Correction: Efficient in situ N-heterocyclic carbene palladium(ii) generated from Pd(OAc)2 catalysts for carbonylative Suzuki coupling reactions of arylboronic acids with 2-bromopyridine under inert conditions leading to unsymmetrical arylpyridine ketones: synthesis,characterization and cytotoxic activities

Correction for ‘Efficient in situ N-heterocyclic carbene palladium(ii) generated from Pd(OAc)₂ catalysts for carbonylative Suzuki coupling reactions of arylboronic acids with 2-bromopyridine under inert conditions leading to unsymmetrical arylpyridine ketones: synthesis, characterization and cytotoxic activities’ by Nedra Touj et al., RSC Adv., 2018, 8, 40000–40015.

Errors were present in the published article in terms of the co-author name spelling for J. Al-Tamimi and the author affiliations. The corrected list of author and affiliation details in this paper is as shown here.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Synthesis and characterisation of κ2-N,O-oxazoline-enolate complexes of nickel(ii): explorations in coordination chemistry and metal-mediated polymerisation

The synthesis and characterisation (UV-Vis, IR, X-ray diffraction, etc.) of a series of Ni(ii) complexes derived from both known and novel 2-acylmethyl-2-oxazolines (2a–g: i.e., (Z)-1-R-2-(4,4′-dimethyl-2′-oxazolin-2′-yl)eth-1-en-1-ol; R = –Ph, –2-furanyl, –p-NO₂-Ph, –t-Bu, –2-thiofuranyl, p-NC-Ph, –CF₃) is reported. These Ni materials (3a–g) represent the first group 10 metal complexes of this ligand class. All derivatives reported are paramagnetic (S = 1) compounds of formulae Ni(κ²-N,O-L)₂ where L represents an enolate of structure (Z)-1-R-2-(4′,4′-dimethyl-2′-oxazolin-2′-yl)eth-1-en-1-ate formed via proton loss from 2. The air- and moisture-stable metal complexes feature a less typical distorted seesaw-shaped disposition of binding atoms around the metal centre for six structurally characterised (X-ray) examples. Preliminary investigations indicate that 3a (R = –Ph) is a useful catalysts for olefin polymerisation in the presence of alkylaluminum reagents.

Novel Ni(ii) enolate complexes derived from (Z)-1-R-2-(4′,4′-dimethyl-2′-oxazolin-2′-yl)eth-1-en-1-ols are synthesised and structurally examined. The complexes display good potency as olefin polymerisation catalysts.     

Oxidative cross-dehydrogenative coupling (CDC) via C(sp2)–H bond functionalization: tert-butyl peroxybenzoate (TBPB)-promoted regioselective direct C-3 acylation/benzoylation of 2H-indazoles with aldehydes/benzyl alcohols/styrenes

An efficient, cost-effective, transition-metal-free, oxidative C_(sp²)–H/C_(sp²)–H cross-dehydrogenative coupling via a C_(sp²)–H bond functionalization protocol for the regioselective direct C-3 acylation/benzoylation of substituted 2H-Indazoles 1a–m with substituted aldehydes 2a–q/benzyl alcohols 5a–e/styrenes 6a–e is reported. The operationally simple protocol proceeds in the presence of tert-butyl peroxybenzoate (TBPB) as an oxidant in chlorobenzene (PhCl) as a solvent at 110 °C for 24 h under an inert atmosphere, which furnished a diverse variety of substituted 3-(acyl/benzoyl)-2H-indazoles 3a–q/4a–l in up to 87% yields. The reaction involves a free-radical mechanism and proceeds via the addition of an in situ generated acyl radical (from aldehydes/benzyl alcohols/styrenes) on 2H-indazoles. The functional group tolerance, broad substrate scope, control/competitive experiments and gram-scale synthesis and its application to the synthesis of anti-inflammatory agent 11 and novel indazole-fused diazepine 13 further signify the versatile nature of the developed methodology.

An efficient transition-metal-free oxidative C_(sp²)–H/C_(sp²)–H cross-dehydrogenative coupling via C_(sp²)–H bond functionalization for regioselective C-3 acylation/benzoylation of 2H-indazoles with aldehydes/benzyl alcohols/styrenes is reported.     

