Site‐Selective Cysteine–Cyclooctyne Conjugation

We report a site‐selective cysteine–cyclooctyne conjugation reaction between a seven‐residue peptide tag (DBCO‐tag, Leu‐Cys‐Tyr‐Pro‐Trp‐Val‐Tyr) at the N or C terminus of a peptide or protein and various aza‐dibenzocyclooctyne (DBCO) reagents. Compared to a cysteine peptide control, the DBCO‐tag increases the rate of the thiol–yne reaction 220‐fold, thereby enabling selective conjugation of DBCO‐tag to DBCO‐linked fluorescent probes, affinity tags, and cytotoxic drug molecules. Fusion of DBCO‐tag with the protein of interest enables regioselective cysteine modification on proteins that contain multiple endogenous cysteines; these examples include green fluorescent protein and the antibody trastuzumab. This study demonstrates that short peptide tags can aid in accelerating bond‐forming reactions that are often slow to non‐existent in water.     

Synthesis,crystal structure studies and solvatochromic behaviour of two 2‐{5‐[4‐(dimethylamino)phenyl]penta‐2,4‐dien‐1‐ylidene}malononitrile derivatives

The synthesis, crystal structure studies and solvatochromic behavior of 2‐{(2E,4E)‐5‐[4‐(dimethylamino)phenyl]penta‐2,4‐dien‐1‐ylidene}malononitrile, C₁₆H₁₅N₃ (DCV[3]), and 2‐{(2E,4E,6E)‐7‐[4‐(dimethylamino)phenyl]hepta‐2,4,6‐trien‐1‐ylidene}malononitrile, C₁₈H₁₇N₃ (DCV[4]), are reported and discussed in comparison with their homologs having a shorter length of the π‐conjugated bridge. The compounds of this series have potential use as nonlinear materials with second‐order effects due to their donor–acceptor structures. However, DCV[3] and DCV[4] crystallized in the centrosymmetric space group P2₁/c which excludes their application as nonlinear optical materials in the crystalline state. They both crystallize with two independent molecules having the same molecular conformation in the asymmetric unit. The series DCV[1]–DCV[4] demonstrated reversed solvatochromic behavior in toluene, chloroform, and acetonitrile.     

Aggregation‐Induced Emission and Sensing Characteristics of Triarylborane–Oligothiophene–Dicyanovinyl Triads

The design, synthesis and aggregation‐induced emission properties of a new series of triarylborane–oligothiophene–dicyanovinyl (DCV) conjugates 4 – 6 (A–D–A’ type molecular configuration) are reported. The optical properties of 4 – 6 can be modulated by judiciously varying the number of thiophene units between electron deficient boryl and dicyanovinyl units. Compound 6 with terthiophene spacer showed highly red‐shifted absorption and emission compared to 5 and 4 with bithiophene and monothiophene spacers, respectively. Compounds 5 and 6 show aggregation‐induced emission enhancement in water/THF mixtures. Compounds 5 and 6 also showed solvent viscosity dependent emission characteristics. All the three compounds show distinct optical responses for small anions such as fluoride and cyanide. Filter paper strips coated with compounds 5 and 6 can detect F^? and CN^? in aqueous media with different colorimetric responses.     

Well‐Defined Polymer–Paclitaxel Prodrugs by a Grafting‐from‐Drug Approach

We report on the design of a polymeric prodrug of the anticancer agent paclitaxel (PTX) by a grafting‐from‐drug approach. A chain transfer agent for reversible addition fragmentation chain transfer (RAFT) polymerization was efficiently and regioselectively linked to the C2′ position of paclitaxel, which is crucial for its bioactivity. Subsequent RAFT polymerization of a hydrophilic monomer yielded well‐defined paclitaxel–polymer conjugates with high drug loading, water solubility, and stability. The versatility of this approach was further demonstrated by ω‐end post‐functionalization with a fluorescent tracer. In vitro experiments showed that these conjugates are readily taken up into endosomes where native PTX is efficiently cleaved off and then reaches its subcellular target. This was confirmed by the cytotoxicity profile of the conjugate, which matches those of commercial PTX formulations based on mere physical encapsulation.     

