Acetyl group removal, from

It may be protested that the reaction of the citric acid cycle by which oxaloacetate is converted to oxo-glutarate does not follow exactly the pattern of Fig. 17-18. The carbon dioxide removed in the decarboxylation step does not come from the part of the molecule donated by the acetyl group but from that formed from oxaloacetate. However, the end result is the same. Furthermore, there are two known citrate-forming enzymes with different stereospecificities (Chapter 13), one of which leads to a biosynthetic pathway strictly according to the sequence of Fig. 17-18. 

Later the estrone produced for commercial purposes was obtained from diosgenin. Diosgenin was first oxidized to its l,4,6-triene-3-one derivative, which was aromatized by pyrolysis at 500-600°C,50 subjected to the Marker degradation and the 17-acetyl group removed by Beckmann rearrangement of the 20-oxime. The overall Syntex process51 for the manufacture of Norethindrone from diosgenin (XVIII) is outlined in Scheme 5. 

A FIGURE 8-9 The citric acid cycle, in which acetyl groups transferred from acetyl CoA are oxidized to CO2. In reaction 1, a two-carbon acetyl residue from acetyl CoA condenses with the four-carbon molecule oxaloacetate to form the six-carbon molecule citrate. In the remaining reactions (2-9) each molecule of citrate is eventually converted back to oxaloacetate, losing two CO2 molecules in the process. In each turn of the cycle, four pairs of electrons are removed from carbon atoms, forming... 

Hydrolysis. The primary functions of hydrolysis are to remove some of the acetyl groups from the cellulose triester and to reduce or remove the combined acid sulfate ester to improve the thermal stabiUty of the acetate. 

Candida cylindracea, phosphate buffer pH 7, Bu20. The 6-0-acetyl of Q -methyl peracetylglucose was selectively removed. Porcine pancreatic lipase will also hydrolyze acetyl groups from carbohydrates. These lipases are not specific for acetate since they hydrolyze other esters as well. In general selectivity is dependent on the ester and the substrate. ... 

Digitalis glycosides Apply the sample solution as a band, then cover the layer, apart from the application zone, with a glass plate and place it in an ammonia chamber for 24 to 48 h, remove excess ammoma and chromatograph Acetyl groups are split off [37]... 

Hydrolysis removes the acetyl group from nitrogen and converts the two ester functions to carboxyl groups. Decarboxylation gives the desired product. 

The benzoic acid moiety common to many of the benzamides is prepared in straightforward manner from the methyl ether of p-aminosalicylic acid 141. Acylation on nitrogen (142) followed by chlorination gives intermediate 143 benzoic acid 144 is then obtained by removal of the acetyl group. Condensation of this acid with an aminopiperidine could be achieved by means of the mixed anhydride (prepared by reaction with ethyl chlonoformate), which affords clebopride (145). Reaction with 3-aminoquinuclidine (146) of the intermediate prepared from acid 144 with carbonyldiimidazole affords zacopride (147) [36]. 

Figure 6.16 Production of 7-aminodeacetyicephalosporanic acid from 7-ACA using an immobilised acetyl esterase. Following enzymatic removal of the acetyl group from 7-ACA, a 3-hydroxymethyl cephalosporin is obtained that can serve as intermediate in the production of cefuroxime.

Histone Deacetylases (HDACs) catalyze the removal of the acetyl groups from lysines (see Fig. 1). Together with the HATs they are responsible for maintaining the level of histone acetylation throughout the genome. The family of HDAC proteins has been divided into four classes based on phylogenetic analysis and sequence comparison. HDACs of the classes I and II share the same Zn2+-based reaction and are evolutionary related. Class IV HDACs also possess a Zn2+-based reaction... 

Enzyme activity ascribed to corepressors, which is the removal of acetyl groups from lysine residues of histone tails. Thereby the assembly of nucleosomes is maintained, which leads to a dense, transcriptional inactive chromatin structure. 

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