Organic & Biomolecular Chemistry (v.9, #13)

Front cover (4697-4698).

Contents list (4699-4713).

Dioxazaborocanes: old adducts, new tricks by Hélène Bonin; Thomas Delacroix; Emmanuel Gras (4714-4724).
Dioxazaborocanes are boronic adducts obtained by condensation of diethanolamine derivatives with boronic compounds. They were first described in the mid-1950's as a practical way to isolate a boronic adduct. Their use has for a long time been restricted to this purpose for the isolation and characterisation of either a final product or a boronic intermediate. Only recently have they been directly involved in chemical transformations in which they proved equivalent or superior to their acid counterpart. In the meantime they have also been used as protected boronic acids. We wish to show in this report that they will likely represent a fluoride-free alternative to organotrifluoroborate salts and therefore an area of intense development.

Planar chiral arenetricarbonylchromium complexes have been intensively investigated and they have been applied as valuable building blocks for asymmetric synthesis and as ligands for asymmetric catalysis. In contrast, in the field of the isoelectronic cationic [(η6-arene)Mn(CO)3]+ complexes, until these last 10 years, very few studies were published involving nonracemic planar chiral cationic complexes and their potential applications, certainly because of the difficult access to enantiopure starting material. In 2009, however, the discovery of the first resolution of such compounds opened a new area for their application in the field of organic as well as of organometallic enantioselective syntheses. We felt it important to write a review on this subject to give an up-to-date summary of the methodologies used to prepare enantiomerically pure planar chiral neutral [(η5-cyclohexadienyl)Mn(CO)3] and cationic [(η6-arene)Mn(CO)3]+ complexes as well as their potential in enantioselective synthesis.

Herein, we report a urea derived directing group for mild and highly selective oxidative C–H bond olefination. Subsequent intramolecular Michael addition affords dihydroquinazolinones in good yields. The N–O bond of the urea substrate exhibits superior oxidative behaviour compared to a variety of other external oxidants.

Catalytic oxidative cleavage of olefins promoted by osmium tetroxide and hydrogen peroxide by Stewart R. Hart; Daniel C. Whitehead; Benjamin R. Travis; Babak Borhan (4741-4744).
Hydrogen peroxide was employed as the terminal oxidant in the osmium tetroxide mediated oxidative cleavage of olefins, producing the corresponding aldehyde and ketone products. Aryl olefins are cleaved in good to excellent yield regardless of arene electronics. Alkyl olefins cleave in moderate to good yield for di- and tri-substituted alkenes.

The clerodane ring system: investigating the viability of a direct Diels–Alder approach by Andrew T. Merritt; Rebecca H. Pouwer; David J. Williams; Craig M. Williams; Steven V. Ley (4745-4747).
A direct synthetic approach to the spiro-γ-lactone clerodane ring system has been investigated. This work builds on that of Jung and highlights the inherent difficulties associated with the otherwise obvious Diels–Alder approach.

Oxidation and disulfide coupling of cysteine, processes central to oxidative stress and biochemical signaling, are modeled using DFT and solvent-assisted proton exchange, a method of microsolvation. Calculated barriers are consistent with experimental kinetics and observed product ratios and suggest a dependence on the polarity of the surrounding medium.

Amplified fluorescence quenching methodology based on massive autocatalytic photo-unmasking of a dual function sensitizer–quencher is developed and adopted for photoassisted ultra-sensitive detection of molecular recognition events. The resulting binding assay, based on a molecular recognition-triggered photo-amplified cascade with concomitant decrease of fluorescence is validated with the biotin–avidin pair, achieving attomolar detection.

Previously discovered alternating reactivity of S-acyl di-, tri-, and tetrapeptide in internal chemical ligation reactions is rationalised using conformational search, virtual screening methods and quantum chemical calculations. Conformational preorganisation is shown to be the major controller of reactivity, with hydrogen bonding providing additional stabilisation for the tetrapeptide structure.

Synthesis and characterization of a cell-permeable near-infrared fluorescent deoxyglucose analogue for cancer cell imaging by Marc Vendrell; Animesh Samanta; Seong-Wook Yun; Young-Tae Chang (4760-4762).
We report the synthesis and characterization of a novel NIR fluorescent deoxyglucose analogue, CyNE 2-DG. Experiments in different cell lines showed a preferential uptake of CyNE 2-DG in cancer cells and its effective competition with unlabeled d-glucose. Cell imaging experiments demonstrated the superior cell-permeability of CyNE 2-DG over the NIR standard IRDye 800CW 2-DG, and validated its application for cancer cell imaging in the NIR region.

