Asymmetric Synthesis and Biological Evaluation of Platensilin, Platensimycin, Platencin, and Their Analogs via a Bioinspired Skeletal Reconstruction Approach.

Platensilin, platensimycin, and platencin are potent inhibitors of ß-ketoacyl-acyl carrier protein synthase (FabF) in the bacterial and mammalian fatty acid synthesis system, presenting promising drug leads for both antibacterial and antidiabetic therapies. Herein, a bioinspired skeleton reconstruction approach is reported, which enables the unified synthesis of these three natural FabF inhibitors and their skeletally diverse analogs, all stemming from a common ent-pimarane core. The synthesis features a diastereoselective biocatalytic reduction and an intermolecular Diels-Alder reaction to prepare the common ent-pimarane core. From this intermediate, stereoselective Mn-catalyzed hydrogen atom-transfer hydrogenation and subsequent Cu-catalyzed carbenoid C-H insertion afford platensilin. Furthermore, the intramolecular Diels-Alder reaction succeeded by regioselective ring opening of the newly formed cyclopropane enables the construction of the bicyclo[3.2.1]-octane and bicyclo[2.2.2]-octane ring systems of platensimycin and platencin, respectively. This skeletal reconstruction approach of the ent-pimarane core facilitates the preparation of analogs bearing different polycyclic scaffolds. Among these analogs, the previously unexplored cyclopropyl analog 47 exhibits improved antibacterial activity (MIC80 = 0.0625 µg/mL) against S. aureus compared to platensimycin.

Discovery of antiproliferative and anti-FAK inhibitory activity of 1,2,4-triazole derivatives containing acetamido carboxylic acid skeleton.

Small molecule inhibitors of the focal adhesion kinase are regarded as promising tools in our armamentarium for treating cancer. Here, we identified four 1,2,4-triazole derivatives that inhibit FAK kinase significantly and evaluated their therapeutic potential. Most tested compounds revealed potent antiproliferative activity in HepG2 and Hep3B liver cancer cells, in which 3c and 3d were the most potent (IC50 range; 2.88 ~ 4.83 µM). Compound 3d possessed significant FAK inhibitory activity with IC50 value of 18.10 nM better than the reference GSK-2256098 (IC50 = 22.14 nM). The preliminary mechanism investigation by Western blot analysis showed that both 3c and 3d repressed FAK phosphorylation comparable to GSK-2256098 in HepG2 cells. As a result of FAK inhibition, 3c and 3d inhibited the pro-survival pathways by decreasing the phosphorylation levels of PI3K, Akt, JNK, and STAT3 proteins. This effect led to apoptosis induction and cell cycle arrest. Taken together, these results indicate that 3d could serve as a potent preclinical candidate for the treatment of cancers.

Ribosomal Elongation of Aminobenzoic Acid Derivatives.

2-Aminobenzoic acid and heterocyclic amino acids are aromatic homologues of ß-amino acids, but their chemical properties are quite distinct. Because of the poor nucleophilicity of the amino group conjugated with the aromatic ring, no literature reports of their successful ribosomal elongation in nascent peptide chains have appeared to date. Here we report for the first time their incorporation in nascent peptide chains by means of a reconstituted translation system in which a designer tRNAPro1E2 capable of recruiting the elongation factors EF-Tu and EF-P was charged with their derivatives and the corresponding peptides were successfully expressed. We also demonstrate the expression of macrocyclic peptides containing exotic amino acids, including aminobenzoic acid derivatives.

Design, synthesis and SARs of novel telomerase inhibitors based on BIBR1532.

Telomerase has become one of the new popular targets for the development of anti-tumor drugs. Based on the structural characteristics of the BIBR1532 which has entered the stage of clinical research, six series total of 64 new compounds with diverse structural characteristics were designed and synthesized. The inhibitory activity against SGC-7901, MGC-803, SMMC-7721, A375 and GES cell lines and their telomerase inhibitory activity were tested. Among them, eight compounds showed good activity against cancer cells, among them compounds 56, 57 and 59 also showed low toxicity. Some of them showed excellent telomerase inhibitory activity with IC50 values ranging from 0.62 µM to 8.87 µM. Based on above, in depth structure-activity relationships were summarized, the compounds by replacing methyl group with cyanide and retaining amide moiety had good anti-tumor activity, moderate cytotoxicity, and better telomerase inhibitory activity. The results should be used for reference in BIBR1532-based structural optimization for further development of small molecule telomerase inhibitors.

