<i>N</i>‑Heterocyclic Carbene-Stabilized Palladium Complexes as Organometallic Catalysts for Bioorthogonal Cross-Coupling Reactions

A small library of water-soluble <i>N</i>-heterocyclic carbene (NHC)-stabilized palladium complexes was prepared and applied for cross-couplings of biomolecules under mild conditions in water. Pd–NHC complexes bearing hydrophilic groups were demonstrated to be efficient catalysts for the Suzuki–Miyaura coupling of various unnatural amino acids and proteins bearing <i>p</i>-iodophenyl functional groups. We further utilized this catalytic system for the rapid bioorthogonal labeling of proteins on the surfaces of mammalian cells. These results demonstrated that NHC-stabilized metal complexes have potential utility in cellular systems

Rhodium-Catalyzed Transannulation of <i>N</i>‑Sulfonyl-1,2,3-triazoles and Epoxides: Regioselective Synthesis of Substituted 3,4-Dihydro‑2<i>H</i>‑1,4-oxazines

Rhodium-catalyzed transannulation of 1,2,3-triazoles and ring-opening reactions of epoxides is described. A number of 3,4-dihydro-2H-1,4-oxazines are obtained in moderate yields probably involving generation of α-imino rhodium­(II) carbene species

Rhodium-Catalyzed Transannulation of <i>N</i>‑Sulfonyl-1,2,3-triazoles and Epoxides: Regioselective Synthesis of Substituted 3,4-Dihydro‑2<i>H</i>‑1,4-oxazines

Rhodium-catalyzed transannulation of 1,2,3-triazoles and ring-opening reactions of epoxides is described. A number of 3,4-dihydro-2<i>H</i>-1,4-oxazines are obtained in moderate yields probably involving generation of α-imino rhodium­(II) carbene species

Multifunctional Superamphiphobic Cotton Fabrics with Highly Efficient Flame Retardancy, Self-Cleaning, and Electromagnetic Interference Shielding

Here, a facile method is reported to prepare multifunctional cotton fabrics with high flame retardancy, high electrical conductivity, superamphiphobicity, and high electromagnetic shielding. The cotton fabric surface was first modified with phytic acid (PA), which promoted dehydration and carbonization of cellulose to increase flame retardancy in the process of pyrolysis. Tannic acid (TA) and 3-aminopropyltriethoxysilane (APTES) coating with nanospheres as interlayers created hierarchical roughness that facilitated the construction of superamphiphobic surfaces and provided adhesion sites for silver nanoparticles. In addition, the TA-APTES coating improved flame retardancy because the APTES-containing silicon could form silicon carbon layers to isolate heat and oxygen. Subsequently, the surface energy of the composite cotton fabric was reduced by fluorine-containing molecules. The prepared composite cotton fabric exhibited excellent superamphiphobicity with contact angles of 160.3 and 152° for water and olive oil, respectively. The conductivity and EMI shielding efficiency of the prepared composite cotton fabric reached 629.93 S/cm and 76 dB, respectively. Importantly, the composite cotton fabric maintained a relatively stable EMI shielding efficiency even after cyclic bending and abrasion tests. Moreover, the composite cotton fabric possessed a high limiting oxygen index (LOI) of 45.3% and self-extinguishing properties with the peak heat release rate (PHHR) and total heat release (THR) reduced by 73 and 67%, respectively, than the pure cotton fabric, indicating the outstanding flame retardancy

Quenched Ligand-Directed Tosylate Reagents for One-Step Construction of Turn-On Fluorescent Biosensors