C(acyl)–C(sp2) and C(sp2)–C(sp2) Suzuki–Miyaura cross-coupling reactions using nitrile-functionalized NHC palladium complexes

Application of N-heterocyclic carbene (NHC) palladium complexes has been successful for the modulation of C–C coupling reactions. For this purpose, a series of azolium salts (1a–f) including benzothiazolium, benzimidazolium, and imidazolium, bearing a CN-substituted benzyl moiety, and their (NHC)₂PdBr₂ (2a–c) and PEPPSI-type palladium (3b–f) complexes have been systematically prepared to catalyse acylative Suzuki–Miyaura coupling reaction of acyl chlorides with arylboronic acids to form benzophenone derivatives in the presence of potassium carbonate as a base and to catalyse the traditional Suzuki–Miyaura coupling reaction of bromobenzene with arylboronic acids to form biaryls. All the synthesized compounds were fully characterized by Fourier Transform Infrared (FTIR), and ¹H and ¹³C NMR spectroscopies. X-ray diffraction studies on single crystals of 3c, 3e and 3f prove the square planar geometry. Scanning Electron Microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), metal mapping analyses and thermal gravimetric analysis (TGA) were performed to get further insights into the mechanism of the Suzuki–Miyaura cross coupling reactions. Mechanistic studies have revealed that the stability and coordination of the complexes by the CN group are achieved by the removal of pyridine from the complex in catalytic cycles. The presence of the CN group in the (NHC)Pd complexes significantly increased the catalytic activities for both reactions.

Nitrile-functionalized Pd(ii) complexes have evaluated for the Suzuki–Miyaura cross-coupling reactions. The highest TON value was reached for the acylative Suzuki–Miyaura cross-coupling reaction of acyl chlorides with phenylboronic acids.     

Syntheses of tetrahydroquinoline-based chiral carbene precursors and the related chiral NHC–Au(i) complex

Four tetrahydroquinoline-based chiral carbene precursors were synthesized using unsymmetrical N,N′-diarylformamidines and chiral 2-allyloxiranes as starting materials. A representative NHC–gold complex has been prepared and fully characterized, the crystal structure of which reveals an intramolecular Au⋯H–C(sp³) interaction between Au(i) and the hydrogen atom of the isopropyl moiety in the N-aryl group.

The facile synthesis of tetrahydroquinoline-based chiral carbene precursors is reported. A rare Au⋯H–C(sp³) interaction between Au(i) and the hydrogen atom was observed in the crystal structure of a related NHC–gold complex.

