Acetanilide, hydroxylation

Commercial PCB Mixtures. Relatively little information is available on hepatic effects of acute-duration oral exposure to PCBs. Liver microsomal enzyme activity (aminopyrine N-demethylation and acetanilide hydroxylation) was increased in rats exposed to 0.5 mg/kg/day (lowest tested level)... 

Vrocttd precisely as in the Determination of the Number of Hydroxyl Groups in Phenol, except that after weighing the flask A, run in about i ml. of pure aniline, and weigh again. Then continue exactly as before. The acetanilide which is formed usually remains in solution when the contents of the flask A are diluted with water for hydrolysis. 

Production is by the acetylation of 4-aminophenol. This can be achieved with acetic acid and acetic anhydride at 80°C (191), with acetic acid anhydride in pyridine at 100°C (192), with acetyl chloride and pyridine in toluene at 60°C (193), or by the action of ketene in alcohoHc suspension. 4-Hydroxyacetanihde also may be synthesized directiy from 4-nitrophenol The available reduction—acetylation systems include tin with acetic acid, hydrogenation over Pd—C in acetic anhydride, and hydrogenation over platinum in acetic acid (194,195). Other routes include rearrangement of 4-hydroxyacetophenone hydrazone with sodium nitrite in sulfuric acid and the electrolytic hydroxylation of acetanilide [103-84-4] (196). 

Udenfriend et al. observed that aromatic compounds are hydroxyl-ated by a system consisting of ferrous ion, EDTA, ascorbic acid, and oxygend Aromatic and heteroaroinatic compounds are hydroxylated at the positions which are normally most reactive in electrophilic substitutions. For example, acetanilide gives rise exclusively to the o-and p-hydroxy isomers whereas quinoline gives the 3-hydroxy prod-uct. - The products of the reaction of this system w ith heterocyclic compounds are shown in Table XIII. 

B. Preparation of acetanilide. Since ketene is a highly reactive gas, it is usually prepared for immediate consumption instead of being isolated as such. It reacts with various groups which contain hydrogen, such as hydroxyl, amino, mercaptan, hydroxylamino, etc., forming acetyl derivatives. 

Oxidations Cytochrome P450-dependen1 Aromatic hydroxylations R ft oxidations C T— C J i / °" j Acetanilide, phenobarbit phenylbutaz warfarin, 17 c naphthalene... 

Hydroxamic acids (4, 202). This oxidant is preferred for oxidation of tri-methylsilylated amides to hydroxamic acids. Although the yields on oxidation of silylated secondary aliphatic amides with 1 are usually only moderate (15-40%), hydroxylation of acetanilides proceeds consistently in yields of 40-50%. The reaction is efficient for oxidation of benzoxazinones, for example, 2->3. The products are useful herbicides because of inhibition of auxin. 

Because the half-life of the epoxide intermediate is short, immediate rearrangement or reaction may lead to a single metabolite or a variety of substituted metabolites. The intermediacy of an epoxide intermediate can be inferred by the identification of para-and meta-hydroxylated and dihydrodiol metabolites, although their relative abundances will vary with substitution and steric considerations. Acetanilide, like phenobarbital discussed previously, exemplifies the aromatic compounds that rearrange rapidly following CYP-mediated arene epoxide formation leading to a single metabolite, as shown in Scheme 11.10. 

FIGURE 16.1 Metabolism of acetanilide. The major route of metabolism is via hydroxylation to form 4-hydroxyacetanilide (acetaminophen). Less than 1% is deacety-lated to form anilme. 

In 1959, we reported that treatment of rats with benzo[a]pyrene had a selective stimulatory effect on the hydroxy lation and N-demethylation of some foreign compounds but not others. Treatment of rats withbenzo[a]pyrene had a large stimulatory effect on the hydroxylation of benzo[a]pyrene, acetanilide, and zoxazolamine, but there was little or no effect on the hydroxy lation of chlorzoxazone (Table 1) (28). Similarly, treatment of rats with benzo[a]pyrene markedly stimulated the N-demethylation of 3-methyl-4-monomethylaminoazobenzene (3-Me-MAB) but had a much smaller stimulatory effect on the N-demethylation of N-methy 1-aniline, and this treatment inhibited the N-demethylation of diphenhydramine (Benadryl ) and meperidine (Table 1) (28). These studies suggested a family of monooxygenases with individual members that were under separate regulatory control. In additional studies, we found that treatment of rats withbenzo[a]pyrene stimulated... 

Hydroxylation of drugs Decrease liver, antipyrine, acetanilide, and zoxazolamine, 60% (AlO) 0... 

AlO. Axelrod, ]., Udenfriend, S., and Brodie, B. B., Ascorbic acid in aromatic hydroxylation. III. Effect of ascorbic acid on hydroxylation of acetanilide, aniline and antipyrine in vivo. J. Pharmacol. Exptl. Therap. Ill, 176-181 (1954). 

Figure 4. Hydroxylation of 4-suhstituted acetanilides with microsomal aryl hydroxylases...

The reagent, peroxytrifluoroacetic acid, also causes migrations of tritium and deuterium during 4-hydroxylation of 4-tritio(deutero) acetanilide and 4-deuterochlorobenzene (Figure 11). The retentions with the acetanilides are lower (8 and 10% vs. 30 and 45% ) than those obtained on enzymatic hydroxylation while the retention obtained with the chlorobenzene is higher (70% vs. 54% ) than the value obtained on enzymatic hydroxylation. Other hydroxylating systems as those of... 

Figure 11. Migration of tritium and deuterium during hydroxylation of acetanilides and chlorobenzene with peroxytrifluoroacetic acid...

Hydroxylation of aromatic compounds, e. g. salicylic acid, phenobarbital, acetanilide, synthetic and natural estrogens, diphenyl. 

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