Enhancing the Drug-Like Profile of a Potent Peptide PACE4 Inhibitor by the Formation of a Host-Guest Inclusion Complex with β-Cyclodextrin

The enzyme PACE4 has been validated as a promising therapeutic target to expand the range of prostate cancer (PCa) treatments. In recent years, we have developed a potent peptidomimetic inhibitor, namely, compound C23 (Ac-(DLeu)LLLRVK-4-amidinobenzylamide). Like many peptides, C23 suffers from an unfavorable drug-like profile which, despite our efforts, has not yet benefited from the usual SAR studies. Hence, we turned our attention toward a novel formulation strategy, i.e., the use of cyclodextrins (CDs). CDs can benefit compounds through the formation of "host-guest" complexes, shielding the guest from degradation and enhancing biological survival. In this study, a series of βCD-C23 complexes have been generated and their properties evaluated, including potency toward the enzyme in vitro, a cell-based proliferation assay, and stability in plasma. As a result, a new βCD-formulated lead compound has been identified, which, in addition to being more soluble and more potent, also showed an improved stability profile.

Second Harmonic Generation Signatures of Supramolecular Assemblies Based on Amide Moieties

Targeting the use of the second harmonic generation (SHG) as a bioimaging technique to unravel the formation of aggregates, the SHG first hyperpolarizabilities (β) of assemblies of benzene-1,3,5-tricarboxamide derivatives have been evaluated at the density functional theory level. Calculations have revealed that i) the assemblies exhibit SHG responses and the total first hyperpolarizability responses of the aggregates are evolving with their size. The largest aggregation effect is a 18-times increase for βHRS of B4 when going from the monomer to the pentamer, that ii) the intrinsic SHG responses described by the hyper-Rayleigh Scattering  are enhanced in presence of iodine atoms on the phenyl core, that iii) the side chains affect the relative orientation of the dipole moment and first hyperpolarizability vectors, which impacts more the EFISHG quantities than their moduli, and that iv) the radial component to β is dominant for the compounds having the largest responses. These results have been obtained using the sequential molecular dynamics then quantum mechanics approach to account for dynamic structural effects on the SHG responses.

Triple Thorpe-Ingold Effect in the Synthesis of 18-Membered C3 Symmetric Lactams Stacking as Endless Supramolecular Tubes

Three C₃ symmetric macrolactams were very efficiently cyclized from their linear precursors. Adequately located substituents are responsible for the enhancement of reactivity that is not observed in the unsubstituted parent. DFT calculations show that the properly folded cyclization precursor, the reactive conformer, is more populated than other conformers, leading to a decrease of free energy of activation. The crystal structure of the ring substituted with three very bulky esters indicates that tubular stacking is preserved.

Computational prediction of the supramolecular self-assembling properties of organic molecules: the role of conformational flexibility of amide moieties

Two families of organic molecules with different backbones have been considered. The first family is based on a macrolactam-like unit that is constrained in a particular conformation. The second family is composed by a substituted central phenyl that allows a larger mobility for its substituents. They have however a common feature, three amide moieties (within the cycle for the macrolactam-like molecule and as substituents for the phenyl) that permit hydrogen bonding when molecules are stacked. In this study we propose a computational protocol to unravel the ability of the different families to self-assemble into organic nanotubes. Starting from the monomer and going towards larger assemblies like dimers, trimers, and pentamers we applied the different protocols to rationalize the behavior of the different assemblies. Both structures and thermodynamics were investigated to give a complete picture of the process. Thanks to the combination of a quantum mechanics approach and molecular dynamics simulations along with the use of tailored tools (non covalent interaction visualization) and techniques (umbrella sampling), we have been able to differentiate the two families and highlight the best candidate for self-assembling purposes.

