Search results for "Cyclic compound"
showing 10 items of 819 documents
Carotenoids
2009
Publisher Summary This chapter provides an overview of what is known about carotenoid metabolism in Chlamydomonas with reference to other green algae and vascular plants. The biosynthesis of carotenoids and the subdivisions of carotenogenesis are described. With respect to subcellular distribution, the carotenoids in vegetative cells localize to the chloroplast where they either serve as photosynthetic pigments bound to the protein complexes of the two photosystems, or as components of the eyespot apparatus is outlined with its functional significance. Carotenoids can serve as precursors of a number of other molecules with important physiological functions in Chlamydomonas.
Chlorine loss from polyvinylchloride under neutron irradiation
1997
PVC samples were irradiated for 1 hour with a thermal neutron flux of Φ th =4.71·1011n·cm−2·s−1 and the chlorine lost during irradiation was measured by γ-ray spectrometry. About 15% of loss of chlorine has been observed for untreated samples while samples heated to temperatures of 60 and 80°C for one minute before irradiation have been found to loose about 8% and 3%, respectively. The results indicate an influence of the polymer structure on the release of chlorine.
Isolation of Alkaloids from Cultured Hybrid Cells of Rauwolfia serpentina*Rhazya stricta.
1996
Two monoterpenoid indole alkaloids and four β-carbolines were isolated from a hydrid cell suspension culture generated from two Apocynaceous plants, Rauwolfia serpentina Benth. and Rhazya stricta Decaisne. This indicates that the function of alkoloid biosynthesis is retained after hybrid formation and that alkaloids not previously detected in the parental plants or cell cultures are formed.
Neue extrem deformierte (Biphenylen‐)Kohlenwasserstoff‐Gerüste
1992
New Extremely Deformed (Biphenylene)Hydrocarbon Skeletons The tetracyclic carbon skeleton 2-oxo[3](1,8)biphenylenophane (4) was synthesized by cyclization of a mixture of the bis(bromomethyl) compounds 7a, b with p-tolylsulfonylmethyl isocyanide. 2-Hydroxy[3](1,8)biphenylenophane (5) and the [3](1,8)biphenylenophane hydrocarbon 6 were obtained by reduction of 4 with LiAlH4 and NaBH4, respectively. X-ray analyses of 4 and 6 illustrate the dramatic deformation of bond lengths and angles in these molecules.
Stereoselective synthesis of the cytotoxic 14-membered macrolide aspergillide A.
2010
A stereoselective synthesis of the cytotoxic 14-membered macrolide aspergillide A has been performed. The preparation of a cis-2,6-disubstituted tetrahydropyran ring via stereoselective reduction of an intermediate cyclic hemiacetal was one key feature of the synthesis. The macrocyclic lactone ring was created by means of a ring-closing metathesis (RCM), whereby the new C=C bond displayed exclusively the undesired Z configuration. Conversion to the required E configuration was achieved via photochemical isomerization.
Regio- and diastereoselective fluorination of alicyclic β-amino acids.
2011
A regio- and stereoselective approach to fluorinated β-aminocyclohexene or cyclohexane esters has been developed, starting from a bicyclic β-lactam (1). The procedure involves six or seven steps, based on regio- and stereoselective iodolactonization, lactone opening and hydroxy–fluorine exchange. The method has been extended to the synthesis of fluorinated amino ester enantiomers.
Asymmetric synthesis of fluorinated amino macrolactones through ring-closing metathesis
2007
The synthesis of new chiral fluorinated amino and azamacrolactones of types 1 and 2 is described. A ring-closing metathesis (RCM) reaction constitutes the key step in this methodology, which uses fluorinated amino alcohols 7 as starting materials. The influence of the CF2 group, which is located in the alpha-position relative to the carbon bearing the amino group, on the efficiency of the RCM reaction is noteworthy. This method allows for the preparation of the desired fluorinated macrolactones in excellent yields.
Heterocyclic rearrangements in constrained media. A zeolite-directed photorearrangement of 1,2,4-oxadiazoles
2005
[reaction: see text] The first intrazeolite-photoinduced rearrangement of a five-membered heterocycle is reported. A completely different behavior compared to solution irradiations has been observed. The zeolite's role in directing the photoreaction of 3-phenyl-1,2,4-oxadiazoles toward the formation of the corresponding 1,3,4-oxadiazoles in a ring contraction-ringexpansion route is discussed.
Cluster dirhenium(III) cis-dicarboxylates with α-amino acids ligands as mighty selective G4s binders.
2021
The synthesis of four dirhenium(III) cis-dicarboxylates with the α-amino acids residues Asp (I), Glu (II), Phe (III) and Tyr (IV) is presented. The G-quadruplex stabilization potential was evaluated by fluorescence resonance energy transfer - melting analysis. All derivatives show specific binding to c-kit1 quadruplex, while II and IV have also strong stabilization activity to HTelo21 quadruplex. At the same time, the compounds do not show any stabilization activity for ds26 DNA, which suggests unique mechanisms of molecular DNA recognition for these complexes.
Reduction of benzo(a)pyrene mutagenicity by dihydrodiol dehydrogenase
1979
THE enigma of how inert chemicals can exert potent mutagenic, carcinogenic, allergenic and cytotoxic effects has been much debated. It has been learned that such compounds are metabolically converted to chemically reactive species1. In the case of aromatic or olefinic compounds, monooxygenases located in the membranes of the cell can transform these compounds into epoxides2–5 which by virtue of electrophilic reactivity can bind chemically to cellular macromolecules such as DNA, RNA and proteins, thereby disturbing biochemical control mechanisms and leading to the above mentioned toxic effects. The same membranes in which such epoxides are produced possess an enzyme, epoxide hydratase, which…