. Traditionally, fat tissue has been considered as the major source of pro‐inflammatory secreted factors in these pathologies. However, in recent years the contribution of other tissues to disease‐causing chronic inflammation has been increasingly appreciated. 3. Peroxisome proliferator‐activated receptor‐γ coactivator‐1α (PGC‐1α) is one of the key regulatory factors in active skeletal muscle. Aberrant expression of PGC‐1α in inactive muscle fibres could be linked to a sedentary lifestyle, persistent systemic inflammation and a higher risk for many chronic diseases. Accordingly, modulation of PGC‐1α activity in skeletal muscle may have a broad range of therapeutic effects. Here, recent advances in the understanding of the role of muscle PGC‐1α in health and disease are reviewed.     

Synthesis,crystal structure and molecular conformation of Nα‐Boc‐l‐leucyl‐(Z)‐β‐(3‐pyridyl)‐α,β‐ dehydroalanyl‐l‐leucine methyl ester*

Abstract: A protected tridehydropeptide containing (Z)‐β‐(3‐pyridyl)‐α,β‐dehydroalanine (Δ^Z3Pal) residue, Boc‐Leu‐Δ^Z3Pal‐Leu‐OMe ( 1 ), was synthesized via Erlenmeyer azlactone method. X‐ray crystallographic analysis revealed that the peptide 1 adopts an extended conformation, which is similar to that of a Δ^ZPhe analog, Boc‐Leu‐Δ^ZPhe‐Leu‐OMe ( 2 ).     

Bioactive N‐terminal undecapeptides derived from parathyroid hormone: the role of α‐helicity*

Abstract: The N‐terminal 1–34 segment of parathyroid hormone (PTH) is fully active in vitro and in vivo and it can reproduce all biological responses in bone characteristic of the native intact PTH. Recent studies have demonstrated that N‐terminal fragments presenting the principal activating domain such as PTH(1–11) and PTH(1–14) with helicity‐enhancing substitutions yield potent analogues with PTH(1–34)‐like activity. To further investigate the role of α‐helicity on biological potency, we designed and synthesized by solid‐phase methodology the following hPTH(1–11) analogues substituted at positions 1 and/or 3 by the sterically hindered and helix‐promoting C^α‐tetrasubstituted α‐amino acids α‐amino isobutyric acid (Aib), 1‐aminocyclopentane‐1‐carboxylic acid (Ac₅c) and 1‐aminocyclohexane‐1‐carboxylic acid (Ac₆c): Ac₅c‐V‐Aib‐E‐I‐Q‐L‐M‐H‐Q‐R‐NH₂ ( I ); Aib‐V‐Ac₅c‐E‐I‐Q‐L‐M‐H‐Q‐R‐NH₂ ( II ); Ac₆c‐V‐Aib‐E‐I‐Q‐L‐M‐H‐Q‐R‐NH₂ ( III ); Aib‐V‐Ac₆c‐E‐I‐Q‐L‐M‐H‐Q‐R‐NH₂ ( IV ); Aib‐V‐Aib‐E‐I‐Q‐L‐M‐H‐Q‐R‐NH₂ ( V ); S‐V‐Aib‐E‐I‐Q‐L‐M‐H‐Q‐R‐NH₂ ( VI ), S‐V‐Ac₅c‐E‐I‐Q‐L‐M‐H‐Q‐R‐NH₂ ( VII ); Ac₅c‐V‐S‐E‐I‐Q‐L‐M‐H‐Q‐R‐NH₂ ( VIII ); Ac₆c‐V‐S‐E‐I‐Q‐L‐M‐H‐Q‐R‐NH₂ ( IX ); Ac₅c‐V‐Ac₅c‐E‐I‐Q‐L‐M‐H‐Q‐R‐NH₂ ( X ); Ac₆c‐V‐Ac₆c‐E‐I‐Q‐L‐M‐H‐Q‐R‐NH₂ ( XI ). All analogues were biologically evaluated and conformationally characterized in 2,2,2‐trifluoroethanol (TFE) solution by circular dichroism (CD). Analogues I – V , which cover the full range of biological activity observed in the present study, were further conformationally characterized in detail by nuclear magnetic resonance (NMR) and computer simulations studies. The results of ligand‐stimulated cAMP accumulation experiments indicated that analogues I and II are active, analogues III , VI and VII are very weakly active and analogues IV , V , VIII–XI are inactive. The most potent analogue, I exhibits biological activity 3500‐fold higher than that of the native PTH(1–11) and only 15‐fold weaker than that of the native sequence hPTH(1–34). Remarkably, the two most potent analogues, I and II , and the very weakly active analogues, VI and VII , exhibit similar helix contents. These results indicate that the presence of a stable N‐terminal helical sequence is an important but not sufficient condition for biological activity.     

