Biosynthesis of cyclic bromoethers from red algae
shifts coupled with biosynthetic postulates, comprise a very useful method for distinguishing among large nos.
Frontiers Biosynthesis of archaeal membrane ether lipids Microbiology
O'Hagan and Jonathan B. (Joe) Spencer of the University of Cambridge have similar hopes for fluorinase. O'Hagan tells C&EN that Spencer's lab has finally isolated the cluster of genes responsible for fluorometabolite biosynthesis, including the gene that allows a fluoroacetate-producing organism to resist being killed by this toxic metabolite. With this fluorinase gene cluster in hand, they hope to insert it into other organisms to produce novel organofluorines by fermentation.
The biogenesis of the large family of halogenated cyclic acetogenins, all functionalized at C-6, C-7, C-9, C-10, C-12 and C-13, has been suggested by Murai as ultimately arising from (Z,Z,Z)-hexadeca-4,7,10,13-tetraenoic acid via (Z)-6,7-epoxide 6 (or a closely related precursor) and electrophilic bromination events . Based on this work, Braddock recently proposed a hypothesis concerning the biosynthesis of an interesting subset of these halogenated C15 acetogenins, the obtusallenes , whose initial steps could explain the biogenetic origin of compounds 1–5. Thus, it seems reasonable to suggest that these compounds derive from epoxide 6 by nucleophilic ring-opening with chloride to provide a threo-hydroxychloride derivative (). Subsequent bromoetherification gives a trans-tetrahydrofuran intermediate that evolves to generate bicyclic oxonium ions, which, in turn, can be fragmented to give compounds 4–5 and the allylic precursors of compounds 1–3. Lastly, the terminal bromoallene moiety in compounds 1–4 may be produced biosynthetically by bromonium ion formation on the terminal enyne, followed by nucleophilic attack of water. Finally, it has to be noted that the configurations proposed by us for these molecules (1–5) are consistent with this biogenetic proposal.
Biosynthesis of the C15-acetogenin laurepoxide may …
The syntheses of L-CCGs were carried out using efficient methods starting from chiral amino acids: (1) cyclopropanation of (2S)-2-amino-3-butenol derivatives for the syntheses of all L-isomers; (2) intramolecular cyclopropanation of 4 for L-III; and (3) cyclopropanation of an α,β-unsaturated-γ-lactam 10 for L-III and δ-lactone 13 for L-IV.
We have demonstrated the value of our simple and efficient NMR protocol based on the measurement of spin-spin coupling constants to achieve the challenging relative configurations of five new halogenated C15 tetrahydrofuranyl-acetogenins isolated from indigenous species of Laurencia (Laurencia marilzae). Furthermore, a detailed study of NMR chemical shifts by DFT calculations was also undertaken with the aim of connecting remote chiralities within these tetrahydrofuranyl-acetogenins. Inspection of the isolated structures also provides new insights into the biosynthetic pathway of this class of compounds.
Halonium-Induced Reactions for the Synthesis of …
These results indicated that the O-methylchalcones 3 and 10 are incorporated into the biosynthetic pathway resulting in the formation of optically active adducts through a Diels-Alder type cycloaddition reaction of the α,β-double bond of the chalcone as a dienophile with the prenyl portion as a diene.
Researchers also hope to make novel organohalogens by mixing and matching the components of biosynthetic gene clusters encoding halogenated natural products. Flavin-dependent tryptophan halogenases have already proven useful in such combinatorial biosynthesis strategies. Microbiologist of the University of Oviedo, in Spain, and synthetic chemist of the University of Kentucky have produced by fermentation a variety of rebeccamycin derivatives with chlorine atoms in novel positions. They did so by substituting 5-tryptophan and 6-tryptophan halogenase genes for the 7-tryptophan halogenase gene of the rebeccamycin gene cluster ( 2005, , 461).
By analyzing the hypothesized biosynthesis of the ..
Halonium-Induced Reactions for the Synthesis of ..
Fukuzawa and Murai's proposed biosynthesis of various bromoethers stemming from bromonium ion is shown in Scheme 1.
Natural Products via Electrophilic Bromination.
Nature's X-Factors | May 22, 2006 Issue - Vol. 84 Issue …
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A vanadium haloperoxidase is involved in snyderol biosynthesis ..
In each of these natural products, the positioning of the haloperoxidase's substrate in the active site determines the site of halogenation, notes chemist of the University of California, Santa Barbara. For example, in snyderol biosynthesis, bromination by vanadium haloperoxidase occurs at just one face of a terminal olefin, leading to diasteroselective cyclization to give the brominated snyderol, she says. But whatever their cofactor, she points out, haloperoxidases can halogenate only double bonds of electron-rich substrates.
C15 acetogenins from the Laurencia complex: 50 years …
An exceedingly complex polymer found especially in xylem and schlerenchymaRoles- The polymer is derived from three : Gymnosperm lignins: Angiosperm lignins: LIGNIN BIOSYNTHESIS See
Total Synthesis of Medium-Ring Ethers from Laurencia …
Natural products made with heme iron haloperoxidase include the human endocrine hormone tetraiodothyronine. A vanadium enzyme has been implicated in the biosynthesis of snyderol and other marine natural products.
Marine Natural Products pp 97-148 | Cite as
And indeed they were. Soon, Walsh's postdoc Frederic Vaillancourt pinpointed a handful of these suspected halogenases in biosynthetic gene clusters for a variety of natural products, including the leaf toxin coronatine and the antibiotic syringomycin. Vaillancourt and Walsh then demonstrated that, like their hydroxylase counterparts, these halogenases are α-ketoglutarate dependent and contain a mononuclear iron center capable of generating a highly reactive oxo-iron species during catalysis ( 2005, , 1191).
Total Synthesis of Medium-Ring Ethers from ..
The one enzyme known to carry out fluorination, however, marches to the beat of a different drummer. The energy required to oxidize fluoride ion is prohibitively high, says O'Hagan, whose lab studies a prototypical fluorinase enzyme involved in the bacterial biosynthesis of fluoroacetate and the amino acid fluorothreonine. Instead, the fluorinase enzyme relies on a constellation of amino acid side chains in the active site to strip fluoride ion of its protective cloak of water, he explains. The naked fluoride ion then undergoes a simple SN2 substitution reaction with a substrate to generate a C-F bond, he says.
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