Imidazolidin-2-ylidene carbenes are among the most important N-heterocyclic carbenes (NHCs) due to their widespread and spectacular applications as organocatalysts and as ligands for organometallic catalysis.¹ Over the past twenty years, a great deal of effort has been made to employ chiral NHCs as organocatalysts and as ligands in asymmetric catalysis.² Despite the successful applications of a variety of chiral NHCs in asymmetric catalysis, the development of facile methodologies for structurally-specific chiral NHCs with structural diversity is highly desirable and a challenging issue in asymmetric catalysis. Several types of chiral backbone-unsaturated NHCs having a fused ring in their scaffolds, such as A,³B,⁴C,⁵ and D,⁶ have been successfully developed for organocatalysts and/or as ligands for organometallic catalysis (Scheme 1a). In their scaffolds, chiral moiety is directly linked to the N-atom and embedded in a fused ring. Due to the rigidity of the fused ring, the rotation of chiral moiety about the N–C bond is restricted, thereby enhancing the asymmetric induction of the NHCs in controlling the stereochemistry of the asymmetric catalytic reaction.Open in a separate windowScheme 1Chiral NHCs having a fused ring in their scaffolds and related NHC–Au(i) complexes with intramolecular Au⋯H–C(sp³) interaction.With different design strategy, Blechert et al. have developed chiral imidazolidin-2-ylidene E having a fused ring in the scaffold, which exhibited high efficiency in Ru-catalyzed asymmetric ring-opening cross-metathesis.⁷ The fused ring in E twists the framework, hampers rotation of the N-aryl substituent, and thus reaches the optimal transfer of chirality, while at the same time second N-mesityl substituent adopts a planar orientation. However, the approach for the synthesis of the carbene precursors, imidazolinium salts requires uncommon starting material and a kinetic enzymatic resolution, which limit modification of NHC ligands. Additionally, only the imidazolinium salt of type E having no C13 substituent was prepared by the method.⁸ Varying the N-aryl substituents with different steric bulkiness in E might create a tunable chiral environment closer to the reactive site. Until very recently, a consecutive intermolecular reductive amination/asymmetric hydrogenation has been developed for the synthesis of the precursors of E.⁸As part of our studies on the design and synthesis of various novel NHC ligands for carbene chemistry and catalysis,⁹ we herein wish to report a new synthetic strategy for the facile preparation of various tetrahydroquinoline-based chiral carbene precursors of NHCs F using unsymmetrical N,N′-diarylformamidines and chiral 2-allyloxiranes as starting materials. A representative NHC–gold complex I has been prepared and structurally characterized. The crystal structure of the NHC–gold reveals an intramolecular Au(i)⋯H–C(sp³) interaction between Au(i) and the hydrogen atom of isopropyl moiety (Scheme 1b). Recently, the Au(i)⋯H–C(sp³) hydrogen-bonding interaction have been observed in NHC–Au(i) complexes G and H, which are believed to either stabilise the out-of-plane conformation (G)^10a or make partial contributions to the luminescence properties of the NHC–Au(i) complex (H)^10b (Scheme 1b). Additionally, Au⋯H–C hydrogen-bonding interactions in NHC–Au complexes have been proposed as key intermediates in the mechanistic studies of NHC–Au catalyzed C–H activation.¹¹We have previously developed a versatile and modular method for the preparation of various backbone-substituted imidazolinium salts from the reaction of formamidines with alkene oxides.^9a The methodology exhibits high regiochemistry. When reacting styrene oxide with the unsymmetrical N,N′-diarylformamidines bearing a mono-o-substituted aryl group and a di-o-substituted aryl group, only one regioisomer in which the backbone-substituted phenyl group is on the carbon atom close to the mono-substituted aryl ring was formed. More importantly, chiral monosubstituted imidazolinium salts, (S)-J could be obtained when using (R)-styrene oxide, indicating that inversion of the configuration of (R)-styrene oxide occurred in the two-step synthesis (Scheme 2).^9a Therefore, we decide to use (S)-2-allyloxirane and the unsymmetrical N,N′-diarylformamidines to synthesize chiral backbone-allyl-substituted imidazolinium salts, which is supposed to undergo intramolecular Friedel–Crafts alkylation¹² to afford chiral imidazolinium salts as the precursors of the chiral NHCs of type F.Open in a separate windowScheme 2Synthesis of chiral backbone-monosubstituted imidazolinium salts from the reaction of formamidines with alkene oxide.^9aAs expected, the ring opening reaction of unsymmetrical N,N′-diarylformamidines 1a–1d with (S)-2-allyloxiranes followed by cyclization afforded four backbone-allyl-substituted imidazolinium salts 2a–2d, respectively (Scheme 3). Therefore, an alternative route was investigated. In the presence of KOtBu as base, the ring opening of 2a–2d followed by reduction using LiAlH₄ afforded diamines 3a–3d (Route b, Scheme 3).¹³ Delightfully, in the presence of either AlCl₃ (for 3a–3c) or H₂SO₄ (3d), the resulting amines could smoothly undergo intramolecular Friedel–Crafts alkylation to give diamines 4a–4d. Finally, cyclization of the diamines 4a–4d with HC(OEt)₃ in the presence of NH₄BF₄ generated the desired chiral imidazolidinium salts 5a–5d. During the transformations, a partial racemization was detected. The ee value of 4a was determined as 88% on the basis of chiral HPLC analysis (p. S8, see ESI^†).Synthesis of chiral backbone-allyl-substituted imidazolinium salts from the reaction of formamidines with chiral 2-allyloxiranes^a