Carrier‐Free Delivery of Precise Drug–Chemogene Conjugates for Synergistic Treatment of Drug‐Resistant Cancer

Combinatorial antitumor therapies using different combinations of drugs and genes are emerging as promising ways to overcome drug resistance, which is a major cause for the failure of cancer treatment. However, dramatic pharmacokinetic differences of drugs greatly impede their combined use in cancer therapy, raising the demand for drug delivery systems (DDSs) for tumor treatment. By employing fluorescent dithiomaleimide (DTM) as a linker, we conjugate two paclitaxel (PTX) molecules with a floxuridine (FdU)‐integrated antisense oligonucleotide (termed chemogene) to form a drug–chemogene conjugate. This PTX–chemogene conjugate can self‐assemble into a spherical nucleic acid (SNA)‐like micellular nanoparticle as a carrier‐free DDS, which knocks down the expression of P‐glycoprotein and subsequently releases FdU and PTX to exert a synergistic antitumor effect and greatly inhibit tumor growth.     

Synthesis and Biological Evaluation of RGD Peptidomimetic–Paclitaxel Conjugates Bearing Lysosomally Cleavable Linkers

Two small‐molecule–drug conjugates (SMDCs, 6 and 7 ) featuring lysosomally cleavable linkers (namely the Val–Ala and Phe–Lys peptide sequences) were synthesized by conjugation of the α_vβ₃‐integrin ligand cyclo[DKP–RGD]‐CH₂NH₂ ( 2 ) to the anticancer drug paclitaxel (PTX). A third cyclo[DKP–RGD]–PTX conjugate with a nonpeptide “uncleavable” linker ( 8 ) was also synthesized to be tested as a negative control. These three SMDCs were able to inhibit biotinylated vitronectin binding to the purified α_Vβ₃‐integrin receptor at nanomolar concentrations and showed good stability at pH 7.4 and pH 5.5. Cleavage of the two peptide linkers was observed in the presence of lysosomal enzymes, whereas conjugate 8 , which possesses a nonpeptide “uncleavable” linker, remained intact under these conditions. The antiproliferative activities of the conjugates were evaluated against two isogenic cell lines expressing the integrin receptor at different levels: the acute lymphoblastic leukemia cell line CCRF‐CEM (α_Vβ₃?) and its subclone CCRF‐CEM α_Vβ₃ (α_Vβ₃+). Fairly effective integrin targeting was displayed by the cyclo[DKP–RGD]–Val–Ala–PTX conjugate ( 6 ), which was found to differentially inhibit proliferation in antigen‐positive CCRF‐CEM α_Vβ₃ versus antigen‐negative isogenic CCRF‐CEM cells. The total lack of activity displayed by the “uncleavable” cyclo[DKP–RGD]–PTX conjugate ( 8 ) clearly demonstrates the importance of the peptide linker for achieving the selective release of the cytotoxic payload.     

Small D–π–A Systems with o‐Phenylene‐Bridged Accepting Units as Active Materials for Organic Photovoltaics

Donor–acceptor (D–π–A) systems that combine triarylamine donor blocks and dicyanovinyl (DCV) acceptor groups have been synthesized. Starting from the triphenylamine (TPA)? thiophene? DCV compound ( 1 ) as a reference system, various synthetic approaches have been developed for controlling the light‐harvesting properties and energy levels of the frontier orbitals in this molecule. Thus, the introduction of methoxy groups onto TPA, the replacement of one phenyl ring of TPA by a thiophene ring, or the extension of the π‐conjugating spacer group lead to the modulation of the HOMO level. On the other hand, the fusion of the DCV group onto the vicinal thiophene ring by an ortho‐phenylene bridge allows for a specific fine‐tuning of the LUMO level. The electronic properties of the molecules were analyzed by using UV/Vis spectroscopy and cyclic voltammetry and the compounds were evaluated as donor materials in basic bilayer planar heterojunction solar cells by using C₆₀ as acceptor material. The relationships between the electronic properties of the donors and the performance of the corresponding photovoltaic devices are discussed. Bilayer planar heterojunction solar cells that used reference compound 1 and C₇₀ afforded power‐conversion efficiencies of up to 3.7 %.     

