Isoprene Oligomers Research Articles

Qiliqiangxin: A multifaceted holistic treatment for heart failure or a pharmacological probe for the identification of cardioprotective mechanisms?

The active ingredients in many traditional Chinese medicines are isoprene oligomers with a diterpenoid or triterpenoid structure, which exert cardiovascular effects by signalling through nutrient surplus and nutrient deprivation pathways. Qiliqiangxin (QLQX) is a commercial formulation of 11 different plant ingredients, whose active compounds include astragaloside IV, tanshione IIA, ginsenosides (Rb1, Rg1 and Re) and periplocymarin. In the QUEST trial, QLQX reduced the combined risk of cardiovascular death or heart failure hospitalization (hazard ratio 0.78, 95% confidence interval 0.68-0.90), based on 859 events in 3119 patients over a median of 18.2 months; the benefits were seen in patients taking foundational drugs except for sodium-glucose cotransporter 2 (SGLT2) inhibitors. Numerous experimental studies of QLQX in diverse cardiac injuries have yielded highly consistent findings. In marked abrupt cardiac injury, QLQX mitigated cardiac injury by upregulating nutrient surplus signalling through the PI3K/Akt/mTOR/HIF-1α/NRF2 pathway; the benefits of QLQX were abrogated by suppression of PI3K, Akt, mTOR, HIF-1α or NRF2. In contrast, in prolonged measured cardiac stress (as in chronic heart failure), QLQX ameliorated oxidative stress, maladaptive hypertrophy, cardiomyocyte apoptosis, and proinflammatory and profibrotic pathways, while enhancing mitochondrial health and promoting glucose and fatty acid oxidation and ATP production. These effects are achieved by an action of QLQX to upregulate nutrient deprivation signalling through SIRT1/AMPK/PGC-1α and enhanced autophagic flux. In particular, QLQX appears to enhance the interaction of PGC-1α with PPARα, possibly by direct binding to RXRα; silencing of SIRT1, PGC-1α and RXRα abrogated the favourable effects of QLQX in the heart. Since PGC-1α/RXRα is also a downstream effector of Akt/mTOR signalling, the actions of QLQX on PGC-1α/RXRα may explain its favourable effects in both acute and chronic stress. Intriguingly, the individual ingredients in QLQX-astragaloside IV, ginsenosides, and tanshione IIA-share QLQX's effects on PGC-1α/RXRα/PPARα signalling. QXQL also contains periplocymarin, a cardiac glycoside that inhibits Na+ -K+ -ATPase. Taken collectively, these observations support a conceptual framework for understanding the mechanism of action for QLQX in heart failure. The high likelihood of overlap in the mechanism of action of QLQX and SGLT2 inhibitors requires additional experimental studies and clinical trials.

Synthesis of New Aliphatic Hydrocarbon Resins on the Basis of Isoprene

Cationic oligomerization of isoprene using a wide range of catalyst systems based on various Lewis acids has been studied. It has been shown that fully soluble isoprene oligomers can be synthesized with the TiCl4–tert-butyl chloride catalyst system throughout the entire range of monomer conversion. The conditions for preparing isoprene oligomers with a softening point of 100–120°C characteristic of aliphatic hydrocarbon resins have been determined. The developed method for preparing aliphatic resins on the basis of isoprene is characterized by a simple technology and a possibility of controlling the softening point of the resins during the process.

Synthesis and characterization of isoprene oligomers to compare different production chemical processes

Synthesis and characterization of isoprene oligomers to compare different production chemical processes

Metathesis Transformations of Natural Products: Cross-Metathesis of Natural Rubber and Mandarin Oil by Ru-Alkylidene Catalysts

This study reports on the degradation of natural rubber (NR) via cross-metathesis with mandarin oil and d-limonene, an abundant compound in essential oils; that were used as chain transfer agents (CTAs) and green solvents. Reactions were performed in the presence of the ruthenium-alkylidene catalysts (PCy3)2(Cl)2Ru=CHPh (I) and (1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) (PCy3)Cl2Ru=CHPh (II), respectively. Catalyst II bears an N-heterocyclic carbene ligand (NHC) bounded to the ruthenium atom, which has a strong basic character; therefore it is more active toward trisubstituted olefins in comparison with catalyst I. In both cases, isolated monoterpene-terminated isoprene oligomers were obtained as products of the cross-metathesis degradation of NR. In the presence of catalyst II molecular weight values around Mn × 102 and yields of 80% were obtained; whereas with catalyst I, the molecular weights of products were about Mn × 104 with yields ranging 70 to 74%. The composition and yield of NR degradation products were determined by GC/MS (EI) analysis and it was found that the oligomers obtained have primarily one vinyl group and one terpene-monocyclic group at the chain end, with isoprene units Am = 2, 3 y 4.