Semisynthetic fluorescent biosensors consisting of a protein framework and a synthetic fluorophore are powerful analytical tools for specific detection of biologically relevant molecules. We report herein a novel method that allows for the construction of turn-on fluorescent semisynthetic biosensors in a one-step manner. The strategy is based on the ligand-directed tosyl (LDT) chemistry, a new type of affinity-guided protein labeling scheme which can site-specifically introduce synthetic probes to the surface of proteins with concomitant release of the affinity ligands. Novel quenched ligand-directed tosylate (Q-LDT) reagents were designed by connecting an organic dye to a conjugate of a protein ligand and a fluorescence quencher through a tosyl linker. The Q-LDT-mediated labeling directly converts a natural protein to a fluorescently labeled protein that remains noncovalently complexed with the cleaved ligand-tethered quencher. The fluorescence of this labeled protein is initially quenched and only in the presence of specific analytes is the fluorescence enhanced (turned on) due to the expulsion of the ligand-quencher fragment. Using a single labeling step, this approach was successfully applied to carbonic anhydrase II (CAII) and a Src homology 2 (SH2) domain to generate turn-on fluorescent biosensors toward CAII inhibitors and phosphotyrosine peptides, respectively. Detailed investigations revealed that the obtained biosensors exhibit their natural ligand selectivity. The high target-specificity of the LDT chemistry also allowed us to prepare the SH2 domain-based biosensor not only in a purified form but also in a bacterial cell lysate. These results demonstrate the utility of the Q-LDT-based approach to expand the applications of semisynthetic biosensors

Synthesis and Structure of Arene Ru(II) N^∧O‑Chelating Complexes: <i>In Vitro</i> Cytotoxicity and Cancer Cell Death Mechanism

A panel of six new structurally related organometallic arene Ru­(II) complexes of general composition [(η6-benzene)­Ru­(L)­Cl] (1–3) and [(η6-p-cymene)­Ru­(L)­Cl] (4–6) (L = dimethylaminobenzhydrazones) have been designed and synthesized in search of new ruthenium anticancer drugs. The identities of the synthesized complexes have been well-established by elemental analysis and various spectral (FT-IR, UV–vis, NMR, and HR-MS) methods. The solid-state molecular structures of the ruthenium complexes were determined with the help of X-ray crystallography and confirms the presence of a pseudo-octahedral geometry around ruthenium. Furthermore, cytotoxicity of the complexes has been unveiled with the aid of MTT assay against A549 (lung carcinoma), LoVo (colon adenocarcinoma), HuH-7 (hepato cellular carcinoma) along with the noncancerous 16HBE (human lung bronchial epithelium) cells and compared with the effect of the standard drug cisplatin. Interestingly, complexes 4, 5, and 6 which contain a p-cymene moiety induce a remarkable decrease of cell viability against all the cancer cells tested. The capacity corresponding to the inhibition of A549 cells proliferation was analyzed by 5-ethynyl-2-deoxyuridine (EdU) incorporation assay and indicated a notable effect of p-cymene counterparts 4, 5, and 6 over cisplatin. Further studies such as AO-EB (acridine orange–ethidium bromide) staining, flow cytometry, and Western blot analyses on cell death mechanism signified that the cytotoxicity was associated with apoptosis in cancer cells. This clearly suggests that p-cymene-capped Ru­(II) complexes are also one of the propitious cancer therapeutic candidates and are worthy of further investigations

Targeting the Mitochondria with Pseudo-Stealthy Nanotaxanes to Impair Mitochondrial Biogenesis for Effective Cancer Treatment

The clinical success of anticancer therapy is usually limited by drug resistance and the metastatic dissemination of cancer cells. Mitochondria are essential generators of cellular energy and play a crucial role in sustaining cell survival and metastatic escape. Selective drug strategies targeting mitochondria are able to rewire mitochondrial metabolism and may provide an alternative paradigm to treat many aggressive cancers with high efficiency and low toxicity. Here, we present a pseudo-stealthy mitochondria-targeted pro-nanotaxane and test it against recurrent and metastatic tumor xenografts. The nanoparticle encapsulates a mitochondria-targetable pro-taxane agent, which can be converted into the chemically unmodified cabazitaxel drug, with further surface cloaking with a low-density lipophilic triphenylphosphonium cation. The resultant nanotaxane could be effectively taken up by cells and consequently specifically localized to the mitochondria. The in situ activated cabazitaxel causes mitochondrial dysfunction and ultimately results in potent cell apoptosis. After intravenous administration to animals, pro-nanotaxane mimics the stealthy behavior of polyethylene glycol-cloaked nanoparticles to provide a long circulation time. The antitumor efficacy of this mitochondria-targeted system was validated in multiple preclinical drug-resistant tumor models. Notably, in a patient-derived metastatic melanoma model that was initially pretreated with cabazitaxel, nanotaxane administration not only produced durable tumor reduction but also substantially suppressed metastatic recurrence. Taken together, these results demonstrate that this combination of a pseudo-stealthy platform with a rationally designed pro-drug is an attractive approach to target mitochondria and enhance drug efficacy

