Synthesis of novel β-lactam fused spiroisoxazolidine chromanones and tetralones as potent antimicrobial agent for human and plant pathogens

Synthesis of novel β-lactam fused spiroisoxazolidine chromanones and tetralones ring systems has been achieved by intermolecular 1,3-dipolar cycloaddition reaction of bicyclic nitrone with unusual dipolarophiles, arylidene chromanones/tetralones under different reaction conditions. The synthesized compounds were evaluated for antimicrobial activities. It was observed that two of the synthesized compounds exhibited relatively good antibacterial and antifungal activities.     

Synthesis and evaluation of 3-aryl piperidine analogs as potent and efficacious dopamine D4 receptor agonists

A series of 3-aryl piperidine analogs with 2-piperidinoalkylamino or 2-piperidinoalkyloxy fused bicyclic rings were prepared and found to be potent and efficacious human dopamine D4 agonists. The synthesis and structure-activity relationship (SAR) studies that led to the identification of these compounds are discussed.     

Identification of fused bicyclic heterocycles as potent and selective 5-HT(2A) receptor antagonists for the treatment of insomnia

A series of fused bicyclic heterocycles was identified as potent and selective 5-HT(2A) receptor antagonists. Optimization of the series resulted in compounds that had improved PK properties, favorable CNS partitioning, good pharmacokinetic properties, and significant improvements on deep sleep (delta power) and sleep consolidation.     

Synthesis and evaluation of the performance of a small molecule library based on diverse tropane-related scaffolds

A unified synthetic approach was developed that enabled the synthesis of diverse tropane-related scaffolds. The key intermediates that were exploited were cycloadducts formed by reaction between 3-hydroxy-pyridinium salts and vinyl sulfones or sulfonamides. The diverse tropane-related scaffolds were formed by addition of substituents to, cyclisation reactions of, and fusion of additional ring(s) to the key bicyclic intermediates. A set of 53 screening compounds was designed, synthesised and evaluated in order to determine the biological relevance of the scaffolds accessible using the synthetic approach. Two inhibitors of Hedgehog signalling, and four compounds with weak activity against the parasite P. falciparum, were discovered. Three of the active compounds may be considered to be indotropane or pyrrotropane pseudo natural products in which a tropane is fused with a fragment from another natural product class. It was concluded that the unified synthetic approach had yielded diverse scaffolds suitable for the design of performance-diverse screening libraries.     

Interaction of aliphatic cap group in inhibition of histone deacetylases by cyclic tetrapeptides

Inhibitors of histone deacetylases (HDACs) are a promising class of anticancer agents that effect gene regulation. To know the interaction of aliphatic cap groups with HDACs, cyclic tetrapeptide and bicyclic peptide disulfide hybrids were synthesized without aromatic ring in their macrocyclic framework. Benzene ring of l-Phe in chlamydocin was replaced with several aliphatic amino acids and also a fused bicyclic tetrapeptide was synthesized by ring closing metathesis using Grubb's first generation catalyst. The inhibitory activities of the cyclic peptides against histone deacetylase enzymes were evaluated, which demonstrated most of them are interesting candidates as anticancer agents.     

Structure based approach to the design of bicyclic-1H-isoindole-1,3(2H)-dione based androgen receptor antagonists

A novel series of isoindoledione based compounds were identified as potent antagonists of the androgen receptor (AR). Co-crystallization of members of this family of inhibitors was successfully accomplished with the T877A AR LBD. A working model of how this class of compounds functions to antagonize the AR was created. Based on this model, it was proposed that expanding the bicyclic portion of the molecule should result in analogs which function as effective antagonists against a variety of AR isoforms. In contrast to what was predicted by the model, SAR around this new series was dictated by the aniline portion rather than the bicyclic portion of the molecule.     

Design, synthesis and biological evaluation of novel bicyclic beta-lactams as potential antimalarials

A series of bicyclic N-substituted and unsubstituted beta-lactams were synthesized and evaluated as targeted potential antimalarials. The compounds MNR4 and MNR5 were found to have highest potency against Plasmodium falciparum in vitro.     