Molecular polarizability of organic compounds and their complexes: LII. Molar volumes of polymeric compounds in solutions, extrapolated to infinite dilution, and steric structure of their molecules

The molar volumes in solutions at infinite dilution were determined for a series of vinyl, glycol, isoprene, and cyclopentadiene polymers and oligomers with various degrees of polymerization. An additive analysis of the molar volumes showed that molecules of vinyl, ethylene glycol, and isoprene polymers exist in solutions in elongated helical conformations. In the majority of polymer molecules, except polystyrenes, polyisoprenes, and polycyclopentadienes, there are randomly disordered regions creating additional volumes inaccessible to solvation with solvent molecules. Cyclopentadiene oligomers formed by the Diels-Alder reaction have in solution the conformation of corrugated bands. The additive scheme for calculating the molar volumes considerably simplifies the determination of the dipole moments and Kerr constants of the compounds for which this scheme has been constructed.

Microbial Degradation of the Natural Rubber in Tire Tread Compound by a Strain of Nocardia

Tread compound of truck tires is based primarily on natural rubber or blends of natural rubber (NR) and synthetic polymers in combination with high grade carbon black. When the tread compound is attacked by a strain of Nocardia capable of degrading NR, part of the NR in the compound is mineralized, and part is disintegrated to very small black particles. The small black particles consist of the residual rubber and inorganic fillers. At higher NR content, large and deep cavities are formed on the surface of the pieces of the tread compound after microbial disintegration. At lower content of NR, large but very shallow cavities or very small pits can be seen on the tread surface. During microbial growth on the tread compound, isoprene oligomers with molecular weight of about two thousand are produced. Not only the isoprene oligomers, but also butadiene oligomers are produced during microbial disintegration of the tread compound of NR/synthetic rubber blend.

Elastomeric Compounds with Silica. Lower Hysteresis in the Presence of Functionalised Isoprene Oligomers

AbstractSilica as reinforcing filler brings about a low hysteresis in elastomeric compounds. Aim of this work was to promote a better silica‐elastomer interaction by using, as minor ingredients of a compound, isoprene oligomers having a functional group as the chain end. The effect of the functionality was investigated by analysing the complex viscosity of silica‐oligomers binary mixtures as well as the morphological and rheological properties of masterbatches and compounds based on isoprene rubbers. A better silica dispersion and a lower Payne effect were clearly observed in the presence of functionalized oligomers.

Computational study of metathesis degradation of rubber. distributions of products for the ethenolysis of 1,4-polyisoprene

The molecular modeling of the product distributions for the ethenolysis of 1,4-polyisoprene at 25 °C using the B3LYP/6-31G(d,p) level of theory reveals that chain–ring and chain–chain equilibria are completely shifted toward the formation of 2-methyl-1,5-hexadiene. The amount of cyclic oligomers at equilibrium with linear molecules is small. The concentration of 2-methyl-1,5-hexadiene at equilibrium with linear isoprene oligomers is of 90 mol%. The value of 1,5-hexadiene at equilibrium with butadiene oligomers for the ethenolysis of 1,4-polybutadiene corresponds to 46 mol%. These results are in agreement with experimental data.

Supercritical fluid extraction of scrap tyres

Extraction of scrap tyres with supercritical solvents was examined. Virtually total extraction of the rubber components of the tyre occurred at 350°C using either n-butanol or toluene as the solvent. At lower temperatures, using ethanol as the supercritical fluid, the extraction yield was significantly lower. The extracted oil was examined by chemical ionization mass spectrometry, using a desorption probe, and GC-MS. Isoprene oligomers were shown to be major components of the extracted oil.

Distribution of cyclized units present in isoprene oligomers synthesized by cationic oligomerization

AbstractThe structure of isoprene oligomers synthesized by cationic oligomerization in the presence of the BF3 · H2O complex as an initiator in a hexane solution at 40°C was investigated. These oligomer fractions obtained with the degree of polymerization (DP) in the range 5‐12, and the completely hydrogenated oligomers were examined using the direct inlet system‐mass spectrometry (DIS‐MS) technique. The distribution of the cyclic and linear structures in the oligomers was obtained by integrating the selected ion current of the different hydrogenated products. The results obtained were interpreted by means of a statistical simulation based on a step‐by‐step competition between cyclization and monomer addition reaction. The value of the probability of cyclization was found to be very high for low‐molecular‐weight oligomers and to decrease with increasing molecular weight of the oligomers.