Design and Structure-Activity Relationship of a Potent Furin Inhibitor Derived from Influenza Hemagglutinin

Furin plays an important role in various pathological states, especially in bacterial and viral infections. A detailed understanding of the structural requirements for inhibitors targeting this enzyme is crucial to develop new therapeutic strategies in infectious diseases, including an urgent unmet need for SARS-CoV-2 infection. Previously, we have identified a potent furin inhibitor, peptide Ac-RARRRKKRT-NH ₂ (CF1), based on the highly pathogenic avian influenza hemagglutinin. The goal of this study was to determine how its N-terminal part (the P8-P5 positions) affects its activity profile. To do so, the positional-scanning libraries of individual peptides modified at the selected positions with natural amino acids were generated. Subsequently, the best substitutions were combined together and/or replaced by unnatural residues to expand our investigations. The results reveal that the affinity of CF1 can be improved (2-2.5-fold) by substituting its P5 position with the small hydrophobic residues (Ile or Val) or a basic Lys.

Promising Performance of 4HMS, a New Zirconium-89 Octadendate Chelator

Over the last decade, the interest in zirconium-89 (⁸⁹Zr) as a positron-emitting radionuclide increased considerably because of its standardized production and its physical half-life (78.41 h), which matches the biological half-life of antibodies and its successful use in preclinical and clinical applications. So far, desferrioxamine (DFO), a commercially available chelator, has been mainly used as a bifunctional chelating system. However, there are some concerns regarding the in vivo stability of the [⁸⁹Zr]Zr-DFO complex. In this study, we report the synthesis of an acyclic N-hydroxy-N-methyl succinamide-based chelator (4HMS) with 8 coordination sites and our first investigations into the use of this new chelator for ⁸⁹Zr complexation. In vitro and in vivo comparative studies with [⁸⁹Zr]Zr-4HMS and [⁸⁹Zr]Zr-DFO are presented. The 4HMS chelator was synthesized in four steps starting with an excellent overall yield. Both chelators were quantitatively labeled with ⁸⁹Zr within 5-10 min at pH 7 and room temperature; the molar activity of [⁸⁹Zr]Zr-4HMS exceeded (>3 times) that of [⁸⁹Zr]Zr-DFO. [⁸⁹Zr]Zr-4HMS remained stable against transmetalation and transchelation and cleared from most tissues within 24 h. The kidney, liver, bone, and spleen uptakes were significantly low for this ⁸⁹Zr-complex. Positron emission tomography images were in accordance with the results of the biodistribution in healthy mice. Based on DFT calculations, a rationale is provided for the high stability of ⁸⁹Zr-4HMS. This makes 4HMS a promising chelator for future development of ⁸⁹Zr-radiopharmaceuticals.

Self-Assembly of C3 Symmetric Rigid Macrolactams into Very Polar and Porous Trigonal Crystals

Cyclohexane and cyclotri-β-alanyl have been used as scaffolds for the design of new C₃ -symmetric rings incorporating conjugated alkenes and dienes. All three C₃ -symmetric lactams share the same triangular shape and their crystal system is trigonal. They all belong to the R3 space group, R3m, R3 and R3c, for the increasingly large 12-, 18- and 24-membered rigid rings, respectively. All lactams stack on top of each other, through H-bonds and van der Waals noncovalent interactions, leading to endless supramolecular cylinders and tubes. The largest member of the family leads to tubes, the central pores of which is wide enough to let water in. A common feature of all the lactams is their very large dipole, of around 9 D, according to DFT calculations. Surprisingly, all the resulting cylinders and tubes pack side by side in the crystals, with all the dipoles pointing to the same direction. As a result, all three crystals are anisotropic and appear to be the first members of a new kind of highly polar crystals.

N-Guanidyl and C-Tetrazole Leu-Enkephalin Derivatives: Efficient Mu and Delta Opioid Receptor Agonists with Improved Pharmacological Properties

Leu-enkephalin and d-Ala₂-Leu-enkephalin were modified at their N- and C-termini with guanidyl and tetrazole groups. The resulting molecules were prepared in solution or by solid phase peptide synthesis. The affinity of the different analogues at mu (MOP) and delta opioid receptors (DOP) was then assessed by competitive binding in stably transfected DOP and MOP HEK293 cells. Inhibition of cAMP production and recruitment of β-arrestin were also investigated. Finally, lipophilicity (logD_7.4) and plasma stability of each compound were measured. Compared to the native ligands, we found that the replacement of the terminal carboxylate by a tetrazole slightly decreased both the affinity at mu and delta opioid receptors as well as the half-life. By contrast, replacing the ammonium at the N-terminus with a guanidyl significantly improved the affinity, the potency, as well as the lipophilicity and the stability of the resulting peptides. Replacing the glycine residue with a d-alanine in position 2 consistently improved the potency as well as the stability of the analogues. The best peptidomimetic of the whole series, guanidyl-Tyr-d-Ala-Gly-Phe-Leu-tetrazole, displayed sub-nanomolar affinity and an increased lipophilicity. Moreover, it proved to be stable in plasma for up to 24 h, suggesting that the modifications are protecting the compound against protease degradation.

