Metabolite acetate-derived

The majority of natural products from tropical macroalgae are terpenoids (mainly sesqui- and diterpenoids), followed by acetogenins (acetate-derived compounds), and metabolites of mixed biosynthetic origin (such as meroditerpenes), frequently composed of terpenoid and aromatic portions (Blunt et al. 2007 and previous reviews see Chap. 1). 

Benzyl acetate is quite soluble in lipids and therefore readily absorbed from the gastrointestinal tract and lung, as well as through the skin, in the species investigated. The absorption after oral administration in the rat was delayed if it was administered in com oil or propylene glycol as compared to neat [wet/zy/ene- Cjbenzyl acetate (Chidgey Caldwell, 1986) the peak plasma concentration of benzyl acetate-derived radioactivity occurred later after 1 h versus 4-6 h) and was lower at a 500 mg/kg benzyl acetate dose at 5 mg/kg benzyl acetate, there was no difference. The urinary excretion of the metabolites was also delayed by com oil, but the extent of absorption seemed not to be affected more than 80% was absorbed and excreted within 24 h, mainly in urine and, ultimately, less than 5% in faeces. In plasma and urine, no intact benzyl acetate was detected at any time only its metabolites were present (Chidgey Caldwell, 1986). Benzyl acetate is rapidly hydrolysed by esterases to benzyl alcohol and acetate (Yuan et al., 1995). These esterases are present in plasma and probably also in the tissues it is... 

Vertebrates cannot convert fatty acids, or the acetate derived from them, to carbohydrates. Conversion of phosphoenolpyruvate to pyruvate (p. 532) and of pyruvate to acetyl-CoA (Fig. 16-2) are so exergonic as to be essentially irreversible. If a cell cannot convert acetate into phosphoenolpyruvate, acetate cannot serve as the starting material for the gluconeogenic pathway, which leads from phosphoenolpyruvate to glucose (see Fig. 15-15). Without this capacity, then, a cell or organism is unable to convert fuels or metabolites that are degraded to acetate (fatty acids and certain amino acids) into carbohydrates. 

Collie s hypothesis that aromatic compounds are made biologically from ethanoic acid was greatly expanded by A. J. Birch to include an extraordinary number of diverse compounds. The generic name acetogenin has been suggested as a convenient classification for ethanoate (acetate)-derived natural products, but the name polyketides also is used. Naturally occurring aromatic compounds and quinones are largely made in this way. An example is 2-hydroxy-6-methylbenzoic acid formed as a metabolite of the mold Penicillium urticae ... 

Sea hares of the genus Stylocheilus prefer the cyanobacteria L. majuscula over other foods, and often contain cyanobacterial metabolites. It was mentioned before (Section 4.12.2.1) that S. longicauda concentrates the deterrent metabolites malyngamides A 4 and B 5 it further converts malyngamide B into an acetate derivative, which is a feeding stimulant rather than a deterrent.32 Given the dietary selection of the chemically rich... 

Figure 2 illustrates the established distribution of intact C2-units in the [ Ci] acetate-derived carbon skeletons of the fungal polyketides dihydrofusarubin (25), rubrofusarin (26), averufin (28), islandicin (29) and hypomycetin (30) also the probable distribution of Ca-units in the streptomycete products tetracenomycin C (35) and cetocycline (36). The full structures of these compounds are shown in Figure 1 and Scheme 4. The carbon skeletons of other products for which [ Cajacetate incorporation patterns have been determined include the fungal metabolite bikaverin (27) and the streptomycete products actinorhodin (31), spectomycin A (33), RM18 (32) and aloesaponarin II (34) (RM18 and aloesaponarin II are formed by streptomycete recombinant strains).

An acetic anhydride derivative of the peak 2 material was then prepared and found to be identical to the acetate derivative of 4-hydroxy-2-ethyl-2-phenylglutarimide, the metabolite on page 966. This metabolite was known to... 

The extender units of the polyketide extension process in fungi are always acetate derived. Intact propionate incorporation has been reported only for the starter acid of a few metabolites. The pendant methyl groups which are observed in many metabolites have been demonstrated to arise from the terminal S-methyl group of L-methionine via S-adenosyl methionine (SAM). 

A facile synthesis of cyclopentadienone epoxides via thermal rDA cycloreversion of a tricyclodece-none epoxide and its acetal derivatives has been applied to the preparation of cyclopentanoid antibiotics. - This procedure has been used in an efficient synthesis of terrein, a mould metabolite from Aspergillus terreus, by rDA synthesis of cyclopentadiene epoxide intermediate (57). FVP conditions for these reactions typically involve temperatures of 420-600 C. Furan-derived DA adducts have also been used to generate cyclopentadienone epoxides. The thermal rDA reaction of the furan-derived DA adduct (58) proceeds at temperatures as low as 330 °C with complete cycloreversion and generation of epoxide (59) in nearly quantitative yield (equation 32). Subsequent elaboration led to epipentenomycin derivatives such as (60). 

The halogenated and non-halogenated acetate-derived algal metabolites have recently been reviewed by Moore (1978). 

In the biosynthetic smdies of aspyrone and its two closely related metabolites (isoasperlactone and asperlactone), incorporation labeled acetate and labeled O2 as precursors was performed. These labeled precursors, using NMR, allowed establishing all the three isomeric metabolites were derived from a common biosynthetic precursor diepoxycarboxylic acid [6]. 

A wide range of aromatic products in the plant kingdom originate from intermediates of the shikimic acid pathway. These include amino acids and ubiquinone among important primary metabolites and also many other compounds (in contrast fo fungi which possess many acetate-derived products), such as lignins, alkaloids, and phenolic acids. Flavonoids (and stilbenes) also arise in part by this route but additionally utilize acetate in the course of their biosynthesis, which will therefore be described in this chapter. 

Incorporation of [l- C]acetate into a polyketide metabolite gives labelling throughout the chain, of alternate carbon atoms, which are of course the normally oxygenated ones. Labelled malonate, on the other hand, tends to label the second and successive acetate-derived units more heavily than the first [ unit in (5.9)] which derives directly from acetate and not malonate. This first acetate unit is called starter acetate. 

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