Search results for "RPE"
showing 10 items of 2566 documents
Stereoselective synthesis of polyoxygenated atisane-type diterpenoids
2001
Abstract A new stereoselective approach to polyoxygenated atisane-type diterpenes starting from (S)-(+)-carvone is described. The key steps involve an intramolecular Diels–Alder reaction, an unusual intramolecular diazo ketone cyclopropanation of an unsaturated ketone, and a regioselective endocyclic cleavage of a cyclopropyl carbinyl radical as key synthetic steps. The synthesis of the bioactive polyoxygenated atisanes atis-16(17)-en-3,14-dione ( 2 ) and 3R-hydroxy-atis-16(17)-en-2,14-dione ( 3 ) following this approach is presented.
A unified synthetic approach to trachylobane-, beyerane-, atisane- and kaurane-type diterpenes
2006
A general synthetic approach to the polycyclic carbon skeleton of biogenetically related trachylobane, beyerane, atisane, and kaurane diterpenes from carvone is described. The skeleton of these diterpenes is prepared from a common intermediate, that is, 25, readily prepared from carvone using an IMDA reaction and an intramolecular diazo ketone cyclopropanation of an unsaturated ketone as key steps. The tetracyclic diterpene ring systems are obtained from this key trachylobane-type intermediate through the regioselective reductive cleavage of the cyclopropane ring, after adequate modification of the functionalization around the tricyclo[3.2.1.02,7]octane moiety.
Photochemical Transformations of Some Neoclerodane and Labdane Diterpene Ketones
1999
Some neoclerodane (2–4) and labdane (5 and 6) diterpene ketones having a β- or γ-hydroxy function, an α-epoxy group, or an α-olefinic double bond have been irradiated at λ = 313 nm in dry solvents (benzene or methanol). Fruticolone (2) yielded the naturally occurring 5,6-seco-neoclerodan-6,1α-olide derivative fruticolide (1), while hispanolone (5) gave the δ-lactone 8, both transformations involving a Norrish type I photoreaction. The α,β-unsaturated ketone derivative 4 was transformed into 7 by a stereoselective intramolecular [2+2] cycloaddition reaction involving its furanic 13(16)-double bond. Finally, the α-epoxy ketone 6 was rearranged to the 10(98)abeo-labda-7,9-dione derivative 10. …
The Creolophins: A Family of Linear Triquinanes fromCreolophus cirrhatus (Basidiomycete)
2007
Complicatic acid and five novel linear triquinanes were isolated from mycelial cultures of Creolophus cirrhatus. The creolophins A, C, D, and E represent a novel type of highly oxidized triquinane sesquiterpenoids. Whereas those compounds with a secondary alcohol moiety in ring A are stable, the exomethylene ketone creolophin E (5) partly dimerized during workup to form the decacyclic 1,4-dioxepin-6-one neocreolophin (6). Compounds 5 and 6 display cytotoxic activities against several tumor cell lines.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
An approach to erythrophleum alkaloids. Synthesis of methyl (−)-4-epi-cassamate
1986
Abstract A synthetic approach to Erythrophleum alkaloids, involving as a key-step the regiospecific deprotonation of the ketone 5a, is described.
Sesquiterpene lactones and lignans from Artemisia arborescens
1997
The aerial parts of Artemisia arborescens yielded, in addition to several known compounds, a new guaianolide, a new homoditerpene endoperoxide, a new lignan of the sesamin type and a new azulene derivative.
Sesquiterpenes, flavonoids and lignans from Onopordon acaulon
1992
Abstract From the methanol extract of Onopordon acaulon , four flavonoids, four lignans and three sesquiterpenes were isolated. Two eudesmane derivatives are described for the first time.
High Pressure Solubility Data of the System Limonene + Linalool + CO2
2001
The feasibility of deterpenating orange peel oil with supercritical CO2 depends on relevant vapor−liquid equilibrium data because the selectivity of this solvent for limonene and linalool (the two key components of the oil) is of crucial importance. In this work the solubility data for the CO2 + limonene + linalool ternary system were measured at (318.2 and 328.2) K. The range of pressures covered was from (70 to 110) bar. Two different mixtures of limonene + linalool were used: a 40 mass % limonene + 60 mass % linalool mixture and a 60 mass % limonene + 40 mass % linalool mixture. To correlate the obtained results, two equations of state were successfully used (Peng−Robinson (PR) and Soav…
A new oleanane glycoside from the roots ofAstragalus caprinus
2006
A novel oleanane-type triterpene saponin (1) together with two known molecules, soyasapogenol B and astragaloside VIII were isolated from the roots of Astragalus caprinus. Their structural elucidation was performed mainly by 2D NMR techniques (COSY, TOCSY, NOESY, HSQC, HMBC) and mass spectrometry. Compound 1 was determined as 3-O-[alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-glucuronopyranosyl]-22-O-beta-D-apiofuranosyl-soyasapogenol B.
Compression-induced anti-nematic order in glassy and semicrystalline polymers
2020
We provide new insights into the molecular origin of the asymmetry between uniaxial tensile and compressive deformation of glassy and semicrystalline polymers using molecular dynamics simulations. The difference between the two responses strongly depends on the chain length and is the largest at intermediate chain lengths. Irrespective of chain length, the intra- and interchain organization of polymers under extension and compression are remarkably distinct. The chains align along the tensile axis leading to a global nematic order of the bonds and end-to-end vectors, whereas compression reorganizes polymers to lie in planes perpendicular to the compressive axis resulting in the emergence of…