Comparative Study of Aluminum Complexes Bearing N,O- and N,S-Schiff Base in Ring-Opening Polymerization of ε‑Caprolactone and l‑Lactide

A series of Al complexes bearing Schiff base and thio-Schiff base ligands were synthesized, and their application for the ring-opening polymerization of ε-caprolactone (CL) and l-lactide (LA) was studied. It was found that steric effects of the ligands caused higher polymerization rate and most importantly the Al complexes with N,S-Schiff base showed significantly higher polymerization rate than Al complexes with N,O-Schiff base (5–12-fold for CL polymerization and 2–7-fold for LA polymerization). The reaction mechanism of CL polymerization was investigated by density functional theory (DFT). The calculations predicted a lower activation energy for a process involved with an Al complex bearing an N,S-Schiff base ligand (17.6 kcal/mol) than for that of an Al complex bearing an N,O-Schiff base ligand (19.0 kcal/mol), and this magnitude of activation energy reduction is comparable to the magnitude of rate enhancement observed in the experiment. The reduction of activation energy was attributed to the catalyst–substrate destabilization effect. Using a sulfur-containing ligand to decrease the activation energy in the ring-opening polymerization process may be a new strategy to design a new Al complex with high catalytic activity

Structural Elucidation and Structure–Anti-inflammatory Activity Relationships of Cembranoids from Cultured Soft Corals <i>Sinularia sandensis</i> and <i>Sinularia flexibilis</i>

New cembranoids 4-carbomethoxyl-10-epigyrosanoldie E (<b>1</b>), 7-acetylsinumaximol B (<b>2</b>), diepoxycembrene B (<b>6</b>), dihydromanaarenolide I (<b>8</b>), and isosinulaflexiolide K (<b>9</b>), along with 11 known related metabolites, were isolated from cultured soft corals <i>Sinularia sandensis</i> and <i>Sinularia flexibilis</i>. The structures were elucidated by means of infrared, mass spectrometry, and nuclear magnetic resonance techniques, and the absolute configurations of <b>1</b>, <b>4</b>, <b>9</b>, and <b>15</b> were further confirmed by single-crystal X-ray diffraction analysis. The absolute configurations of these coral metabolites and comparison with known analogues showed that one hypothesis (that cembrane diterpenes possessing an absolute configuration of an isopropyl group at C1 obtained from Alcyonacean soft corals belong to the α series, whereas analogues isolated from Gorgonacean corals belong to the β series) is not applicable for a small number of cembranoids. An <i>in vitro</i> anti-inflammatory study using LPS-stimulated macrophage-like cell line RAW 264.7 revealed that compounds <b>9–14</b> significantly suppressed the accumulation of pro-inflammatory proteins, iNOS and COX-2. Structure–activity relationship analysis indicated that cembrane-type compounds with one seven-membered lactone moiety at C-1 are potential anti-inflammatory agents. This is the first culture system in the world that has successfully been used to farm <i>S. sandensis</i>

Improvement in Titanium Complexes Bearing Schiff Base Ligands in the Ring-Opening Polymerization of <i>L</i>‑Lactide: A Dinuclear System with Hydrazine-Bridging Schiff Base Ligands

A series of titanium (Ti) complexes bearing hydrazine-bridging Schiff base ligands were synthesized and investigated as catalysts for the ring-opening polymerization (ROP) of <i>L</i>-lactide (LA). Complexes with electron withdrawing or steric bulky groups reduced the catalytic activity. In addition, the steric bulky substituent on the imine groups reduced the space around the Ti atom and then reduced LA coordination with Ti atom, thereby reducing catalytic activity. All the dinuclear Ti complexes exhibited higher catalytic activity (approximately 10–60-fold) than mononuclear <b>L</b>^{<b>Cl–H</b>}<b>-TiOPr</b>_<b>2</b> did. The strategy of bridging dinuclear Ti complexes with isopropoxide groups in the ROP of LA was successful, and adjusting the crowded heptacoordinated transition state by the bridging isopropoxide groups may be the key to our successful strategy

Enhanced Catalytic Activity of Aluminum Complexes for the Ring-Opening Polymerization of ε‑Caprolactone

A series of dinuclear aluminum (Al₂Pyr₂) complexes bridged by two pyrazole ligands were synthesized, and their catalytic activity toward ring-opening polymerization of ε-caprolactone (CL) was investigated. Different types of the Al–N–N–Al–N–N skeletal ring were found among these Al₂Pyr₂ complexes. The butterfly form, <b>L</b>^<b>Thio</b>_<b>2</b><b>Al</b>_<b>2</b><b>Me</b>_<b>4</b>, exerted the highest catalytic activity for CL polymerization. κ²-CL coordination with both Al centers within the butterfly form <b>L</b>^<b>Thio</b>_<b>2</b><b>Al</b>_<b>2</b><b>Me</b>_<b>4</b> facilitates the initiation process. Generally speaking, the Al₂Pyr₂ complexes exhibited substantially higher catalytic activity for CL polymerization than literature examples such as β-diketiminate- or traiaza-bearing aluminum complexes. In fact, the Al₂Pyr₂ complexes can even carry out CL polymerization at room temperature

Secondary Metabolites from the Roots of <i>Neolitsea daibuensis</i> and Their Anti-inflammatory Activity