Polar crystal of vanillylformamide through replacement of the alkene by an isosteric formamide group

Vanillylformamide [systematic name: N-(4-hydroxy-3-methoxybenzyl)formamide], C9H11NO3, (II), has been synthesized from vanillylamine hydrochloride and studied by single-crystal X-ray diffraction. Compound (II) and the well known biologically active eugenol compound (I) can be considered to be `isosteres' of each other, since they share comparable molecular shape and volume. The product (II) crystallizes in the space group P1. In the crystal, the vanillylformamide molecules are linked mainly by N—H...O, O—H...O and Csp 2—H...O hydrogen bonds, forming infinite two-dimensional polar sheets. These two-dimensional layers pack in a parallel fashion, constructing a polar three-dimensional network. Except for van der Waals forces and weak Csp 3—H...O hydrogen bonds, there are no significant intermolecular interactions between the layers. A Cambridge Structural Database search revealed that vanillylamide-related crystals are scarce.

Improving the Selectivity of PACE4 Inhibitors through Modifications of the P1 Residue

Paired basic amino acid cleaving enzyme 4 (PACE4), a serine endoprotease of the proprotein convertases family, has been recognized as a promising target for prostate cancer. We previously reported a selective and potent peptide-based inhibitor for PACE4, named the multi-Leu peptide (Ac-LLLLRVKR-NH₂ sequence), which was then modified into a more potent and stable compound named C23 with the following structure: Ac-dLeu-LLLRVK-Amba (Amba: 4-amidinobenzylamide). Despite improvements in both in vitro and in vivo profiles of C23, its selectivity for PACE4 over furin was significantly reduced. We examined other Arg-mimetics instead of Amba to regain the lost selectivity. Our results indicated that the replacement of Amba with 5-(aminomethyl)picolinimidamide increased affinity for PACE4 and restored selectivity. Our results also provide a better insight on how structural differences between S1 pockets of PACE4 and furin could be employed in the rational design of selective inhibitors.

Rational Design of a Highly Potent and Selective Peptide Inhibitor of PACE4 by Salt Bridge Interaction with D160 at Position P3

PACE4, a member of the proprotein convertases (PCs) family of serine proteases, is a validated target for prostate cancer. Our group has developed a potent and selective PACE4 inhibitor: Ac-LLLLRVKR-NH₂ . In seeking for modifications to increase the selectivity of this ligand toward PACE4, we replaced one of its P3 Val methyl groups with a basic group capable of forming a salt bridge with D160 of PACE4. The resulting inhibitor is eight times more potent than the P3 Val parent inhibitor and two times more selective over furin, because the equivalent salt bridge with furin E257 is not optimal. Moreover, the β-branched nature of the new P3 residue favors the extended β-sheet conformation usually associated with substrates of proteases. This work provides new insight for better understanding of β-sheet backbone-backbone interactions between serine proteases and their peptidic ligands.

Isomorphous crystal structures of chlorodi-acetyl-ene and iododi-acetyl-ene derivatives: simultaneous hydrogen and halogen bonds on carbon-yl

tert-Butyl (5-chloro­penta-2,4-diyn-1-yl)carbamate and tert-butyl (5-iodo­penta-2,4-diyn-1-yl)carbamate are new members of the isostructural family of compounds with the general formula BocNHCH₂CCCCX (X = H, Cl, Br, I). In the crystals of all these di­acetyl­enes, mol­ecules are linked via a bifurcated N—H⋯O hydrogen bond and C—X⋯O halogen bond involving the same carbonyl group.