2-Alkynylbenzaldoxime reacts with amine catalyzed by silver triflate under mild conditions, leading to 1-aminoisoquinolines in good yield. This reaction proceeds efficiently with good functional group tolerance.

Peroxidase activity enhancement of horse cytochrome c by dimerization by Zhonghua Wang; Takashi Matsuo; Satoshi Nagao; Shun Hirota (4766-4769).
The peroxidase activity of horse cytochrome c was enhanced by its dimerization, where its Compound III (oxy-form) and Compound I (oxoferryl porphyrin π-cation radical) species were detected in the reactions with hydrogen peroxide and meta-chloroperbenzoic acid, respectively. These results show that oligomeric cytochrome c can contribute as a proapoptotic conformer by the increased peroxidase activity.

A bifunctionalised carboxymethyl-cellulose polymer bearing adamantane units and an antigenic fragment forms a highly stable interfacial complex with a βCD-containing surface. This allows the highly sensitive detection of antibodies using an amperometric immunosensor.

Highly enantioselective aldol reaction of acetone with β,γ-unsaturated α-keto esters promoted by simple chiral primary–tertiary diamine catalysts by Lin Peng; Liang-Liang Wang; Jian-Fei Bai; Li-Na Jia; Yun-Long Guo; Xi-Ya Luo; Fei-Ying Wang; Xiao-Ying Xu; Li-Xin Wang (4774-4777).
A series of primary–tertiary diamine catalysts were successfully applied to promote the enantioselective aldol reaction of acetone with β,γ-unsaturated α-keto esters in excellent yields (up to 99%) and enantioselectivities (up to 96% ee).

Conia-ene annulation of the α-cyano β-TMS-capped alkynyl cycloalkanone system and its synthetic application by Chih-Lung Chin; Cheng-Feng Liao; Hsing-Jang Liu; Ying-Chieh Wong; Ming-Tsang Hsieh; Prashanth K. Amancha; Chun-Ping Chang; Kak-Shan Shia (4778-4781).
Under catalysis with ZnI2, an effective annulation process of ω-silylacetylenic α-cyano ketones, leading to the formation of various bicyclic frameworks characterized with a TMS-containing methylenecyclopentane ring, has been developed.

An easy, efficient and concise approach to tetrahydrofluorene [6,5,6]ABC tricyclic core embedded new polycycles has been achieved under relatively mild and catalytic Nazarov type electrocyclization conditions, using 2 mol% of Sc(OTf)3 in anhydrous DCM (dichloromethane) at room temperature, with high yields. The generality of the reaction has been illustrated by synthesizing diverse polycycles embedded with rare heterotricyclic [6,5,5]ABC skeletons.

Gold(iii) chloride catalysed synthesis of 5-alkylidene-dihydrothiazoles by Thomas S. A. Heugebaert; Leander P. D. Vervaecke; Christian V. Stevens (4791-4794).
A two step synthesis of dihydrothiazoles is presented. First, the previously unknown N-propargylic dithiocarboimidates are produced in good yields from easily available, cheap starting materials. The subsequent gold catalysed ring closure is fast and efficient, leading to dihydrothiazoles through a cascade of 5-exo-dig cyclisation and 1,3-alkyl migration. The yields range from 74% to 95%.

This paper compares covalent and non-covalent approaches for the organisation of ligand arrays to bind integrins. In the covalent strategy, linear RGD peptides are conjugated to first and second generation dendrons, and using a fluorescence polarisation competition assay, the first generation compound is demonstrated to show the most effective integrin binding, with an EC50 of 125 μM (375 μM per peptide unit). As such, this dendritic compound is significantly more effective than a monovalent ligand, which does not bind integrin, even at concentrations as high as 1 mM. However, the second generation compound is significantly less effective, demonstrating that there is an optimum ligand density for multivalency in this case. In the non-covalent approach to multivalency, the same RGD peptide is functionalised with a hydrophobic C12 chain, giving rise to a lipopeptide which is demonstrated to be capable of self-assembly. This lipopeptide is capable of effective integrin binding at concentrations of 200 μM. These results therefore demonstrate that covalent (dendritic) and non-covalent (micellar self-assembly) approaches have, in this case, comparable efficiency in terms of achieving multivalent organisation of a ligand array.

