Cyclic dermorphin tetrapeptide analogues obtained via ring-closing metathesis

The dermorphin-derived cyclic tetrapeptide analogues H-Tyr-c[D-Cys-Phe-Cys]NH(2) and H-Tyr-c[D-Cys-Phe-D-Cys]NH(2) are opioid agonists at the mu and delta receptor. To enhance the metabolic stability of these peptides, we replaced the disulfide bridge with a bis-methylene moiety. This was achieved by solid-phase synthesis of the linear precursor peptide containing allylglycine residues in place of the Cys residues, followed by ring-closing metathesis. In the case of the peptide with L-configuration in the 4-position both the cis and the trans isomer of the resulting olefinic peptides were formed, whereas the cis isomer only was obtained with the peptide having the D-configuration in position 4. Catalytic hydrogenation yielded the saturated -CH(2)-CH(2)- bridged peptides. In comparison with the cystine-containing parent peptides, all olefinic peptides showed significantly reduced mu and delta agonist potencies in the guinea pig ileum and mouse vas deferens assays. The -CH(2)-CH(2)-bridged peptide with l-configuration in the 4-position was equipotent with its cystine-containing parent in both assays, whereas the bis-methylene analogue with D-configuration in position 4 was 10-27-fold less potent compared to its parent. The effect of the disulfide replacements with the -CH=CH- and -CH(2)-CH(2)- moieties on the conformational behavior of these peptides was examined by theoretical conformational analysis which provided plausible explanations in terms of structural parameters for the observed changes in opioid activity.     

New dinucleoside analogues via cross-coupling metathesis

Synthesis of 3'-3', 5-5', and 3'-5' dimeric thymidine, linked by an olefinic chain between glycosidic moieties is described. Cross metathesis reaction of 3' or 5' O-allyl analogues of thymidine led to the expected 3'-3' and 5'-5' dimeric compounds, respectively. In order to obtain the 3'-5' dimer, 5'-O-allyl and 3'-O-allyl monomers were first linked by their free 3' OH and 5' OH groups through a glutaryl spacer; ring closing metathesis was then operated upon this temporary dimer, followed by glutaryl removal.     

Binaphthyl scaffolded peptoids via ring-closing metathesis reactions and their anti-bacterial activities

An efficient synthesis of four new acyclic and four new cyclic binaphthyl-based cationic peptoids is described. These compounds had anti-bacterial activities with MIC values of 4–62 μg/mL against Staphylococcus aureus.     

Synthesis of a natural product-inspired eight-membered ring lactam library via ring-closing metathesis

We have prepared a novel speculative eight-membered lactam demonstration library based on the skeletal structure of the potent antitumor marine natural product octalactin A. The basic scaffold was readily constructed in a convergent fashion via ring-closing metathesis chemistry from the corresponding diene amides. A cursory examination of the biological properties of the library validates the relevance and significance of these structures.     

Efficient synthesis of 4'-cyclopropylated carbovir analogues with use of ring-closing metathesis from glycolate

The first synthetic route of novel 4'-cyclopropylated carbovir analgues is described. The construction of cyclopropylated quaternary carbon at 4'-position of carbocyclic nucleosides was successfully made via sequential Johnson's orthoester rearrangement and ring-closing metathesis (RCM) starting from ethyl glycolate. Synthesized compounds 15 and 16 showed moderate antiviral activity without any cytotoxicity up to 100 micromol.     

Versatile approach for the synthesis of novel seven-membered iminocyclitols via ring-closing metathesis dihydroxylation reaction

Seven-membered iminocyclitols with diverse diastereomers were prepared starting with d- and l-serines and employing ring-closing olefin metathesis and dihydroxylation reaction sequence. The iminocyclitols were assayed for glycosidase inhibition and compound 20 was found to be a competitive inhibitor for beta-glucosidase with Ki 26.3 microM.     

Conformationally restricted dinucleotides: tandem ring-closing metathesis and hydrogenation approach

Cyclic dinucleotides with saturated connections between a nucleobase and the phosphate are synthesised using a tandem ring-closing metathesis (RCM) and hydrogenation protocol and found to be significantly stabilised towards ammonia.     

