Synthesis of an O-acyl isopeptide by using native chemical ligation to efficiently construct a hydrophobic polypeptide

By using dimethylformamide to suppress the O-to-N acyl migration, we efficiently synthesized an O-acyl isopeptide by native chemical ligation of a peptide-thioester and a Cys-O-acyl isopeptide. The reaction mixture was then loaded onto an octadecylsilane reverse-phase HPLC column, and the isopeptide was purified by using a linear gradient of CH₃CN in 0.1% aqueous trifluoroacetic acid. The recovery rate of the O-acyl isopeptide was considerably higher than that of the corresponding native polypeptide. Synthesis of O-acyl isopeptides via native chemical ligation, with O-to-N acyl migration as the final step to give the native form, has potential as an efficient method of constructing hydrophobic polypeptides.     

Controlled-release system mediated by a retro Diels-Alder reaction induced by the photothermal effect of gold nanorods

Controlled-release systems that respond to external stimuli have received great interest for use in medical treatments such as for drug delivery to specific sites. Gold nanorods have an absorption band at the near-infrared region and convert the absorbed light energy into heat, which is known as a "photothermal effect". Therefore, gold nanorods are expected to act not only as an on-demand thermal converter for photothermal therapy but also as a controller of a drug-release system capable of responding to the near-infrared light irradiation. In this study, to construct a controlled-release system that responds to near-infrared light irradiation, we modified gold nanorods with polyethylene glycol (PEG) through Diels-Alder cycloadducts. When the modified gold nanorods were irradiated by near-infrared light, the PEG chains were released from the gold nanorods because of the retro Diels-Alder reaction induced by the photothermal effect. As a result of the PEG release, the gold nanorods formed aggregates. This type of controlled-release system coupled with the aggregate formation of the gold nanorods triggered by near-infrared light could be expanded to applications of gold nanorods in medical fields such as drug and photothermal therapy.     

Importance of sialic acid residues illuminated by live animal imaging using phosphorylcholine self-assembled monolayer-coated quantum dots

Glycans are expected to be one of the potential signal molecules for controlling drug targeting/delivery or long-term circulation of biopharmaceuticals. However, the effect of the carbohydrates of artificially glycosylated derivatives on in vivo dynamic distribution profiles after intravenous injection of model animals remains unclear due to the lack of standardized methodology and a suitable platform. We report herein an efficient and versatile method for the preparation of multifunctional quantum dots (QDs) displaying common synthetic glycosides with excellent solubility and long-term stability in aqueous solution without loss of quantum yields. Combined use of an aminooxy-terminated thiol derivative, 11,11'-dithio bis[undec-11-yl 12-(aminooxyacetyl)amino hexa(ethyleneglycol)], and a phosphorylcholine derivative, 11-mercaptoundecylphosphorylcholine, provided QDs with novel functions for the chemical ligation of ketone-functionalized compounds and the prevention of nonspecific protein adsorption concurrently. In vivo near-infrared (NIR) fluorescence imaging of phosphorylcholine self-assembled monolayer (SAM)-coated QDs displaying various simple sugars (glyco-PC-QDs) after administration into the tail vein of the mouse revealed that distinct long-term delocalization over 2 h can be achieved in cases of QDs modified with α-sialic acid residue (Neu5Ac-PC-QDs) and control PC-QDs, while QDs bearing other common sugars, such as α-glucose (Glc-PC-QDs), α-mannose (Man-PC-QDs), α-fucose (Fuc-PC-QDs), lactose (Lac-PC-QDs), β-glucuronic acid (GlcA-PC-QDs), N-acetyl-β-D-glucosamine (GlcNAc-PC-QDs), and N-acetyl-β-D-galactosamine (GalNAc-PC-QDs) residues, accumulated rapidly (5-10 min) in the liver. Sequential enzymatic modifications of GlcNAc-PC-QDs gave Galβ1,4GlcNAc-PC-QDs (LacNAc-PC-QDs), Galβ1,4(Fucα1,3)GlcNAc-PC-QDs (Le(x)-PC-QDs), Neu5Acα2,3Galβ1,4GlcNAc-PC-QDs (sialyl LacNAc-PC-QDs), and Neu5Acα2,3Galβ1,4(Fucα1,3)GlcNAc-PC-QDs (sialyl Le(x)-PC-QDs) in quantitative yield as monitored by direct matrix-assisted laser desorption ionization time-of-flight mass spectrometry analyses. Live animal imaging uncovered for the first time that Le(x)-PC-QDs also distributed rapidly in the liver after intravenous injection and almost quenched over 1 h in similar profiles to those of LacNAc-PC-QDs and Lac-PC-QDs. On the other hand, sialyl LacNAc-PC-QDs and sialyl Le(x)-PC-QDs were still retained stably in the whole body after 2 h, while they showed significantly different in vivo dynamics in the tissue distribution, suggesting that structure/sequence of the neighboring sugar residues in the individual sialyl oligosaccharides might influence the final organ-specific distribution. The present results clearly visualize the evidence of an essential role of the terminal sialic acid residue(s) for achieving prolonged in vivo lifetime and biodistribution of various glyco-PC-QDs as a novel class of functional platforms for nanomaterial-based drug targeting/delivery. A standardized protocol using multifunctional PC-QDs should facilitate live animal imaging of ligand-displayed QDs using versatile NIR fluorescence photometry without influence of size-dependent accumulation/excretion pathway for nanoparticles (e.g., viruses) >10 nm in hydrodynamic diameter by the liver.     