Synthesis,photophysical and nonlinear optical properties of push–pull tetrazoles

A 2,5-disubstituted tetrazole with p-nitrophenyl and 3-pyridyl units as acceptors (1a), and three push–pull tetrazoles with p-nitrophenyl as an acceptor and phenyl (1b), 2-(dibenzo[b,d]furan-4-yl) (1c), and 4-(N,N-diphenylamino)phenyl (1d) as donor groups, were synthesized by copper-catalyzed aerobic C–N coupling of p-nitrophenyl tetrazole with appropriately substituted aryl boronic acids. The absorption and emission spectra of 1a–c showed minimal dependence on the polarity of the solvent; however, in the case of 1d a blue shift was noted in the longest absorption band (λ₁) as the polarity increased. The fluorescence intensity of the title compounds was found to be solvent-dependent; however, no apparent correlation to solvent polarity could be established. The absorption and emission characteristics of 1a–d were also influenced by the nature of the substituent as 1d, bearing a strong electron donating 4-(N,N-diphenylamino)phenyl group, displayed a significant red shifted absorption (λ₁) as well as emission (λ_em) bands compared to other compounds. Time dependent density functional calculations (CAM-B3LYP/6-311++G**) revealed that the longest wavelength band (λ₁) is associated with an intramolecular charge transfer (ICT) from HOMO/HOMO-1/HOMO-2 → LUMO/LUMO+1 in these molecules. The first hyperpolarizability values, β_HRS, of 1a–d were measured using the solution-based hyper-Rayleigh scattering technique using a femtosecond Ti:Sapphire laser and the highest NLO activity was measured for 1d with the greatest push–pull characteristics. A strong correlation was observed between the calculated hyperpolarizability (β_tot) and experimentally measured values (β_HRS).

A 2,5-disubstituted tetrazole with a p-nitrophenyl unit as an acceptor and a 4-(N,N-diphenylamino) phenyl group as a donor exhibits strong push–pull characteristics and displays high NLO activity.     

Highly selective cross-coupling reactions of 1,1-dibromoethylenes with alkynylaluminums for the synthesis of aryl substituted conjugated enediynes and unsymmetrical 1,3-diynes

A highly efficient method for the synthesis of aryl substituted conjugated enediynes and unsymmetrical 1,3-diynes via selective cross-coupling reactions of 1,1-dibromoethylenes with alkynylaluminums using the Pd(OAc)₂–DPPE and Pd₂(dba)₃–TFP complexes as catalysts, respectively, has been successfully developed. Though the alkyl substituted conjugated enediynes and unsymmetrical 1,3-diynes were not obtained, this case is also remarkable as the same starting materials could selectively produce either aryl substituted conjugated enediynes or unsymmetrical 1,3-diynes in moderate to excellent yields (up to 99%) in the different Pd–phosphine catalytic systems.

A highly efficient method for the synthesis of aryl substituted conjugated enediynes and unsymmetrical 1,3-diynes via selective cross-coupling reactions of 1,1-dibromoethylenes with alkynylaluminums has been successfully developed.     

Exploring unsymmetrical diboranes(4) as boryl ligand precursors: platinum(ii) bis-boryl complexes

A series of five unsymmetrical platinum(ii) bis-boryl complexes, bearing two distinct boryl ligands, are obtained by the oxidative addition reaction of unsymmetrical diborane(4) derivatives, bearing either two different dialkoxy or one dialkoxy and one diamino boryl moiety, with [(Ph₃P)₂Pt(C₂H₄)]. All five complexes were structurally and spectroscopically characterised. The bis-boryl platinum(ii) complexes exhibit slightly distorted square-planar cis-boryl structures with acute B–Pt–B angles, short B⋯B distances of 2.44–2.55 Å and relatively long trans-boryl P–Pt distances around 2.34 Å. The ³¹P–¹⁹⁵Pt NMR coupling constants are indicative for the strongly donating/trans-influencing boryl ligands. Despite the structural and spectroscopic data at hand no finally conclusive order of the donor properties/trans-influence of the boryl ligands can be deduced on the basis of these data. This may be explained by an (residual) interaction of two boryl ligands.

Five unsymmetrical platinum(ii) bis-boryl complexes are reported, the spectroscopic and structural data allow the first comparative study on these complexes.     