Synthesis, crystal structure and living cell imaging of a Cu2+-specific molecular probe by Wei-Yong Liu; Hai-Ying Li; Bao-Xiang Zhao; Jun-Ying Miao (4802-4805).
We report the development of a rhodamine chromene-based fluorescence probe to monitor the intracellular Cu2+ level in living cells. The new fluorescent probe exhibits a fluorescence response towards Cu2+ under physiological conditions with high sensitivity and selectivity, and facilitates the naked-eye detection of Cu2+. The fluorescence intensity was significantly increased by about 40-fold with 10 equiv. of added Cu2+.

Cationic antimicrobial peptides are potent inhibitors of growth of a broad spectrum of micro-organisms but often have large cytotoxic effects. We prepared some novel sugar amino acid containing cyclic cationic peptides and their Au nanoparticle attached counterparts and studied their antimicrobial activities and cytotoxic behaviour, including an investigation of the mechanism of the cytotoxicity.

A new host molecule, having two azacrown derivatives bridged by luminescent naphthalene diimide functionality, is found to form a [3]pseudorotaxane derivative with imidazolim ion-based guest molecules in non-polar solvents through hydrogen-bonded adduct formation. Depending upon the length of the covalent linker that links the imidazolium ion and the luminescent naphthalene fragment in the guests, the [3]pseudorotaxane adducts adopt different conformation or orientation with varying π–π/donor–acceptor interaction. The mechanism for the naphthalene-based luminescence quenching by NDI fragment on adduct formation was found to be a combination of static, as well as dynamic with static quenching as the dominant one.

A mechanistic study of sialic acid mutarotation: Implications for mutarotase enzymes by Jefferson Chan; Gurtej Sandhu; Andrew J. Bennet (4818-4822).
The mutarotation of N-acetylneuraminic acid (Neu5Ac) proceeds by four kinetically distinct pathways: (i) the acid-catalyzed reaction of neutral Neu5Ac; (ii) the spontaneous reaction of the carboxylic acid (the kinetically equivalent acid-catalyzed reaction on the anion being ruled out by the solvent deuterium kinetic isotope effect of 3.74 ± 0.68); (iii) a spontaneous, water-catalyzed, reaction of the anion; and (iv) a specific-base catalyzed reaction of the anion. The magnitude of the solvent kinetic isotope effect, kH2O/kD2O = 4.48 ± 0.74 is consistent with a ring-opening transition state in which a water molecule is deprotonating the anomeric hydroxyl group in concert with strengthening solvation of the ring oxygen atom. The mechanistic implications for Neu5Ac mutarotases are discussed.

Concise synthesis of the C-1–C-12 fragment of amphidinolides T1–T5 by J. Stephen Clark; Flavien Labre; Lynne H. Thomas (4823-4830).
The C-1–C-12 segment of the amphidinolides T1–T5 has been synthesised in an efficient manner. The key transformations are highly diastereoselective rearrangement of an oxonium ylide, or metal-bound ylide equivalent, produced by intramolecular reaction of a copper carbenoid with an allylic ether, and macrocyclic fragment coupling by one-pot ring-closing metathesis and hydrogenation.

Synthesis and reactivity of furoquinolines bearing an external methylene-bond: access to reduced and spirocyclic structures by Xavier Bantreil; Carine Vaxelaire; Thomas Godet; Evelyne Parker; Carole Sauer; Philippe Belmont (4831-4841).
A family of furoquinolines were efficiently obtained through a tandem acetalization/cycloisomerization process catalyzed by (5 mol%) silver imidazolate polymer and triphenylphosphine, and diversity was brought by the use of 7 different alcohol groups. From these furoquinolines, 3 examples of reduced derivatives could be obtained (d.r. up to 94 : 6), 10 different spiroketal derivatives by hetero-Diels–Alder reaction (d.r. up to 20 : 1), 8 hetero-[5,5]-spirocycles by cycloaddition with dibromoformaldoxime (d.r. up to 86 : 14) and finally 6 hetero-[5,6]-spirocycles by [4 + 2] cycloaddition with ethyl 3-bromo-2-(hydroxyimino)propanoate (d.r. up to 90 : 10).

