Dynamic Titania Nanotube Surface Achieves UV-Triggered Charge Reversal and Enhances Cell Differentiation

Stimuli-responsive biomaterials supply a promising solution to adapt to the complex physiological environment for different biomedical applications. In this study, a dynamic UV-triggered pH-responsive biosurface was constructed on titania nanotubes (TNTs) by loading photoacid generators, diphenyliodonium chloride, into the nanotubes, and grafting 2,3-dimethyl maleic anhydride (DMMA)-modified hyperbranched poly(l-lysine) (HBPLL) onto the surface. The local acidity was dramatically enhanced by UV irradiation for only 30 s, leading to the dissociation of DMMA and thereby the transformation of surface chemistry from negatively charged caboxyl groups to positively charged amino groups. The TNTs-HBPLL-DMMA substrate could better promote proliferation and spreading of rat bone mesenchymal stem cells (rBMSCs) after UV irradiation. The osteogenic differentiation of rBMSCs was enhanced because of the charge reversal in combination with the titania-based substrates.

Protecting group-free radical decarboxylation of bile acids: Synthesis of novel steroidal substituted maleic anhydrides and maleimides and evaluation of their cytotoxicity on C6 rat glioma cells

We report the first Barton radical decarboxylation of unprotected bile acids via in situ irradiation of their thiohydroxamic esters in the presence of citraconic anhydride and citracoimide, leading to the synthesis a series of steroidal maleic anhydrides and maleimides as novel hybrid bile acids. The cytotoxic activities were evaluated on C6 rat glioma cells.

Peptide-functionalized ZCIS QDs as fluorescent nanoprobe for targeted HER2-positive breast cancer cells imaging

In this paper, the synthesis of alloyed CuInZnxS2+x quantum dots (ZCIS QDs), their transfer into aqueous solution via a polymer coating technique, and the use of these nanocrystals to selectively target HER2-positive cells, are reported. By optimizing first the ZnS shell deposition process onto the CuInS2 core, and next the encapsulation of the dots with the amphiphilic poly(maleic anhydride-alt-1-octadecene) (PMAO) polymer, water-dispersible ZCIS QDs were successfully prepared. The nanocrystals with a photoluminescence quantum yield of 35% were purified via centrifugation and ultracentrifugation and high quality nanoparticles with narrow size distributions and surface charges were obtained. After verifying the biocompatibility of PMO-coated ZCIS QDs, we coupled these nanocrystals with the LTVSPWY peptide and demonstrated via MTT assay that both bare and the peptide-linked QDs exhibit low cytotoxicity. The HER2-mediated delivery of the peptide-linked QDs was confirmed by confocal microscopy. This study indicates that as engineered QDs can efficiently be used as fluorescent nanoprobes for selective labelling of HER2-positive SKBR3 cancer cells.

Controlled release of doxorubicin loaded within magnetic thermo-responsive nanocarriers under magnetic and thermal actuation in a microfluidic channel

We report a procedure to grow thermo-responsive polymer shells at the surface of magnetic nanocarriers made of multiple iron oxide superparamagnetic nanoparticles embedded in poly(maleic anhydride-alt-1-ocatadecene) polymer nanobeads. Depending on the comonomers and on their relative composition, tunable phase transition temperatures in the range between 26 and 47 °C under physiological conditions could be achieved. Using a suitable microfluidic platform combining magnetic nanostructures and channels mimicking capillaries of the circulatory system, we demonstrate that thermo-responsive nanobeads are suitable for localized drug delivery with combined thermal and magnetic activation. Below the critical temperature nanobeads are stable in suspension, retain their cargo, and cannot be easily trapped by magnetic fields. Increasing the temperature above the critical temperature causes the aggregation of nanobeads, forming clusters with a magnetic moment high enough to permit their capture by suitable magnetic gradients in close proximity to the targeted zone. At the same time the polymer swelling activates drug release, with characteristic times on the order of one hour for flow rates of the same order as those of blood in capillaries.