Streamlined Expressed Protein Ligation: Site-Specific Antibody-Drug Conjugate.

Protein semisynthesis is a powerful tool for studying proteins and has contributed to a better understanding of protein structure and function and also driven innovations in protein science. Expressed protein ligation (EPL) is a widely used method to generate chemically modified proteins. However, EPL has some limitations, particularly relevant to modify challenging proteins such as antibodies. The method termed streamlined expressed protein ligation (SEPL) overcomes some of the problems of EPL, and other methods of protein semisynthesis, to generate challenging modified proteins such as antibody-drug conjugates (ADCs). ADCs targeting highly cytotoxic molecules to cancer cells, offer an attractive strategy to selectively eliminate tumor cells with improved therapeutic index than the antibodies or cytotoxic molecules themselves. Despite the potential of ADCs, the development of such complex molecules is challenging. We provide here protocols to prepare site-specifically modified ADCs by streamlined expressed protein ligation (SEPL), which does not require the incorporation of unnatural modifications into the antibody. Therefore, fully native antibodies, with only the desired cytotoxic molecules attached, can be generated.

Bio-Organometallic Derivatives of Antibacterial Drugs.

Overuse and misuse of antibacterial drugs has resulted in bacteria resistance and in an increase in mortality rates due to bacterial infections. Therefore, there is an imperative necessity of new antibacterial drugs. Bio-organometallic derivatives of antibacterial agents offer an opportunity to discover new active antibacterial drugs. These compounds are well-characterized products and, in several examples, their antibacterial activities have been studied. Both inhibition of the antibacterial activity and strong increase in the antibiotic activity of the parent drug have been found. The synthesis of the main classes of bio-organometallic derivatives of these drugs, as well as examples of the use of structure-activity relation (SAR) studies to increase the activity and to understand the mode of action of bio-organometallic antimicrobial peptides (BOAMPs) and platensimicyn bio-organometallic mimics is presented in this article.

Acyclic peptides incorporating the d-Phe-2-Abz turn motif: Investigations on antimicrobial activity and propensity to adopt ß-hairpin conformations.

Three linear peptides incorporating d-Phe-2-Abz as the turn motif are reported. Peptide 1, a hydrophobic ß-hairpin, served as a proof of principle for the design strategy with both NMR and CD spectra strongly suggesting a ß-hairpin conformation. Peptides 2 and 3, designed as amphipathic antimicrobials, exhibited broad spectrum antimicrobial activity, with potency in the nanomolar range against Staphylococcus aureus. Both compounds possess a high degree of selectivity, proving non-haemolytic at concentrations 500 to 800 times higher than their respective minimal inhibitory concentrations (MICs) against S. aureus. Peptide 2 induced cell membrane and cell wall disintegration in both S. aureus and Pseudomonas aeruginosa as observed by transmission electron microscopy. Peptide 2 also demonstrated moderate antifungal activity against Candida albicans with an MIC of 50 µM. Synergism was observed with sub-MIC levels of amphotericin B (AmB), leading to nanomolar MICs against C. albicans for peptide 2. Based on circular dichroism spectra, both peptides 2 and 3 appear to exist as a mixture of conformers with the ß-hairpin as a minor conformer in aqueous solution, and a slight increase in hairpin population in 50% trifluoroethanol, which was more pronounced for peptide 3. NMR spectra of peptide 2 in a 1:1 CD3 CN/H2 O mixture and 30 mM deuterated sodium dodecyl sulfate showed evidence of an extended backbone conformation of the ß-strand residues. However, inter-strand rotating frame Overhauser effects (ROE) could not be detected and a loosely defined divergent hairpin structure resulted from ROE structure calculation in CD3 CN/H2 O. The loosely defined hairpin conformation is most likely a result of the electrostatic repulsions between cationic strand residues which also probably contribute towards maintaining low haemolytic activity.

In vivo instability of platensimycin and platencin: Synthesis and biological evaluation of urea- and carbamate-platensimycin.