Synthesis of internal fluorinated alkenes via facile aryloxylation of substituted phenols with aryl trifluorovinyl ethers by Justin D. Moody; Don VanDerveer; Dennis W. Smith Jr.; Scott T. Iacono (4842-4849).
Nucleophilic addition–elimination of ortho- or para-substituted phenols to aryl trifluorovinyl ethers (TFVEs) in N,N-dimethylformamide was studied. Using sodium hydride as a base afforded vinyl substitution products R–Ar–O–CFCF–O–Ar–R′, where R or R′ = H, Br, OMe, tert-Bu, or Ph. The vinyl substitution products produced mixtures of (Z)/(E)-isomers and this isomer ratio was influenced by substitution with more sterically encumbered phenol nucleophiles. Reactions using caesium carbonate afforded addition products R–Ar–O–CHFCF2–O–Ar–R′ whereas upon dehydrofluorination using sodium hydride produced vinyl substitution products. The preparation of vinyl substituted and addition products proceeded in overall good isolated yields and were elucidated using 1H and 19F NMR, GC-MS, and X-ray analysis. Vinyl substituted products were inert to UV light and chemical reactivity using common polymerization promoters. Thermal activation of the (Z)/(E)-fluoroolefin (-CFCF-) was observed at an onset of 310 °C in nitrogen using differential scanning calorimetry (DSC) producing insoluble network material. The synthesis, characterization, and mechanism for stereoselectivity are discussed.

A straightforward synthesis of 2-aminobenzothiazoles from Herz compounds by Ana G. Neo; Rosa M. Carrillo; Carlos F. Marcos (4850-4855).
2-Aminobenzothiazoles are readily synthesised from anilines, sulfur monochloride and isocyanides. The key step consists of an iodine-catalysed insertion of isocyanides into the S–S bond of hydrolysed Herz salts, with concomitant extrusion of sulfur monoxide.

Towards new ligands of nuclear receptors. Discovery of malaitasterol A, an unique bis-secosterol from marine sponge Theonella swinhoei by Simona De Marino; Valentina Sepe; Maria Valeria D'Auria; Giuseppe Bifulco; Barbara Renga; Sylvain Petek; Stefano Fiorucci; Angela Zampella (4856-4862).
Malaitasterol A, an unprecedented bis-secosterol, was isolated from a Solomon collection of Theonella swinhoei. The structure was elucidated on the basis of a combination of comprehensive 1D and 2D NMR analysis, high-resolution mass spectrometry and DFT 13C chemical shift calculations. The biological characterization of malaitasterol A provided evidence that this compound is a potent agonist of pregnane-X-receptor and its putative binding mode to PXR has been obtained through docking calculations.

Forchlorfenuron-mimicking haptens: from immunogen design to antibody characterization by hierarchical clustering analysis by Celia Suárez-Pantaleón; Josep V. Mercader; Consuelo Agulló; Antonio Abad-Somovilla; Antonio Abad-Fuentes (4863-4872).
To obtain highly-specific and selective forchlorfenuron binders, a collection of functionalized derivatives with different spacer arm locations and lengths was prepared. By immunization with target-mimicking haptens, a large battery of monoclonal and polyclonal antibodies against this synthetic cell regulator was produced and exhaustively characterized in two immunoassay formats using homologous and heterologous conjugates. Antibodies with IC50 values lower than 0.3 nM were successfully raised from the prepared immunogens, thus evidencing the efficacy of the explored strategies. In order to identify significant epitopes in the antibody–antigen interaction, a series of new chemical forchlorfenuron analogues, with slight modifications at both rings of the target molecule, were synthesized and evaluated in competitive assays. As a novel approach in hapten recognition studies, data processing was performed by computational classification methods based on hierarchical clustering. This strategy was shown to be highly valuable for a straightforward profiling of antibodies according to analogue recognition patterns. A relationship could be established between the antigen binding properties of antibodies and the structure of the immunogen. Whereas antibodies with equivalent affinities had been obtained from all of the derivatives, their specificity was found to be largely influenced by the differential exposition of the molecule to the immune system.

Elaboration of vinblastine hybrids using a reactive in situ generated N-carboxyanhydride by Claire Rannoux; Fanny Roussi; Marie-Thérèse Martin; Françoise Guéritte (4873-4881).
Hybrids of vinblastine and phomopsin, designed by a molecular modelling study, were elaborated in order to target tubulin. The key step of the synthesis (fragmentation and insertion of vindoline) was mediated by an internal N-carboxyanhydride (or O-acylcarbamate). This reaction was diastereospecific and addition of silver salts could reverse the diastereoselectivity. Even if the synthesized compounds are inactive, this synthesis represents an original example of a C–N fragmentation mediated by a N-carboxyanhydride.

