title: Environmentally Benign CO2-Based Copolymers: Degradable Polycarbonates Derived from Dihydroxybutyric Acid and Their Platinum-Polymer Conjugates.
abstract: (S)-3,4-Dihydroxybutyric acid ((S)-3,4-DHBA), an endogenous straight chain fatty acid, is a normal human urinary metabolite and can be obtained as a valuable chiral biomass for synthesizing statin-class drugs. Hence, its epoxide derivatives should serve as promising monomers for producing biocompatible polymers via alternating copolymerization with carbon dioxide. In this report, we demonstrate the production of poly(tert-butyl 3,4-dihydroxybutanoate carbonate) from racemic-tert-butyl 3,4-epoxybutanoate (rac-(t)Bu 3,4-EB) and CO2 using bifunctional cobalt(III) salen catalysts. The copolymer exhibited greater than 99% carbonate linkages, 100% head-to-tail regioselectivity, and a glass-transition temperature (Tg) of 37 °C. By way of comparison, the similarly derived polycarbonate from the sterically less congested monomer, methyl 3,4-epoxybutanoate, displayed 91.8% head-to-tail content and a lower Tg of 18 °C. The tert-butyl protecting group of the pendant carboxylate group was removed using trifluoroacetic acid to afford poly(3,4-dihydroxybutyric acid carbonate). Depolymerization of poly(tert-butyl 3,4-dihydroxybutanoate carbonate) in the presence of strong base results in a stepwise unzipping of the polymer chain to yield the corresponding cyclic carbonate. Furthermore, the full degradation of the acetyl-capped poly(potassium 3,4-dihydroxybutyrate carbonate) resulted in formation of the biomasses, β-hydroxy-γ-butyrolacetone and 3,4-dihydroxybutyrate, in water (pH = 8) at 37 °C. In addition, water-soluble platinum-polymer conjugates were synthesized with platinum loading of 21.3-29.5%, suggesting poly(3,4-dihydroxybutyric acid carbonate) and related derivatives may serve as platinum drug delivery carriers.
authors.affiliation: Department of Chemistry, Texas A&M University , College Station, Texas 77843, United States.
authors.forename: Fu-Te
authors.initials: FT
authors.lastname: Tsai
authors.affiliation: Department of Chemistry, Texas A&M University , College Station, Texas 77843, United States.
authors.forename: Yanyan
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Chemistry, Texas A&M University , College Station, Texas 77843, United States.
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Darensbourg
mesh_terms: D002072:Butylene Glycols / Q000737:chemistry*; D002087:Butyrates / Q000737:chemistry*; D002245:Carbon Dioxide / Q000737:chemistry*; D002254:Carbonates; D002384:Catalysis; D003035:Cobalt / Q000737:chemistry; D004337:Drug Carriers / Q000737:chemistry; D016503:Drug Delivery Systems; D004852:Epoxy Compounds / Q000737:chemistry; D005029:Ethylenediamines; D006801:Humans; D015394:Molecular Structure; D009944:Organoplatinum Compounds / Q000737:chemistry*; D010984:Platinum / Q000737:chemistry*; D011076:Polycarboxylate Cement / Q000737:chemistry*; D058105:Polymerization; D011108:Polymers / Q000737:chemistry*; D014867:Water
chemical_list: C014489:3,4-dihydroxybutyrate; D002072:Butylene Glycols; D002087:Butyrates; D002254:Carbonates; D004337:Drug Carriers; D004852:Epoxy Compounds; D005029:Ethylenediamines; D009944:Organoplatinum Compounds; D011076:Polycarboxylate Cement; D011108:Polymers; D014867:Water; D002245:Carbon Dioxide; C005506:polycarbonate; D003035:Cobalt; D010984:Platinum; C011452:disalicylaldehyde ethylenediamine