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Triacetic acid lactone

Chemoselective C-alkylation of the highly acidic and enolic triacetic acid lactone 104 (pAl, = 4.94) and tetronic acid (pA, = 3.76) is possible by use of DBU[68]. No 0-alkylation takes place. The same compound 105 is obtained by the regioslective allylation of copper-protected methyl 3,5-dioxohexano-ate[69]. It is known that base-catalyzed alkylation of nitro compounds affords 0-alkylation products, and the smooth Pd-catalyzed C-allylation of nitroalkanes[38.39], nitroacetate[70], and phenylstilfonylnitromethane[71] is possible. Chemoselective C-allylation of nitroethane (106) or the nitroacetate 107 has been applied to the synthesis of the skeleton of the ergoline alkaloid 108[70]. [Pg.305]

Divergent reports are available regarding the action of diazomethane on triacetic acid lactone (83). In the first investigations the sole formation of 6-methyl-2-methoxypyran-4-one (85) or of 6-methyl-4-methoxypyran-2-one (84) " w as reported. Later it was shown that a mixture of both compounds is formed albeit the 2-methoxy derivative (85) in small yield. The discrepancies are in... [Pg.277]

When the catalytic reaction of 6-hydroxymellein synthase is carried out in the absence of NADPH or with monomeric enzyme, keto-reduction of the carbonyl group of the triketomethylene chain does not take place, and the synthase liberates triacetic acid lactone instead of 6-hydroxymellein [64, 71]. However, the efficiencies of product formation are markedly lower than for the normal reaction. Two mechanisms could account for the low efficiency of triacetic acid lactone formation observed in the monomeric and the NADPH-depleted dimeric forms of 6-hydroxymellein synthase. These are 1) Reduced affinity of the cosubstrates acetyl-CoA and/or malonyl-CoA for the enzyme protein with the incomplete reaction centers 2) Reduced rate of reaction of acyl-CoA condensation and/or product liberation. To examine these possibilities, kinetic parameters of the two triacetic acid lactone-forming reactions were compared with those of the normal reaction which produces 6-hydroxymellein. The Km value of 6-hydroxymellein synthase for acetyl-CoA in the normal reaction was estimated to be 22 pM, while in both the NADPH-depleted dimer and the monomer reactions the affinity of 6-hydroxymellein synthase protein for acetyl-CoA was markedly lower at 284 and 318 pM respectively. By contrast the Km values for malonyl-CoA in the normal and the two abnormal reactions were essentially the same (40 - 43 pM), indicating that the affinity of 6-hydroxymellein... [Pg.501]

Moreno-Manas, M., Pleixats, R., Dehydroacetic Acid, Triacetic acid Lactone, and Related Pyrones, 53, 1. [Pg.296]

Dehydroacetic acid, triacetic acid lactone, and related pyrones, 53, 1 Developments in the chemistry of furans (1952-1963), 7, 377 of Reissert compounds (1968-1978), 24, 187 of thiopyrans, selenopyrans, and telluropyrans, 59, 179... [Pg.306]

Hydroxy-6-methyl-2-pyrone (Triacetic Acid Lactone). 96... [Pg.73]

The reversibility of O-allylation and the stereochemistry of the Pd(0)-catalyzed allylations have been studied in triacetic acid lactone 129, a natural polyketide. Thus, efficient and controlled C-allylations of 129 take place under Pd(0) catalysis to afford monoallylation products 130 (in toluene)... [Pg.96]

Methoxy-6-methyl-2-pyranone (1). Mol. wt. 140.13, m.p. 83-86°. Supplier Aldrich. This ether can be prepared by methylation of triacetic acid lactone (2) with dimethyl sulfate. Exposure of 2 to methyl fluorosulfonate produces the isomeric ether (3). ... [Pg.156]

Fig. 5. Biosynthetic pathways for (I) 6-methylsalicylic acid and (II) the triacetic acid lactone. The structures of the intermediates have not been identified. The stereochemical course of the prochiral carbons (C-2 and C-4 in the triketide intermediate, C-3 and C-5 in 6-MSA) was investigated using R)- and (S)- [l- C,2- H]malonic acid extender substrate analogs in a coupled assay with 6-MSAS and succinyl-CoA transferase. The distinguishable hydrogens originating from the chiral malonyl CoA are labeled with H and H. Triacetic acid lactone synthesis is catalyzed by 6-MSAS in the absence NADPH... Fig. 5. Biosynthetic pathways for (I) 6-methylsalicylic acid and (II) the triacetic acid lactone. The structures of the intermediates have not been identified. The stereochemical course of the prochiral carbons (C-2 and C-4 in the triketide intermediate, C-3 and C-5 in 6-MSA) was investigated using R)- and (S)- [l- C,2- H]malonic acid extender substrate analogs in a coupled assay with 6-MSAS and succinyl-CoA transferase. The distinguishable hydrogens originating from the chiral malonyl CoA are labeled with H and H. Triacetic acid lactone synthesis is catalyzed by 6-MSAS in the absence NADPH...
Dimroth P, Greull G, Seyfferet R, Lynen F (1972) Hoppe Syler s Z Physiol Chem 353 126 Dimroth P,Ringelmann E, Lynen F (1976) Eur J Biochem 68 591 Bhogal P, Shoolingin-Jordan P. Incorporation of novel substrates into 6-methylsalicylic acid and triacetic acid lactone analogues by 6-methyl salicylic acid synthase. In Polyketides chemistry, biochemistry, molecular genetics. 1996. Royal Society of Chemistry, Bristol, UK, p 19... [Pg.124]

Methylation of Triacetic Acid Lactone with Diazomethane in Ether163... [Pg.278]

In general, products with free OH groups at C4 show UV spectra very similar to those of the corresponding 4-methoxy-2-pyrones. Therefore, formulae such as la better represent the structure of triacetic acid lactone and related pyrones in solution. [Pg.7]

Since acyl chains at C3 can be efficiently eliminated by treatment with 90% sulfuric acid, this method affords pyrones monosubstituted at C6. Triacetic acid lactone (1) is prepared from 2 by this procedure (1891JCS607). [Pg.19]

Triacetic acid lactone (1) is one of the simplest polyketides, and its formation from acetyl-CoA and malonyl-CoA has been proved (68JBC5471). Biogenetic formation of triacetic acid lactone has been considered a derailment from fatty acid biosynthesis promoted by the absence of the reductant NADPH (69MII). Pyrone 1 has been isolated from microorganisms (67JA676) and is transformed into tropolone derivatives by Penicillium stipitatum (67JA681). [Pg.21]


See other pages where Triacetic acid lactone is mentioned: [Pg.310]    [Pg.278]    [Pg.217]    [Pg.162]    [Pg.498]    [Pg.498]    [Pg.500]    [Pg.62]    [Pg.147]    [Pg.47]    [Pg.98]    [Pg.351]    [Pg.84]    [Pg.278]    [Pg.6]    [Pg.12]   
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See also in sourсe #XX -- [ Pg.541 ]




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Methyl triacetic acid lactone

Triacet

Triacetate

Triacetic acid lactone and related pyrones

Triacetic acid lactone formation

Triacetic acid lactone, methylation

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