Bioassay-guided fractionation of the roots of <i>Neolitsea daibuensis</i> afforded three new β-carboline alkaloids, daibucarbolines A–C (<b>1</b>–<b>3</b>), three new sesquiterpenoids, daibulactones A and B (<b>4</b> and <b>5</b>) and daibuoxide (<b>6</b>), and 20 known compounds. The structures of <b>1</b>–<b>6</b> were determined by spectroscopic analysis and single-crystal X-ray diffraction. Daibucarboline A (<b>1</b>), isolinderalactone (<b>7</b>), 7-<i>O</i>-methylnaringenin (<b>8</b>), and prunetin (<b>9</b>) exhibited moderate iNOS inhibitory activity, with IC₅₀ values of 18.41, 0.30, 19.55, and 10.50 μM, respectively

Reactivity Study of Unsymmetrical β‑Diketiminato Copper(I) Complexes: Effect of the Chelating Ring

β-Diketiminato copper­(I) complexes play important roles in bioinspired catalytic chemistry and in applications to the materials industry. However, it has been observed that these complexes are very susceptible to disproportionation. Coordinating solvents or Lewis bases are typically used to prevent disproportionation and to block the coordination sites of the copper­(I) center from further decomposition. Here, we incorporate this coordination protection directly into the molecule in order to increase the stability and reactivity of these complexes and to discover new copper­(I) binding motifs. Here we describe the synthesis, structural characterization, and reactivity of a series of unsymmetrical <i>N</i>-aryl-<i>N</i>′-alkylpyridyl β-diketiminato copper­(I) complexes and discuss the structures and reactivity of these complexes with respect to the length of the pyridyl arm. All of the aforementioned unsymmetrical ß-diketiminato copper­(I) complexes bind CO reversibly and are stable to disproportionation. The binding ability of CO and the rate of pyridyl ligand decoordination of these copper­(I) complexes are directly related to the competition between the degree of puckering of the chelate system and the steric demands of the <i>N</i>-aryl substituent

Reactivity Study of Unsymmetrical β‑Diketiminato Copper(I) Complexes: Effect of the Chelating Ring

β-Diketiminato copper­(I) complexes play important roles in bioinspired catalytic chemistry and in applications to the materials industry. However, it has been observed that these complexes are very susceptible to disproportionation. Coordinating solvents or Lewis bases are typically used to prevent disproportionation and to block the coordination sites of the copper­(I) center from further decomposition. Here, we incorporate this coordination protection directly into the molecule in order to increase the stability and reactivity of these complexes and to discover new copper­(I) binding motifs. Here we describe the synthesis, structural characterization, and reactivity of a series of unsymmetrical <i>N</i>-aryl-<i>N</i>′-alkylpyridyl β-diketiminato copper­(I) complexes and discuss the structures and reactivity of these complexes with respect to the length of the pyridyl arm. All of the aforementioned unsymmetrical ß-diketiminato copper­(I) complexes bind CO reversibly and are stable to disproportionation. The binding ability of CO and the rate of pyridyl ligand decoordination of these copper­(I) complexes are directly related to the competition between the degree of puckering of the chelate system and the steric demands of the <i>N</i>-aryl substituent

Reactivity Study of Unsymmetrical β‑Diketiminato Copper(I) Complexes: Effect of the Chelating Ring

β-Diketiminato copper­(I) complexes play important roles in bioinspired catalytic chemistry and in applications to the materials industry. However, it has been observed that these complexes are very susceptible to disproportionation. Coordinating solvents or Lewis bases are typically used to prevent disproportionation and to block the coordination sites of the copper­(I) center from further decomposition. Here, we incorporate this coordination protection directly into the molecule in order to increase the stability and reactivity of these complexes and to discover new copper­(I) binding motifs. Here we describe the synthesis, structural characterization, and reactivity of a series of unsymmetrical <i>N</i>-aryl-<i>N</i>′-alkylpyridyl β-diketiminato copper­(I) complexes and discuss the structures and reactivity of these complexes with respect to the length of the pyridyl arm. All of the aforementioned unsymmetrical ß-diketiminato copper­(I) complexes bind CO reversibly and are stable to disproportionation. The binding ability of CO and the rate of pyridyl ligand decoordination of these copper­(I) complexes are directly related to the competition between the degree of puckering of the chelate system and the steric demands of the <i>N</i>-aryl substituent

Bioactive 6<i>S</i>‑Styryllactone Constituents of <i>Polyalthia parviflora</i>

Parvistones A–E (<b>1</b>–<b>5</b>), five new styryllactones possessing a rare α,β-lactone moiety and a 6<i>S</i> configuration, were isolated from a methanolic extract of <i>Polyalthia parviflora</i> leaves. The structures and the absolute configuration of the isolates were elucidated using NMR spectroscopy, specific rotation, circular dichroism, and X-ray single-crystal analysis. Compounds <b>8</b>, <b>9</b>, <b>11</b>, and <b>12</b> were isolated for the first time. The results were supported by comparing the data measured to those of 6<i>R</i>-styryllactones. Moreover, a plausible biogenetic pathway of the isolated compounds was proposed. The structure–activity relationship of the compounds in an in vitro anti-inflammatory assay revealed the 6<i>S</i>-styryllactones to be more potent than the 6<i>R</i> derivatives. However, the effect was opposite regarding their cytotoxic activity. In addition, 6<i>S</i>-styrylpyrones isolated showed more potent anti-inflammatory and cytotoxic activity when compared to the 1<i>S</i>-phenylpyranopyrones obtained