Synthesis and Biological Evaluation of New (−)‐Englerin Analogues

We report the synthesis and biological evaluation of a series of (?)‐englerin A analogues obtained along our previously reported synthetic route based on a stereoselective gold(I) cycloaddition process. This synthetic route is a convenient platform to access analogues with broad structural diversity and has led us to the discovery of unprecedented and easier‐to‐synthesize derivatives with an unsaturation in the cyclopentyl ring between C4 and C5. We also introduce novel analogues in which the original isopropyl motif has been substituted with cyclohexyl, phenyl, and cyclopropyl moieties. The high selectivity and growth‐inhibitory activity shown by these new derivatives in renal cancer cell lines opens new ways toward the final goal of finding effective drugs for the treatment of renal cell carcinoma (RCC).     

Total Synthesis of Viniferifuran,Resveratrol‐Piceatannol Hybrid,Anigopreissin A and Analogues – Investigation of Demethylation Strategies

Resveratrol‐based natural products constitute a valuable source of unique compounds with diverse biological activities. In this report we investigate demethylation strategies to minimize formation of cyclized and dimerized products during the synthesis of viniferifuran and analogues. We found that boron trichloride/tetra‐n‐butylammonium iodide (BCl₃/TBAI) is typically more effective than boron tribromide (BBr₃). Based on these findings we carried out the first syntheses of dehydro‐δ‐viniferin, resveratrol‐piceatannol hybrid and anigopreissin A. In addition, we have developed a short and efficient route to viniferifuran that was obtained in 13% yield over six steps.

     

Synthesis and Biological Evaluation of N‐Substituted Noscapine Analogues

Noscapine is a phthalideisoquinoline alkaloid isolated from the opium poppy Papaver somniferum. It has long been used as an antitussive agent, but has more recently been found to possess microtubule‐modulating properties and anticancer activity. Herein we report the synthesis and pharmacological evaluation of a series of 6′‐substituted noscapine derivatives. To underpin this structure–activity study, an efficient synthesis of N‐nornoscapine and its subsequent reduction to the cyclic ether derivative of N‐nornoscapine was developed. Reaction of the latter with a range of alkyl halides, acid chlorides, isocyanates, thioisocyanates, and chloroformate reagents resulted in the formation of the corresponding N‐alkyl, N‐acyl, N‐carbamoyl, N‐thiocarbamoyl, and N‐carbamate derivatives, respectively. The ability of these compounds to inhibit cell proliferation was assessed in cell‐cycle cytotoxicity assays using prostate cancer (PC3), breast cancer (MCF‐7), and colon cancer (Caco‐2) cell lines. Compounds that showed activity in the cell‐cycle assay were further evaluated in cell viability assays using PC3 and MCF‐7 cells.     

Alcohol Dehydrogenase‐Catalyzed Synthesis of Enantiomerically Pure δ‐Lactones as Versatile Intermediates for Natural Product Synthesis

Starting from ethyl 4‐bromobutyrate, the chemoenzymatic synthesis of 6‐vinyl‐tetrahydro‐pyran‐2‐one has been accomplished. A screening of a number of available alcohol dehydrogenases and intense optimization of reaction parameters enabled us to establish an efficient synthesis of either enantiomer of the vinyllactone with excellent enantiomeric excess (>99%). The scope of possible applications of enantiopure vinyllactones has been verified by subjection to cross‐metathesis resulting in the total synthesis of the insect pheromone (S)‐5‐hexadecanolide and the cytotoxic styryllactone goniothalamine as well as derivatives thereof.     

Chemoenzymatic Total Synthesis of Sorbicatechol Structural Analogues and Evaluation of Their Antiviral Potential

Sorbicillinoids are fungal polyketides characterized by highly complex and diverse molecular structures, with considerable stereochemical intricacy combined with a high degree of oxygenation. Many sorbicillinoids possess promising biological activities. An interesting member of this natural product family is sorbicatechol A, which is reported to have antiviral activity, particularly against influenza A virus (H1N1). Through a straightforward, one-pot chemoenzymatic approach with recently developed oxidoreductase SorbC, the characteristic bicyclo[2.2.2]octane core of sorbicatechol is structurally diversified by variation of its natural 2-methoxyphenol substituent. This facilitates the preparation of a focused library of structural analogues bearing substituted aromatic systems, alkanes, heterocycles, and ethers. Fast access to this structural diversity provides an opportunity to explore the antiviral potential of the sorbicatechol family.     

Rational Design,Synthesis, and Biological Evaluation of Lactam‐Bridged Gramicidin A Analogues: Discovery of a Low‐Hemolytic Antibacterial Peptide

A linear peptide, gramicidin A (GA), folds into a β^6.3‐helix, functions as an ion channel in the cell membrane, and exerts antibacterial activity. Herein we describe the rational design, synthesis, and biological evaluation of lactam‐bridged GA analogues. The GA analogue with a 27‐membered macrolactam was found to adopt a stable β^6.3‐helical conformation and exhibits higher ion‐exchange activity than GA. Furthermore, this GA analogue retains the potent antibiotic activity of GA, but its hemolytic activity and toxicity toward mammalian cells are significantly lower than those of GA. This study thus dissociates the antibacterial and hemolytic/cytotoxic activities of GA, and charts a rational path forward for the development of new ion‐channel‐based antibiotics.     