Exploiting a basic chemosensitizing pharmacophore hypothesis. Part 1: synthesis and biological evaluation of novel arylbromide and bicyclic chemosensitizers against drug-resistant malaria parasites

An exploratory series of novel arylbromide and bicyclic chemosensitizers (modulators) against chloroquine-resistant Plasmodium falciparum were designed and synthesized on the basis of a basic chemosensitizing pharmacophore hypothesis in malaria. ortho-Substituted bromo and biphenyl ether compounds displayed the best activity from the series.     

Discovery of spirocyclic sulfonamides as potent Akt inhibitors with exquisite selectivity against PKA

We describe the design and synthesis of novel bicyclic spiro sulfonamides as potent Akt inhibitors. Through structure-based rational design, we have successfully improved PKA selectivity of previously disclosed spirochromanes. Representative compounds showed favorable Akt potency while exhibiting up to 1000-fold selectivity against PKA.     

Antimicrobial activity of the marine alkaloids haminol and pulo'upone and related compounds

The marine alkaloids haminol A, haminol B and pulo'upone as well as 17 related compounds (twelve 2-substituted pyridine derivatives, four 3-substituted ones and one analogue of the bicyclic terminus of pulo'upone) were tested for antimicrobial activity against a panel of six microbes (Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus epidermidis, Candida albicans and Saccharomyces cerevisiae) using the paper disc agar diffusion method. Six compounds were tested also against the mold Aspergillus niger. Some of the compounds displayed noteworthy antimicrobial activity, only one congener being completely devoid of activity. Nearly all compounds had activity against B. cereus and S. epidermidis. The growth of E. coli, C albicans and S. cerevisiae was also distinctly inhibited by many compounds. In contrast, most compounds were inactive or had minimal activity against P. aeruginosa. Interestingly, most of the compounds tested against the opportunistic pathogen A. niger were active, one of them having noteworthy inhibitory potency.     

Potent inhibitors of malarial P. Falciparum protein kinase G: Improving the cell activity of a series of imidazopyridines

Development of a class of bicyclic inhibitors of the Plasmodium falciparum cyclic GMP-dependent protein kinase (PfPKG), starting from known compounds with activity against a related parasite PKG orthologue, is reported. Examination of key sub-structural elements led to new compounds with good levels of inhibitory activity against the recombinant kinase and in vitro activity against the parasite. Key examples were shown to possess encouraging in vitro ADME properties, and computational analysis provided valuable insight into the origins of the observed activity profiles.     

Bicyclic nucleoside inhibitors of varicella-zoster virus: 5'-chloro and 3'-chloro derivatives

We have recently discovered bicyclic furopyrimidines as potent and selective inhibitors of VZV. In order to investigate the structural requirements for antiviral activity we have succesfully synthesised some 3'-chloro and 5'-chloro derivatives. The compounds have been tested against VZV and CMV, but displayed no significant in vitro activity.     

Antiplasmodial and antitrypanosomal activity of bicyclic amides and esters of dialkylamino acids

Several bicyclic amides and esters of dialkylamino acids were prepared. Their activities against a multiresistant strain of Plasmodium falciparum and against Trypanosoma brucei rhodesiense (STIB 900) were examined. Structure–activity relationships were discussed. Particularly the ester compounds showed good antiplasmodial and antitrypanosomal activity and a single compound was tested in vivo against Plasmodium berghei.     

Synthesis of fused bicyclic thioglycosides of N-acylated glucosamine as analogues of mycothiol

The synthesis of a fused bicyclic thioglycoside analogue of mycothiol, (3R)-3-acetylamino-4-one-6,7-dihydro-(1',2'-dideoxy-beta-D-glucopyranoso)[2',1'-f]-1,5-thiazepane (5), is reported. Treatment of phthalimido-protected peracetylated glucosamine with N-acetyl-cysteine and boron trifluoride-etherate gave the beta-linked thioglycoside, which was deprotected and cyclized, using HOBt and EDCl to form the lactam and giving the target structure. This mycothiol mimic and its tri-O-acetate will be investigated as potential inhibitors of enzymes involved in the biosynthesis of mycothiol. The protected derivative also has the potential to be an alpha-selective N-cysteinyl glucosamine donor; however, initial glycosylation attempts failed due to the apparent stability of the fused bicyclic system.     