Communication: a new hybrid exchange correlation functional for band-gap calculations using a short-range Gaussian attenuation (Gaussian-Perdue-Burke-Ernzerhof)

We have developed a new hybrid functional [Gaussian-Perdue-Burke-Ernzerhof (Gau-PBE)] that is suitable for the calculation of solid state bandgaps using a periodic boundary condition. The characteristic of this functional is the use of a Gaussian attenuation scheme (Gau) to include a short-range Hartree-Fock (HF) exchange. This new functional can perform barrier height calculations with an accuracy comparable to the middle-range hybrid functional and bandgap calculations with an accuracy comparable to the Heyd-Scuseria-Ernzerhof (HSE) functional. However, the point is that the performance can be achieved using a Gaussian HF exchange, while the HISS functional calculates twice HF-exchange integrations using an error function to obtain both performances. In addition, Gau-PBE functional can decrease the time cost of bandgap calculations by an average of 40% compared to the HSE functional.     

L-DMDP, L-homoDMDP and their C-3 fluorinated derivatives: synthesis and glycosidase-inhibition

L-DMDP and L-homoDMDP, the enantiomers of naturally occurring DMDP and homoDMDP have been synthesized from D-xylose derived cyclic nitrone 9. Their 3-deoxy-3-fluorinated analogues were also obtained from polyhydroxylated fluorinated cyclic nitrone 10, which was prepared from fluorinated sugar 12 in seven steps. Bioactivities of these iminosugars against various glycosidases were evaluated. While L-DMDP and L-homoDMDP are potent inhibitors of α-glucosidases, a sharp decrease of inhibition was found when the C-3 hydroxyl group of these compounds was replaced by fluoride, which showed the great importance of the C-3 hydroxyl in their interaction with enzymes.     

Toward the racemic total synthesis of hederacines A and B: construction of an advanced tricyclic intermediate

Progress toward the total synthesis of hederacines A and B is described. Our approach involves an allylic cyanate-to-isocyanate rearrangement, eneyne ring-closing metathesis, and a transannular reaction between the C-5 amino group and the C-12 position of the perhydroazuleno[5,6-b]furanone intermediate.     

Enhanced catalytic activity on titanosilicate molecular sieves controlled by cation-π interactions

A new class of heterogeneous catalytic systems utilizing cation-guest interactions was designed based on microporous titanosilicate molecular sieves. Introducing heavier alkali metal cations on ion-exchange sites of the framework resulted in a significant enhancement of the catalytic activity for oxidation of cyclohexene and styrene, whereas such an enhancement was not observed in oxidation of cyclohexane without π systems. Distinct relationships between the catalytic activities and intermolecular interaction energies which were determined by IR spectroscopic and computational approaches clearly evidenced the predominance of the cation-π interaction in this catalytic system.     

Formulation and pharmacokinetic evaluation of tetracycline-loaded solid lipid nanoparticles for subcutaneous injection in mice

The aim of this work was to prepare tetracycline-loaded solid lipid nanoparticles (Tet-SLN), and to evaluate the potential of these colloidal carriers for subcutaneous injection. Tet-SLN was prepared by microemulsion method and the preparation conditions were optimized by ternary phase diagram. At optimized process conditions, lyophilized Tet-SLN showed spherical particles with a mean diameter of 87.2±46.9 nm and a negative zeta potential of -6.69 mV, up to 1.7% tetracycline drug content was achieved after loading. In vitro release test showed a biphasic release profile for Tet-SLN and more than 80% of the drug was liberated from Tet-SLN in 48 h. After subcutaneous injection of Tet-SLN to mice, a considerable sustained release was observed; tetracycline in blood could be detected lasting 36 h, and lower concentrations of tetracycline in all tissues tested compared to the free tetracycline solution were observed. In conclusion, Tet-SLN can be prepared well by microemulsion method and subcutaneous injection of SLN provide a new perspective for drug sustained release.     

One-pot synthesis of benzo[f]indole-4,9-diones from 1,4-naphthoquinones and terminal acetylenes

In this paper, a concise one-pot method for the construction of benzo[f]indole-4,9-dione motifs is described. These transformations proceed via a sequential palladium- and copper-catalyzed coupling reaction of 1,4-naphthoquinones with terminal acetylenes, followed by a copper-catalyzed intramolecular cyclization reaction of the resulting coupling product.