Mapping of Some Further Alkylation-Initiated Pathways to Polyheterocyclic Compounds from Indigo and Indirubin.

The reaction of indigo with two equivalents of the electrophile ethyl bromoacetate with caesium carbonate as a base result in the formation of structurally complex polyheterocyclics, including a fused spiroimidazole and a spiro[1,3]oxazino derivative, together with a biindigoid-type derivative, through a convenient one-pot reaction. Further assessment of the reaction using five equivalents of the electrophile gave rise to other molecules incorporating the 2-(7,13,14-trioxo-6,7,13,14-tetrahydropyrazino[1,2-a:4,3-a']diindol-6-yl) scaffold. The reaction of ethyl bromoacetate with the less reactive indirubin resulted in the synthesis of three derivatives of a new class of polyheterocyclic system via a cascade process, although yields were low. These compounds were derived from the parent indolo[1,2-b]pyrrolo[4,3,2-de]isoquinoline skeleton. Despite the modest yields of the reactions, they represent quick cascade routes to a variety of heterocycles from cheap starting materials, with these structures otherwise being difficult to synthesise in a traditional stepwise manner. These outcomes also contribute significantly to the detailed understanding of the indigo/indirubin cascade reaction pathways initiated by base-catalysed N-alkylation.

An investigation of the allylation cascade reactions of substituted indigos.

In a continuation of the exploration of indigo cascade reactions, a series of -OMe, -Ph, -Br and -NO2 substituted indigos 1a-i were synthesised to probe electronic effects upon the outcome of allylation cascade reactions. When indigos 1a-i in the presence of base were reacted with allyl bromide, spiroindolinepyridoindolones 17-25 (36-75%) were obtained as the major products in each case, marking a shift in outcome relative to that previously reported for unsubstituted indigo. In electron-rich derivatives (-OMe, -Ph), C-allylspiroindolinepyridoindolediones 26-29 (3-11%) were also isolated, which are most likely formed via a Claisen rearrangement of the respective spiroindolinepyridoindolones 18-21. Additionally, the isolation of diallylbiindolone 16, oxazinobiindole 30 and N,N'-diallyl-3,3'-bis(allyloxy)biindole 31 each represented novel polyheterocyclic derivatives, providing intriguing new mechanistic insights, reaction pathways and in the case of 30 the first common heterocyclic skeletal outcome shared in both allylation and propargylation cascade reactions of indigo.

The Detosylation of Chiral 1,2-Bis(tosylamides).

The deprotection of chiral 1,2-bis(tosylamides) to their corresponding 1,2-diamines is mostly unsuccessful under standard conditions. In a new methodology, the use of Mg/MeOH with sufficient steric additions allows the facile synthesis of 1,2-diamines in 78-98% yields. These results are rationalized using density functional theory and the examination of inner and outer-sphere reduction mechanisms.

The Cascade Reactions of Indigo with Propargyl Substrates for Heterocyclic and Photophysical Diversity.

The synthesis of structurally diverse heterocycles for chemical space exploration was achieved via the cascade reactions of indigo with propargylic electrophiles. New pyrazinodiindolodione, naphthyridinedione, azepinodiindolone, oxazinoindolone and pyrrolodione products were prepared in one pot reactions by varying the leaving group (-Cl, -Br, -OMs, -OTs) or propargyl terminal functionality (-H, -Me, -Ph, -Ar). Mechanistic and density functional theory studies revealed that the unsaturated propargyl moiety can behave as an electrophile when aromatic terminal substitutions are made, and therefore competes with leaving group substitution for new outcomes. Selected products from the cascade reactions were investigated for their absorption and fluorescence properties, including transient absorption spectroscopy. This revealed polarity dependent excited state relaxation pathways, fluorescence, and triplet formation, thus highlighting these reactions as a means to access diverse functional materials rapidly.

Synthesis of spirocyclic heterocycles from α,ß-unsaturated N-acyliminium ions.

