Synthesis and Properties of Alternating Copolymers of 3‑Hydroxybutyrate and Lactate Units with Different Stereocompositions

Alternating copolymers of (<i>R</i>)-3-hydroxybutyrate ((<i>R</i>)-3HB) and lactate (2-hydroxypropionate: 2HP) units were synthesized by polycondensation reaction of preprepared dimeric monomers, (<i>R</i>)-3HB-(<i>R</i>)-2HP and (<i>R</i>)-3HB-(<i>S</i>)-2HP, in the presence of condensation agent. On the basis of the NMR analyses, it was confirmed that the obtained copolymers had an alternating sequence of (<i>R</i>)-3HB and 2HP units. In contrast to random copolymers of (<i>R</i>)-3HB and 2HP units, the repeating sequence of alternately connected (<i>R</i>)-3HB and 2HP units formed crystalline region. The copolymer with alternating sequence of (<i>R</i>)-3HB and (<i>S</i>)-2HP units had a melting temperature at 83 °C. On the other hands, the melting temperature of copolymer of (<i>R</i>)-3HB and (<i>R</i>)-2HP units was quite higher than those of the corresponding homopolymers (around 180 °C) and reached to 233 °C. When the alternating copolymers were prepared from a mixture of stereoisomeric dimers, both the melting temperature and crystallinity varied in the wide ranges depending on the composition of stereoisomeric dimers

Total Synthesis of Paralemnolide A

The first total synthesis of tricyclic bisnorsesquiterpene paralemnolide A, isolated from the soft coral <i>Paralemnalia thyrsoides</i>, was achieved. This synthesis features the lactonization of the cyclohexene derivative having a <i>tert</i>-butyl ester via stereoselective epoxidation followed by treatment with a Brønsted acid and construction of the novel tricyclic skeleton by an intramolecular Reformatsky–Honda reaction

Total Synthesis of Paralemnolide A

The first total synthesis of tricyclic bisnorsesquiterpene paralemnolide A, isolated from the soft coral <i>Paralemnalia thyrsoides</i>, was achieved. This synthesis features the lactonization of the cyclohexene derivative having a <i>tert</i>-butyl ester via stereoselective epoxidation followed by treatment with a Brønsted acid and construction of the novel tricyclic skeleton by an intramolecular Reformatsky–Honda reaction

Total Synthesis of Paralemnolide A

The first total synthesis of tricyclic bisnorsesquiterpene paralemnolide A, isolated from the soft coral <i>Paralemnalia thyrsoides</i>, was achieved. This synthesis features the lactonization of the cyclohexene derivative having a <i>tert</i>-butyl ester via stereoselective epoxidation followed by treatment with a Brønsted acid and construction of the novel tricyclic skeleton by an intramolecular Reformatsky–Honda reaction

Concise Total Synthesis of Spirocurcasone

A concise total synthesis of spirocurcasone was accomplished. Key features of the synthesis involved a vinylogous Mukaiyama aldol reaction, a Carroll rearrangement of β-keto allyl ester derivative, an intramolecular aldol condensation, and a spiro ring formation by ring-closing metathesis of the pentaene compound. This synthetic work was complete in nine steps from (<i>S</i>)- or (<i>R</i>)-perillaldehyde without the use of protecting groups. Interestingly, the optical rotation of the synthetic spirocurcasone was different from the reported value of the natural product

Superior CO Catalytic Oxidation on Novel Pt/Clay Nanocomposites

Nanostructured novel Pt/Clay nanocomposites consisting of well-defined Pt nanoparticles prepared by clay-mediated in situ reduction displays very high thermal stability, large BET surface area and superior catalytic activity for CO oxidation as compared to a model reference Pt/SiO₂ catalysts. CO oxidation has attracted renewed attention because of its technological importance in the area of pollution control. The Pt/Clay system consisting of Pt nanoparticles strongly immobilized between the atomic layers of clay inhibits nanoparticle sintering and loss of catalytic activity even after prolonged heating at high temperatures. At elevated temperatures (300 °C), the Pt/Clay system demonstrates significant enhancement of catalytic activity, with almost 100% CO conversion in less than 5 min. Emphasis is given to the role played by the clay supporting material which is chemically and thermally stable under the catalytic conditions of exhaust purification

Concise Total Synthesis of Albaflavenone Utilizing Sequential Intramolecular Aldol Condensation: Determination of Absolute Configuration

The first total synthesis of albaflavenone, a novel antibiotic sesquiterpene, has been accomplished via the concise construction of its zizaene skeleton utilizing sequential intramolecular aldol condensation followed by chemo- and diastereoselective reduction of the conjugated carbon–carbon double bond. This synthetic work was completed in nine steps from 2-cyclopenten-1-one as a starting material without the use of protecting groups and with high stereocontrol. In addition, the absolute configuration of naturally occurring albaflavenone was determined to be 1<i>R</i>,2<i>S</i> and 8<i>S</i>

Real-Time Observation of Enzymatic Polyhydroxyalkanoate Polymerization Using High-Speed Scanning Atomic Force Microscopy

The initial stage of in vitro polyhydroxyalkanoate (PHA) polymerization by PHA synthase from Ralstonia eutropha (PhaC_Re) on a mica substrate in water was observed using high-speed scanning atomic force microscopy (HS-AFM). Before PHA polymerization, the adsorption–desorption cycle of the PhaC_Re molecule on mica was observed in real time. For approximately 30 s after the addition of the PHA monomer, no significant change was observed on the mica substrate, but PhaC_Re could be transformed into an active enzyme in water upon contact with the monomer during this period. Subsequently, linearly elongating rod-shaped objects were observed on the mica substrate, plausibly as a result of the polymerization reaction. The height of these elongating objects was considerably larger than the expected height for a single PHA chain. This observation suggests that PHA chains generated during the reported experiments might form some kind of a semiregular structure

Real-Time Observation of Enzymatic Polyhydroxyalkanoate Polymerization Using High-Speed Scanning Atomic Force Microscopy

The initial stage of in vitro polyhydroxyalkanoate (PHA) polymerization by PHA synthase from Ralstonia eutropha (PhaC_Re) on a mica substrate in water was observed using high-speed scanning atomic force microscopy (HS-AFM). Before PHA polymerization, the adsorption–desorption cycle of the PhaC_Re molecule on mica was observed in real time. For approximately 30 s after the addition of the PHA monomer, no significant change was observed on the mica substrate, but PhaC_Re could be transformed into an active enzyme in water upon contact with the monomer during this period. Subsequently, linearly elongating rod-shaped objects were observed on the mica substrate, plausibly as a result of the polymerization reaction. The height of these elongating objects was considerably larger than the expected height for a single PHA chain. This observation suggests that PHA chains generated during the reported experiments might form some kind of a semiregular structure