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Polyketides classes

The o-DPPB-directed hydroformylation of methallylic alcohol derivatives could be applied for the construction of stereotriads - central building blocks of the polyketide class of natural products. Thus, starting from the methallylic o-DPPB esters 9, 11 the anti-syn and all-syn stereotriad building blocks 10 and 12 could be obtained in good yields and diastereoselec-tivities [12],... [Pg.71]

Towards this goal, the potential of the o-DPPB group to control diastereoselectivity in a carbon carbon bond forming reaction, following the hydroformylation step was explored [IS]. Enoates 17, were chosen as the test substrates since the stereoselective 1,4-addition of a methyl would provide a structural building block found in biologically important natural products of the polyketide class (e.g. antitumor agent dictyostatin 1 and the ionophore calci-mycin). [Pg.73]

A series of new examples has recently emerged in the literature. Aquaticol (10), an unusual cuparane-type bis-sesquiterpene isolated from the medicinal plant Veronica anagailis-aquatica, can be derived from a Diels-Alder cyclodimerization of the ortfco-quinol 11, itself derived from an enantiospecific oxidative hydroxylation of (—)-d-cuparenol (12) (Figure 5) [37, 38]. Sorbicillinoid members of the vertinoid polyketide class of natural products also present the same chemical filiation inasmuch as they appear to originate biosynthetically from the sorbicillinol (13)-derived ortho-quinol 14 (Figure 6) (Section 15.3.3) [39, 40]. [Pg.544]

Extracts of Pterogorgia anceps contain a fraction enriched in ancepsenolide metabolites of the polyketide class, one of which (134) is individually deterrent in shipboard assays with T. bifasciatum 0 This last study illustrates that chemical defense mechanisms in gorgonians do not solely rely on the terpenoid biosynthetic pathway. [Pg.519]

Johnson, T.A. et al. Sponge-denved fijianolide polyketide class further evaluation of their structural and cytotoxicity properties. J. Med. Chem. 50, 3795-3803 (2007). [Pg.72]

The biosynthesis of two major classes of red tide toxins, saxitoxin analogs and brevetoxins, have been studied. It was shown that saxitoxin is biosynthesized from arginine, acetate, and methionine methyl group. Brevetoxins were shown to be unique polyketides, which are probably biosynthesized from dicarboxylic acids. Some details of the biosynthetic mechanism have been elucidated. [Pg.21]

Quinones represent a very large and heterogeneous class of biomolecules. Three major biosynthetic pathways contribute to the formations of various quinones. The aromatic skeletons of quinones can be synthesized by the polyketide pathway and by the shikimate pathway. The isoprenoid pathways are involved in the biosynthesis of the prenyl chain and in the formation of some benzoquinones and naphthoquinones. ... [Pg.102]

In this chapter, we will introduce an exciting class of natural product biosynthetic enzymes, the modular synthases, as well as their associated enzyme partners. We will discuss the use of metabolic engineering as a tool for small-molecule discovery and development, both through directed fermentation and combinatorial biosynthesis. In addition, we will review six classes of partner enzymes involved in the modification of polyketide (PK) and nonribosomal peptide (NRP) natural products. We believe that these enzymatic transformations hold great opportunities for synthetic chemists and will serve as the foundation for a new trend in both discovery and process chemistry. [Pg.288]

An unusual class of heterocydes are polyketide-derived macrodiolide natural produds. The groups of Porco and Panek have recently shown that stereochemically well-defined macrodiolides of this type can be obtained by cyclodimerization (transesterification) of non-racemic chiral hydroxy esters (Scheme 6.154) [301]. Preliminary experiments involving microwave irradiation demonstrated that exposing dilute solutions of the hydroxy ester (0.02 m) in chlorobenzene to sealed-vessel microwave irradiation conditions (200 °C, 7 min) in the presence of 10 mol% of a distannoxane transesterification catalyst led to a 60% isolated yield of the 16-mem-bered macrodiolide heterocycle. Conventional reflux conditions in the same solvent (0.01 m in the hydroxy ester) provided a 75% yield after 48 h at ca. 135 °C. [Pg.208]

The second largest class of compounds reported from macroalgae is the polyketides, which comprise approximately a quarter of known algal compounds (Blunt et al. 2007). Polyketides are polymers of acetate (C2) and occasionally propionate (C3) and are very similar to fatty acids in their biosynthetic origin. Polyketides can be found in plants, animals, bacteria, and fungi. With a range of activities as broad as their structures, the polyketides are a diverse family of natural products classified based upon the polyketide synthases (PKSs) responsible for their biosynthesis, primarily type I and type II. [Pg.10]