Cyclization and oxidation of isoprene oligomers during polymerization on kaolinite

The structure of isoprene oligomers prepared by cationic polymerization on kaolinite acid centrs was studied by PMR and IR spectroscopic methods. It was shown that during polymerization the oligomer undergoes cyclization, forming two- and three-cycle structures by an intramolecular chain transfer reaction. The oligoisoprene is easily oxidized, with additional cyclization taking place simultaneously with oxidation. Oxidation leads to the formation of a great variety of oxygen containing groups. A system of PMR signal assignment in cyclized and oxidized oligoisoprene was developed. A method for the calculation of the structure of cyclized low-molecular weight oligoisoprenes from PMR spectroscopic data is presented.

Molecular design of functional polymers having amino groups

Three topics on molecular design of functional polymers having amino groups will be discussed. The first topic is on the synthesis of functional isoprene oligomers with one amino end group. The best condition for the synthesis is to seed a small amount of the amino-ended oligomer into a reaction system where isoprene was polymerized with lithium diisopropylamide as initiator. The highly active behavior of the amino-ended oligomer as chain transfer agent was ascribed to a “macromolecular effect”. The second topic is concerned with a study on the soluble poly(1,4-divinylbenzene) which was formed by polymerizing 1,4-divinylbenzene with lithium diisopropylamide in the presence of excess diisopropylamine in THF. Structural analyses with 400MHz1H NMR and 25 MHz13C NMR showed that there were 2 or 3 branchings per 100 monomeric units along the main chain. Population of the triad tacticities suggested the steric course of polymerization to proceed according to the Bernoulli statistics with respect to diad placements, m and r. Third topic is on a polyamine macromer which was prepared by allowing an ethylenediamine homologue, N,N′-diethylethylene-diamine (DEDA), to react with 1,4-divinylbenzene in the presence of lithium diisopropylamide as catalyst. Results on syntheses and properties of polystyrene-polyamine (SA) and poly(2-hydroxyethyl methacrylate)-polyamine (HA) graft copolymers will be presented with the emphasis on their biomedical behavior.

Microbial Degradation ofcis-1, 4-Polyisoprene

An organism isolated from soil grew well on isoprene oligomers and degraded 60 percent of a sample of synthetic cis-1,4-polyisoprene (Mn=940) in 4 days. The organism hardly degraded synthetic polyisoprene with higher average molecular weight of 2,500. From gel permeation chromatography, oligomers with molecular weight as high as 1,000 were shown to be attacked. The residual substrate after degradation was shown by infrared spectroscopy to have a relatively higher amount of 3,4-structure than the original. From these results, it was supposed that 3,4-linkages in synthetic polymers prevent biodegradation of higher oligomers.

Production of regular, linear isoprene oligomers in the presence of nickel-containing homogeneous catalysts

1. The oligomerization of isoprene was studied in the presence of nickel complexes activated by o- and m-borates. 2. The borates, in contrast to phosphorus-containing activators, direct the reaction primarily towards the formation of linear trimers and tetramers of isoprene, namely, 3-methylene-7,11-dimethyl-1-trans-6,11-dodecatriene, 2,6,10-trimethyl-1-trans-3,5,10-dodecatriene, and 2,6,10,14-tetramethyl-1-trans-3,6,10,14-hexadecapentane.

Degradation of synthetic oligomers by microorganisms. III. Microbial degradation of cis-1, 4-polyisoprene.

An organism isolated from soil grew well on isoprene oligomers and degraded 60 percent of a sample of synthetic cis-1,4-polyisoprene (Mn=940) in 4 days. The organism hardly degraded synthetic polyisoprene with higher average molecular weight of 2,500. From gel permeation chromatography, oligomers with molecular weight as high as 1,000 were shown to be attacked. The residual substrate after degradation was shown by infrared spectroscopy to have a relatively higher amount of 3,4-structure than the original. From these results, it was supposed that 3,4-linkages in synthetic polymers prevent biodegradation of higher oligomers.

Synthesis of terpene alcohols from isoprene oligomers

AbstractVarious terpene alcohols were prepared from isoprene oligomers via two steps: epoxidation with peracetic acid and isomerisation with aluminium triisopropoxide. For example, 2‐methylene‐6‐methyl‐7‐octene‐1‐o1 was prepared from 2,6‐dimethyl‐1,7‐octadiene. From 2,6‐dimethyl‐2,7‐octadiene, 3,3,6‐trimethyl‐1,5‐heptadiene, 2,7‐dimethyl‐2,6‐octadiene, 2,6‐dimethyl‐1,3,6‐octatriene, 1‐methyl‐4‐isopropenyl‐1‐cyclohexene, and 1,5‐dimethyl‐1,5‐cyclooctadiene, the corresponding alcohols were obtained, respectively.

Synthesis of terpene alcohols from isoprene oligomers

Synthesis of terpene alcohols from isoprene oligomers