The crystal structures of tert-butyl (5-chloro­penta-2,4-diyn-1-yl)carbamate, C₁₀H₁₂ClNO₂ (II), and tert-butyl (5-iodo­penta-2,4-diyn-1-yl)carbamate, C₁₀H₁₂INO₂ (IV), are isomorphous to previously reported structures and accordingly their mol­ecular and supra­molecular structures are similar. In the crystals of (II) and (IV), mol­ecules are linked into very similar two-dimensional wall organizations with anti­parallel carbamate groups involved in a combination of hydrogen and halogen bonds (bifurcated N—H⋯O=C and C≡C—X⋯O=C inter­actions on the same carbonyl group). There is no long-range parallel stacking of diynes, so the topochemical polymerization of di­acetyl­ene is prevented. A Cambridge Structural Database search revealed that C≡C—X⋯O=C contacts shorter than the sum of the van der Waals radii are scarce (only one structure for the C≡C—Cl⋯O=C inter­action and 13 structures for the similar C≡C—I⋯O=C inter­action).

Diffusion of chiral molecules and propagation of structural chirality in anisotropic liquids

Diffusion in nature is usually considered as a smooth redistribution process. However, it appears that the diffusion of chiral molecules and the propagation of chirality may proceed in quite different ways. Indeed, in the present work, unexpected quantization of the spatial concentration of chiral molecules is discovered in self-aligned molecular liquids. It is shown that the interpenetration of two liquids is forming discrete diffusion barrier walls resulting in steplike concentration distribution of chiral molecules in space. The concentration gradient is at least an order of magnitude stronger from both sides of the barrier wall compared to the gradient between those walls. It is also shown that this microscopic diffusion process may be controlled by macroscopic boundary conditions imposed on the host molecular system. Both of those phenomena are related to the collective long-range orientational "elastic" interactions of molecules of the host. The observed phenomena may radically change our understanding of diffusion of chiral molecules, among others, in biological tissue, which contains many examples of self-aligned molecular liquids. This, in turn, has the potential to revolutionize drug design and delivery techniques.

Synthesis of Gly-ψ[(Z)CF═CH]-Phe, a Fluoroalkene Dipeptide Isostere, and Its Incorporation into a Leu-enkephalin Peptidomimetic

A new Leu-enkephalin peptidomimetic designed to explore the hydrogen bond acceptor ability of the third peptide bond has been prepared and studied. This new analog is produced by replacing the third amide of Leu-enkephalin with a fluoroalkene. An efficient and innovative synthesis of the corresponding dipeptide surrogate Fmoc-Gly-ψ[(Z)CF═CH]-Phe-OH is described. The key step involves the alkylation of a tin dienolate from the less hindered face of its chiral sulfonamide auxiliary derived from camphor. Once its synthesis was complete, its incorporation into the peptidomimetic sequence was achieved on a solid support with chlorotrityl resin following the Fmoc strategy. The peptidomimetic was characterized using competition binding with [¹²⁵I]-deltorphin I on membrane extracts of HEK293 cells expressing the mouse delta opioid receptor (DOPr) and based on its abilities to inhibit the electrically induced contractions of the mouse vas deferens and to activate the ERK1/2 signaling pathway in DRGF11/DOPr-GFP cells. Together with our previous observations, our findings strongly suggest that the third amide bond of Leu-enkephalin primarily acts as a hydrogen bond acceptor in DOPr. Consequently, this amide bond can be successfully replaced by an ester, a thioamide, or a fluoroalkene without greatly impacting the binding or biological activity of the corresponding analogs. The lipophilicity (LogD_7.4) of the active analog was also measured. It appears that fluoroalkenes are almost as efficient at increasing the lipophilicity as normal alkenes.