The reactions of α,ß-unsaturated N-acyliminium ions, generated in situ from 4(S)-O-substitutedhydroxy-5-hydroxy-5-vinyl-N-alkylpyrrolidin-2-ones, with allylsilanes and indoles leading to the formation of spirocyclic heterocycles, are reported. Six single crystal X-ray structures and extensive 2D NMR experiments confirmed the structures and stereochemistries of these products. In addition, computational studies provided mechanistic insights and an understanding of the stereochemical outcomes of these reactions.

Gold(I)-Catalyzed Intramolecular Hydroarylation of Phenol-Derived Propiolates and Certain Related Ethers as a Route to Selectively Functionalized Coumarins and 2H-Chromenes.

Methods are reported for the efficient assembly of a series of phenol-derived propiolates, including the parent system 56, and their Au(I)-catalyzed cyclization (intramolecular hydroarylation) to give the corresponding coumarins (e.g., 1). Simple syntheses of natural products such as ayapin (144) and scoparone (145) have been realized by such means, and the first of these subject to single-crystal X-ray analysis. A related process is described for the conversion of propargyl ethers such as 156 into the isomeric 2H-chromene precocene I (159), a naturally occurring inhibitor of juvenile hormone biosynthesis.

High-Pressure-Promoted and Facially Selective Diels-Alder Reactions of Enzymatically Derived cis-1,2-Dihydrocatechols and Their Acetonide Derivatives: Enantiodivergent Routes to Homochiral and Polyfunctionalized Bicyclo[2.2.2]octenes.

cis-1,2-Dihydrocatechols 5 (X = Me and Cl), which are available in the homochiral form through the whole-cell biotransformation of toluene and chlorobenzene, respectively, undergo Diels-Alder cycloaddition reactions with a range of electron-deficient dienophiles at 19 kbar (1.9 GPa). The favored products of such reactions are adducts of the general form 7 and that arise through the operation of a contrasteric or syn-addition pathway. In contrast, the acetonide derivatives of metabolites 5 undergo anti-selective addition reactions under the same conditions and so producing adducts of the general form 11. Bicyclo[2.2.2]octenes 7 and 11, which embody carbocyclic frameworks of opposite enantiomeric form, are useful scaffolds for chemical synthesis. Computational studies reveal that syn-adduct formation is kinetically and normally thermodynamically favored over anti-adduct formation when the free diols 5 are involved, but the reverse is so when the corresponding acetonides participate as the 4π-addend. Furthermore, the reactions become more exothermic as pressure increases while, concurrently, the activation barrier diminishes and at 6 GPa (60 kbar) almost vanishes.

Iterative Suzuki-Miyaura Cross-coupling/Bromo-desilylation Reaction Sequences for the Assembly of Chemically Well-defined, Acyclic Oligopyrrole/Benzenoid Hybrids Embodying Mixed Modes of Connectivity.

Syntheses of a range of chemically well-defined oligopyrrole/benzenoid hybrids are described using tandem Suzuki-Miyaura cross-coupling/bromo-desilyation reaction sequences for linking borylated pyrroles, halogenated pyrroles and/or dibromobenzenes to one another. By such means, including iterative variants, a range of all α-linked, all ß-linked oligopyrroles as well as certain combinations thereof have been assembled, some of them for the first time. The conductivities of iodine-treated thin films formed from certain such systems have been determined.

Isolation of CFTR and TMEM16A inhibitors from Neorautanenia mitis (A. Rich) Verdcourt: Potential lead compounds for treatment of secretory diarrhea.