Design,Synthesis, and in vitro Biological Evaluation of 3,5‐Dimethylisoxazole Derivatives as BRD4 Inhibitors

BRD4 has been identified as a potential target for blocking proliferation in a variety of cancer cell lines. In this study, 3,5‐dimethylisoxazole derivatives were designed and synthesized with excellent stability in liver microsomes as potent BRD4 inhibitors, and were evaluated for their BRD4 inhibitory activities in vitro. Gratifyingly, compound 11 h [3‐((1‐(2,4‐difluorophenyl)‐1H‐1,2,3‐triazol‐4‐yl)methyl)‐6‐(3,5‐dimethylisoxazol‐4‐yl)‐4‐phenyl‐3,4‐dihydroquinazolin‐2(1H)‐one] exhibited robust potency for BRD4(1) and BRD4(2) inhibition with IC₅₀ values of 27.0 and 180 nm , respectively. Docking studies were performed to illustrate the strategy of modification and analyze the conformation in detail. Furthermore, compound 11 h was found to potently inhibit cell proliferation in the BRD4‐sensitive cell lines HL‐60 and MV4‐11, with IC₅₀ values of 0.120 and 0.09 μm , respectively. Compound 11 h was further demonstrated to downregulate c‐Myc levels in HL‐60 cells. In summary, these results suggest that compound 11 h is most likely a potential BRD4 inhibitor and is a lead compound for further investigations.     

Synthesis,Characterisation and Reactivity of 3‐Mercaptopyruvic Acid

The synthesis, isolation and spectroscopic characterisation of the sulfur metabolic compound 3‐mercaptopyruvic acid (3‐MPH) is reported, for the first time. The compound is isolated without tedious workup, with a purity of 97 %, as indicated by chemical and biochemical analyses. Detailed kinetic and thermodynamic studies of its complex behaviour in solution are discussed. 3‐MPH is stable in the enol form in non‐polar solvent. In polar solvent, a fast equilibrium between the α‐ketoacid and a cyclic dimer dithiane is observed. The formation of the dimer confers increased stability to 3‐MPH towards hydrogen peroxide, in comparison with cysteine.     

Design and Synthesis of A‐Ring Simplified Pyripyropene A Analogues as Potent and Selective Synthetic SOAT2 Inhibitors

Currently, pyripyropene A, which is isolated from the culture broth of Aspergillus fumigatus FO‐1289, is the only compound known to strongly and selectively inhibit the isozyme sterol O‐acyltransferase 2 (SOAT2). To aid in the development of new cholesterol‐lowering or anti‐atherosclerotic agents, new A‐ring simplified pyripyropene A analogues have been designed and synthesized based on total synthesis, and the results of structure–activity relationship studies of pyripyropene A. Among the analogues, two A‐ring simplified pyripyropene A analogues exhibited equally efficient SOAT2 inhibitory activity to that of natural pyripyropene A. These new analogues are the most potent and selective SOAT2 inhibitors to be used as synthetic compounds and attractive seed compounds for the development of drug for dyslipidemia, including atherosclerotic disease and steatosis.     

Nucleophilic Water Capture or Proton Loss: Single Amino Acid Switch Converts δ‐Cadinene Synthase into Germacradien‐4‐ol Synthase

δ‐Cadinene synthase is a sesquiterpene cyclase that utilises the universal achiral precursor farnesyl diphosphate (FDP) to generate predominantly the bicyclic sesquiterpene δ‐cadinene and about 2 % germacradien‐4‐ol, which is also generated from FDP by the cyclase germacradien‐4‐ol synthase. Herein, the mechanism by which sesquiterpene synthases discriminate between deprotonation and reaction with a nucleophilic water molecule was investigated by site‐directed mutagenesis of δ‐cadinene synthase. If W279 in δ‐cadinene synthase was replaced with various smaller amino acids, the ratio of alcohol versus hydrocarbon product was directly proportional to the van der Waals volume of the amino acid side chain. DCS‐W279A is a catalytically highly efficient germacradien‐4‐ol synthase (k_cat/K_M=1.4×10^?3 μm s^?1) that produces predominantly germacradien‐4‐ol in addition to 11 % δ‐cadinene. Water capture is not achieved through strategic positioning of a water molecule in the active site, but through a coordinated series of loop movements that allow bulk water access to the final carbocation in the active site prior to product release.     

4‐Biphenylalanine‐ and 3‐Phenyltyrosine‐Derived Hydroxamic Acids as Inhibitors of the JumonjiC‐Domain‐Containing Histone Demethylase KDM4A

Overexpression of the histone lysine demethylase KDM4A, which regulates H3K9 and H3K36 methylation states, has been related to the pathology of several human cancers. We found that a previously reported hydroxamate‐based histone deacetylase (HDAC) inhibitor (SW55) was also able to weakly inhibit this demethylase with an IC₅₀ value of 25.4 μm . Herein we report the synthesis and biochemical evaluations, with two orthogonal in vitro assays, of a series of derivatives of this lead structure. With extensive chemical modifications on the lead structure, also by exploiting the versatility of the radical arylation with aryldiazonium salts, we were able to increase the potency of the derivatives against KDM4A to the low‐micromolar range and, more importantly, to obtain demethylase selectivity with respect to HDACs. Cell‐permeable derivatives clearly showed a demethylase‐inhibition‐dependent antiproliferative effect against HL‐60 human promyelocytic leukemia cells.     