Reduction‐responsive poly (ethylene glycol)‐dexamethasone biarm conjugate and its self‐assembled nanomicelles: Preparation,physicochemical characterization,and thiol‐triggered drug release

In this study, a reduction‐responsive poly (ethylene glycol)‐dexamethasone biarm conjugate was synthesized as intracellular targeted drug delivery carriers. The hydroxyl end group of methoxy poly (ethylene glycol) (mPEG) was modified to introduce a biarm structure with bioreducible disulfide bond and amine end groups. Dexamethasone (Dex) as a nuclear targeting moiety was conjugated to the amine end groups of mPEG biarm derivatives, mPEG‐(NH₂)₂ or mPEG‐(ss‐NH₂)₂, with or without bioreducible disulfide bonds. The bioreducible and nonreducible mPEG‐Dex biarm conjugates, R‐mPEG‐Dex and N‐mPEG‐Dex, were synthesized and characterized by various analytical methods, proton nuclear magnetic resonance (¹H‐NMR), Fourier transform infraredspectroscopy (FT‐IR), dynamic light scattering (DLS), and fluorescence measurements. Amphiphilic mPEG‐Dex conjugates self‐assembled in aqueous solutions to form nanoparticles (NPs) with a size range of 130 to 150 nm, and their critical micelle concentrations (CMCs) were determined to be 12.4 and 15.3 mg/L, respectively, for bioreducible and nonreducible ones. The R‐mPEG‐Dex NPs maintained good colloidal stability in the presence of bovine serum albumin (BSA) for more than 1 week but demonstrated a significant change in colloidal stability in the presence of dithiothreitol (DTT). In DTT‐containing phosphate‐buffered saline (PBS), the bioreducible NPs showed not only reduction‐responsive destabilization with PEG shedding but also thiol‐dependent drug release profile. Our observations indicated that the R‐mPEG‐Dex NPs have a promising prospective as an efficient nanocarrier for intracellular targeted delivery of various anticancer drugs.     

Kinetics of thiol–ene and thiol–acrylate photopolymerizations with real‐time fourier transform infrared

We used real‐time Fourier transform infrared to monitor the conversion of both thiol and ene (vinyl) functional groups independently during photoinduced thiol–ene photopolymerizations. From these results, the stoichiometry of various thiol–ene and thiol–acrylate polymerizations was determined. For thiol–ene polymerizations, the conversion of ene functional groups was up to 15% greater than the conversion of thiol functional groups. For stoichiometric thiol–acrylate polymerizations, the conversion of the acrylate functional groups was roughly twice that of the thiol functional groups. With kinetic expressions for thiol–acrylate polymerizations, the acrylate propagation kinetic constant was found to be 1.5 times greater than the rate constant for hydrogen abstraction from the thiol. Conversions of thiol–acrylate systems of various initial stoichiometries were successfully predicted with this ratio of propagation and chain‐transfer kinetic constants. Thiol–acrylate systems with different initial stoichiometries exhibited diverse network properties. Thiol–ene systems were initiated with benzophenone and 2,2‐dimethoxy‐2‐phenylacetophenone as initiators and were also polymerized without a photoinitiator. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3311–3319, 2001     

ROS‐Responsive N‐Alkylaminoferrocenes for Cancer‐Cell‐Specific Targeting of Mitochondria

Mitochondrial membrane potential is more negative in cancer cells than in normal cells, allowing cancer targeting by delocalized lipophilic cations (DLCs). However, as the difference is rather small, these drugs affect also normal cells. Now a concept of pro‐DLCs is proposed based on an N‐alkylaminoferrocene structure. These prodrugs are activated by the reaction with reactive oxygen species (ROS) forming ferrocenium‐based DLCs. Since ROS are overproduced in cancer, the high‐efficiency cancer‐cell‐specific targeting of mitochondria could be achieved as demonstrated by fluorescence microscopy in combination with two fluorogenic pro‐DLCs in vitro and in vivo. We prepared a conjugate of another pro‐DLC with a clinically approved drug carboplatin and confirmed that its accumulation in mitochondria was higher than that of the free drug. This was reflected in the substantially higher anticancer effect of the conjugate.     