A phytochemical study on the root extracts of Neorautanenia mitis, a Nigerian medicinal plant used in the management of diarrhea, led to the isolation of one new and 19 known natural products. These compounds and crude extracts were evaluated for Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Cl- channel and calcium-activated Cl- channel (TMEM16A) inhibitory activities in T84 and Calu-3 cells, respectively. Four compounds namely dolineon, neodulin, pachyrrhizine, and neotenone inhibited cAMP-induced Cl- secretion across T84 cell monolayers with IC50 values of ~0.81 µM, ~2.42 µM, ~2.87 µM, and ~4.66 µM, respectively. Dolineon having the highest inhibitory activity also inhibited a Ca + activated Cl- channel (TMEM16A) with an IC50 value of ~4.38 µM. The in vitro antidiarrheal activity of dolineon was evaluated on cholera toxin (CT) induced chloride secretion in T84 cells, where it inhibited CT-induced chloride secretion by >70% at 100 µM. Dolineon also inhibited CT-induced fluid secretion by ~70% in an in vivo mouse closed loop model at a dose of 16.9 µg/loop. The cytotoxicity of the extracts and compounds was evaluated on KB, Vero and BHK21 cells, dolineon showed low cytotoxicity of >29.6 µM and 57.30 + 6.77 µM against Vero and BHK21 cells, respectively. Our study revealed that several compounds isolated from N. mitis showed antidiarrheal activity. The most active compound dolineon can potentially serve as a lead compound towards the development of CFTR and TMEM16A inhibitors as future therapeutics for secretory diarrhea.

The effect of isomerism and other structural variations on the G-quadruplex DNA-binding properties of some nickel Schiff base complexes.

A series of novel isomeric nickel Schiff base complexes, as well as nickel complexes of related ligands having asymmetric structures have been prepared and characterised using microanalysis, 1H and 13C NMR spectroscopy and ESI-MS. The Schiff base ligands were prepared by condensation reactions involving ethylenediamine and different derivatives of benzophenone. The solid-state structures of eight of the complexes were also determined and revealed that each possessed a regular square planar coordination geometry around the metal ion. Many of the new complexes featured at least one, and in many instances two, protonatable pendant groups that enhance aqueous solubility. This enabled the DNA binding properties of the latter complexes to be explored using a variety of instrumental approaches, including ESI-MS, circular dichroism (CD) spectroscopy, FRET melting assays and FID assays, as well as molecular docking studies. The results of experiments performed using ESI-MS suggested that none of the nickel complexes exhibit a high affinity towards either a double stranded DNA (dsDNA) molecule D2, or the parallel unimolecular quadruplex DNA (qDNA) molecule Q1. In contrast, complexes (8) and (12) both gave spectra which reflected a significant level of binding to the parallel tetramolecular qDNA Q4. The results of binding experiments performed using CD spectroscopy suggested that (12) exhibits a significant level of affinity towards most types of DNA, while (4) shows a preference for interacting with parallel, unimolecular qDNA molecules. Complex (4) produced the lowest values of DC50 in FID assays performed using parallel Q1 or Q4, confirming its affinity for these qDNA molecules. The results of FRET melting experiments provided further evidence that (12), along with (8), can interact extensively with anti-parallel unimolecular qDNA. Experiments which monitored the effect of the nickel complexes on the melting temperature of D2 showed that none had a stabilising effect on this dsDNA molecule.

In Search of Fulminate Analogues: Ln M≡CP=NR.

The "CPNR" ligand may be viewed as being isolobal with fulminate, CNO; however, attempts to prepare a complex of such a ligand resulted instead in a range of novel imino and aminophosphinocarbyne complexes. Sequential treatment of [Mo(≡CBr)(CO)2 (Tp*)] (Tp*=hydrotris(dimethylpyrazolyl)borate) with nBuLi and ClP=NMes* (Mes*=C6 H2 tBu3 -2,4,6) afforded mixtures of the complexes [Mo(≡CPnBuNHMes*)(CO)2 (Tp*)] and traces of the bimetallic products [Mo2 {µ2 -C2 P2 O(NHMes)2 }(CO)4 (Tp*)2 ] and [Mo2 (µ2 -C2 PNHMes)(CO)4 (Tp*)2 ]. The reaction of [W(≡CBr)(CO)2 (Tp*)] with nBuLi and ClP=NMes* afforded predominantly the mononuclear carbyne [W{≡CP(=NMes*)nBu2 })(CO)2 (Tp*)] and traces of the binuclear complex [W2 (µ-C2 PNHMes)(CO)4 (Tp*)2 ] which is also obtained when tBuLi is used. Although not isolable, the intended complexes [M(≡CPNMes*)(CO)2 (Tp*)] could be generated in situ and spectroscopically characterized via the reactions of the stannyl carbynes [M(≡CSnnBu3 )(CO)2 (Tp*)] and ClP=NMes*. The preceding observations are mechanistically interpreted with reference to a computational interrogation of the model complex [Mo(≡CP=NCH3 )(CO)2 (Tp*)], the LUMO of which has considerable phosphorus character.