The Proprotein Convertase Subtilisin/Kexin Type 9-resistant R410S Low Density Lipoprotein Receptor Mutation: A NOVEL MECHANISM CAUSING FAMILIAL HYPERCHOLESTEROLEMIA

Familial hypercholesterolemia (FH) is characterized by severely elevated low density lipoprotein (LDL) cholesterol. Herein, we identified an FH patient presenting novel compound heterozygote mutations R410S and G592E of the LDL receptor (LDLR). The patient responded modestly to maximum rosuvastatin plus ezetimibe therapy, even in combination with a PCSK9 monoclonal antibody injection. Using cell biology and molecular dynamics simulations, we aimed to define the underlying mechanism(s) by which these LDLR mutations affect LDL metabolism and lead to hypercholesterolemia. Our data showed that the LDLR-G592E is a class 2b mutant, because it mostly failed to exit the endoplasmic reticulum and was degraded. Even though LDLR-R410S and LDLR-WT were similar in levels of cell surface and total receptor and bound equally well to LDL or extracellular PCSK9, the LDLR-R410S was resistant to exogenous PCSK9-mediated degradation in endosomes/lysosomes and showed reduced LDL internalization and degradation relative to LDLR-WT. Evidence is provided for a tighter association of LDL with LDLR-R410S at acidic pH, a reduced LDL delivery to late endosomes/lysosomes, and an increased release in the medium of the bound/internalized LDL, as compared with LDLR-WT. These data suggested that LDLR-R410S recycles loaded with its LDL-cargo. Our findings demonstrate that LDLR-R410S represents an LDLR loss-of-function through a novel class 8 FH-causing mechanism, thereby rationalizing the observed phenotype.

Novel Insights into Structure-Activity Relationships of N-Terminally Modified PACE4 Inhibitors

PACE4 plays important roles in prostate cancer cell proliferation. The inhibition of this enzyme has been shown to slow prostate cancer progression and is emerging as a promising therapeutic strategy. In previous work, we developed a highly potent and selective PACE4 inhibitor, the multi-Leu (ML) peptide, an octapeptide with the sequence Ac-LLLLRVKR-NH2 . Here, with the objective of developing a useful compound for in vivo administration, we investigate the effect of N-terminal modifications. The inhibitory activity, toxicity, stability, and cell penetration properties of the resulting analogues were studied and compared to the unmodified inhibitor. Our results show that the incorporation of a polyethylene glycol (PEG) moiety leads to a loss of antiproliferative activity, whereas the attachment of a lipid chain preserves or improves it. However, the lipidated peptides are significantly more toxic when compared with their unmodified counterparts. Therefore, the best results were achieved not by the N-terminal extension but by the protection of both ends with the d-Leu residue and 4-amidinobenzylamide, which yielded the most stable inhibitor, with an excellent activity and toxicity profile.

Therapeutic uses of furin and its inhibitors: a patent review

INTRODUCTION

Since the discovery of furin, numerous reports have studied its role in health and diseases, including cancer, inflammatory and infectious diseases. This interest has led to the development of both large protein- and peptide-based inhibitors aiming to control furin activity to treat these disorders. The most recent advances include the development of potent peptidomimetic furin inhibitors, considerably expanding the field of therapeutic applications.

AREA COVERED

In this review, the use of furin or its inhibitors for therapeutic conditions is described through the patent literature since 1994. Only compounds with biological efficacy or augmented properties demonstrated within the patent literature or the associated publications concerning their claimed uses are discussed.

EXPERT OPINION

Considering the diseases that may benefit from furin inhibition, several patents detail the use of the restricted number of furin inhibitors. However, there have been recent reports of new scaffolds, and even the use of furin itself, as a therapeutic agent. Despite considerable evidence of in vivo efficacy, limited confirmation from clinical trials supports or refutes the further use of these compounds in a therapeutic context. The most advanced application is the use of furin knockdown in the generation of an autologous cancer vaccine, which has initiated clinical trials.

Optimization of furin inhibitors to protect against the activation of influenza hemagglutinin H5 and Shiga toxin

Proprotein convertases (PCs) are crucial in the processing and entry of viral or bacterial protein precursors and confer increased infectivity of pathogens bearing a PC activation site, which results in increased symptom severity and lethality. Previously, we developed a nanomolar peptide inhibitor of PCs to prevent PC activation of infectious agents. Herein, we describe a peptidomimetic approach that increases the stability of this inhibitor for use in vivo to prevent systemic infections and cellular damage, such as that caused by influenza H5N1 and Shiga toxin. The addition of azaβ(3)-amino acids to both termini of the peptide successfully prevented influenza hemagglutinin 5 fusogenicity and Shiga toxin Vero toxicity in cell-based assays. The results from a cell-based model using stable shRNA-induced proprotein convertase knockdown indicate that only furin is the major proprotein convertase required for HA5 cleavage.