A p‐Hydroxyphenacyl–Benzothiazole–Chlorambucil Conjugate as a Real‐Time‐Monitoring Drug‐Delivery System Assisted by Excited‐State Intramolecular Proton Transfer

Among the well‐known phototriggers, the p‐hydroxyphenacyl (pHP) group has consistently enabled the very fast, efficient, and high‐conversion release of active molecules. Despite this unique behavior, the pHP group has been ignored as a delivery agent, particularly in the area of theranostics, because of two major limitations: Its excitation wavelength is below 400 nm, and it is nonfluorescent. We have overcome these limitations by incorporating a 2‐(2′‐hydroxyphenyl)benzothiazole (HBT) appendage capable of rapid excited‐state intramolecular proton transfer (ESIPT). The ESIPT effect also provided two unique advantages: It assisted the deprotonation of the pHP group for faster release, and it was accompanied by a distinct fluorescence color change upon photorelease. In vitro studies showed that the p‐hydroxyphenacyl–benzothiazole–chlorambucil conjugate presents excellent properties, such as real‐time monitoring, photoregulated drug delivery, and biocompatibility.     

Functionalization of Carbon Nanotubes with Well‐Defined Functional Polymers via Thiol‐Coupling Reaction

Summary: Thiol‐reactive‐functionality decorated multi‐walled carbon nanotubes (MWNTs) have been obtained. Trithiocarbonate‐ended poly(N‐(2‐hydroxypropyl)methacrylamide) (PHPMA) is prepared by reversible addition‐fragmentation chain transfer (RAFT) polymerization of N‐(2‐hydroxypropyl)methacrylamide (HPMA) using S‐1‐dodecyl‐S′‐(α,α′‐dimethyl‐α″‐acetic acid)trithiocarbonate as chain transfer agent, subsequently, thiol‐terminated PHPMA (PHPMA‐SH) is obtained by treating trithiocarbonate‐ended PHPMA with hexylamine. The PHPMA‐S‐S‐MWNT conjugate is formed by simply stirring the mixture of thiol‐reactive‐functionality decorated MWNTs with PHPMA‐SH in phosphate buffered saline by a thiol‐coupling reaction. FT‐IR, HRTEM, ¹H NMR, and TGA results show that this thiol‐coupling reaction is effective to produce aqueous soluble polymer–MWNT conjugates under mild conditions.

Thiol‐reactive‐functionality decorated multi‐walled carbon nanotubes are modified with thiol end‐capped polymers by a thiol‐coupling reaction.     

Direct UV‐Induced Functionalization of Surface Hydroxy Groups by Thiol–Ol Chemistry

A novel UV‐initiated surface modification method for the direct functionalization of surface hydroxy groups with thiol‐containing molecules (termed “thiol–ol” modification) is described. This method is based on the oxidative conjugation of thiols to hydroxy groups. We demonstrate that different thiol‐containing molecules, such as fluorophores, thiol‐terminated poly(ethylene glycol) (PEG‐SH), and a cysteine‐containing peptide, can be attached onto the surface of porous poly(2‐hydroxyethyl methacrylate‐co‐ethylene dimethacrylate). Direct functionalization of other hydroxy‐group‐bearing surfaces, fabrication of micropatterns, and double patterning have been also demonstrated using the thiol–ol method.     