A new class of quadruplex DNA-binding nickel Schiff base complexes.

We have prepared six new nickel Schiff base complexes via reactions of substituted benzophenones with different diamines in the presence of nickel(ii). These new complexes were then reacted with 1-(2-choroethyl)piperidine to afford a further six novel nickel(ii) Schiff base complexes bearing pendant ethylpiperidine groups. The complexes bearing the ethylpiperidine moieties had greater solubility in water, and were therefore suitable for use in DNA binding experiments. ESI mass spectra of solutions containing 4 and the parallel, tetramolecular quadruplex Q4, contained ions attributable to formation of non-covalent complexes. In contrast, no ions from non-covalent complexes were observed when the experiments were repeated using 4 and either a double stranded DNA (dsDNA) molecule (D2), or parallel Q1, a unimolecular quadruplex DNA (qDNA). The ESI-MS binding study also revealed that 14 has a significant ability to form non-covalent complexes with qDNA, but does not interact to the same extent with D2. This is supported by the large changes to the ellipticity of bands observed in the circular dichroism spectra of two different unimolecular qDNA molecules (c-kit1 and Q1), including the latter annealed under conditions designed to induce formation of alternative topologies (antiparallel and hybrid). In Fluorescent Indicator Displacement (FID) assays conducted using the new nickel complexes, 14 gave the lowest values of DC50 for experiments conducted with Q1 and Q4. Furthermore, 14 showed greater stabilisation of an antiparallel qDNA molecule in FRET assays than when the other new complexes were examined. These results highlight the potential of 14 as a lead complex for future structure/DNA binding investigations. This is reinforced by the results obtained from cytotoxicity studies performed using four of the nickel complexes, including 14, and Chinese hamster lung cancer (V79) cells, which gave IC50 values between 4 and 12 µM. These complexes were also shown to have the ability to induce apoptosis in the same cancer cell line.

Styryllactones from Goniothalamus tamirensis.

The phytochemical investigation of the twig and leaf extracts of Goniothalamus tamirensis led to the isolation and identification of 15 compounds including three rare previously undescribed styryllactones, goniotamirenones A-C, together with 12 known compounds. (Z)-6-Styryl-5,6-dihydro-2-pyranone and 5-(1-hydroxy-3-phenyl-allyl)-dihydro-furan-2-one are reported here for the first time as previously undescribed natural products. Their structures were elucidated by spectroscopic methods. Goniotamirenone A was synthesized via a [2 + 2] cycloaddition reaction of 6-styrrylpyran-2-one in quantitative yield. The absolute configurations of goniotamirenones B and C were identified from experimental and calculated ECD data, while the absolute configurations of (-)-5-acetoxygoniothalamin, (-)-isoaltholactone, parvistone E, and 5-(1-hydroxy-3-phenyl-allyl)-dihydro-furan-2-one were identified by single-crystal X-ray diffraction analysis using Cu Kα radiation. The absolute configurations of the other related compounds were determined from comparisons of their ECD spectra with relevant compounds reported in the literature. (-)-5-Acetoxygoniothalamin exhibited potent cytotoxicity against the colon cancer cell line (HCT116) with an IC50 value of 8.6 µM which was better than the standard control (doxorubicin, IC50 = 9.7 µM), while (Z)-6-styryl-5,6-dihydro-2-pyranone was less active with an IC50 value of 22.1 µM.

Relative hemilabilities of H2B(az)2 (az = pyrazolyl, dimethylpyrazolyl, methimazolyl) chelates in the complexes [M(η-C3H5)(CO)2{H2B(az)2}] (M = Mo, W).