Estimation of absorption rate of α‐human atrial natriuretic peptide from the plasma profile and diuretic effect after intranasal administration to rats

The absorption rate of α‐human atrial natriuretic peptide (α‐hANP) after intranasal (i.n.) administration to rats was estimated from the plasma profile and pharmacological effect (diuretic effect) using a pharmacokinetic (PK) model and a PK–pharmacodynamic (PD) model involving data obtained after intravenous (i.v.) bolus injection. The plasma concentrations of α‐hANP after i.v. administration at different doses were fitted to a two‐compartment PK model with zero‐order excretion and input of endogenous α‐rat atrial natriuretic peptide (α‐rANP) and two elimination processes represented by Michaelis–Menten and first‐order kinetics. However, the saturable process was ignored at low doses. The plasma concentrations after low doses via the i.n. route could also be expressed by this model, but with first‐order absorption, so that an absorption rate constant was calculated using a deconvolution method. In addition, the diuretic effect plotted against the i.v. dose was represented by the Hill equation and showed an anti‐clockwise hysteresis loop versus the plasma concentration. These results suggest that the diuretic effect could be estimated by a PK–PD model having an ‘effect’ compartment or a homeostatic system. Such a PK–PD model accurately expressed the diuretic effect of α‐hANP at all doses after i.v. and i.n. administrations. The resulting absorption rate constant calculated using the PK–PD model agreed closely with that obtained by the PK model alone. The absorption rate and simulated diuretic effect suggest that, for i.n. administration of α‐hANP, a higher absorption rate constant causes a more potent diuretic effect (a dramatic effect over the early period), whereas greater bioavailability is associated with a better hypotensive effect (sustained effect). Copyright © 2001 John Wiley & Sons, Ltd.     

Conformational investigation of αβ-dehydropeptides

Solution conformations of three series of model peptides, homochiral Ac-Pro-L-Xaa-NHCH₃ and heterochiral Ac-Pro-D-Xaa-NHcH₃ (Xaa = Val, Phe, Leu, Abu. Ah) as well as αβ-unsaturated Ac-Pro-ΔXaa-NHCH₃ [Δ Xaa =ΔVal, (Z)-ΔPhe, (Z)-ΔLeu, (Z)-ΔAbu] were investigated in CDCl₃ and CH₂Cl₂ by ¹H-, ¹³C-NMR, and FTIR spectroscopy. NH stretching absorption spectra, solvent shifts Δδ for NH (Xaa) and NHCH₃ on going from CDCl₃ to (CD₃)₂SO, diagnostic interresidue proton NOEs, and trans-cis isomer ratios were examined. These studies performed showed the essential difference in conformational propensities between homochiral peptides (L-Xaa) on the one hand and heterochiral (D-Xaa) and αβ-dehydropeptides (ΔXaa) on the other. Former compounds are conformationally flexible with an inverse γ-bend, a β-turn, and open forms in an equilibrium depending on the nature of the Xaa side chain. Conformational preferences of heterochiral and αβ-dehydropeptides are very similar, with the type-II β-turn as the dominating structure. There is no apparent correlation between conformational properties and the nature of the Xaa side chain within the two groups. The β-turn formation propensity seems to be somewhat greater in αβ-unsaturated than in heterochiral peptides, but an estimation of β-folded conformers is risky.