Silver(I)‐N‐heterocyclic carbene complexes of bis‐imidazol‐2‐ylidenes having different aromatic‐spacers: synthesis,crystal structure,and in vitro antimicrobial and anticancer studies

A series of Ag(I) complexes ( 6 , 7 , 8 , 9 ) derived from imidazol‐2‐ylidenes was synthesized by reacting Ag₂O with an o‐, m‐, p‐xylyl or 1,3,5‐triazine‐linked imidazolium salts ( 1 , 2 , 3 , 4 ) and then characterizing these using various spectro‐analytical techniques. Additionally, triazine‐linked bis‐imidazolium salt 5 was characterized using the single‐crystal X‐ray diffraction method. Complexes 6–9 were formed from the N‐heterocyclic carbene ligand precursors 1–3 as PF₆^‐ salts in good yields. Conversely, salt 5 does not form Ag(I) complex even under various reaction conditions. Using ampicillin as a standard, complexes 6–9 were tested against bacteria strains Escherichia coli and Staphylococcus aureus as Gram‐negative and Gram‐positive bacteria, respectively, showing potent antimicrobial activities against the tested bacteria even at minimum inhibition concentration and bacterial concentration levels. Furthermore, the potential anticancer activities of the reported complexes were evaluated against the human colorectal cancer (HCT 116) cell lines, using 5‐fluorouracil as a standard drug. The highest anticancer activities were observed for complex 8 with an IC₅₀ value of 3.4 μm , whereas the lowest was observed for complex 9 with an IC₅₀ value of 18.1 μm . Copyright © 2013 John Wiley & Sons, Ltd.     

Drug Conjugation to Cyclic Peptide–Polymer Self‐Assembling Nanotubes

We show for the first time how polymeric nanotubes (NTs) based on self‐assembled conjugates of polymers and cyclic peptides can be used as an efficient drug carrier. RAPTA‐C, a ruthenium‐based anticancer drug, was conjugated to a statistical co‐polymer based on poly(2‐hydroxyethyl acrylate) (pHEA) and poly(2‐chloroethyl methacrylate) (pCEMA), which formed the shell of the NTs. Self‐assembly into nanotubes (length 200–500 nm) led to structures exhibiting high activity against cancer cells.     

Preliminary toxicological studies of selected water‐soluble polymer–platinum conjugates

The objective of this preliminary investigation of a number of water‐soluble carrier‐bound platinum(II) complexes for potential use in cancer chemotherapy was to assess the toxicological behavior of representative platinum coordination compounds anchored to, or incorporated into, polymeric carriers via polymer‐attached amine ligands. The conjugates included linear polyaspartamides (1–4, 6, 7), each composed of a major fraction of subunits featuring side‐chain‐attached tertiary amino groups as water‐solubilizing entities, and a minor fraction of subunits comprising the anchored platinum complexes, again as side‐chain components. Whereas in 1–4 the platinum atom was polymer‐bound through a single amino group, both 6 and 7 contained polymer‐attached cis‐diamine‐chelating ligands coordinating to the metal center. Also included in this study was a linear polyamidoamine (5), which contained a poly(ethylene oxide) segment in the backbone in addition to intrachain ethylenediamine segments acting as cis‐diamine chelating ligands for coordination to the platinum center. The compounds were injected as aqueous (phosphate‐buffered saline) solutions into the tail veins of CD‐1 mice (four to eight mice per conjugate), and the maximally tolerated dose was determined for each compound. For polyaspartamides 1–4 the dose levels ranged from about 25 mg Pt (kg body weight⁻¹) (in conjugate 4) to 500 mg Pt kg⁻¹ (in compound 1), the latter conjugate proving some 100‐fold less toxic than cisplatin (3–4 mg Pt kg⁻¹), which was included in this study for comparison. Low toxicity (tolerated dose 160 mg Pt kg⁻¹) was also observed for the intrachain cis‐diamineplatinum complex polymer (5). The polyaspartamide conjugates 6 and 7, on the other hand, both characterized by a cis‐diamineplatinum complex system in the side chain, were toxic even below the dose level of 20–25 mg Pt kg⁻¹. The preliminary findings of this study, while providing a basis for more extensive and broad‐based toxicological studies, will serve to direct and optimize structural conjugate designs in forthcoming synthetic programs. Copyright © 2000 John Wiley & Sons, Ltd.     