Platensimycin (PTM) and platencin (PTN), two natural products and promising drug leads that target bacterial and mammalian fatty acid synthases, are known to have unfavorable pharmacokinetic properties. It is not clear, however, what the metabolic fates of PTM and PTN are and no efforts have been reported to address this key roadblock in the development of these compounds as viable drug options. Here we describe the pharmacokinetics of PTM and PTN, and reveal rapid renal clearance as the primary metabolic liability with three additional sites of chemical liability: (i) amide hydrolysis, (ii) glucuronidation, and (iii) oxidation. We determined that hydrolysis is a viable clearance mechanism in vivo and synthesized two PTM analogues to address in vivo hydrolysis. Urea- and carbamate-PTM analogues showed no detectable hydrolysis in vivo, at the expense of antibacterial activity, with no further improvement in systemic exposure. The antibacterial sulfur-containing analogues PTM D1 and PTM ML14 showed significant decreases in renal clearance. These studies set the stage for continued generation of PTM and PTN analogues in an effort to improve their pharmacokinetics while retaining or improving their biological activities.

A Mutasynthetic Library of Platensimycin and Platencin Analogues.

Inactivation of ptmB1, ptmB2, ptmT2, or ptmC in Streptomyces platensis SB12029, a platensimycin (PTM) and platencin (PTN) overproducer, revealed that PTM and PTN biosynthesis features two distinct moieties that are individually constructed and convergently coupled to afford PTM and PTN. A focused library of PTM and PTN analogues was generated by mutasynthesis in the ΔptmB1 mutant S. platensis SB12032. Of the 34 aryl variants tested, 18 were incorporated with high titers.

3-Amino-4-hydroxybenzoic acid production from sweet sorghum juice by recombinant Corynebacterium glutamicum.

The production of the bioplastic precursor 3-amino-4-hydroxybenzoic acid (3,4-AHBA) from sweet sorghum juice, which contains amino acids and the fermentable sugars sucrose, glucose and fructose, was assessed to address the limitations of producing bio-based chemicals from renewable feedstocks. Recombinant Corynebacterium glutamicum strain KT01 expressing griH and griI derived from Streptomyces griseus produced 3,4-AHBA from the sweet sorghum juice of cultivar SIL-05 at a final concentration (1.0 g l(-1)) that was 5-fold higher than that from pure sucrose. Fractionation of sweet sorghum juice by nanofiltration (NF) membrane separation (molecular weight cut-off 150) revealed that the NF-concentrated fraction, which contained the highest concentrations of amino acids, increased 3,4-AHBA production, whereas the NF-filtrated fraction inhibited 3,4-AHBA biosynthesis. Amino acid supplementation experiments revealed that leucine specifically enhanced 3,4-AHBA production by strain KT01. Taken together, these results suggest that sweet sorghum juice is a potentially suitable feedstock for 3,4-AHBA production by recombinant C. glutamicum.

Exploring S1 plasticity and probing S1' subsite of mammalian aminopeptidase N/CD13 with highly potent and selective aminobenzosuberone inhibitors.

In order to probe the S1 and S1' mammalian aminopeptidase N subsites, racemic 1- or 4-substituted 7-aminobenzocyclohepten-6-one derivatives were synthesized and evaluated for their ability to inhibit mammalian aminopeptidase N. We focused on improving the physicochemical and ADME properties of this series by targeting lipophilicity and LELP score. Some 4-heteroaryl substituted analogues displayed reduced lipophilicity and enhanced inhibition potency with Ki values in the nanomolar range.

Synthesis, characterization, crystal structure and antimicrobial activity of copper(II) complexes with the Schiff base derived from 2-hydroxy-4-methoxybenzaldehyde.

A novel Schiff base, ethyl 4-[(E)-(2-hydroxy-4-methoxyphenyl)methylene-amino]benzoate (HL), was prepared and structurally characterized on the basis of elemental analyses, (1)H NMR, (13)C NMR, UV-Vis and IR spectral data. Six new copper(II) complexes, [Cu(L)(NO3)(H2O)2] (1), [Cu(L)2] (2), [Cu(L)(OAc)] (3), [Cu2 (L)2Cl2(H2O)4] (4), [Cu(L)(ClO4)(H2O)] (5) and [Cu2(L2S)(ClO4)(H2O)]ClO4·H2O (6) have been synthesized. The characterization of the newly formed compounds was done by IR, UV-Vis, EPR, FAB mass spectroscopy, elemental and thermal analysis, magnetic susceptibility measurements and molar electric conductivity. The crystal structures of Schiff base and the complex [Cu2(L2S)(ClO4)(H2O)]ClO4·H2O (6) have been determined by single crystal X-ray diffraction studies. Both copper atoms display a distorted octahedral coordination type [O4NS]. This coordination is ensured by three phenol oxygen, two of which being related to the µ-oxo-bridge, the nitrogen atoms of the azomethine group and the sulfur atoms that come from the polydentate ligand. The in vitro antimicrobial activity against Escherichia coli ATCC 25922, Salmonella enteritidis, Staphylococcus aureus ATCC 25923, Enterococcus and Candida albicans strains was studied and compared with that of free ligand. The complexes 1, 2, 5 showed a better antimicrobial activity than the Schiff base against the tested microorganisms.