Preparation and properties of invertase immobilized on a poly(maleic anhydride-hexen-1) membrane

Poly(maleic anhydride-alt-hexen-1)(poly(MA-alt-H-1)) has been synthesized by radical polymerization and characterized by DSC, FT-IR, acid number determination, viscometric and NMR methods. Data showed that the co-polymer is an alternating co-polymer whose composition does not depend on the monomer feed composition. Invertase was immobilized onto a poly(MA-alt-H-1) membrane via glutaraldehyde and bovine serum albumin. The Km value of poly(MA-alt-H-1)-invertase was approximately 4.4-fold higher than the free enzyme, indicating decreased affinity by the invertase for its substrate (sucrose), whereas Vmax was lower for the immobilized invertase. Immobilization improved the pH stability of the enzyme, as well as its temperature stability. Immobilized samples obtained were stable and could be used many times over a period of 2 months without considerable activity loss.

Synthesis and biological evaluation of dialkylsubstituted maleic anhydrides as novel inhibitors of Cdc25 dual specificity phosphatases

An efficient synthesis of dialkylsubstituted maleic anhydrides 1a-j is described. The inhibitory potential of these original anhydride derivatives was tested toward the three human isoforms A, B and C of dual specific phosphatases Cdc25. A micromolar range inhibition of Cdc25s was observed with the maleic anhydrides bearing simple alkyl side chains longer than C(9), to reach the optimal activity with a C(17) chain length.

pH-Responsive Poly(styrene-alt-maleic anhydride) Alkylamide Copolymers for Intracellular Drug Delivery

Many macromolecular therapeutics such as peptides, proteins, antisense oligodeoxynucleotides (ASODN), and short interfering RNA (siRNA) are active only in the cytoplasm or nucleus of targeted cells. Endocytosis is the primary route for cellular uptake of these molecules, which results in their accumulation in the endosomal-lysosomal trafficking pathway and loss of therapeutic activity. In this article, we describe the synthesis and pH-dependent membrane-destabilizing activity of a new "smart" polymer family that can be utilized to enhance the intracellular delivery of therapeutic macromolecules through the endosomal membrane barrier into the cytoplasm of targeted cells. These polymers are propylamine, butylamine, and pentylamine derivatives of poly(styrene-alt-maleic anhydride) (PSMA) copolymers. The PSMA-alkylamide derivatives are hydrophilic and membrane-inactive at physiological pH; however, they become hydrophobic and membrane-disruptive in response to endosomal pH values as measured by their hemolytic activity. Results show that the pH-dependent membrane-destabilizing activity of PSMA derivatives can be controlled by varying the length of the alkylamine group, the degree of modification of the copolymer, and the molecular weight of the PSMA copolymer backbone. Butylamine and pentylamine derivatives of PSMA copolymers exhibited more than 80% hemolysis at endosomal pH values, which suggests their potential as a platform of "smart" polymeric carriers for enhanced cytoplasmic delivery of a variety of therapeutic macromolecules.

Shell-crosslinked nanostructures from amphiphilic AB and ABA block copolymers of styrene-alt-(maleic anhydride) and styrene: polymerization, assembly and stabilization in one pot

Shell-crosslinked nanostructures having unusual rosette morphologies have been produced by a simple process from styrene and maleic anhydride.

Studies on the Total Synthesis of (−)-CP-263,114

Alkoxyl radicals have a wide range of applications in organic synthesis due to their remarkable chemical properties in molecular transformation. The present study shows two types of alkoxyl radicals (primary vs tertiary) to selectively undergo dehydrogenation and beta-scission to give rise to key structural elements of (-)-CP-263,114 (1). By alkoxyl radical transformation followed by installation of the C19-C25 (CP numbering) side chain and the bridged bisacetal unit, the functionalized CP precursor 2 was obtained.

