Near-infrared dyes,nanomaterials and proteins

Near-infrared probes including dyes, nanoparticles and proteins have been particularly useful for in vivo imaging because of their ability to penetrate tissue deeper with minimal scattering and autofluorescence, opening the door to study cell biology in physiological conditions.     

Palladium-catalyzed arylation/cyclization/desulfonation cascades toward 4-aryl quinolin-2(1H)-ones with diaryliodonium salts

Palladium-catalyzed cascades of arylation/cyclization/desulfonation of ortho-aminocinnamate esters by using diaryliodonium salts afforded a wide range of 4-aryl quinolin-2(1H)-ones. As such, the desired 4-aryl quinolin-2(1H)-ones with potential biological activity has been synthesized in the yields of 34–96%.     

New NIR-II dyes without a benzobisthiadiazole core

Compared to the well-studied NIR-I small-molecule fluorophores, the structures of NIR-II fluorophores are scarce yet. Most NIR-II fluorophores are composed of D-A-D structures. It is essential to search for the new structures of NIR-II fluorophores to enlarge the field of NIR-II dyes.     

Bousigonine A and B,bis- and tri-indole alkaloids from Bousigonia mekongensis and their preventing high glucose-induced podocyte injury activity

Bousigonine A (1), an unprecedented eburnamine-voaphylline type dimeric indole alkaloid, and Bousigonine B (2), the first example of eburnamine-eburnamine-aspidospermine type trimeric indole alkaloid were isolated from Bousigonia mekongensis. Their structures were elucidated mainly by spectroscopic analysis and compared to published data. Their preventing high glucose-induced podocyte injury activity were evaluated for the first time, and compound 1 exhibited significant effect with EC₅₀ value of 2.5 μM.     

Green synthesis of gold nanoclusters using papaya juice for detection of l-lysine

P-AuNCs was rapidly synthesized, while papaya juice served as a capping and reducing agent. Due to the surface electron density increase-induced fluorescence enhancing principle, the prepared fluorescent probe provided high selectivity and sensitivity for monitoring L-lysine in human urines.     

Chemoselective aerobic oxidation of 2-amino-N-benzylanilines into N-(2-aminophenyl)imines via a nitroxide-free copper catalysis

Chemoselective oxidative synthesis of N-(2-aminophenyl)imines from 2-amino-N-benzylanilines was accomplished through combined use of O₂(air) and copper salt. This transformation was performed at room temperature, and the mild oxidation was efficient and chemoselective without using nitroxyl radicals and ligands.     

Development of a catalytic enantioselective synthesis of the guanacastepene and heptemerone tricyclic core

For nearly two decades, synthetic chemists have been fascinated by the structural complexity and synthetic challenges afforded by the guanacastepene and heptemerone diterpenoids. Numerous synthetic approaches to these compounds have been reported, but to date the application of enantioselective catalysis to this problem has not been realized. Herein we report an enantioselective synthesis of an advanced intermediate corresponding to the tricyclic core common to the guanacastepenes and heptemerones. Highlights of this work include sequential Pd-catalyzed decarboxylative allylic alkylation reactions to generate the two all carbon quaternary stereocenters, the use of ring-closing metathesis to close the A ring in the presence of a distal allyl sidechain, and a regio- and diastereoselective oxidation of a trienol ether to introduce oxygenation on the A ring.     

Synthesis,properties and application of novel 5,6,5,6-tetracyclic pyrazine/pyrrole-fused unsymmetric bis(BF2) fluorescent dyes: BOPYPYs

Novel 5,6,5,6-tetracyclic pyrazine/pyrrole-fused unsymmetric bis(BF₂) fluorescent dyes (BOPYPYs) were obtained by reaction of pyrrole-2-carboxaldehyde with 1-(pyrazin-2-yl)hydrazine in the presence of Et₃N-BF₃·Et₂O for the first time. The absorption maxima of pyrazine-fused BOPYPY are obviously bathochromic shifts, in contrast to those of the reported BOPPY, indicating that the discrepant substitute groups between pyridine and pyrazine result in the remarkable wavelength difference. The new series of BOPYPYs possess high molar extinction coefficients, high fluorescence quantum yields, and larger Stokes shifts. A Knoevenagel reaction of BOPYPY with 4-dimethylaminobenzaldehyde smoothly produced the dye with the extension of π-conjugation. Dimethylamino-containing BOPYPY as a pH-responsive fluorescent sensor could detect pH value.     