Design, synthesis, and structure-activity relationship studies of a potent PACE4 inhibitor

PACE4 plays an important role in the progression of prostate cancer and is an attractive target for the development of novel inhibitor-based tumor therapies. We previously reported the design and synthesis of a novel, potent, and relatively selective PACE4 inhibitor known as a Multi-Leu (ML) peptide. In the present work, we examined the ML peptide through detailed structure-activity relationship studies. A variety of ML-peptide analogues modified at the P8-P5 positions with leucine isomers (Nle, DLeu, and DNle) or substituted at the P1 position with arginine mimetics were tested for their inhibitory activity, specificity, stability, and antiproliferative effect. By incorporating d isomers at the P8 position or a decarboxylated arginine mimetic, we obtained analogues with an improved stability profile and excellent antiproliferative properties. The DLeu or DNle residue also has improved specificity toward PACE4, whereas specificity was reduced for a peptide modified with the arginine mimetic, such as 4-amidinobenzylamide.

Preparation and evaluation at the delta opioid receptor of a series of linear leu-enkephalin analogues obtained by systematic replacement of the amides

Leu-enkephalin analogues, in which the amide bonds were sequentially and systematically replaced either by ester or N-methyl amide bonds, were prepared using classical organic chemistry as well as solid phase peptide synthesis (SPPS). The peptidomimetics were characterized using competition binding, ERK1/2 phosphorylation, receptor internalization, and contractility assays to evaluate their pharmacological profile over the delta opioid receptor (DOPr). The lipophilicity (LogD7.4) and plasma stability of the active analogues were also measured. Our results revealed that the last amide bond can be successfully replaced by either an ester or an N-methyl amide bond without significantly decreasing the biological activity of the corresponding analogues when compared to Leu-enkephalin. The peptidomimetics with an N-methyl amide function between residues Phe and Leu were found to be more lipophilic and more stable than Leu-enkephalin. Findings from the present study further revealed that the hydrogen-bond donor properties of the fourth amide of Leu-enkephalin are not important for its biological activity on DOPr. Our results show that the systematic replacement of amide bonds by isosteric functions represents an efficient way to design and synthesize novel peptide analogues with enhanced stability. Our findings further suggest that such a strategy can also be useful to study the biological roles of amide bonds.

The Multi-Leu peptide inhibitor discriminates between PACE4 and furin and exhibits antiproliferative effects on prostate cancer cells

The proprotein convertases (PCs) play an important role in protein precursor activation through processing at paired basic residues. However, significant substrate cleavage redundancy has been reported between PCs. The question remains whether specific PC inhibitors can be designed. This study describes the identification of the sequence LLLLRVKR, named Multi-Leu (ML)-peptide, that displayed a 20-fold selectivity on PACE4 over furin, two enzymes with similar structural characteristics. We have previously demonstrated that PACE4 plays an important role in prostate cancer and could be a druggable target. The present study demonstrates that the ML-peptide significantly reduced the proliferation of DU145 and LNCaP prostate cancer-derived cell lines and induced G₀/G₁ cell cycle arrest. However, the ML-peptide must enter the cell to inhibit proliferation. It is concluded that peptide-based inhibitors can yield specific PC inhibitors and that the ML-peptide is an important lead compound that could potentially have applications in prostate cancer.

Simultaneous chirality transfer and structured aggregation of a cyclopeptide in a liquid crystal

We report the finding that a chiral cyclopeptide dissolved in a nematic liquid crystal (LC) host could aggregate in a manner that is controlled by the texture (LC director configuration) of a cholesteric phase that is induced by the cyclopeptide itself. On one hand, with the fingerprint texture, where the helical axis formed by rotating LC molecules, that lies in the substrate plane, the cyclopeptide can use the LC texture as a template to aggregate and form long-range-ordered ribbons that mimic the helical configuration of the LC director. On the other hand, with the planar texture, where the helical axis is normal to the substrate plane, the cyclopeptide can migrate into the "oily-streak" defect regions of the cholesteric phase and stabilize a network of defects that dictates the electrooptical response of the LC. This is the first example of a molecular species exhibiting such a structured aggregation and defect stabilization effect in a cholesteric LC, but similar phenomena were previously reported for platinum nanoparticles and silica colloidal particles, respectively, dispersed in a cholesteric LC host. This study provides more evidence for the potential interest of exploring LCs as an anisotropic medium for mediating the aggregation and assembly of cyclopeptides.

