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1. Chemical synthesis of perfectly isotactic and high melting bacterial poly(3-hydroxybutyrate) from bio-sourced racemic cyclic diolide

   https://doi.org/10.1038/s41467-018-04734-3  

   Tang, Xiaoyan; Chen, Eugene Y. -X. (June 2018, Nature Communications)

   Abstract Bacterial poly(3-hydroxybutyrate) (P3HB) is a perfectly isotactic, crystalline material possessing properties suitable for substituting petroleum plastics, but high costs and low volumes of its production are impractical for commodity applications. The chemical synthesis of P3HB via ring-opening polymerization (ROP) of racemicβ-butyrolactone has attracted intensive efforts since the 1960s, but not yet produced P3HB with high isotacticity and molecular weight. Here, we report a route utilizing racemic cyclic diolide (rac-DL) derived from bio-sourced succinate. With stereoselective racemic catalysts, the ROP ofrac-DL under ambient conditions produces rapidly P3HB with perfect isotacticity ([mm] > 99%), high melting temperature (T_m = 171 °C), and high molecular weight (M_n = 1.54 × 10⁵ g mol⁻¹,Đ = 1.01). With enantiomeric catalysts, kinetic resolution polymerizations ofrac-DL automatically stops at 50% conversion and yields enantiopure (R,R)-DL and (S,S)-DL with >99%e.e. and the corresponding poly[(S)-3HB] and poly[(R)-3HB] with highT_m = 175 °C. 

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2. Catalyst‐Sidearm‐Induced Stereoselectivity Switching in Polymerization of a Racemic Lactone for Stereocomplexed Crystalline Polymer with a Circular Life Cycle

   https://doi.org/10.1002/anie.201813006  

   Zhu, Jian‐Bo; Chen, Eugene Y. ‐X. (December 2018, Angewandte Chemie International Edition)

   Abstract Construction of robust, stereocomplexed (sc) crystalline material, based on a recently discovered infinitely recyclable polymer system, requires blending of enantiomeric polymer chains produced from respective enantiopure, fused six‐five bicyclic lactones. Herein, the stereoselective polymerization of the racemic monomer by yttrium catalysts bearing tetradentate ligands is reported, where the tethered donor sidearm switches the heteroselectivity of the catalyst to isoselectivity when it is changed from the β‐OMe to β‐NMe₂sidearm. The latter catalyst produces an isotactic stereoblock polymer (P_mup to 0.95) that forms the crystalline sc‐material with aT_mof up to 171 °C. This sc‐material can be fully depolymerized back to rac‐monomer in a quantitative yield and purity, thus establishing its circular life cycle. 

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3. Biodegradable Polyhydroxyalkanoates by Stereoselective Copolymerization of Racemic Diolides: Stereocontrol and Polyolefin‐Like Properties

   https://doi.org/10.1002/ange.201916415  

   Tang, Xiaoyan; Westlie, Andrea H.; Caporaso, Lucia; Cavallo, Luigi; Falivene, Laura; Chen, Eugene Y. ‐X. (March 2020, Angewandte Chemie)

   Abstract Bacterial polyhydroxyalkanoates (PHAs) are a unique class of biodegradable polymers because of their biodegradability in ambient environments and structural diversity enabled by side‐chain groups. However, the biosynthesis of PHAs is slow and expensive, limiting their broader applications as commodity plastics. To overcome such limitation, the catalyzed chemical synthesis of bacterial PHAs has been developed, using the metal‐catalyzed stereoselective ring‐opening (co)polymerization of racemic cyclic diolides (rac‐8DL^R, R=alkyl group). In this combined experimental and computational study, polymerization kinetics, stereocontrol, copolymerization characteristics, and the properties of the resulting PHAs have been examined. Most notably, stereoselective copolymerizations ofrac‐8DL^Mewithrac‐8DL^R(R=Et, Bu) have yielded high‐molecular‐weight, crystalline isotactic PHA copolymers that are hard, ductile, and tough plastics, and exhibit polyolefin‐like thermal and mechanical properties. 

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4. Chemical synthesis of the organoarsenical antibiotic arsinothricin

   https://doi.org/10.1039/d1ra06770b  

   Howlader, A. Hasan; Suzol, Sazzad H.; Nadar, Venkadesh Sarkarai; Galván, Adriana Emilce; Nedovic, Aleksandra; Cudic, Predrag; Rosen, Barry P.; Yoshinaga, Masafumi; Wnuk, Stanislaw F. (October 2021, RSC Advances)

   We report two routes of chemical synthesis of arsinothricin (AST), the novel organoarsenical antibiotic. One is by condensation of the 2-chloroethyl(methyl)arsinic acid with acetamidomalonate, and the second involves reduction of the N -acetyl protected derivative of hydroxyarsinothricin (AST-OH) and subsequent methylation of a trivalent arsenic intermediate with methyl iodide. The enzyme AST N -acetyltransferase (ArsN1) was utilized to purify l -AST from racemic AST. This chemical synthesis provides a source of this novel antibiotic for future drug development. 

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5. Stereosequenced crystalline polyhydroxyalkanoates from diastereomeric monomer mixtures

   https://doi.org/10.1126/science.aax8466  

   Tang, Xiaoyan; Westlie, Andrea H.; Watson, Eli M.; Chen, Eugene Y. -X. (November 2019, Science)

   Stereoselective polymerization of chiral or prochiral monomers is a powerful method to produce high-performance stereoregular crystalline polymeric materials. However, for monomers with two stereogenic centers, it is generally necessary to separate diastereomers before polymerization, resulting in substantial material loss and added energy cost associated with the separation and purification process. Here we report a diastereoselective polymerization methodology enabled by catalysts that directly polymerize mixtures of eight-membered diolide (8DL) monomers with varying starting ratios of chiral racemic (rac) and achiralmesodiastereomers into stereosequenced crystalline polyhydroxyalkanoates with isotactic and syndiotactic stereodiblock or stereotapered block microstructures. These polymers show enhanced ductility and toughness relative to polymers of purerac-8DL, subject to tuning by variation of the diastereomeric ratio and structure of the 8DL monomers. 

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