Core–Shell Hollow Microspheres of Magnetic Iron Oxide@Amorphous Calcium Phosphate: Synthesis Using Adenosine 5′‐Triphosphate and Application in pH‐Responsive Drug Delivery

Drug nanocarriers with magnetic targeting and pH‐responsive drug‐release behavior are promising for applications in controlled drug delivery. Magnetic iron oxides show excellent magnetism, but their application in drug delivery is limited by low drug‐loading capacity and poor control over drug release. Herein, core–shell hollow microspheres of magnetic iron oxide@amorphous calcium phosphate (MIO@ACP) were prepared and investigated as magnetic, pH‐responsive drug nanocarriers. Hollow microspheres of magnetic iron oxide (HMIOs) were prepared by etching solid MIO microspheres in hydrochloric acid/ethanol solution. After loading a drug into the HMIOs, the drug‐loaded HMIOs were coated with a protective layer of ACP by using adenosine 5′‐triphosphate (ATP) disodium salt (Na₂ATP) as stabilizer, and drug‐loaded core–shell hollow microspheres of MIO@ACP (HMIOs/drug/ACP) were obtained. The as‐prepared HMIOs/drug/ACP drug‐delivery system exhibits superparamagnetism and pH‐responsive drug‐release behavior. In a medium with pH 7.4, drug release was slow, but it was significantly accelerated at pH 4.5 due to dissolution of the ACP shell. Docetaxel‐loaded core–shell hollow microspheres of MIO@ACP exhibited high anticancer activity.     

Integrin‐Targeting Knottin Peptide–Drug Conjugates Are Potent Inhibitors of Tumor Cell Proliferation

Antibody–drug conjugates (ADCs) offer increased efficacy and reduced toxicity compared to systemic chemotherapy. Less attention has been paid to peptide–drug delivery, which has the potential for increased tumor penetration and facile synthesis. We report a knottin peptide–drug conjugate (KDC) and demonstrate that it can selectively deliver gemcitabine to malignant cells expressing tumor‐associated integrins. This KDC binds to tumor cells with low‐nanomolar affinity, is internalized by an integrin‐mediated process, releases its payload intracellularly, and is a highly potent inhibitor of brain, breast, ovarian, and pancreatic cancer cell lines. Notably, these features enable this KDC to bypass a gemcitabine‐resistance mechanism found in pancreatic cancer cells. This work expands the therapeutic relevance of knottin peptides to include targeted drug delivery, and further motivates efforts to expand the drug‐conjugate toolkit to include non‐antibody protein scaffolds.     

A Facial Synthesis and Anticancer Activity of (Z)‐2‐((5‐(4‐nitrobenzylidene)‐4‐oxo‐4,5‐dihydrothiazol‐2‐yl)amino)‐substituted Acid

In order to explore the anticancer and antimicrobial activity associated with the thiazole framework, we synthesized the new series (Z )‐2‐((5‐(4‐nitrobenzylidene)‐4‐oxo‐4,5‐dihydrothiazol‐2‐yl)amino)‐substituted acid derivatives 6a – l . All the synthesized compounds were evaluated for anticancer and antimicrobial activity in vitro. Among these, the compounds 6a , 6b, 6c , 6e , 6f , 6g , 6h , 6i , 6j , and 6k showed highest antibacterial and antifungal activity. The compound 6a exhibited significant antibacterial activity against Bacillus subtilis , whereas compound 6j displays significant antifungal activity against fungal strains, that is, A. oryzae . The in vitro anticancer studies revealed that 6e , 6g , 6h , 6k , and 6l are the most active compounds against MCF‐7 and BT‐474 human breast cancer cell lines, which can be regarded as the promising drug candidate for development of anticancer drugs.