8,8′-(Benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(quinolin-4(1H)-one): a twisted photosensitizer with AIE properties

A new benzothiadiazole (BTZ) luminogen is prepared via the Suzuki–Miyaura Pd-catalysed C–C cross-coupling of 8-iodoquinolin-4(1H)-one and a BTZ bispinacol boronic ester. The rapid reaction (5 min) affords the air-, thermo-, and photostable product in 97% yield as a yellow precipitate that can be isolated by filtration. The luminogen exhibits aggregated-induced emission (AIE) properties, which are attributed to its photoactive BTZ core and nonplanar geometry. It also behaves as a molecular heterogeneous photosensitizer for the production of singlet oxygen under continuous flow conditions.

A new benzothiadiazole (BTZ) luminogen is prepared via the Suzuki–Miyaura Pd-catalysed C–C cross-coupling of 8-iodoquinolin-4(1H)-one and a BTZ bispinacol boronic ester.     

Liquid crystal behavior,photoluminescence and gas sensing: A new series of ionic liquid crystal imidazole and benzoimidazole bearing chalcone groups,synthesis and characterization

Four new series of chalcones containing imidazole bromonium and benzimidazole bromonium salts with spacer alkyl chains (C_n, n = 2 and 4) were synthesized and the chemical structure, thermal behavior, photoluminescence and gas sensing were characterized by several technical methods. The studies have indicated similar mesomorphic properties of the synthesized compounds, dependent on the terminal alkyl-chain and lengths of the alkoxy-spacer. Almost compounds with shorter alky chains, 4a–4e, 5a–5c, 6a–6c and 7a–7d, did not show liquid crystal properties, while the results of other compounds confirm the existence of smectic A in cooling and heating cycles. Photoluminescence of compounds 5a–5i and 7a–7i was also studied. The emission in the blue region reveals that the material has blue light emission properties. Sensing behavior of compounds 4i and 5i was investigated for NH₃ and NO₂ gases. The sensors exhibited high sensitivity toward NH₃, while sensitivity toward the oxidizing gas NO₂ is lower.

Four new series of chalcones containing imidazole bromonium and benzimidazole bromonium salts with spacer alkyl chains (C_n, n = 2 and 4) were synthesized and their chemical structure, thermal behavior, photoluminescence and gas sensing ability were characterized.     

Pyridylbenzimidazole based Re(i)(CO)3 complexes: antimicrobial activity,spectroscopic and density functional theory calculations

fac-[ReBr(CO)₃(L^1,2)] L¹ = 1-ethyl-2-(pyridin-2-yl)benzimidazole (1) and L² = 1-[(pyridin-2-yl) benzimidazole]-propyl-sulfonic acid (2), fac-[Re₂Br₂(CO)₆L³] (3) L³ = 1,1′-(hexane-1,6-diyl)bis[2-(pyridin-2-yl)1H-benzimidazole] and fac-[ReBr(CO)₃(L^4,5-κ²N¹N²)] (L⁴ = 2,6-bis(benzimidazol-2′-yl)pyridine (4) and L⁵ = 2,6-bis(1-ethyl-benzimidazol-2′-yl)pyridine (5) were synthesized and fully characterized using different spectrocopic and analytical tools. The spectrocopic data showed coordination of L^1–3 to fac-ReBr(CO)₃via the benzimidazole and pyridine N-atoms. For 4 and 5, the absence of a two-fold axis of symmetry for L^4,5 in the ¹H NMR spectra reflect the κ²N¹,N² mode of coordination. The electronic properties of 1–5 were investigated by time-dependent density functional theory calculations in the singlet and triplet states. The ligands and their Re(i) complexes were assessed for their potential antimicrobial activity. Compound 5 was screened against non-malignant cell line (noncancerous human embryonic kidney cell line (HEK293)) as well as evaluated for its blood compatibility.

Mono- and binuclear pyridylbenzimidazole based Re(i) tricarbonyl complexes exhibited antibacterial activity against Gram(+) bacterium. TDDFT calculation, in singlet and triplet states, assigned the lowest energy transition to MLCT and MLCT/³IL, respectively.     