Highly ordered combined structure of anodic TiO2 nanotubes and TiO2 nanoparticles prepared by a novel route for dye-sensitized solar cells

Combined structure of anodic TiO₂ nanotubes and TiO₂ nanoparticles (TiNTs-TiNPs) has been synthesized by a facile combination of hydrothermal and chemical vapor deposition methods. Ordered TiO₂ nanotubes with smooth walls were fabricated by two step anodization method in ethylene glycol containing NH₄F at 50 V. This nanotubular array after annealing at 450 °C was subjected to the hydrothermally produced gaseous environment in an autoclave with diluted TiCl₄ solution at its bottom. Vapors of TiCl₄ were allowed to react chemically with water vapors for predefined time durations at 180 °C that resulted in the deposition of TiO₂ nanoparticles on tubes’ surface and side walls. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed that for one hour reaction duration, nanoparticles were evenly coated on the walls of nanotubes, whereas, longer durations tend to deteriorate the tubular structure. Consequently, the ordered TiNTs-TiNPs array produced after one hour coating has shown better performance for dye-sensitized solar cell DSSC) in back illumination mode with 130% increase in efficiency as compared to the device based on bare TiO₂ nanotubes. The same photoanode has higher reflective properties with higher scattering ability. The solar cell based on this photoanode exhibits higher external quantum efficiency and effective charge transport properties. This study shows that porous ordered 1D structures based on TiO₂ are of crucial importance for the high performance of DSSCs.     

Facile synthesis of 2-C-methyl-d-arabino-γ-1,4-lactones and mechanism study

In our previous research on the synthesis of 3,5-di-O-benzoyl-2-C-methyl-d-arabino-γ-lactone 4a, the reaction mechanism of DMSO-mediated configuration inversion of C2 hydroxyl group in the lactone was ambiguous. As a follow-up to this research, we used ¹⁸O-labelled H₂O and DMSO to investigate the mechanism. It was surprisingly discovered that DMSO served as an oxygen donor to stereoselectively displace the leaving group, and was regenerated in the reaction. The protecting groups had no influence on the inversion, but would significantly affect the yield. We also disclosed another approach for the synthesis of 4a without using the expensive Tf₂O, which was more suitable for application.     

Photodynamic therapy based on organic small molecular fluorescent dyes

Photodynamic therapy (PDT) has shown promise as an effective treatment modality for cancer and other localized diseases due to its noninvasive properties and spatiotemporal selectivity. Near-infrared (NIR) fluorescent dyes based on organic small molecules are characterized with low cytotoxicity, good biocompatibility and excellent phototoxicity, which are widely used in PDT. In this review, we attempt to summarize the development of imaging-induced PDT based on organic small molecules and classify it according to the structures of dyes including cyanines, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) analogues, phthalocyanine and other agents such as rhodamine analogues.     

Asymmetric transfer hydrogenations of β-N-substituted enamino esters with ammonia borane

Optically active β-amino acids and their derivatives are very useful building blocks in synthetic and medicinal chemistry. The catalytic asymmetric reduction of β-enamino esters is one of the most efficient approaches for their synthesis. Ammonia borane with low molecular weight, high hydrogen capacity, and good stability, is an ideal hydrogen source for the transfer hydrogenation. However, only a few successful examples have been reported for the asymmetric reduction with ammonia borane. In this work, an asymmetric metal-free transfer hydrogenation of β-N-substituted enamino esters with ammoinia borane was successfully realized by using a frustrated Lewis pair of Piers’ borane and (S)-tert-butylsulfinamide as a chiral catalyst. A variety of β-amino acid derivatives were obtained in 51–90% yields with up to 91% ee.     

An internal oxidant-directing strategy enabling transition metal-free C–S bond ligation

Organic sulfur compounds have broad applications in biology, medicine and material sciences and intensive efforts have been devoted to developing mild and general C–S bond-forming methods. However, a mild, transition-metal-free, direct C–H bond functionalization method remains elusive. Here, we report the use of an internal oxidant-directing strategy to achieve this goal. The cascade reactions described here show excellent chemoselectivity and a wide substrate scope for both oxyamines and sulfenylation reagents. This study enlarges the synthesis toolbox for preparing structurally diverse sulfilimines under mild conditions.     

Bistachybotrysins D and E,one stereoisomeric pair of cytotoxic phenylspirodrimane dimers from Stachybotrys chartarum

Bistachybotrysins D and E (1 and 2), one stereoisomeric pair of phenylspirodrimane dimers, were isolated from Stachybotrys chartarum CGMCC 3.5365. They represent novel phenylspirodrimane dimers with a central [6,5,6]-tricyclic carbon scaffold containing a cyclopentanone core. The structures of 1 and 2 were elucidated through extensive spectroscopic data analysis, and their absolute configurations were characterized by calculated electronic circular dichroism (ECD). Compounds 1 and 2 displayed potent cytotoxic activity against the four human tumor cell lines HCT116, BGC823, Daoy and HepG2 with IC_ (50)values ranging from 6.7 μmol/L to 11.6 μmol/L. Furthermore, a plausible biogenetic pathway for 1 and 2 is proposed.     