Effect of molar mass of an experimental primer on shear bond strength to dentin

A novel oligomer was synthesized in different molecular masses and used as a primer in dentin bonding. The hypothesis was that an intermediate molecular mass would optimize the conflicting needs for diffusion into etched dentin (low M(w)) and high mechanical properties (high M(w)). The initial oligomer synthesized was tert butylmethacrylate-co-maleic anhydride, which was further reacted to add hyrdoxyethyl methacrylate (HEMA) across the anhydride. The oligomer was synthesized in a series of molecular masses from approximately 800-6000 amu. The oligomer with an average M(w) of approximately 1000 amu provided the highest bond strength (16 MPa), with both lower and higher molar mass oligomers producing lower bond strengths. A polynomial model was fitted to the data with an R(2) = 0.606, while a linear model only had an R(2) = 0.534. This implies that the graph of molar mass to bond strength has a maximum in the range of molar masses examined, and that an optimum molar mass can be found between 800 and 6000 amu.

Development of New Synthetic Methods and Their Application to Synthesis of Useful Compounds

Development of novel synthetic methodologies and their application to synthesis of natural products are described. The first topic is about an extension of the scope of our indole synthesis by radical cyclization of o-alkenylphenyl isocyanides. By utilizing this methodology and nitrogenzenesulfonamide chemistry, an efficient total synthesis of hexacyclic aspidosperma indole alkaloid, aspidophytine, was accomplished. As the second generation indole synthesis, we then developed the method by radical cyclization of o-akenylthioanilides. Synthetic utility of this method was fully demonstrated by a total synthesis of iboga alkaloid, catharanthine. Furthermore, a total synthesis of vinca alkaloid, vinblastine through a practical synthesis of vindoline was achieved, in which the stereochemistry of the crucial coupling reaction of two indole fragments could be completely controlled. In addition to the indole chemistry, exceptionally mild transformations of thiol esters to ketones and alkenyl ketones have been developed. Examples of application of the protocols for the synthesis of natural products are also described.

A new synthetic route to phomoidride B and its derivatives

We have developed a new synthetic route to phomoidride B, which could also be applied to the synthesis of phomoidride B derivatives using Pd-catalyzed coupling reaction of a thiolester with an organozinc reagent. In addition, direct construction of the maleic anhydride moiety has been achieved by a Pd-catalyzed carbonylation reaction.

An approach to the synthesis of the phomoidrides

The phomoidrides are a structurally fascinating family of natural products which possess moderate inhibitory activity against Ras farnesyl transferase and squalene synthase. Since their discovery they have inspired a great deal of attention from synthetic chemists. Our own work, culminating in an efficient synthesis of the fully elaborated tetracyclic core of phomoidrides B and D, is described herein. The synthesis relies on a late stage tandem reaction involving a novel carbonylation reaction that delivers the strained bicyclic pseudoester system, which strain in turn drives a highly efficient silyloxy-Cope rearrangement that delivers the tetracyclic core of phomoidrides B and D. Several examples of this powerful tandem reaction are presented that document its tolerance of significant structural variation. The application of this methodology to the synthesis of a phomoidride D precursor lacking only the maleic anhydride is described, and the prospects for the completion of a total synthesis are discussed.

The CP molecule labyrinth: a paradigm of how endeavors in total synthesis lead to discoveries and inventions in organic synthesis

Imagine an artist carving a sculpture from a marble slab and finding gold nuggets in the process. This thought is not a far-fetched description of the work of a synthetic chemist pursuing the total synthesis of a natural product. At the end of the day, he or she will be judged by the artistry of the final work and the weight of the gold discovered in the process. However, as colorful as this description of total synthesis may be, it does not entirely capture the essence of the endeavor, for there is much more to be told, especially with regard to the contrast of frustrating failures and exhilarating moments of discovery. To fully appreciate the often Herculean nature of the task and the rewards that accompany it, one must sense the details of the enterprise behind the scenes. A more vivid description of total synthesis as a struggle against a tough opponent is perhaps appropriate to dramatize these elements of the experience. In this article we describe one such endeavor of total synthesis which, in addition to reaching the target molecule, resulted in a wealth of new synthetic strategies and technologies for chemical synthesis. The total synthesis of the CP molecules is compared to Theseus' most celebrated athlos (Greek for exploit, accomplishment): the conquest of the dreaded Minotaur, which he accomplished through brilliance, skill, and bravery having traversed the famous labyrinth with the help of Ariadne. This story from Greek mythology comes alive in modern synthetic expeditions toward natural products as exemplified by the total synthesis of the CP molecules which serve as a paradigm for modern total synthesis endeavors, where the objectives are discovery and invention in the broader sense of organic synthesis.

