Substituted 1,3,5-triazaadamantanes: biocompatible and degradable building blocks

1,4,6,10-Tetraazaadamantanes (TAADs) with N-amino groups: synthesis and formation of boron chelates and host–guest complexes

A synthetic route to 1,4,6,10-tetraazaadamantanes (TAADs) bearing free and protected amino groups at the bridge N-atoms has been developed via intramolecular cyclotrimerization of C=N units in the corresponding tris(hydrazonoalkyl)amines. In a similar fashion, unsymmetrically substituted TAADs having both amino and hydroxy groups at the bridge N-atoms were prepared via a hitherto unknown co-trimerization of oxime and hydrazone groups. The use of N-TAAD derivatives as potential ligands and receptors was showcased through forming boron chelates and host–guest complexes with water and simple alcohols.

Facile construction of the all-bridge-position-functionalized 2,4,6,8-tetraazaadamantane skeleton and conversion of its N-functionalities

An unusual protocol of a “one-pot” three-step strategy to build the 2,4,6,8-tetraazaadamantane skeleton was developed. 17 products were obtained in 19–46% yields, and the N-benzyl groups were transferred to nitroso, acetyl, benzoyl and nitro groups.

Biorenewable triblock copolymers consisting of l-lactide and ε-caprolactone for removing organic pollutants from water: a lifecycle neutral solution

Background

Current methods of removing organic pollutants from water are becoming ineffective as the world population increases. In this study, a series of biorenewable triblock copolymers with hydrophobic poly(ε-caprolactone) block and hydrophilic poly(l-lactide) blocks were synthesized and tested as agents to remove environmental pollutants from an aqueous solution. The percent of pollutant removed and equilibrium inclusion constants were calculated for the polymers. These values were compared to previously known removal agents for their effectiveness.

Results

Triblock copolymer samples removed over 70% of the polycyclic aromatic hydrocarbon (PAH) phenanthrene from an aqueous solution, with selectivity for the adsorption of phenanthrene over other PAHs tested. The inclusion constant was 7.4 × 10⁵ M⁻¹ and adsorption capacity was 5.8 × 10⁻⁷ mol phenanthrene/g polymer. Rose Bengal was used to further probe the nature of interactions between the copolymers and a small molecule guest. Solid samples of the block-poly(l-lactide)–block-poly(ε-caprolactone)–block-poly(l-lactide) (PLLA–PCL–PLLA) systems were found to rapidly remove over 90% of Rose Bengal from aqueous solution, resulting in a complete disappearance of the characteristic pink color. Solutions of the copolymers in dichloromethane also removed Rose Bengal from water with a similar level of efficiency. Large inclusion constant values were obtained, ranging from 1.0 × 10⁵ to 7.9 × 10⁵ M⁻¹, and the average adsorption capacity value of 6.2 × 10⁻⁷ mol/g polymer was determined. Aged polymer samples exhibited different adsorption characteristics and mechanistic theories for the removal of Rose Bengal were determined.

Conclusion

The triblock copolymer consisting of l-lactide and ε-caprolactone was effective in removing various organic pollutants in aqueous environments. It is a biorenewable material which leads to minimal waste production during its lifecycle. These polymers were in general more effective in removing organic pollutants than commercially available pollution removal systems.

Synthesis of 2-Azaadamantan-6-one: A Missing Isomer

2-Azaadamantan-6-one and its Boc and ethylene ketal derivatives were synthesized from 9-oxo endo-bicyclo[3.3.1]non-6-ene-3-carboxylic acid. Similarly, the Cbz, Boc, and ethylene ketal derivatives of 2-azaadamantan-4-one were synthesized from endo-bicyclo[3.3.1]non-6-ene-3-carboxylic acid. Key steps were Curtius rearrangements to form benzyl carbamates, followed by spontaneous intramolecular attack of the carbamate nitrogen on transient bromonium ion or epoxide intermediates to effect ring closure to azaadamantane intermediates. The reaction sequence leading to 2-azaadamantan-6-one is consistent with the formation of a transient tetracyclic keto aziridine intermediate.

Biodegradable dendrimers for drug delivery

Dendrimers, as a type of artificial polymers with unique structural features, have been extensively explored for their applications in biomedical fields, especially in drug delivery. However, one important concern about the most commonly used dendrimers exists - the nondegradability, which may cause side effects induced by the accumulation of synthetic polymers in cells or tissues. Therefore, biodegradable dendrimers incorporating biodegradability with merits of dendrimers such as well-defined architectures, copious internal cavities and surface functionalities, are much more promising for developing novel nontoxic drug carriers. Herein, we review the recent advances in design and synthesis of biodegradable dendrimers, as well as their applications in fabricating drug delivery systems, with the aim to provide researchers in the related fields a good understanding of biodegradable dendrimers for drug delivery.