Self-Assembled Gemcitabine Prodrug Nanoparticles Show Enhanced Efficacy against Patient-Derived Pancreatic Ductal Adenocarcinoma

Effective new therapies for pancreatic ductal adenocarcinoma (PDAC) are desperately needed as the prognosis of PDAC patients is dismal and treatment remains a major challenge. Gemcitabine (GEM) is commonly used to treat PDAC; however, the clinical use of GEM has been greatly compromised by its low delivery efficacy and drug resistance. Here, we describe a very simple yet cost-effective approach that synergistically combines drug reconstitution, supramolecular nanoassembly, and tumor-specific targeting to address the multiple challenges posed by the delivery of the chemotherapeutic drug GEM. Using our developed PUFAylation technology, the GEM prodrug was able to spontaneously self-assemble into colloidal stable nanoparticles with sub-100 nm size on covalent attachment of hydrophobic linoleic acid via amide linkage. The prodrug nanoassemblies could be further refined by PEGylation and PDAC-specific peptide ligand for preclinical studies. In vitro cell-based assays showed that not only were GEM nanoparticles superior to free GEM but also the decoration with PDAC-homing peptide facilitated the intracellular uptake of nanoparticles and thereby augmented the cytotoxic activity. In two separate xenograft models of human PDAC, one of which was a patient-derived xenograft model, the administration of targeted nanoparticles resulted in marked inhibition of tumor progression as well as alleviated systemic toxicity. Together, these data unequivocally confirm that the hydrophilic and rapidly metabolized drug GEM can be feasibly transformed into a pharmacologically efficient nanomedicine through exploiting the PUFAylation technology. This strategy could also potentially be applied to rescue many other therapeutics that show unfavorable outcomes in the preclinical studies because of pharmacologic obstacles

Chemical Cell-Surface Receptor Engineering Using Affinity-Guided, Multivalent Organocatalysts

Catalysts hold promise as tools for chemical protein modification. However, the application of catalysts or catalyst-mediated reactions to proteins has only recently begun to be addressed, mainly in in vitro systems. By radically improving the affinity-guided DMAP (4-dimethylaminopyridine) (AGD) catalysts that we previously reported (Koshi, Y.; Nakata, E.; Miyagawa, M.; Tsukiji, S.; Ogawa, T.; Hamachi, I. J. Am. Chem. Soc. 2008, 130, 245.), here we have developed a new organocatalyst-based approach that allows specific chemical acylation of a receptor protein on the surface of live cells. The catalysts consist of a set of ‘multivalent’ DMAP groups (the acyl transfer catalyst) fused to a ligand specific to the target protein. It was clearly demonstrated by in vitro experiments that the catalyst multivalency enables remarkable enhancement of protein acylation efficiency in the labeling of three different proteins: congerin II, a Src homology 2 (SH2) domain, and FKBP12. Using a multivalent AGD catalyst and optimized acyl donors containing a chosen probe, we successfully achieved selective chemical labeling of bradykinin B2 receptor (B2R), a G-protein coupled receptor, on the live cell-surface. Furthermore, the present tool allowed us to construct a membrane protein (B2R)-based fluorescent biosensor, the fluorescence of which is enhanced (tuned on) in response to the antagonist ligand binding. The biosensor should be applicable to rapid and quantitative screening and assay of potent drug candidates in the cellular context. The design concept of the affinity-guided, multivalent catalysts should facilitate further development of diverse catalyst-based protein modification tools, providing new opportunities for organic chemistry in biological research