Diastereoselective cyclization of an aminobenzoic acid derivative and chiroptical properties of triple-stranded helical bis(phenylethynyl)benzene.

The diastereoselective cyclization of 2,5-dibromo-4-hexylaminobenzoic acid was achieved by the microwave-assisted condensation using SiCl4. Moreover, the triple-stranded helical structure of bis(phenylethynyl)benzene units embedded in the cyclic tri(benzamide) scaffold was obtained by a Sonogashira-Hagihara coupling reaction. Two optically active enantiomers that do not racemize even at the elevated temperature were separated by chiral HPLC. The chiral helical topology was revealed by the spectroscopic data and theoretical calculation.

3,4-diaminobenzoic acid derivatives as inhibitors of the oxytocinase subfamily of M1 aminopeptidases with immune-regulating properties.

Members of the oxytocinase subfamily of M1 aminopeptidases (ERAP1, ERAP2, and IRAP) play important roles in both the adaptive and innate human immune responses. Their enzymatic activity can contribute to the pathogenesis of several major human diseases ranging from viral and parasitic infections to autoimmunity and cancer. We have previously demonstrated that diaminobenzoic acid derivatives show promise as selective inhibitors for this group of aminopeptidases. In this study, we have thoroughly explored a series of 3,4-diaminobenzoic acid derivatives as inhibitors of this class of enzymes, achieving submicromolar inhibitors for ERAP2 (IC50 = 237 nM) and IRAP (IC50 = 105 nM). Cell-based analysis indicated that the lead compounds can be effective in downregulating macrophage activation induced by lipopolysaccharide and interferon-γ as well as cross-presentation by bone marrow-derived dendritic cells. Our results indicate that this class of inhibitors may be useful for the targeted downregulation of immune responses.

Bioactivity of a family of chiral nonracemic aminobenzylnaphthols towards Candida albicans.

Chiral nonracemic aminobenzylnaphthols were obtained by a Betti multi-component reaction between 2-naphthol, aryl aldehydes and enantiopure arylethylamine. Moreover, some new aminobenzylnaphthols were synthesized by a similar reaction between 2-naphthol, aryl aldehydes and prolinol. These aminobenzylnaphthols, synthesized from different components and thus having different structural features, were tested as anti-yeast agents inhibiting Candida albicans. The effect towards the test strain was studied with a microdilution approach and three different concentrations (150, 300 and 450 µg/mL) were tested. The best results were found for the aminobenzylnaphthols obtained from 1-naphthylethylamine and from natural prolinol. The use of the two-way ANOVA highlighted the better performances of the prolinol derivative among the differently structured aminobenzylnaphthols that were screened. The activity towards C. albicans of this prolinol derivative resulted to be interesting and could represent a promising alternative to overcome the problem of the strains resistant to the traditional antifungals.

Discovery of novel FabF ligands inspired by platensimycin by integrating structure-based design with diversity-oriented synthetic accessibility.

An approach for designing bioactive small molecules has been developed in which de novo structure-based ligand design (SBLD) was focused on regions of chemical space accessible using a diversity-oriented synthetic approach. The approach was exploited in the design and synthesis of a focused library of platensimycin analogues in which the complex bridged ring system was replaced with a series of alternative ring systems. The affinity of the resulting compounds for the C163Q mutant of FabF was determined using a WaterLOGSY competition binding assay. Several compounds had significantly improved affinity for the protein relative to a reference ligand. The integration of synthetic accessibility with ligand design enabled focus to be placed on synthetically-accessible regions of chemical space that were relevant to the target protein under investigation.