The reactions of [M(η3-C3H5)Br(CO)2(NCMe)2] (M = Mo, W) or [Mo(η3-C3H5)Br(CO)2(PMe2Ph)2] with Na[H2B(mt)2] (mt = methimazolyl) affords the complexes [M(η3-C3H5)(CO)2{κ3-H,S,S'-H2B(mt)2}], the 3-centre, 2-electron B-H-M interaction of which was found to be inert with respect to opening under mild conditions, while more forcing conditions (heating with PMe2Ph) resulted in cleavage of the entire allyl and borate ligands to form [Mo(CO)3(PMe2Ph)3]. In contrast, the reaction of [Mo(η3-C3H5)Br(CO)2(NCMe)2] with Na[H2B(pz)2] affords either [Mo(η3-C3H5)(CO)2{κ3-H,N,N'-H2B(pz)2}] or (more likely) [Mo(η3-C3H5)(CO)2(NCMe){κ2-N,N'-H2B(pz)2}] which in turn reacts with phosphines to provide [[Mo(η3-C3H5)(CO)2(PPhR2){κ2-N,N'-H2B(pz)2}] (R = Me, Ph). The reactions discussed indicate the propensity for 3-centre, 2-electron B-H-Mo interactions increases in the order H2B(pz)2 < H2B(pz*)2 < H2B(mt)2 (pz* = 3,5-dimethypyrazolyl).

Total Syntheses of the 3H-Pyrrolo[2,3-c]quinolone-Containing Alkaloids Marinoquinolines A-F, K, and Aplidiopsamine A Using a Palladium-Catalyzed Ullmann Cross-Coupling/Reductive Cyclization Pathway.

Compounds 1-6 and 11 representing key members of the marinoquinoline family of natural products, together with the related marine alkaloid aplidiopsamine A (12), have been synthesized using various combinations of palladium-catalyzed Ullmann cross-coupling and reductive cyclization processes involving a C3-arylated pyrrole as the common intermediate. These natural products have been characterized by single-crystal X-ray analyses and evaluated as inhibitors of acetylcholinesterase (AChE) with congener 2 proving to be the most active.

Regioselective convergent synthesis of 2-arylidene thiazolo[3,2-a]pyrimidines as potential anti-chikungunya agents.

Convergent and convenient regioselective synthesis of novel thiazolo[2,3-a]pyrimidine derivatives was accomplished using the one-pot reaction of 6-ethylthiouracil, bromoacetic acid, anhydrous sodium acetate, acetic anhydride, acetic acid and suitable aldehyde. X-ray crystallographic study reveals the presence of the Z configuration of only one regioisomer confirmed by computational studies as being the most likely isomer present.

Nickel(II) Complex with a Flexidentate Ligand Derived from Acetohydrazide: Synthesis, Structural Characterization and Hirshfeld Surface Analysis.

The mononuclear Ni(II) complex [Ni(Lp)2(CH3OH)2]Cl2 has been synthesized by reacting 1-(5-hydroxy-3-methyl-5-phenyl-4,5-dihydro-1H-pyrazol-1-yl)ethan-1-one ligand (HL) with NiCl2·6H2O in methanol solution. In the reaction, the tridentate ligand, HL, was converted in situ into 4-hydroxy-4-phenylbut-3-en-2-ylidene)acetohydrazid ligand, (pyrazole, Lp). The pyrazole ligand acts as bidentate neutral ligand and the hydroxyl group is left uncoordinated. The structure of the Ni(II) complex has been established by X-ray crystallography. The Ni(II) is six-coordinate and has a distorted octahedral geometry. It is bonded by two nitrogen and by two oxygen atoms of the two pyrazole ligands and two oxygen atoms of methanol molecules. The Hirshfeld surface analysis and the 2D the fingerprint plot are used to analyses all of the intermolecular contacts in the crystal structures. The main intermolecular contacts are H/H and Cl/H interactions.

Syntheses of Dimethyl (1S,2R)-3-Bromocyclohexa-3,5-diene-1,2-dicarboxylate and Its Enantiomer.

The title compounds, (-)-2 and (+)-2, representing potentially valuable building blocks for chemical synthesis, have each been prepared from cyclopentanone in eight steps. The pivotal one involves a resolution, through the quinine- or quinidine-promoted methanolysis of the cyclic anhydride (±)-10, leading to chromatographically separable pairs of enantiomerically pure forms of regioisomeric methyl half esters.