Use of polymers as protecting groups in organic synthesis. III. Selective functionalization of polyhydroxy alcohols

Insoluble polymers containing trityl chloride residues were used to block one primary alcohol functional group of several polyhydroxy alcohols. After protecting the remaining hydroxyl groups by benzoylation, the ether linkage between the polymer and the protected alcohol was cleaved in acidic medium. Depending on the reaction conditions and the nature of the starting alcohol, several alcohols or bromides in which only one of the two primary hydroxyls had been esterified, were obtained. In some cases benzoyl migrations were observed. The trityl chloride polymers could be regenerated in one step without degradation or appreciable loss of activity.

A Novel Strategy for Encapsulation and Release of Proteins:  Hydrogels and Microgels with Acid-Labile Acetal Cross-Linkers

A new acid-labile acetal cross-linker was synthesized and used to prepare protein-loaded hydrogels and microgels. This cross-linker undergoes an acid-catalyzed degradation with a half-life of 5.5 min at pH 5.0 and 24 h at pH 7.4. Protein-loaded hydrogels were synthesized with this cross-linker, and their release profiles were measured as a function of pH. Hydrogels made with the acetal cross-linker release their contents in a pH-dependent manner. The acetal cross-linker was also used to synthesize microgels with sizes between 1 and 10 mum, a range suitable for phagocytosis. The unique acid sensitivity of the acetal cross-linker should make it a useful synthetic intermediate in the design of acid-sensitive drug or gene delivery systems.

Synthese par reaction de diphenylamine avec des iodures d'aryle en presence de K 2 CO 3 -18-crown-6 dans le dichloro-1,2 benzene

Synthesis and properties of novel linear-dendritic block copolymers. Reactivity of dendritic macromolecules toward linear polymers

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis and properties of novel linear-dendritic block copolymers. Reactivity of dendritic macromolecules toward linear polymersIvan Gitsov, Karen L. Wooley, Craig J. Hawker, Pavlina T. Ivanova, and Jean M. J. FrechetCite this: Macromolecules 1993, 26, 21, 5621–5627Publication Date (Print):October 1, 1993Publication History Published online1 May 2002Published inissue 1 October 1993https://pubs.acs.org/doi/10.1021/ma00073a014https://doi.org/10.1021/ma00073a014research-articleACS PublicationsRequest reuse permissionsArticle Views830Altmetric-Citations162LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

Dendritic Encapsulation of Function: Applying Nature's Site Isolation Principle from Biomimetics to Materials Science

The convergence of our understanding of structure-property relationships for selected biological macromolecules and our increased ability to prepare large synthetic macromolecules with a structural precision that approaches that of proteins have spawned a new area of research where chemistry and materials science join with biology. While evolution has enabled nature to perfect processes involving energy transfer or catalysis by incorporating functions such as self-replication and repair, synthetic macromolecules still depend on our synthetic skills and abilities to mesh structure and function in our designs. Clearly, we can take advantage of our understanding of natural systems to mimic the structural features that lead to optimized function. For example, numerous biological systems make use of the concept of site isolation whereby an active center or catalytic site is encapsulated, frequently within a protein, to afford properties that would not be encountered in the bulk state. The ability of the dendritic shell to encapsulate functional core moieties and to create specific site-isolated nanoenvironments, and thereby affect molecular properties, has been explored. By utilizing the distinct properties of the dendrimer architecture active sites that have either photophysical, photochemical, electrochemical, or catalytic functions have been placed at the core. Applying the general concept of site isolation to problems in materials research is likely to prove extremely fruitful in the long term, with short-term applications in areas such as the construction of improved optoelectronic devices. This review focuses on the evolution of a natural design principle that contributes to bridging the gap between biology and materials science. The recent progress in the synthesis of dendrimer-encapsulated molecules and their study by a variety of techniques is discussed. These investigations have implications that range from the preliminary design of artificial enzymes, catalysts, or light-harvesting systems to the construction of insulated molecular wires, light-emitting diodes, and fiber optics.

Use of Polymers as Protecting Groups in Organic Synthesis. VII. Preparation of Monobenzoates of Acyclic Triols

Abstract Crosslinked resins containing styrylboronic acid units were used in the protection of 1,2 and 1,3‐diol groupings with several acyclic triols. With 1,2,3‐propanetriol, a five‐membered ring boronate was formed almost exclusively while with 1, 2, 4‐butanetriol a six‐membered ring boronate predominated. The fully recyclable polymer could be used in a fast and efficient synthesis of monobenzoyl derivatives of triols. Macroreticular and 1% crosslinked solvent‐swellable resins were tested and the latter were found to perform better on repeated use.

Resist system based on the cationic photocrosslinking of poly(4‐hydroxystyrene) and polyfunctional electrophiles

Abstract New resist systems based on acid‐catalyzed, electrophilic aromatic substitution are described. These new resists show high sensitivity to deep UV and E‐beam radiation with values approaching 2 mJ/cm 2 and 2 μC/cm 2 , respectively. The resists are based on a three component system consisting of poly(4‐hydroxystyrene), a polyfunctional, low molecular weight, latent electrophile, and a photoactive onium salt used as an acid generator. Irradiation of the resist film produces a latent image of acid dispersed in the matrix. During the postbaking step the photo‐generated acid reacts with the latent polyfunctional electrophile and releases a reactive carbocationic intermediate with concomitant liberation of acetic acid. The carbocationic intermediate then reacts with neighboring phenolic moieties in a crosslinking reaction. The substitution reaction liberates a proton, making the process catalytic in nature, thus incorporating the concept of chemical amplification. These highly sensitive materials can be used as nonswelling negative multipurpose resists that function in deep‐UV, x‐ray or E‐beam modes. © 1993 John Wiley & Sons, Inc.

