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Halogenation biosynthetic

6-Dichloro-3,5-dimethoxytoluene an Dibromoindigo principal constituent of a dye antifungal compound isolated from lily known as Tyrian purpie and prized by ancient plants cultures, isolated from a species of Mediterranean [Pg.464]

Thyroxine a hormone of the thyroid gland the (S)-enantiomer is a widely used drug prescribed to increase metabolic rate [Pg.464]

The presence of the halc en in these and in other haloge-nated natural products has a strong effect on their properties, and their biosynthetic origin was a scientific puzzle of longstanding. What are the biolc ical halogenating agents, what enzymes catalyze the halogenation, and how do they do it Recent studies have unlocked the answers to some of these questions. [Pg.464]

Biosynthetic halogenation can occur through multiple pathways, but many halogenase enzymes use electrophilic halogenating species that are produced by oxidation of halide ions. [Pg.464]

The biosynthesis of the antifungai antibiotic pyrrolnitrin begins with enzyme-cataiyzed chiorination of the benzene ring of [Pg.464]


The formation of a reactive halogenating species through oxidation occurs in biosynthetic halogenation, described in the Boxed Essay. Syntheses of aryl fluorides and aryl iodides... [Pg.486]

Representative Electrophilic Aromatic Substitution Reactions of Benzene 457 Mechanistic Principles of Electrophilic Aromatic Substitution 458 Nitration of Benzene 459 Sulfonation of Benzene 461 Halogenation of Benzene 462 Biosynthetic Halogenation 464 Friedel-Crafts Alkylation of Benzene Friedel-Crafts Acylation of Benzene Synthesis of Alkylbenzenes by Acylation-Reduction 469 Rate and Regioselectivity in Electrophilic Aromatic Substitution 470 Rate and Regioselectivity in the Nitration ofToluene 472... [Pg.456]

The activity of PK and NRPSs is often precluded and/or followed by actions upon the natural products by modifying enzymes. There exists a first level of diversity in which the monomers for respective synthases must be created. For instance, in the case of many NRPs, noncanonical amino acids must be biosynthesized by a series of enzymes found within the biosynthetic gene cluster in order for the peptides to be available for elongation by the NRPS. A second level of molecular diversity comes into play via post-synthase modification. Examples of these activities include macrocyclization, heterocyclization, aromatization, methylation, oxidation, reduction, halogenation, and glycosylation. Finally, a third level of diversity can occur in which molecules from disparate secondary metabolic pathways may interact, such as the modification of a natural product by an isoprenoid oligomer. Here, we will cover only a small subsection of... [Pg.299]

In the biosynthetic schemes proposed for some halogenated natural products, positive halogen intermediates are attacked by electrons from the n bond of an alkene or alkyne in an addition reaction. [Pg.318]

While common biosynthetic pathways may provide the framework for the various classes of secondary metabolites, their functionality is imparted by specialized tailoring enzymes that are often unique to natural products (Walsh 2004 Hertweck et al. 2007). Whether it is the addition of alcohol groups, halogenation (Gribble 1998), oxidation, reduction, stereochemical manipulation, or cyclization, it is often these functionalities that make secondary metabolites unique and bioactive. [Pg.8]

In addition to this, it has been reported that nonprotein amino acids could be formed by structural modifications to protein amino acids (methylation, hydroxylation, and halogenation) through modified L-a-amino acid biosynthetic pathways and through novel biosynthetic routes. Some examples of the nonprotein amino acids derived through these biosynthetic pathways are given below (Figure 3). A detailed discussion of known biosyntheses for certain nonprotein amino acids will be discussed later in this chapter. [Pg.11]

Nature utilizes the shikimate pathway for the biosynthesis of amino acids with aryl side chains. These nonprotein amino acids are often synthesized through intermediates found in the shikimate pathway. In many cases, L-a-amino acids are functionalized at different sites to yield nonprotein amino acids. These modifications include oxidation, hydroxylation, halogenation, methylation, and thiolation. In addition to these modifications, nature also utilizes modified biosynthetic pathways to produce compounds that are structurally more complex. When analyzing the structures of these nonprotein amino acids, one can generally identify the structural similarities to one of the L-a-amino acids with aromatic side chains. [Pg.19]

A practical racemic synthesis of the known chlorovulone II from the Okinawan soft coral Clavularia viridis has been accomplished (922). This coral has more recently afforded the new prostanoids 852-856 (923), 857-871 (924), and, from a Taiwanese collection, 872, 873 in addition to 857 and 858 (925). The absolute configuration of the previously known punaglandin 8 (852, X = Cl) was determined as shown (923). This soft coral also contains several non-halogenated possible biosynthetic precursors to these halogenated metabolites (926). [Pg.127]

Cyanobacteria blooms can pose an extremely serious threat to human health (970-972), and some of the causative toxins contain halogen. The fresh water toxic cyanobacterium Oscillatoria agardhii produces oscillaginin A (916), which features the novel 3-amino-10-chloro-2-hydroxydecanoic acid, and is the source of the micro-cystins, which are heptatoxins (973). The prolific cyanobacterium Lyngbya majuscula from Curacao has furnished the novel barbamide (917) (974) and dechlorobarbamide (918) (975). Extensive biosynthetic studies show that the amino acids leucine, cysteine, and phenylalanine are involved in barbamide production (976-982). The chlorination of leucine is of great interest and may involve a radical mechanism (976, 980-983). [Pg.135]

Beck HC (1997) Biosynthetic Pathway for Halogenated Methoxybenzaldehydes in the White Rot Fungus Bjerkandera adusta. FEMS Microbiol Lett 149 233... [Pg.494]

To illustrate mechanisms by which complex halogenated secondary metabolites are elaborated, the haloperoxidase-mediated biosynthesis of selected halometabolites elaborated by marine microorganisms will be described. The discussion given by Neidleman20 of chloramphenicol biosynthesis provides an example of bacterial halometabolite biosynthesis, while fungal halometabolite biosynthetic schemes are found in the monograph by Turner21. [Pg.1495]

Dimethylethylcydohexanes.—Two new halogenated monoterpenoids are violacene (150) from Plocamium violaceum,250 a 1,4-dimethyl-1-ethylcyclohexane which can be rationalized biosynthetically from the cyclization of an acyclic precursor via a bromonium ion, and plocamene B (151), again from Plocamium violaceum, which may be the first member of a series of non-isoprenoid monoterpenoids from this species.251... [Pg.33]

Some early attempts at metabolic oligosaccharide engineering using haloge-nated and deoxy sugars resulted in cell death. In retrospect, we now know that some of these compounds are inhibitory of intracellular biosynthetic pathways [37,38], However, the toxicity of halogenated and deoxy sugars could possibly be exploited therapeutically for antiviral, antibacterial, or anticancer therapy. Examples are presented in detail later in this chapter. [Pg.652]

Halogenated compounds are produced both by de novo synthesis involving direct incorporation of halide ion and by transmethylation reactions (Section 6.11.4). The former include reactions mediated by haloperoxidases in the presence of hydrogen peroxide and halide ion, and these enzyme systems have wide biosynthetic capability (Neidleman and Geigert 1986 van P6e 1996) including oxidative dimerization resulting, for example, in the formation of 2,3,7,8-tetrachlorodibenzo[l,4]dioxin from 2,4,5-trichlorophenol (Svenson et al. 1989). [Pg.25]


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See also in sourсe #XX -- [ Pg.486 ]

See also in sourсe #XX -- [ Pg.464 ]




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