N-Phenyl-substituted poly(benzimidazole imide)s with high glass transition temperature and low coefficient of thermal expansion

To obtain high thermostable materials for flexible display substrates, a series of copoly(benzimidazole imide)s was prepared using 5-amine-2-(4-aminobenzene)-1-phenyl-benzimidazole (N-PhPABZ) and 6(5)-amino-2-(4-aminobenzene)-benzimidazole (PABZ). Incorporating N-phenyl groups effectively healed the brittleness of the poly(benzimidazole imide)s (PBIIs) derived from pyromellitic dianhydride (PMDA), and the resultant homo- and copoly(benzimidazole imide)s displayed an outstandingly high glass transition temperature (T_g > 450 °C) and a low coefficient of thermal expansion (CTE < 10 ppm K⁻¹). Furthermore, the influence of removing intermolecular hydrogen bonds on the properties of these poly(benzimidazole imide)s was systematically analyzed. These data provide a feasible method to prepare superheat-resistant poly(benzimidazole imide)s without H-bonding.

N-PhPABZ successfully cured the brittleness of PMDA-based poly(benzimidazole imide)s. N-PhPABZ-PMDA film illustrated an extremely high T_g of 486 °C and a low CTE of 9.7 ppm K⁻¹.     

Nopinone-based aggregation-induced emission (AIE)-active difluoroboron β-diketonate complex: photophysical,electrochemical and electroluminescence properties

Four difluoroboron (BF₂) β-diketonate nopinone complexes 3a–3d that exhibited typical aggregation-induced emission (AIE) properties were synthesized using the natural renewable β-pinene derivative nopinone as the starting material. The thermal, photophysical, electrochemical and electroluminescent properties as well as the AIE properties of complexes 3a–3d were analyzed systematically. The data of photophysical and electrochemical demonstrated that compound 3b with a methoxy group exhibited the largest bathochromic shift, the highest absolute photoluminescence quantum yields and narrowest optical bandgap among 3a–3d. Using 3b as the emitter, electroluminescent (EL) device I exhibits blue-green light with CIE coordinates of (0.2774, 0.4531) and showed a better performance with a luminous efficacy (η_p) of 7.09 lm W⁻¹ and correlated color temperature (T_C) of 7028 K. The results demonstrate that new AIE compounds are promising solid-state luminescent materials with practical utility in electroluminescent materials.

Four difluoroboron (BF₂) β-diketonate nopinone complexes 3a–3d which exhibited typical AIE property were synthesized. Owing to high absolute fluorescence quantum yields of 3b, EL device based on 3b was fabricated, which exhibits a blue-green light.     

The discovery of new phloroglucinol glycosides from Agrimonia pilosa and the mechanism of oxidative dearomatization of the methyl-substituted phloroglucinol derivatives

Six methyl-substituted phloroglucinol glycosides (1–6) were isolated from Agrimonia pilosa, including four new compounds (1–3, 6). The aglycones (1a–4a) of 1–4 and their corresponding oxidized products (1c–4c) were also obtained from A. pilosa. The structures were determined by a series of spectroscopic analyses and chiral separation. Notably, the structures of aglycones 1a–4a were unstable and prone to oxidation spontaneously, to yield the dearomatized structures 1c–4c. The mechanism of oxidative dearomatization was disclosed as a free-radical chain reaction with ³O₂ by the techniques of HPLC-HR-MS², EPR spectra and DFT-calculation, and hydroperoxide was defined as the intermediate.

New phloroglucinol glycosides, aglycones, and oxidative dearomatized products of aglycones were discovered from Agrimonia pilosa, and the mechanism of the auto oxidative dearomatization was disclosed as a free radical chain reaction with ³O₂.     