A facile method to construct a 2,4,9-triazaadamantane skeleton and synthesize nitramine derivatives

An unusual protocol for a “one-pot” three-step reaction to build a 2,4,9-triazaadamantane skeleton from triallylcarbinol was developed.

Trigger chemistries for better industrial formulations

In recent years, innovations and consumer demands have led to increasingly complex liquid formulations. These growing complexities have provided industrial players and their customers access to new markets through product differentiation, improved performance, and compatibility/stability with other products. One strategy for enabling more complex formulations is the use of active encapsulation. When encapsulation is employed, strategies are required to effect the release of the active at the desired location and time of action. One particular route that has received significant academic research effort is the employment of triggers to induce active release upon a specific stimulus, though little has translated for industrial use to date. To address emerging industrial formulation needs, in this review, we discuss areas of trigger release chemistries and their applications specifically as relevant to industrial use. We focus the discussion on the use of heat, light, shear, and pH triggers as applied in several model polymeric systems for inducing active release. The goal is that through this review trends will emerge for how technologies can be better developed to maximize their value through industrial adaptation.

The Present and the Future of Degradable Dendrimers and Derivatives in Theranostics

Interest in dendrimer-based nanomedicines has been growing recently, as it is possible to precisely manipulate the molecular weight, chemical composition, and surface functionality of dendrimers, tuning their properties according to the desired biomedical application. However, one important concern about dendrimer-based therapeutics remains-the nondegradability under physiological conditions of the most commonly used dendrimers. Therefore, biodegradable dendrimers represent an attractive class of nanomaterials, since they present advantages over conventional nondegradable dendrimers regarding the release of the loaded molecules and the prevention of bioaccumulation of synthetic materials and subsequent cytotoxicity. Here, we present an overview of the state-of-the-art of the design of biodegradable dendritic structures, with particular focus on the hurdles regarding the use of these as vectors of drugs and nucleic acids, as well as macromolecular contrast agents.

Reduction-sensitive amphiphilic copolymers made via multi-component Passerini reaction for drug delivery

One-step synthesis of amphiphilic polymers containing disulfide bond within the hydrophobic backbone was demonstrated via multi-component Passerini reaction. The obtained polymer was self-assembled into micelles in aqueous solution. Curcumin (CUR), an effective and safe anticancer agent, which was limited by its water insolubility and poor bioavailability, was loaded into the micelles as a model drug. The nanoscale polymeric micelles were confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Faster intracellular CUR release was observed by confocal laser scanning microscopy (CLSM) in the HeLa cells pretreated with GSH than in the unpretreated ones. Micelles also loaded with NH2-BODIPY which was almost non-fluorescent and gave strong enhanced fluorescence under acid conditions. The phenomenon of the stronger enhanced fluorescence in the pretreated HeLa cells showed further that the obtained polymer was reduction-sensitive. In vitro MTT assays showed that the micelles were biocompatible and CUR-loaded micelles had higher cellular proliferation inhibition in contrast to free CUR toward HeLa cells. These results highlight the potential of using multi-component Passerini reaction to make functional copolymers as smart nanocarriers for drug delivery.

Clickable polyglycerol hyperbranched polymers and their application to gold nanoparticles and acid-labile nanocarriers

A one-step, large-scale preparation of alkyne-containing hyper-branched polyglycerols (HPG) is reported. The HPGs undergo click reactions to organic azides allowing a range of applications.

Tuning hydrogel properties and function using substituent effects

The physical properties and function of hydrogels are shown to depend on the substituents present in three novel 1,3,5-tri-azaadamantane (TAA) cross-linkers. Gel stiffness and degradation rate at varied pHs could be predictably tuned with the cross-linker substituents used to form the gel. Subsequently, protein release from the hydrogel were controlled with chemical structure of the cross-linker.

Photoresponsive crosslinked hyperbranched polyglycerols as smart nanocarriers for guest binding and controlled release

A convenient methodology for the synthesis of photolabile crosslinked hyperbranched polyglycerol nanocapsules is presented. These nanocarriers selectively and efficiently bind ionic guest molecules. The stability of the host-guest complexes formed depends on the counterion of the guest molecules. Moreover, the control over guest binding can be achieved by modification of the polymer building blocks, in particular the outer shell. In addition, photo-triggered degradation of the nanocarrier leads to efficient release of encapsulated guest molecules. This approach, using photolabile dendritic nanocarriers to bind and release guest molecules, is of particular relevance for biomedical applications where selective guest binding and controlled release are crucial.