Progress toward a biomimetic synthesis of phomoidride B

[reaction: see text]. An intramolecular cyclization strategy for effecting a biomimetic synthesis of the core structure of the fungal secondary metabolites phomoidrides A and B is described. The cyclization substrate 20 is prepared in eight steps from dibromide 10. Treatment of 20 with triethylamine in acetonitrile results in a rapid cyclization to give 21 and 22 in good yield.

Synthetic study on CP-263,114 (phomoidride B) by SET-mediated fragmentation

Assembly of the highly functionalized carbocyclic core of CP-263,114 has been accomplished by using radical-mediated fragmentation with lithium naphthalenide as a key step.

Total synthesis of the CP-molecules (CP-263,114 and CP-225,917, phomoidrides B and A). 1. Racemic and asymmetric synthesis of bicyclo[4.3.1] key building blocks

A brief introduction into the chemistry of the CP-molecules is followed by first-generation synthetic sequences toward key building blocks for their total synthesis. Processes for both racemic and enantiomerically enriched bicyclo[4.3.1] ketone 6 or its equivalent are described, and the absolute stereochemistries of the optically enriched intermediates are determined. The efficient route developed to racemic 6 and the ready access to both enantiomers of key building blocks provided the opportunity for the total synthesis of the CP-molecules and determination of their absolute stereochemistry.

Total synthesis of the CP-molecules (CP-263,114 and CP-225,917, phomoidrides B and A). 3. Completion and synthesis of advanced analogues

The completion of the total syntheses of the CP-molecules is reported. Several strategies and tactics, including the use of amide-based protecting groups for the homologated C-29 carboxylic acid and the use of an internal pyran protecting group scheme, are discussed. The endeavors leading to the design of new methods for the homologation of hindered aldehydes and to the isolation of a polycyclic byproduct (23), which inspired the development of a new series of reactions based on iodine(V) reagents, are described. In addition, the discovery and development of the LiOH-mediated conversion of CP-263,114 (1) to CP-225,917 (2) is described, and a mechanistic rationale is presented. Finally, a synthetic route to complex analogues of the CP-molecules harboring a maleimide moiety in place of the maleic anhydride is presented.

Total synthesis of the CP-molecules (CP-263,114 and CP-225,917, phomoidrides B and A). 2. Model studies for the construction of key structural elements and first-generation strategy

Crucial model synthetic and mechanistic studies directed toward the development of methodology for the construction of the maleic anhydride moiety of the CP-molecules are described. Studies directed toward the stereoselective attachment of the upper side chain, culminating in the discovery of long-range stereochemical control, are also discussed. In addition, a first-generation strategy toward the CP-molecules, establishing key intermediate 5 as a "beachhead" from which all future operations would diverge, is also presented. Although this first-generation strategy failed to yield the target molecules, the endeavor laid the important groundwork for the next-generation drives toward the CP-molecules.

Application of Lewis acid catalyzed tropone [6+4] cycloadditions to the synthesis of the core of CP-225,917

The carbocyclic core of CP-225,917 and CP-263,114 is accessible through the [6+4] cycloaddition of a tropone with a 2-substituted cyclopentadiene. Examination of this reaction has revealed for the first time that this cycloaddition process is catalyzed by Lewis acids, including lanthanide triflates. Cycloadditions of several mono-, di-, and trisubstituted tropones with 2-silyloxycyclopentadienes using ZnCl(2) catalysis are found to proceed in good yield and, in many cases, with excellent diastereoselectivity. Subsequent transformation to the core of the CP-molecules involves a site-selective Baeyer-Villiger oxidation of a tricyclic diketone, followed by a syn-elimination process. [reaction: see text]

An expeditious approach toward the total synthesis of CP-263,114

[reaction: see text] Assembly of the carbocyclic core of CP-263,114 has been accomplished efficiently and in high yield. Key steps include a phenolic oxidation/intramolecular Diels-Alder sequence, tandem radical cyclization, and the late-stage fragmentation of a densely functionalized isotwistane skeleton.