Novel quinazolin-4(3H)-one derivatives containing a 1,3,4-oxadiazole thioether moiety as potential bactericides and fungicides: Design,synthesis, characterization and 3D-QSAR analysis

A series of quinazolin-4(3H)-one derivatives containing a 1,3,4-oxadiazole thioether moiety were designed, synthesized and evaluated for their biological activities against phytopathogenic microorganisms. Antimicrobial bioassays in vitro indicated that most of the target compounds exhibited more significant antibacterial activities against Xanthomonas oryzae pv. oryzae (Xoo) than the agricultural bactericide thiadiazole-copper. A comparative molecular similarity index analysis (CoMSIA) model with cross-validated q² and non-cross-validated r² values of 0.561 and 0.882 was generated to investigate the structure-activity relationships of title compounds against Xoo. Title compound 6w, which was rationally designed under the guidance of obtained CoMSIA model, exhibited the excellent anti-Xoo effect in vitro with an EC₅₀ value of 29.10 μg/mL, which is approximately 3-folds more effective than thiadiazole-copper (113.93 μg/mL). In addition, compound 6i demonstrated the impressive antifungal effects against Rhizoctonia solani (Rs) and Fusarium graminearum (Fg) in vitro, with the corresponding EC₅₀ values of 11.01 μg/mL and 36.00 μg/mL, which is obviously better than the agricultural fungicide hymexazol (76.74 μg/mL and 56.19 μg/mL, respectively). The above researches indicate that quinazolin-4(3H)-one derivatives containing a 1,3,4-oxadiazole thioether moiety could be further studied as template molecules of novel agricultural microbicides.     

Copper-catalyzed cross-coupling of chloramine salts and arylboronic acids in water: A green and practical route to N-arylsulfonamides

A green and practical method for the synthesis of N-arylsulfonamides from chloramine salts and arylboronic acids is herein developed. The reaction proceeds readily in the presence of 5?mol% of CuI and 2.5?equiv. K₂CO₃ in water at room temperature, generating a variety of N-arylsulfonamides in moderate to good yields with good functional group tolerance.     

Iridium complexes with P-stereogenic phosphino imidazole ligands: Synthesis,structure and catalysis

The synthesis of optically and diastereomerically pure P-stereogenic phosphine-imidazole ligands is reported. The new ligands contain either a benzoimidazole or a 4-phenylimidazole as a N-donor fragment. The ligands have been coordinated to iridium and the structure of the corresponding cationic COD complexes has been determined by X-ray analysis. The combination of the chiral phosphorus atom and the imidazole substituents generate a strong chiral environment around the metal center. Preliminary hydrogenation reactions with a model cyclic β-enamide are also reported.     

Ultraviolet irradiation of terarylenes: A facile,efficient, and environmentally friendly method for the synthesis of fused polycyclic products

Ultraviolet irradiation of hydroxyl substituted terarylenes provided a simple, efficient, and environmentally friendly method for the synthesis of imidazo[1,2-a]pyridines. The starting terarylenes were prepared via the one-pot, three-component condensation of readily accessible arylglyoxals, 2-aminopyridines, and dimedone.     

Divergent total synthesis of aspinolides B,E and J

Stereoselective total synthesis of aspinolides B, E and J, naturally occurring 10-membered lactones, were accomplished by divergent strategies starting from the commercially available 2,3-O-isopropylidene-d-ribose and methyl d-lactate. The synthesis features rapid access to the both key fragments from chiral pool and the formation of 10-membered ring lactones containing trans double bond employing cross-metathesis reaction (CM) and intramolecular Shiina macrolactonization.     

Synthesis of tubuphenylalanine and epi-tubuphenylalanine via regioselective aziridine ring opening with carbon nucleophiles followed by hydroboration-oxidation of 1,1-substituted amino alkenes

An efficient synthesis of N-Boc-tubuphenylalanine benzyl ester (N-Boc-Tup-OBn, 1a) and N-Boc-epi-tubuphenylalanine benzyl ester (N-Boc-epi-Tup-OBn, 1b) is reported herein. Regioselective aziridine 4 ring opening with carbon nucleophiles followed by hydroboration of 1,1-substituted aminoalkene 3 using 9-BBN and subsequent oxidation in an alkaline medium are used as the key steps to provide N-tosyl 1,4-aminoalcohols. The 1,4-aminoalcohols are successfully transformed into the desired products with an overall yield of 23% for 1a and 11% for 1b over 8 consecutive steps separately.