Evaluation of macrocyclic Grb2 SH2 domain-binding peptide mimetics prepared by ring-closing metathesis of C-terminal allylglycines with an N-terminal beta-vinyl-substituted phosphotyrosyl mimetic

Preferential binding of ligands to Grb2 SH2 domains in beta-bend conformations has made peptide cyclization a logical means of effecting affinity enhancement. This is based on the concept that constraint of open-chain sequences to bend geometries may reduce entropy penalties of binding. The current study extends this approach by undertaking ring-closing metathesis (RCM) macrocyclization between i and i+3 residues through a process involving allylglycines and beta-vinyl-functionalized residues. Ring closure in this fashion results in minimal macrocyclic tetrapeptide mimetics. The predominant effects of such macrocyclization on Grb2 SH2 domain binding affinity were increases in rates of association (from 7- to 16-fold) relative to an open-chain congener, while decreases in dissociation rates were less pronounced (approximately 2-fold). The significant increases in association rates were consistent with pre-ordering of solution conformations to near those required for binding. Data from NMR experiments and molecular modeling simulations were used to interpret the binding results. An understanding of the conformational consequences of such i to i+3 ring closure may facilitate its application to other systems where bend geometries are desired.     

Application of ring-closing metathesis to Grb2 SH3 domain-binding peptides

Molecular processes depending on protein–protein interactions can use consensus recognition sequences that possess defined secondary structures. Left-handed polyproline II (PPII) helices are a class of secondary structure commonly involved with cellular signal transduction. However, unlike -helices, for which a substantial body of work exists regarding applications of ring-closing metathesis (RCM), there are few reports on the stabilization of PPII helices by RCM methodologies. The current study examined the effects of RCM macrocyclization on left-handed PPII helices involved with the SH3 domain-mediated binding of Sos1–Grb2. Starting with the Sos1-derived peptide “Ac-V1-P2-P3-P4-V5-P6-P7-R8-R9-R10-amide,” RCM macrocyclizations were conducted using alkenyl chains of varying lengths originating from the pyrrolidine rings of the Pro4 and Pro7 residues. The resulting macrocyclic peptides showed increased helicity as indicated by circular dichroism and enhanced abilities to block Grb2–Sos1 interactions in cell lysate pull-down assays. The synthetic approach may be useful in RCM macrocyclizations, where maintenance of proline integrity at both ring junctures is desired.     

Conformationally restricted macrocyclic analogues of combretastatins

New analogues of combretastatins have been evaluated as inhibitors of tubulin polymerization. These compounds present a macrocyclic structure, in which the para positions of the aromatic moieties have been linked by a 5- or 6-atoms chain, in order to produce a conformational restriction. This could contribute to determine the active conformation for these ligands. Such a conformational restriction and/or the steric hindrance makes them less potent inhibitors than the model compound CA-4.     

Monitoring ring-closing metathesis: Limitations on the utility of H NMR analysis

The utility and limitations of ¹H NMR methods for monitoring the progress of ring-closing metathesis (RCM) reactions are examined. ¹H NMR analysis of RCM reactions that yield macrocyclic and medium-ring products can be more problematic than is generally recognized. Interpretation is complicated by the formation of oligomers with an NMR signature identical or closely similar to that of the diene precursor, the RCM target, or a composite of the two. DOSY-NMR can aid in resolving ambiguities in signal assignment, but reliable quantitation requires ancillary methods.     

Application of ring-closing metathesis macrocyclization to the development of Tsg101-binding antagonists

HIV-1 viral budding involves binding of the viral Gag^p6 protein to the ubiquitin E2 variant domain of the human tumor susceptibility gene 101 protein (Tsg101). Recognition of p6 by Tsg101 is mediated in part by a proline-rich motif that contains the sequence ‘Pro-Thr-Ala-Pro’ (‘PTAP’). Using the p6-derived 9-mer sequence ‘PEPTAPPEE’, we had previously improved peptide binding affinity by employing N-alkylglycine (‘peptoid’) residues. The current study applies ring-closing metathesis macrocyclization strategies to Tsg101-binding peptide–peptoid hybrids as an approach to stabilize binding conformations and to observe the effects of such macrocyclization on Tsg101-binding affinity and bioavailability.     