CH activation and CH2 double activation of indolines by radical translocation: Understanding the chemistry of the indolinyl radical by David C. Harrowven; Kerri J. Stenning; Sally Whiting; Toby Thompson; Robert Walton (4882-4885).
CH activation and CH2 double activation of indolines at C2 may be achieved efficiently through radical translocation. The fate of the C2 indolinyl radical is dictated by the substitution at C3. Fragmentation, cyclisation and tandem cyclisation reactions leading to indole, azaheterocycle and azapropellane formation, respectively, are reported.

New methodology for the N-alkylation of 2-amino-3-acylthiophenes by Luigi Aurelio; Bernard L. Flynn; Peter J. Scammells (4886-4902).
2-Amino-3-acylthiophenes are known to allosterically modulate the A1 adenosine receptor and are also used as intermediates in the synthesis of therapeutic agents and pharmacophores such as thienoazepines and thienopyrimidines. The N-alkylation of 2-aminothiophenes has been notoriously difficult to accomplish under mild conditions and there are very few examples of N-alkylated 2-aminothiophenes in the literature, all of which use forcing conditions to effect the alkylation. Here we describe the synthesis of such compounds under mild conditions utilising 2-carbamoylamino and 2-acylamino-3-acylthiophenes with caesium carbonate, and tetrabutylammonium iodide in DMF.

Cu(i)-catalysed [2 + 2] photocycloaddition of 1,6-dienes embedded in a furano sugar is described in connection to a synthetic approach to an abnormal marine prostanoid tricycloclavulone. An unprecedented influence of remote substituents on the reactivity and stereoselectivity of the photocycloaddition reaction has been uncovered during this investigation. While an alkene substituent inhibits cycloaddition through steric effects, a substituent having a hydroxyl or alkoxy group at the same location facilitates cycloaddition exclusively from its own side. This investigation has led to the synthesis of a functionalised 5,4-fused core unit of tricycloclavulone.

Suzuki–Miyaura cross coupling reactions with Phenoldiazonium salts by Bernd Schmidt; Frank Hölter (4914-4920).
The Suzuki–Miyaura coupling of phenol diazonium salts and aryl trifluoroborates yields 4-hydroxybiaryls in a protecting group-free synthesis.

Design and synthesis of bile acid–peptide conjugates linked via triazole moiety by Nadezhda V. Sokolova; Gennadij V. Latyshev; Nikolay V. Lukashev; Valentine G. Nenajdenko (4921-4926).
A conjugation of bile acids with peptides via Cu(i)-catalyzed click chemistry has been described. Novel bile acid–peptide conjugates linked via a 1,2,3-triazole moiety based on cholic, deoxycholic and lithocholic acid derivatives were synthesized using Cu(i)-catalyzed 1,3-dipolar cycloaddition (“click” reaction). It was shown that up to three peptide fragments can be attached to a central steroid core, thus forming complex three-dimensional polyconjugate structures, which can find important applications in biochemistry, medicinal chemistry, and coordination chemistry.

Intramolecular N-arylation of pyrrole and indole carboxamides and carboxylates linked with a pendant haloarene by Cu-catalyzed reactions to synthesize pyrrole and indole quinoxalinone and oxazinone derivatives is reported. The ring closure reactions were carried out by conventional heating and MW irradiation. The use of conventional heating affords moderate to good yields of the quinoxalinone and oxazinone derivatives (34–72%), while by using MW heating the best results are obtained (41–99%).

Oxidation of 4-substituted TEMPO derivatives reveals modifications at the 1- and 4-positions by David L. Marshall; Meganne L. Christian; Ganna Gryn'ova; Michelle L. Coote; Philip J. Barker; Stephen J. Blanksby (4936-4947).
Potenital pathways for the deactivation of hindered amine light stabilisers (HALS) have been investigated by observing reactions of model compounds—based on 4-substituted derivatives of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO)—with hydroxyl radicals. In these reactions, dilute aqueous suspensions of photocatalytic nanoparticulate titanium dioxide were irradiated with UV light in the presence of water-soluble TEMPO derivatives. Electron spin resonance (ESR) and electrospray ionisation mass-spectrometry (ESI-MS) data were acquired to provide complementary structural elucidation of the odd- and even-electron products of these reactions and both techniques show evidence for the formation of 4-oxo-TEMPO (TEMPONE). TEMPONE formation from the 4-substituted TEMPO compounds is proposed to be initiated by hydrogen abstraction at the 4-position by hydroxyl radical. High-level ab initio calculations reveal a thermodynamic preference for abstraction of this hydrogen but computed activation barriers indicate that, although viable, it is less favoured than hydrogen abstraction from elsewhere on the TEMPO scaffold. If a radical is formed at the 4-position however, calculations elucidate two reaction pathways leading to TEMPONE following combination with either a second hydroxyl radical or dioxygen. An alternate mechanism for conversion of TEMPOL to TEMPONE via an alkoxyl radical intermediate is also considered and found to be competitive with the other pathways. ESI-MS analysis also shows an increased abundance of analogous 4-substituted piperidines during the course of irradiation, suggesting competitive modification at the 1-position to produce a secondary amine. This modification is confirmed by characteristic fragmentation patterns of the ionised piperidines obtained by tandem mass spectrometry. The conclusions describe how reaction at the 4-position could be responsible for the gradual depletion of HALS in pigmented surface coatings and secondly, that modification at nitrogen to form the corresponding secondary amine species may play a greater role in the stabilisation mechanisms of HALS than previously considered.