Selective cytotoxic effect against the MDA-MB-468 breast cancer cell line of the antibacterial palindromic peptide derived from bovine lactoferricin

The cytotoxic effect against the breast cancer cell line MDA-MB-468 of the palindromic peptide LfcinB (21–25)_Pal: ¹RWQWRWQWR⁹ and its analogous peptides, obtained via alanine scanning, was evaluated. The results indicate that the palindromic peptide exhibited a concentration-dependent cytotoxic effect against this cell line. The cytotoxic effect of the palindromic peptide was fast and selective and was sustained for up to 48 h of treatment. MDA-MB-468 cells treated with the palindromic peptide exhibited severe cellular damage, acquiring rounded forms and shrinkage, a behavior typical of apoptotic events. The analogous peptides exhibited fewer cytotoxic effects than the original palindromic peptide, suggesting that the substitution of any amino acid with alanine diminishes the cytotoxic effect. The Arg and Trp residues proved to be the most relevant for the cytotoxic effect; the analogous peptides with substitutions of Trp with Ala did not induce a change in cellular morphology, while analogous peptides with substitutions of Arg or Gln with Ala induced cellular damage. Also, neither the palindromic peptide nor its analogues exerted a significant cytotoxic effect on normal fibroblasts, indicating that the peptides had a selective cytotoxic effect on cancerous cells. The peptide LfcinB (21–25)_Pal, and its analogues exhibited antibacterial activity against E. coli and S. aureus strains and a selective cytotoxic effect against the breast cancer cell line MDA-MB-468.

The cytotoxic effect against the breast cancer cell line MDA-MB-468 of the palindromic peptide LfcinB (21–25)_Pal: ¹RWQWRWQWR⁹ and its analogous peptides, obtained via alanine scanning, was evaluated.     

The synthesis of N,N′-disulfanediyl-bis(N′-((E)-benzylidene)acetohydrazide) from (E)-N′-benzylideneacetohydrazide and S8

Herein we report an oxidative coupling reaction for N–S/S–S bond formation from (E)-N′-benzylideneacetohydrazide and S₈ to furnish substituted N,N′-disulfanediyl-bis(N′-((E)-benzylidene) acetohydrazide). It provides a direct approach for the synthesis of disulfides with good yields.

Herein we report an oxidative coupling reaction for N–S/S–S bond formation substituted N,N′-disulfanediyl bis(N′-((E)-benzylidene)acetohydrazide). It provides a direct approach for the synthesis of disulfides with good yields.     

Highly efficient Ru(ii)–alkylidene based Hoveyda–Grubbs catalysts for ring-closing metathesis reactions

Three novel phosphine-free Ru-alkylidenes (7a–7c) have been synthesized and utilized as efficient catalysts for ring closing metathesis (RCM) reaction. Spectroscopic data, i.e. NMR and HRMS, along with single crystal X-ray diffraction analysis, were used to confirm their chemical structures. The tosylated carbenoid 7b showed the highest efficiency in cyclizing different acyclic diene substrates. RCM of various (un)substituted N,N-diallylaniline derivatives and stereoselective RCM of different macromolecular dienes were well tolerated using only a catalytic amount (0.5–2.0 mol%) of the additive catalyst (7b) as compared to the well-known Grubbs (II) and Hoveyda–Grubbs (II) catalysts.

Three novel phosphine-free Ru-alkylidenes (7a–7c) have been synthesized and utilized as efficient catalysts for ring closing metathesis (RCM) reaction.     

Ru(ii)–N-heterocyclic carbene complexes: synthesis,characterization, transfer hydrogenation reactions and biological determination

A series of ruthenium(ii) complexes with N-heterocyclic carbene ligands were successfully synthesized by transmetalation reactions between silver(i) N-heterocyclic carbene complexes and [RuCl₂(p-cymene)]₂ in dichloromethane under Ar conditions. All new compounds were characterized by spectroscopic and analytical methods. These ruthenium(ii)–NHC complexes were found to be efficient precatalysts for the transfer hydrogenation of ketones by using 2-propanol as the hydrogen source in the presence of KOH as a co-catalyst. The antibacterial activity of ruthenium N-heterocyclic carbene complexes 3a–f was measured by disc diffusion method against Gram positive and Gram-negative bacteria. Compounds 3d exhibited potential antibacterial activity against five bacterial species among the six used as indicator cells. The product 3e inhibits the growth of all the six tested microorganisms. Moreover, the antioxidant activity determination of these complexes 3a–f, using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azinobis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS) as reagent, showed that compounds 3b and 3d possess DPPH and ABTS antiradical activities. From a concentration of 1 mg ml⁻¹, these two complexes presented a similar scavenging activity to that of the two used controls gallic acid (GA) and butylated hydroxytoluene (BHT). From a concentration of 10 mg ml⁻¹, the percentage inhibition of complexes 3b and 3d was respectively 70% and 90%. In addition, these two Ru–NHC complexes exhibited antifungal activity against Candida albicans. Investigation of the anti-acetylcholinesterase activity of the studied complexes showed that compounds 3a, 3b, 3d and 3e exhibited good activity at 100 μg ml⁻¹ and product 3d is the most active. In a cytotoxicity study the complexes 3 were evaluated against two human cancer cell lines MDA-MB-231 and MCF-7. Both 3d and 3e complexes were found to be active against the tested cell lines showing comparable activity with examples in the literature.