Combinatorial Approaches to Recognition of Chirality: Preparation and Use of Materials for the Separation of Enantiomers

Abstract For Abstract see ChemInform Abstract in Full Text.

Polymeric Reagents.II. Synthesis and Applications of Crosslinked Poly(vinylpyridinium Hydrobromide Perbromide) Resins

Abstract Crosslinked bead polymers containing vinylpyridine units were prepared by pearl copolymerization of monomer mixtures containing various percentagesof 4-vinylpyridine, styrene, and di-vinylbenzene. The polymers were functionalized by reaction with hydrogen bromide and bromine, and the resulting poly-(vinylpyridinium hydrobromide perbromide) resins, which were stable for long periods of time, were used to brominate a number of alkenes and ketones. In most cases, the brominated products were obtained in excellent yields and could be separated from the polymeric by-product by a simple filtration. The polymeric reagent could be fully regenerated after use without loss of activity.

Synthesis of new dialkylaminopyridine acylation catalysts and their attachment to insoluble polymer supports

High molecular weight polymers (> 20 000 Da) have been widely used as soluble drug carriers to improve drug targeting and therapeutic efficacy. Dendritic polymers are exceptional candidates for the preparation of near monodisperse drug carriers due to their well-defined structure, multivalency, and flexibility for tailored functionalization. We evaluated various dendritic architectures composed of a polyester dendritic scaffold based on the monomer unit 2,2-bis(hydroxymethyl)propanoic acid for their suitability as drug carriers both in vitro and in vivo. These systems are both water soluble and nontoxic. In addition, the potent anticancer drug, doxorubicin, was covalently bound via a hydrazone linkage to a high molecular weight 3-arm poly(ethylene oxide)-dendrimer hybrid. Drug release was a function of pH, and the release rate was more rapid at pH < 6. The cytotoxicity of the DOX-polymer conjugate measured on multiple cancer lines in vitro was reduced but not eliminated, indicating that some active doxorubicin was released from the drug polymer conjugate under physiological conditions. Furthermore, biodistribution experiments show little accumulation of the DOX-polymer conjugate in vital organs, and the serum half-life of doxorubicin attached to an appropriate high molecular weight polymer has been significantly increased when compared to the free drug. Thus, this new macromolecular system exhibits promising characteristics for the development of new polymeric drug carriers.

ChemInform Abstract: USE OF POLYMERS AS PROTECTING GROUPS IN ORGANIC SYNTHESIS. III. SELECTIVE FUNCTIONALIZATION OF POLYHYDROXY ALCOHOLS

Abstract Unlösliche Polymere (II) mit Trityl‐ (Tr)chloridresten werden zur Blockierung einer prim. Alkoholfunktion von Polyalkoholen wie (I) und (VII) eingesetzt; nach Schutz der restlichen OH‐Gruppen durch Benzoylierung [‐ (IIIa)‐(IIIc) bzw. (VIIIa) [ im Gemisch mit (VIIIb)], (VIIIc)] wird die Ätherbindung zwischen Polymer und geschütztem Alkohol in saurem Medium gespalten; Mit Trifluoressigsäure (TF A) entstehen dabei die Verbindungen (IV) [daneben die Trifluoracetate (V), die mit wäßrigem Bicarbonat in (IV) übergefuhrt werden können]; die Verbindungen (IVa) werden in guter Ausbeute auch aus (IIIa) mit HBr erhalten.

Since their introduction in 1985 by Tomalia et al. (1) and Newkome et al. (2), dendrimers have attracted much attention because of their fascinating structure and unique properties (3, 4). Dendrimers are globular, size monodisperse macromolecules in which all bonds emerge radially from a central focal point or core with a regular branching pattern and with repeat units that each contribute a branch point. Not all regularly branched molecules are dendrimers because properties of the dendritic state (4), such as core encapsulation (5, 6) and unusually low intrinsic viscosity in solution (7), are reached only when globularity is achieved at a certain generation or size threshold. Therefore, many low-generation dendrons or the early cascade molecules of Vogtle and coworkers (8) are too small to exhibit the properties of dendrimers, but they are frequently used as branched oligomeric building blocks in their construction, and have a size relationship to dendrimers somewhat akin to that between oligomers and polymers.

Grafted Macroporous Polymer Monolithic Disks:  A New Format of Scavengers for Solution-Phase Combinatorial Chemistry

Polyethylene encased porous poly(chloromethylstyrene-co-divinylbenzene) disks have been prepared by polymerization in a cylindrical glass mold and cut to a disk format. Following attachment of a free radical azo initiator 4,4'-azobis(4-cyanovaleric acid) to available functionalities at the surface of the pores, the polymerization of 2-vinyl-4,4-dimethylazlactone was initiated from the surface. To avoid an undesirable increase in flow resistance and to improve the yield of grafting, divinylbenzene was added to the polymerization mixture in order to form a layer of swellable reactive polymer gel within the pores. The use of these disks as scavenging filters to remove various amines from solutions in flow-through operations was demonstrated by effective removal of amines in a very short period of time from their solutions in a variety of solvents, even including alcohols and water.