Acetyl group cleavage

The cycle shown in Figure 20.4 at first appears to be a complicated way to oxidize acetate units to COg, but there is a chemical basis for the apparent complexity. Oxidation of an acetyl group to a pair of COg molecules requires C—C cleavage ... 

DDQ, CH3CN, H2O, 80°, 43-95% yield."" These conditions also resulted in the cleavage of acetyl groups a dithiolane was stable to the conditions. 

The four steps of the /3-oxidation pathway, resulting in the cleavage of an acetyl group from the end of the fatty-acid chain. The key chain-shortening step is a retro-Claisen reaction of a /3-keto thioester. Individual steps are explained in the text. 

The starting material is aspirin. The acetyl group in (35) is an activating group, present to allow the synthesis of (35) and removed by 1,3-dicarbonyl cleavage. The strategy is therefore a 1,5-dlcarbonyl disconnection to (37) and a 1,3-dicarbonyl disconnection to (38). 

AE catalyses the cleavage of acetyl groups from different substrates. The enzyme activity was determined by measuring the release of acetic acid. The amount of acetic acid was measured spectrophotometrically using an acetic acid analysis kit (Boehringer, Mannheim). The activity of AE was measured in 0.6% sugar beet pectin solubilised in 25 mM Na-succinate pH 6.2 and incubated with enzyme fraction in total 500 nl assay. The samples were incubated at 40°C and aliquots were examined after 0, 1, 2 and 3 hours of incubation. The enzyme reaction was stopped by incubating the samples at lOO C for 5 min. Precipitated... 

Several studies have dealt with the problem of discriminating between mastic and dammar, and three marker compounds of mastic have been identified moronic, masticadienonic and acetyl masticadienolic acids [42], The chemical structure of (iso)masticadienonic acid and 3-0-acetyl-3-epi(iso)masticadienonic acid is characterized by a side chain, as for dammarane molecules, but with a carboxylic acid end group (Table 12.1). Under pyrolysis conditions this side chain is susceptible to cleavage as demonstrated by the presence, among the pyrolysis products of mastic, of 2-methyl-pent-2,4-dienoic acid, that perfectly matches with the chemical structure of the side chain end. In addition 3-(9-acetyl-3-epi-(iso)masticadienolic acid also loses the acetyl group and, in contrast to masticadienonic acid, is not detected at all. 

The spectrum of benzyl acetate is shown in Figure 9.56. The parent peak at m/z 150 is prominent (Rule 1) as is the tropylium ion peak at m/z 91 (Rule 2). The base peak at m/z 108 is due to a rearrangement (Rule 4) after cleavage of the acetyl group which itself gives a prominent peak at m/z 43... 

The same thiosugar derivatives were condensed with the monobrominated porphyrin 123 in dry DMF, giving rise to the expected compounds 124b in good yields and from these, by cleavage of the acetyl groups, the desired compounds 124a have been obtained (Scheme 18).81... 

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