Facile synthesis of dopa‐functional polycarbonates via thiol‐Ene‐coupling chemistry towards self‐healing gels

Since extraction of the naturally occurring mussel‐foot proteins is expensive and time‐consuming, routes towards synthetic analogues are continuously being explored. Often, these methods involve several protection and deprotection steps, making the synthesis of synthetic analogues time‐consuming and expensive as well. Herein, we show that UV‐initiated thiol‐ene coupling between a thiol‐functional dopamine derivative and an allyl‐functional aliphatic polycarbonate can be used as a fast and facile route to dopa‐functional materials. Different thiol‐to‐allyl ratios and irradiation protocols were used and it was found that nearly 50% of the allyl groups could be functionalized with dopa within short reaction times, without the need of protecting the catechol. It is also demonstrated herein that the dopa‐functional polymers can be used to form self‐healing gels through complexation with Fe³⁺ ions at increased pH. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2370–2378     

Synthesis and UCST‐type phase behavior of polypeptide with alkyl side‐chains in alcohol or ethanol/water solvent mixtures

A series of thermoresponsive polypeptides bearing 1‐butyl, 1‐hexyl, or 1‐dodecyl side‐chains (i.e., 6a ‐ 6c ) were synthesized by copper‐mediated 1,3‐dipolar cycloaddition with high grafting efficiency (>95%) between side‐chain “clickable” polypeptide, namely poly(γ‐4‐(propargoxycarbonyl)benzyl‐_L‐glutamate) ( 5 ) and 1‐azidoalkanes. 5 with different degree of polymerization (DP = 48–86) were prepared from triethylamine initiated ring‐opening polymerization of γ‐4‐(propargoxycarbonyl)benzyl‐_L‐glutamic acid based N‐carboxyanhydride ( 4 ). ¹H NMR, FTIR, and GPC results revealed the successful preparation of the resulting polypeptides. 6a ‐ 6c showed reversible UCST‐type phase behaviors in methanol, ethanol, and ethanol/water solvent mixtures depending on the polymer main‐chain length, alkyl side‐chain length, weight percentage of ethanol (f_w) in the binary solvent, and so forth. FTIR analysis revealed the presence of the van der Waals interaction between the alkyl pendants of polypeptides and alkyl groups of alcoholic solvents. Variable‐temperature UV‐vis spectroscopy revealed that the UCST‐type phase transition temperature (T_pt) increased as polymer main‐chain length or concentration increased. In ethanol/water solvent mixtures, polypeptide with short alkyl pendant (i.e., 1‐butyl group) and short main‐chain length (DP = 41) showed the widest f_w range and T_pts in the range of 61.0–71.1 °C. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3425–3435     

Rhodium(II)‐Catalyzed Annulation of Azavinyl Carbenes Through Ring‐Expansion of 1,3,5‐Trioxane: Rapid Access to Nine‐Membered 1,3,5,7‐Trioxazonines

The rhodium(II)‐catalyzed denitrogenative coupling of N‐alkylsulfonyl 1,2,3‐triazoles with 1,3,5‐trioxane led to nine‐membered‐ringed trioxazonines in moderate‐to‐good yields. 1,3,5‐Trioxane, acting as an oxygen nucleophile, reacted with the α‐aza‐vinylcarbene intermediate, giving rise to ylide formation, which was probably the key step in the reaction. Triazoles that contained aryl substituents with various electronic and steric features on the C4 carbon atom were well‐tolerated. The synthesis of trioxazonine derivatives was achieved through a one‐pot, two‐step procedure from 1‐mesylazide and a terminal alkyne by combining Cu^I‐catalyzed 1,3‐dipolar cycloaddition and rhodium‐catalyzed transformations.     

Efficient Regioselective Ring Opening of Activated Aziridine-2-Carboxylates with [18F]Fluoride

Aziridines can undergo a range of ring-opening reactions with nucleophiles. The regio- and stereochemistry of the products depend on the substituents on the aziridine. Aziridine ring-opening reactions have rarely been used in radiosynthesis. Herein we report the ring opening of activated aziridine-2-carboxylates with [¹⁸F]fluoride. The aziridine was activated for nucleophilic attack by substitution of various groups on the aziridine nitrogen atom. Fluorine-18 radiolabelling was followed by ester hydrolysis and removal of the activation group. Totally regioselective ring opening and subsequent deprotection was achieved with tert-butyloxycarbonyl- and carboxybenzyl-activated aziridines to give α-[¹⁸F]fluoro-β-alanine in good radiochemical yield.     

Advanced Developments in Cyclic Polymers: Synthesis,Applications, and Perspectives

Due to the topological effect, cyclic polymers demonstrate different and unique physical and biological properties in comparison with linear counterparts having the same molecular-weight range. With advanced synthetic and analytic technologies, cyclic polymers with different topologies, e.g. multicyclic polymers, have been reported and well characterized. For example, various cyclic DNA and related structures, such as cyclic duplexes, have been prepared conveniently by click chemistry. These types of DNA have increased resistance to enzymatic degradation and have high thermodynamic stability, and thus, have potential therapeutic applications. In addition, cyclic polymers have also been used to prepare organic–inorganic hybrids for applications in catalysis, e.g. catalyst supports. Due to developments in synthetic technology, highly pure cyclic polymers could now be produced in large scale. Therefore, we anticipate discovering more applications in the near future. Despite their promise, cyclic polymers are still less explored than linear polymers like polyolefins and polycarbonates, which are widely used in daily life. Some critical issues, including controlling the molecular weight and finding suitable applications, remain big challenges in the cyclic-polymer field. This review briefly summarizes the commonly used synthetic methodologies and focuses more on the attractive functional materials and their biological properties and potential applications.