New 3,4-diaminobenzoic acid Schiff base compounds and their complexes: synthesis, characterization and thermodynamics.

Some new tetradentate Schiff base ligands (H3L) were prepared via condensation of 3,4-diaminobenzoic acid with 2-hydroxybenzaldehyde derivatives, such as 3,4-bis((E)-2,4-dihydroxybenzylideneamino)benzoic acid (H3L(1)), 3,4-bis((E)-2-hydroxy-3-methoxybenzylideneamino)benzoic acid (H3L(2)) and 3,4-bis((E)-5-bromo-2-hydroxybenzylideneamino)benzoic acid (H3L(4)). Additionally, a tetradentate Schiff base ligand 3,4-bis((E)-2-hydroxybenzylideneamino)benzoic acid (H3L(3)) and its complexes were synthesized. Their metal complexes of Co(II), Ni(II), Cu(II) and Zn(II) were prepared in good yields from the reaction of the ligands with the corresponding metal acetate. They were characterized based on IR, (1)H NMR, Mass spectroscopy and UV-Vis spectroscopy. Also, the formation constants of the complexes were measured by UV-Vis spectroscopic titration at constant ionic strength 0.1M (NaClO4), at 25 °C in dimethylformamide (DMF) as a solvent.

Dimethocaine, a synthetic cocaine derivative: studies on its in vitro metabolism catalyzed by P450s and NAT2.

Dimethocaine (DMC), a synthetic derivative of cocaine, is distributed and consumed as "new psychoactive substance" (NPS) without any safety testing at the forefront. It is mainly metabolized by N-acetylation, N-deethylation or hydroxylation. Therefore, the aim of the presented study was to determine the human NAT and P450 isozymes involved in this major metabolic steps, to measure the kinetics of the reactions, and to estimate the contribution on in vivo hepatic clearance. For these studies, cDNA-expressed NATs and P450s were used and formation of metabolites after incubation was measured using LC-MS or LC-MS(n). For N-acetylation, NAT2 could be shown to be the only isoform catalyzing the reaction in vitro hence assuming to be the only relevant enzyme for in vivo acetylation. Kinetic profiles of all P450 catalyzed metabolite formations followed classic Michaelis-Menten behavior with enzyme affinities (Km values) between 3.6 and 220 µM. Using the relative activity factor approach, the net clearances for deethylation of DMC were calculated to be 3% for P450 1A2, 1% for 2C19, <1% for 2D6, and 96% for 3A4. The net clearances for hydroxylation of DMC were calculated to be 32% for P450 1A2, 5% for 2C19, 51% for 2D6, and 12% for 3A4. Furthermore, these data were confirmed by chemical inhibition tests in human liver microsomes. As DMC is metabolized via two main steps and different P450 isoforms were involved in the hepatic clearance of DMC, a clinically relevant interaction with single P450 inhibitors should not be expected. However, a slow acetylation phenotype or inhibition of NAT2 could lead to decreased N-acetylation and hence leading to an increased risk of side effects caused by this arylamine.

Stereodivergent resolution of oxabicyclic ketones: preparation of key intermediates for platensimycin and other natural products.

An improved methodology for the preparation of enantiopure oxabicyclo[3.2.1]octadienes via a stereodivergent resolution is reported. High catalyst control proximal to the oxabridged stereocenter produces readily separable diastereomers in high yield (>92%) and with excellent optical purity (>95% ee). This resolution strategy is amenable to large-scale preparations, and the utility of the resolution was further demonstrated in the asymmetric preparation of a key intermediate used in the synthesis of the antibiotic (-)-platensimycin.

Formal syntheses of (±)-platensimycin and (±)-platencin via a dual-mode Lewis acid induced cascade cyclization approach.

A mild and efficient dual-mode Lewis acid induced Diels-Alder (DA)/carbocyclization cascade cyclization reaction has been developed for construction of the tricyclic core of ent-kaurenoids in one pot with the aid of a theoretical study on the π,σ-Lewis acidities of a variety of Lewis acids. With ZnBr2 as the dual-mode Lewis acid, a series of substituted enones and dienes underwent DA/carbocyclization cascade cyclization reaction smoothly at room temperature and provided the tricyclic cyclized products in one pot with good yields and high diastereoselectivity. The tricyclic cyclized product has been successfully utilized as a common intermediate for formal syntheses of (±)-platensimycin and (±)-platencin.