Evolution of a synthetic approach to CP-263,114

[structure: see text] Three different approaches to the carbocyclic core of CP-263,114 are presented that illustrate a strategic evolution from an oxy-Cope rearrangement to variants of the Wharton fragmentation.

Asymmetric synthesis of the core structure of (-)-CP-263,114

The enantioselective construction of a fully functionalized core structure of (-)-CP-263,114 (1), containing most of the required functionality for total synthesis, was conducted through sequential radical fragmentation-reductive olefination.

Stereoconvergent palladium-catalyzed carbonylation of both E and Z isomers of a 2-trifloxy-1,3-butadiene

[reaction: see text] Carbonylation of the illustrated Z-tetrasubstituted enol triflate followed by tandem silyloxy-Cope rearrangement leads to the CP-263, 114 core ring system with the all-carbon quaternary stereocenter intact in 46% yield. Subjection of the corresponding E isomer to the same conditions gives the same product in 56% yield. This observation is explained by a mechanism involving isomerization of a pi-allyl palladium species involving an allenic intermediate.

An exploratory study of type II [3 + 4] cycloadditions between vinylcarbenoids and dienes

The intramolecular type II [3 + 4] cycloaddition between vinylcarbenoids and furans is a practical method for the construction of 5-oxo-10-oxatricyclo[6.2.1.0(4,9)]undeca-3, 8(11)-dienes, containing two anti-Bredt double bonds. These tricyclic systems are well functionalized for eventual elaboration to the natural product CP-263,114. The rhodium-stabilized vinylcarbenoids are generated by dirhodium tetracarboxylate catalyzed decomposition of vinyldiazoacetates. The [3 + 4] cycloaddition is generally considered to occur by a tandem cyclopropanation/Cope rearrangement, although evidence is presented that with these substrates the [3 + 4] cycloaddition may occur in a concerted manner.

Novel strategies to construct the gamma-hydroxy lactone moiety of the CP molecules. Synthesis of the CP-225,917 core skeleton

[formula: see text] The array of challenging structural lineaments embodied in the CP molecules (1 and 2, Figure 1) offers synthetic chemists uncharted realms of exploration and discovery. In this communication, we focus on the chemical hurdies posed by the gamma-hydroxy lactone moiety of these exciting targets. Thus, the examination of the general reactivity of these systems, the development of a novel tandem oxidation sequence to construct the gamma-hydroxy lactone moiety, and the successful construction of the complete polycyclic core of 2 (compound 28, Scheme 5) is enumerated within.

Polyethylene glycol derivative-modified cholesterol oxidase soluble and active in benzene

Cholesterol oxidase from Nocardia sp. was modified with a synthetic copolymer of polyoxyethylene allylmethyldiether (PEG) and maleic acid anhydride (MA anhydride), poly(PEG-MA anhydride). The modified cholesterol oxidase, in which 64% of the amino groups in the protein molecule were coupled to poly(PEG-MA), was soluble in organic solvents and catalyzed the oxidation reaction of cholesterol in benzene to form 4-cholesten-3-one with the enzymic activity of 0.6 mumol/min/mg protein. Using the modified cholesterol oxidase together with polyethylene glycol-modified peroxidase, coupled reactions shown below took place in Cholesterol + O2----4-Cholesten-3-one + H2O2 H2O2 + o-Phenylenediamine----H2O + Oxidized o-Phenylenediamine transparent benzene solution, not in an emulsified system. The oxidation of cholesterol was directly determined in benzene by measuring the absorbance of oxidized o-phenylenediamine at 490 nm.