Three-state molecular shuttles operated using acid/base stimuli with distinct outputs by Yuji Tokunaga; Masanori Kawabata; Naoki Matsubara (4948-4953).
This paper describes the acid/base-mediated three-state translational isomerization of two [2]rotaxanes, each containing N-alkylaniline and N,N-dialkylamine centers as binding sites for threaded dibenzo[24]crown-8 units. Under neutral conditions, the dialkylamine unit predominantly recognized the crown ether component through cooperative binding of a proton; when both amino units were protonated under acidic conditions, both translational isomers were generated; the addition of a strong base caused aniline–crown ether interactions to dominate. The three states of the [2]rotaxane featuring the 3,5-diphenylaniline terminus in its dumbbell-shaped component were accompanied by distinct absorptive outputs that were detectable using UV spectroscopy.

A ratiometric fluorescent probe for cyanide based on FRET by Xin Lv; Jing Liu; Yunlong Liu; Yun Zhao; Maliang Chen; Pi Wang; Wei Guo (4954-4958).
On the basis of FRET from 4-(N,N-dimethylamino)benzamide to fluorescein, a new ratiometric fluorescence probe bearing a hydrazone binding unit was developed for highly selective and sensitive detection of CN in aqueous solution.

The synthetic and biological studies of discorhabdins and related compounds by Yasufumi Wada; Yu Harayama; Daigo Kamimura; Masako Yoshida; Tomoyuki Shibata; Kousaku Fujiwara; Koji Morimoto; Hiromichi Fujioka; Yasuyuki Kita (4959-4976).
Various analogues of the marine alkaloids, discorhabdins, have been synthesized. The strategy contains spirocyclization with phenyliodine(iii) bis(trifluoroacetate) (PIFA), oxidative fragmentation of the β-amino alcohols with the hypervalent iodine reagent C6F5I(OCOCF3)2, the detosylation and dehydrogenation reaction of the pyrroloiminoquinone unit in the presence of a catalytic amount of NaN3 and the bridged ether synthesis with HBr–AcOH as the key reactions. All the synthesized compounds were evaluated by in vitro MTT assay for cytotoxic activity against the human colon cancer cell line HCT-116. Furthermore, the discorhabdin A oxa analogues were also evaluated against four kinds of tumor model cells, a human colon cancer cell line (WiDr), a human prostate cancer cell line (DU-145) and murine leukemia cell lines (P388 and L1210). For the identification of the target, discorhabdin A and the discorhabdin A oxa analogue were evaluated by an HCC panel assay. In the test, discorhabdins could have a novel mode of action with the tumor cells.

N–N bond cleavage in hydrazines is widely used in the preparation of amines and thus occupies a significant place in organic synthesis. In this paper, we report a new method for the reductive cleavage of N–N bonds in hydrazines by commercially available and cheap aqueous titanium(iii) trichloride. The reaction proceeds smoothly under a broad pH range from acidic to neutral and basic conditions to afford amines in good yields. This method is compatible with substrates containing functionalities such as C–C double bonds, benzyl–nitrogen bonds, benzyloxy and acyl groups.

A wide range of free N-H 2-arylindoles were synthesised via the copper(ii)-catalyzed amination of 2-bromo-arylacetylenes with aqueous ammonia and sequential intramolecular cyclization. The convenience and atom economy of aqueous ammonia, and the low cost of the copper catalytic system make this protocol readily superior in practical application.

Back cover (4987-4988).