Michael加成反应及其在天然产物全合成中的应用

综述了各种类型Michael加成反应及其机理,以及Michael加成反应在天然产物和具有生物活性的复杂化合物合成中的应用。     

Total Synthesis of the Endocannabinoid Uptake Inhibitor Guineensine and SAR Studies

Guineensine ((2E,4E,12E)-13-(benzo[d][1,3]dioxol-5-yl)-N-isobutyltrideca-2,4,12-trienamide) is a plant-derived natural product that inhibits reuptake of the endocannabinoid anandamide with sub-micromolar potency. We have established a highly efficient total synthesis of guineensine, which provided the natural product in only five steps from commercially available 3-nonyn-1-ol in 17 % overall yield, relying on the attachment of the benzodioxolyl moiety to the unsaturated fatty acid chain by means of a Suzuki coupling as the key step. Subsequent SAR studies revealed that replacement of the N-isobutyl group in the natural product by various alkyl, arylalkyl, or aryl groups is generally well tolerated, and derivatives could be identified that are slightly more potent anandamide reuptake inhibitors than guineensine itself. In contrast, modifications of the benzodioxolyl moiety led to decreased activity. Intriguingly, a change in the configuration of the C4=C5 double bond from E to Z was found to be very well tolerated, in spite of the associated change in the overall geometry of the molecule.     

Enantiospecific Synthesis and Cytotoxicity Evaluation of Oximidine II Analogues

Analogues of the anticancer natural product oximidine II were prepared and evaluated for cytotoxicity. One analogue of oximidine II that carries a C15 allylic amide side chain as well as two analogues with C15 vinyl sulfone side chains were found to lack cytotoxicity against the cancer cell line SK‐Mel‐5, thereby confirming the necessity of the C15 enamide side chain of oximidine II for cytotoxicity. Four analogues, designed by comparative molecular similarity index analysis (CoMSIA), that feature a less complex macrolactone scaffold were prepared and tested. The two analogues carrying a C15 vinyl sulfone group and the two analogues with a C15 oximidine II enamide side chain showed weak cytotoxicity against the SK‐Mel‐5 cell line and other cell lines, indicating that the designed simplified macrocycles cannot replace the oximidine II macrocycle.     

5‐Stabilized Phosphatidylinositol 3,4,5‐Trisphosphate Analogues Bind Grp1 PH,Inhibit Phosphoinositide Phosphatases,and Block Neutrophil Migration

Metabolically stabilized analogues of PtdIns(3,4,5)P₃ have shown long‐lived agonist activity for cellular events and selective inhibition of lipid phosphatase activity. We describe an efficient asymmetric synthesis of two 5‐phosphatase‐resistant analogues of PtdIns(3,4,5)P₃, the 5‐methylene phosphonate (MP) and 5‐phosphorothioate (PT). Furthermore, we illustrate the biochemical and biological activities of five stabilized PtdIns(3,4,5)P₃ analogues in four contexts. First, the relative binding affinities of the 3‐MP, 3‐PT, 5‐MP, 5‐PT, and 3,4,5‐PT₃ analogues to the Grp1 PH domain are shown, as determined by NMR spectroscopy. Second, the enzymology of the five analogues is explored, showing the relative efficiency of inhibition of SHIP1, SHIP2, and phosphatase and tensin homologue deleted on chromosome 10 (PTEN), as well as the greatly reduced ability of these phosphatases to process these analogues as substrates as compared to PtdIns(3,4,5)P₃. Third, exogenously delivered analogues severely impair complement factor C5a‐mediated polarization and migration of murine neutrophils. Finally, the new analogues show long‐lived agonist activity in mimicking insulin action in sodium transport in A6 cells.     

Human Acid β‐Glucosidase Inhibition by Carbohydrate Derived Iminosugars: Towards New Pharmacological Chaperones for Gaucher Disease

A collection of carbohydrate‐derived iminosugars belonging to three structurally diversified sub‐classes (polyhydroxylated pyrrolidines, piperidines, and pyrrolizidines) was evaluated for inhibition of human acid β‐glucosidase (glucocerebrosidase, GCase), the deficient enzyme in Gaucher disease. The synthesis of several new pyrrolidine analogues substituted at the nitrogen or α‐carbon atom with alkyl chains of different lengths suggested an interpretation of the inhibition data and led to the discovery of two new GCase inhibitors at sub‐micromolar concentration. In the piperidine iminosugar series, two N‐alkylated derivatives were found to rescue the residual GCase activity in N370S/RecNcil mutated human fibroblasts (among which one up to 1.5‐fold). This study provides the starting point for the identification of new compounds in the treatment of Gaucher disease.