Exploring the Backbone of Enkephalins To Adjust Their Pharmacological Profile for the δ-Opioid Receptor

The role of each of the four amide bonds in Leu(5)-enkephalin was investigated by systematically and sequentially replacing each with its corresponding trans-alkene. Six Leu(5)-enkephalin analogs based on six dipeptide surrogates and two Met(5)-enkephalin analogs were synthesized and thoroughly tested using a δ-opioid receptor internalization assay, an ERK1/2 activation assay, and a competition binding assay to evaluate their biological properties. We observed that an E-alkene can efficiently replace the first amide bond of Leu(5)- and Met(5)-enkephalin without significantly affecting biological activity. By contrast, the second amide bond was found to be highly sensitive to the same modification, suggesting that it is involved in biologically essential intra- or intermolecular interactions. Finally, we observed that the affinity and activity of analogs containing an E-alkene at either the third or fourth position were partially reduced, indicating that these amide bonds are less important for these intra- or intermolecular interactions. Overall, our study demonstrates that the systematic and sequential replacement of amide bonds by E-alkene represents an efficient way to explore peptide backbones.

Efficient parallel synthesis of macrocyclic peptidomimetics

A new method for solid phase parallel synthesis of chemically and conformationally diverse macrocyclic peptidomimetics is reported. A key feature of the method is access to broad chemical and conformational diversity. Synthesis and mechanistic studies on the macrocyclization step are reported.

Efficient Synthesis and Astonishing Supramolecular Architectures of Several Symmetric Macrolactams

The synthesis of four C(n) symmetric macrocyclic lactams cyclo-[NH-CH(2)-CH=CH-CH(2)-CO](n) (1, n=2; 2, n=3; 3, n=4) and cyclo-[NH-CH(2)-CH(2)-CH=CH-CO](3) (4) has been achieved by two approaches. A linear route leads to precursors that are subsequently macrocyclized in a separate step. The second, convergent approach relies on the symmetry of the targets: it includes suitably activated subunits, which are subjected to macrocyclization conditions. The subunits first oligomerize, then cyclize to form either pure macrolactams or mixtures. The macrolactam units 1, 2 and 4 stack on top each other through weak interactions (hydrogen bond and van der Waals), to form endless square, rectangular and triangular prisms, respectively. These stacks are further packed side by side in crystals grown from isotropic media. The overall dipoles in the crystals from lactams 1 and 4, which result mostly from the alignment of amide groups, are zero and large, respectively. Macrolactam 2 displays an astonishing isomorphism when allowed to cool down in anisotropic liquid crystal solutions. Large hollow hexagonal tubes are then obtained through a fractal process. Contrary to the three previous rings, 3 yields crystals where prisms of any shape are absent.

Synthesis and structure-activity relationships of analogs of EM-652 (acolbifene), a pure selective estrogen receptor modulator. Study of nitrogen substitution

EM-652 (acolbifene) analogs have been synthesized as selective estrogen receptor modulators. Substitution on the nitrogen atom of these 2H-1-benzopyran derivatives has been studied for its influence on antiestrogenic activity. Binding to the rat estrogen receptor, inhibition of estradiol-stimulated proliferation of T-47D breast cancer cells, as well as antiuterotrophic and uterotrophic activities in ovariectomized mice have been evaluated. 2H-1-Benzopyran 1b (EM-343, racemic form of EM-652), which contains a piperidine ring, shows the best pharmacological profile; RBA = 380, IC50 value = 0.110 nM (in T-47D cells), as well as 63% and 84% antiuterotrophic inhibitions at the 7.5 and 75 nmol doses, respectively.