Synthesis of a novel potent cyclic peptide MC4-ligand by ring-closing metathesis

The synthesis of a novel potent cyclic peptide MC4-ligand by ring-closing metathesis (RCM) is described. Based on the Ac-Nle-Gly-Lys-D-Phe-Arg-Trp-Gly-NH2-MC4 ligand, Ac-Nle-Alg-Lys-D-Phe-Arg-Trp-Alg-NH2 was designed and synthesized followed by cyclization using RCM. Both compounds are high affinity and selective MC4-R-agonists. The cyclic RCM-peptide was more potent in a rat-grooming assay.     

Synthesis and biological activity of macrocyclic taxane analogues

A series of paclitaxel analogues possessing a macrocyclic structure between the 7 and 10 positions has been prepared. These compounds possess in vitro activity against a paclitaxel resistant cell line and have in vivo activity comparable to paclitaxel.     

Synthesis of conformationally restricted nucleic acid fragments using ring-closing alkene and enyne metathesis reactions

In the aim of constructing conformationally restricted nucleic acid fragments for the recognition of secondary RNA structures, we have synthesized different mono- and dinucleotides containing extra rings. These rings were prepared by ring-closing alkene or enyne metathesis reactions from nucleotide substrates in which double or triple bonds have been introduced.     

Expeditious synthesis of enantiopure symmetrical macroheterocycles by ring-closing metathesis of ether and tether-linked 1,2-O-isopropylidenefuranosides

Bis-olefinic symmetrical carbohydrate derivatives were prepared by joining two 1,2-O-isopropylidenefuranose units either through an ether linkage or by a tether of variable size. The ring-closing metathesis (RCM) of these substrates using Grubbs' first-generation catalyst led to the synthesis of enantiopure symmetrical macroheterocycles containing nine- to twenty-five-membered rings fused to the 1,2-O-isopropylidenefuranose ring.     

Synthesis and properties of new bolaform and macrocyclic galactose-based surfactants obtained by olefin metathesis

A series of galactose-based surfactants with various structures likely to display new interesting properties were synthesized. Four monocatenary surfactants were elaborated by microwave-assisted galactosylation of undecanol or 10-undecenol. These compounds were slightly soluble in water. Their tensioactive properties were determined at 45 degrees C. Olefin metathesis was used to synthesize the two single-chain bolaforms from undec-10-enyl galactopyranosides; two pseudomacrocyclic bolaforms were prepared by grafting two carbamates at O-4 and O-4' sugar positions of the single-chain bolaforms. These four surfactants are insoluble in water and undergo monolayer compression. Cyclization of these bolaforms by olefin metathesis led to macrocyclic surfactant analogues of archaeobacterial membrane components.     

Metabolism and toxicity of synthetic analogues of macrocyclic diester pyrrolizidine alkaloids