Posttranslational modifications can be broken down into two main classes those that are reversible and those that are irreversible. Included in the large group of reversible posttranslational modifications are phosphorylation, acetylation, and disulfide formation. Irreversible posttranslational modifications include peptide bond cleavage as in intein splicing also irreversible is the introduction of a phosphopantetheinyl group during fatty acid, polyketide, and nonribosomal peptide biosyntheses. The current debate is whether to classify lysine N-methylation as reversible or irreversible. Recently, there have been reports of lysine demethylases. ... [Pg.434]

Phosphopantetheine tethering is a posttranslational modification that takes place on the active site serine of carrier proteins - acyl carrier proteins (ACPs) and peptidyl carrier proteins (PCPs), also termed thiolation (T) domains - during the biosynthesis of fatty acids (FAs) (use ACPs) (Scheme 23), polyketides (PKs) (use ACPs) (Scheme 24), and nonribosomal peptides (NRPs) (use T domain) (Scheme 25). It is only after the covalent attachment of the 20-A Ppant arm, required for facile transfer of the various building block constituents of the molecules to be formed, that the carrier proteins can interact with the other components of the different multi-modular assembly lines (fatty acid synthases (FASs), polyketide synthases (PKSs), and nonribosomal peptide synthetases (NRPSs)) on which the compounds of interest are assembled. The structural organizations of FASs, PKSs, and NRPSs are analogous and can be divided into three broad classes the types I, II, and III systems. Even though the role of the carrier proteins is the same in all systems, their mode of action differs from one system to another. In the type I systems the carrier proteins usually only interact in cis with domains to which they are physically attached, with the exception of the PPTases and external type II thioesterase (TEII) domains that act in trans. In the type II systems the carrier proteins selectively interact... [Pg.455]

Of the four major classes of biochemicals (carbohydrates, proteins, nucleic acids and lipids), experiments have shown that the first three classes could have arisen through prebiotic chemistry. Although the biosynthesis of many natural products can be traced back to acetate (e.g. fatty acids, terpenes and polyketide biosynthesis) or amino acids (e.g. alkaloid biosynthesis), there are many whose biosynthetic origins are either obscure or result from a complex combination of pathways (Fig. 2). [Pg.6]

For each biome, the metabolites are grouped per chemical class in graphical charts, in tte order alkaloids, peptides (including also depsipeptides, lipopeptides, and glycopeptides), polypeptides, isoprenoids, frtty acids and polyketides, shikimates, and carbohydrates. Attention is also paid to... [Pg.19]

Overall, however, the immensity of temperate land corresponds to a most various secondary metabolic production, different from that of tropical land. The most renowned alkaloids belong to the morphine class (Chart 6.2.A1), and, in combination with isoprenoids, to the ergot and triterpene classes (Chart 6.2. A2). Prominent in the peptides are the cyclosporins (the first of which was isolated from a fiingus collected in Norway), streptogramins, and P-lactams (Chart 6.2.P). The isoprenoids are represented by pyrethrin monoterpenes, cedrane sesquiterpenes, ginkgolide and taxane diterpenes, ophiobolane sesterterpenes, and arborane and amyrin-like triterpenes (Chart 6.2.1). In the polyketides, epothilones, recently discovered from Myxobacteria, and the long known rapamycin, are two prominent classes of macrolides (Chart 6.2.FA/PO/C). [Pg.27]

X axis biogenetic class (A = alkaloids P = amino acids, peptides, peptides, polypeptides and proteins FA/PO = fatty acids and polyketides S = shikimates C = carbohydrates). [Pg.99]

There are several classes of alkaloids. Among these are purines such as xanthine and caffeine, ter-penes (Chapter 22), polyketides (Chapter 21), and alkaloids derived from amino acids. The basic amino acids ornithine, arginine, histidine, and lysine as well as the aromatic amino acids, anthranilate, and nicoti-nate are some of the starting materials.199 201 Robinson202 203 in 1917 recognized that many alkaloids are derived directly from aromatic amino acids. He proposed that alkaloids arise from Mannich reactions (Eq. 25-12) in which an amine and an aldehyde (probably through a Schiff base) react with a nucleophilic carbon such as that of an enolate anion. Many of the... [Pg.1443]


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