Comparative effects of conjugated and deconjugated isomeric enones on the transannular Diels-Alder reaction

Two isomeric cyclic trienones 2 and 3 (with four methyl esters at positions 3 and 10) underwent transannular Diels-Alder (TADA) reaction at very different temperatures. This drastic difference could be traced to the capacity of the enone dienophile to be conjugated or unconjugated at the transition state. Molecular modeling could confirm this explanation. The calculated enone proved to be very distorted in transition state ts2, and the TADA reaction temperature was accordingly much higher than the one corresponding to ts3 in which the enone was flat. [reaction: see text]

Hydrolysis of alpha- and beta-glycosides. New experimental data and modeling of reaction pathways

[reaction: see text] The cyclization of oxocarbenium ion conformers 6alpha and 6beta (from 11E and 11Z) gave only the beta-glycoside 1beta, and the addition of methanol to the oxocarbenium ion 3 yielded mainly the alpha-glycoside 1alpha with both experiments being carried out under kinetically controlled conditions. RHF/6.31G calculations reproduce well these experimental results and show that the endocyclic and the exocyclic C-O bond cleavage processes can compete in the hydrolysis of 1beta, whereas 1alpha gets hydrolyzed by exocyclic C-O bond cleavage only.

Characteristics of the Two Frontier Orbital Interactions in the Diels−Alder Cycloaddition

Two electron-deficient dienes were reacted with a series of twelve electron-poor and electron-rich dienophiles to give, in some cases, the corresponding Diels-Alder adducts. Clear differences in the roles played by the two frontier orbital interactions emerged. It was demonstrated that in the case of normal Diels-Alder cycloadditions, the FMO theory could predict the relative reactivities between dienophiles, while in the case of inverse-electron demand Diels-Alder reactions, it could not. It was shown that the dissymmetry in electron-rich dienophiles increases their reactivities.

First experimental and theoretical evidence of a deactivating enone dienophile in the transannular Diels-Alder reaction

A thorough study of the transannular Diels-Alder (TADA) reaction of trans-trans-trans macrocyclic trienes was carried out. It led to a better understanding of various parameters that govern the TADA reaction in particular and the Diels-Alder reaction in general. Thus, carbonyl activation of the dienophile is thoroughly discussed in light of new experimental and theoretical data. An enone dienophile is found to deactivate the reaction, although it remains planar at the transition state. This unusual result was discussed in terms of tether substituents that provoke destabilization of the transition state.

Use of the transannular Diels–Alder (TADA) reaction to probe biological receptors: Rational design and synthesis of tricyclic TADA adducts capable of rigidly holding pharmacophore parts

Transannular Diels–Alder (TADA) adducts constitute a collection of rigid structures, whose conformational diversity is rich. It is possible to design such specifically functionalized molecules capable of binding to known biological targets by molecular modelling MCSS–HOOK (multiple copy simultaneous search). Here we show that such carefully designed compounds can be easily built from small synthons. TADA adducts are very interesting due to their huge conformational diversity, their rigidity (biological interest), and their ease of synthesis (chemical interest).Key words: tricycles, synthesis, transannular Diels–Alder, macrocyclization, conformation, diversity.

Theoretical and experimental determination of the effects governing the transannular Diels-Alder reaction of trans-trans-cis systems with or without activation of the dienophile

A thorough study of the transannular Diels-Alder (TADA) reaction of trans-trans-cis macrocyclic trienes was carried out. It led to a better understanding of various parameters that govern the TADA reaction in particular and the Diels-Alder reaction in general. Thus, carbonyl activation of the dienophile and substitution of the diene are discussed, as well as the presence of substituents on the macrocycle and their respective effects at the transition-state level.

Solid phase combinatorial synthesis of a library of macro-heterocycles and related acyclic compounds

A solid phase synthesis of macrolactones from three building blocks and in eight steps is described. The synthesis which is carried out on the DHP resin includes Mitsunobu and DIC couplings. The macrocyclization occurs by SN2 displacement of an allylic chloride by a malonate anion. The synthetic methodology is suitable for the synthesis of arrays of macrocycles as well as linear compounds.