Seven macrocyclic diesters analogous to hepatotoxic pyrrolizidine alkaloids have been tested in male weanling Wistar rats. The compounds were the succinate (VII), 2,3-dimethylsuccinate (VIII), phthalate (IX), glutarate (X), 2,4-dimethylglutarate (XI), 3,3-dimethylglutarate (XII) and 3,3-pentamethyleneglutarate (XIII) of the synthetic amino dialcohol, synthanecine A. Single doses of these compounds were given i.p. to rats, and liver levels of pyrrolic metabolites were measured 2 h later. For these experiments both normal rats and rats pretreated with the esterase inhibitor tri-orthocresylphosphate (TOCP) were used. In normal rats, low levels of pyrrolic metabolites were formed from compounds VII, IX, X and XI, but these levels were greatly enhanced in rats with inhibited esterase activity. Much higher pyrrole levels were formed from compounds VIII, XII and XIII in normal rats, and esterase inhibition had relatively little effect on their metabolic conversion to pyrroles. This indicated that the last mentioned compounds were relatively resistant to enzymic hydrolysis, whereas VII, IX, X and XI were easily hydrolysed in normal rats, providing an alternative metabolic path which limited their conversion to pyrrolic metabolites. Comparison of results obtained using the 2,4-dimethylglutarate (XI), the 3,3-dimethylglutarate (XII) and the 3,3,-pentamethyleneglutarate (XIII) showed that 3,3-disubstitution but not 2,4-disubstitution in the glutaric acid moiety conferred high resistance to esterase attack. Toxicity tests using four of the compounds confirmed that acute hepatotoxicity was dose related, and associated with the formation of pyrrolic metabolites in the liver. The 3,3-dimethylglutarate (XII) was highly toxic both in normal and in TOCP treated rats, doses of 25-30 mg/kg causing moderate to severe centrilobular necrosis of the liver. In contrast the toxicity of the unsubstituted succinate (VII), glutarate (X) and 2,4-dimethylglutarate (XI) was very low in normal rats but high in rats with inhibited esterase activity. Thus, the glutarate (X) was non-toxic at 200 mg/kg in normal rats, but in TOCP treated rats, in which pyrrolic metabolite formation was enhanced by a factor of 17.5, a 50 mg/kg dose of this compound was severely hepatotoxic. Kidney damage, which was generally limited to the presence of isolated necrotic cells, sometimes accompanied the liver damage caused by these compounds, but acute toxic effects were not observed in any other tissues.(ABSTRACT TRUNCATED AT 400 WORDS)     

P2-P1' macrocyclization of P2 phenylglycine based HCV NS3 protease inhibitors using ring-closing metathesis

Macrocyclization is a commonly used strategy to preorganize HCV NS3 protease inhibitors in their bioactive conformation. Moreover, macrocyclization generally leads to greater stability and improved pharmacokinetic properties. In HCV NS3 protease inhibitors, it has been shown to be beneficial to include a vinylated phenylglycine in the P2 position in combination with alkenylic P1' substituents. A series of 14-, 15- and 16-membered macrocyclic HCV NS3 protease inhibitors with the linker connecting the P2 phenylglycine and the alkenylic P1' were synthesized by ring-closing metathesis, using both microwave and conventional heating. Besides formation of the expected macrocycles in cis and trans configuration as major products, both ring-contracted and double-bond migrated isomers were obtained, in particular during formation of the smaller rings (14- and 15-membered rings). All inhibitors had K(i)-values in the nanomolar range, but only one inhibitor type was improved by rigidification. The loss in inhibitory effect can be attributed to a disruption of the beneficial π-π interaction between the P2 fragment and H57, which proved to be especially deleterious for the d-phenylglycine epimers.     

Design,synthesis, and opioid activity of arodyn analogs cyclized by ring-closing metathesis involving Tyr(allyl)

Kappa (κ) opioid receptor selective antagonists are useful pharmacological tools in studying κ opioid receptors and have potential to be used as therapeutic agents for the treatment of a variety of diseases including mood disorders and drug addiction. Arodyn (Ac[Phe^1–3,Arg⁴,d-Ala⁸]Dyn A-(1–11)NH₂) is a linear acetylated dynorphin A (Dyn A) analog that is a potent and selective κ opioid receptor antagonist (Bennett et al. J Med Chem 2002;45:5617–5619) and prevents stress-induced reinstatement of cocaine-seeking behavior following central administration (Carey et al. Eur J Pharmacol 2007;569:84–89). To restrict its conformational mobility, explore possible bioactive conformations and potentially increase its metabolic stability we synthesized cyclic arodyn analogs on solid phase utilizing a novel ring-closing metathesis (RCM) reaction involving allyl-protected Tyr (Tyr(All)) residues. This approach preserves the aromatic functionality and directly constrains the side chains of one or more of the Phe residues. The novel cyclic arodyn analog 4 cyclized between Tyr(All) residues incorporated in positions 2 and 3 exhibited potent κ opioid receptor antagonism in the [³⁵S]GTPγS assay (K_B?=?3.2?nM) similar to arodyn. Analog 3 cyclized between Tyr(All) residues in positions 1 and 2 also exhibited nanomolar κ opioid receptor antagonist potency (K_B?=?27.5?nM) in this assay. These are the first opioid peptides cyclized via RCM involving aromatic residues, and given their promising pharmacological activity represent novel lead peptides for further exploration.