Novel amodiaquine congeners as potent antimalarial agents

To develop new classes of antimalarial agents, the possibility of replacing the phenolic ring of amodiaquine, tebuquine, and isoquine with other aromatic nuclei was investigated. Within a first set of pyrrole analogues, several compounds displayed high activity against both D10 (CQ-S) and W-2 (CQ-R) strains of Plasmodium falciparum. The isoquine structure was also modified by replacing the diethylamino group with more metabolically stable bicyclic moieties and by replacing the aromatic hydroxyl function with a chlorine atom. Among these compounds, two quinolizidinylmethylamino derivatives (6f and 7f) displayed high activity against both CQ-S and CQ-R strains.     

Bicyclic γ-amino acids as inhibitors of γ-aminobutyrate aminotransferase

The γ-aminobutyrate (GABA)-degradative enzyme GABA aminotransferase (GABA-AT) is regarded as an attractive target to control GABA levels in the central nervous system: this has important implications in the treatment of several neurological disorders and drug dependencies. We have investigated the ability of newly synthesized compounds to act as GABA-AT inhibitors. These compounds have a unique bicyclic structure: the carbocyclic ring bears the GABA skeleton, while the fused 3-Br-isoxazoline ring contains an electrophilic warhead susceptible of nucleophilic attack by an active site residue of the target enzyme. Out of the four compounds tested, only the one named (+)-3 was found to significantly inhibit mammalian GABA-AT in vitro. Docking studies, performed on the available structures of GABA-AT, support the experimental findings: out of the four tested compounds, only (+)-3 suitably orients the electrophilic 3-Br-isoxazoline warhead towards the active site nucleophilic residue Lys329, thereby explaining the irreversible inhibition of GABA-AT observed experimentally.     

Cytotoxic activity of new racemic and optically active N-phosphonoalkyl bicyclic β-amino acids against human malignant cell lines

The cytotoxic effects of novel racemic and optically active constrained N-phosphonoalkyl bicyclic β-amino acids were tested against a panel of human tumor cell lines. All of the compounds investigated exhibited different concentration-dependent antiproliferative effects against the HT-29, MDA-MB-231, HepG2 and HeLa cell lines after 24?h treatment. The most sensitive cells were the HeLa cells at various concentrations of the four compounds tested. The aminophosphonate 3 exerted the most pronounced antiproliferative effect against the HeLa cells (inhibition of the cell vitality up to 70% at 0.5?mg/ml) and was not toxic to the normal Lep3 cells at lower concentration. Furthermore, the N-phosphonophenyl derivatives 1 and 2 displayed antiproliferative effect against mainly the MDA-MB-231 tumour cells at higher concentration.     

Bicyclic Nucleoside Inhibitors of Varicella-Zoster Virus: 5′-Chloro and 3′-Chloro Derivatives

Abstract

We have recently discovered bicyclic furopyrimidines as potent and selective inhibitors of VZV. In order to investigate the structural requirements for antiviral activity we have succesfully synthesised some 3′-chloro and 5′-chloro derivatives. The compounds have been tested against VZV and CMV, but displayed no significant in vitro activity.     

Preparation of l-proline based aeruginosin 298-A analogs: Optimization of the P1-moiety

Aeruginosins are a family of naturally occurring oligopeptides that share a common bicyclic amino acid core structure. Many compounds in the family are inhibitors of serine proteases, such as thrombin and trypsin. Thrombin is an important enzyme in the blood coagulation cascade, and is a promising target for anticoagulant drug development. In order to understand the structure–activity relationship (SAR) and to find selective thrombin inhibitors, we synthesized a series of aeruginosin 298-A analogs, in which the P₂ bicyclic amino acid was replaced by a l-proline residue. The structure optimization was focused on modification of the P₁ position. In choosing the P₁ group, an effort was made to avoid using the highly basic guanidine groups present in nearly all naturally occurring aeruginosins. The synthesis and enzyme assays of these aeruginosin analogs against thrombin and trypsin are reported. We found that several compounds with neutral P₁ groups exhibit excellent selectivity over trypsin and good potency against thrombin. The SAR data of the P₁ groups obtained here can be used in preparing other thrombin inhibitors with better selectivity against trypsin.