A series of ruthenium(ii) complexes with N-heterocyclic carbene ligands were successfully synthesized by transmetalation reactions between silver(i) N-heterocyclic carbene complexes and [RuCl₂(p-cymene)]₂ in dichloromethane under Ar conditions.     

Heptaketides from the endophytic fungus Pleosporales sp. F46 and their antifungal and cytotoxic activities

Six new heptaketides, pleosporalins A–F (1–5, and 7), and a new heptaketide derivative, pleosporalin G (9), together with four biosynthetically related known compounds (6, 8, 10, and 11), were isolated from an endophytic fungus, Pleosporales sp. F46, found in the medicinal plant Mahonia fortunei. The structures and stereochemistry of these compounds were established by extensive spectroscopic analyses including LC-HRMS, NMR spectroscopy, optical rotations, ECD calculations, and single-crystal X-ray diffraction. The antifungal activities of isolated compounds 1–11 were investigated against Candida albicans, and their cytotoxic activities were evaluated against A549, SMMC-721, and MDA-MB-231 cancer cell lines. Compound 1 was active against C. albicans with an MIC₈₀ of 128 μg mL⁻¹, and compound 7 showed moderate cytotoxicity against MDA-MB-231 with an IC₅₀ of 22.4 ± 1.1 μM. By comparing compounds 1 and 7 with structurally related metabolites, it was revealed that alterations to their C-1 or C-2 substitutions could significantly influence their antifungal or cytotoxic efficacies.

New bioactive heptaketide derivatives were isolated and characterized from an endophytic fungus, Pleosporales sp. F46.     

Discovery of quinolone derivatives as antimycobacterial agents

Tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis (M. tuberculosis), is an important public health issue. Current first-line drugs administered to TB patients have been in use for over 40 years, whereas second-line drugs display strong side effects and poor compliance. Additionally, designing effective regimens to treat patients infected with multi- and extremely-drug-resistant (MDR and XDR) strains of TB is challenging. In this report, we screened our compound library and identified compound 1 with antituberculosis activity and a minimal inhibitory concentration (MIC) against M. tuberculosis of 20 μg mL⁻¹. Structure optimization and the structure–activity relationship of 1 as the lead compound enabled the design and synthesis of a series of quinolone derivatives, 6a1–6a2, 6b1–6b36, 6c1, 6d1–6d14, 7a1–7a2, 7b1–7b2, 7c1, 8a1–8a5, 9a1–9a4 and 10a1–10a6. These compounds were evaluated in vitro for anti-tubercular activity against the M. tuberculosis H₃₇Rv strain. Among them, compounds 6b6, 6b12 and 6b21 exhibited MIC values in the range of 1.2–3 μg mL⁻¹ and showed excellent activity against the tested MDR-TB strain (MIC: 3, 2.9 and 0.9 μg mL⁻¹, respectively). All three compounds were non-toxic toward A549 and Vero cells (>100 and >50 μg mL⁻¹, respectively). In addition, an antibacterial spectrum test carried out using compound 6b21 showed that this compound specifically inhibits M. tuberculosis. These can serve as a new starting point for the development of anti-TB agents with therapeutic potential.

6b21: MIC against M. tb H₃₇Rv = 1.2 μg mL⁻¹, MIC against drug-resistant strains = 0.9 μg mL⁻¹, solubility = 132 μg mL⁻¹, non-cytotoxicity.