Improvedsynthesis of 2-hydroxy-p-phenetidine and derivatives

Differences in the reactions of isomeric ortho- and para-aminophenols with hemoglobin

The metabolites of phenacetin, 2-hydroxyphenetidine and 4-nitrosophenetol, rapidly produced ferrihemoglobin both in vivo (dogs) and in vitro. At low concns, 2-hydroxyphenetidine was superior to 4-nitrosophenetol in ferrihemoglobin formation. The kinetics of ferrihemoglobin formation by 2-hydroxyphenetidine in solutions of purified human hemoglobin was biphasic and exhibited an unusual dose response. Similar to p-aminophenols, 2-hydroxyphenetidine was oxidized by oxyhemoglobin, and the oxidation product(s) were reduced by ferrohemoglobin with the formation of ferrihemoglobin. In addition, these oxidation products condensed to 2-amino-7-ethoxy-3H-phenoxazine-3-one (u.v., i.r., 1H-NMR and mass spectroscopy). This metabolite produced ferrihemoglobin by itself and was responsible for the slow phase of ferrihemoglobin formation observed with 2-hydroxyphenetidine. This condensation reaction, which was also observed with 2-aminophenol, prevented thioether formation of the transient o-quinonimines with the cysteine residues of hemoglobin and reduced glutathione as observed with 4-aminophenol and 4-dimethylaminophenol. Phenoxazone formation, which depends on the square of the o-quinonimine concn, was negligible at micromolar concns. At similar concns addition reactions to thiols prevailed also with 2-hydroxyphenetidine and 2-aminophenol. Other electrophilic reactions, e.g. with primary amino groups of amino acids, were insignificant. These dose-dependent differences in the reactions of isomeric aminophenols may explain the low nephrotoxicity of those o-aminophenols capable of forming phenoxazones when given in a single dose. This self-detoxication of some o-quinonimines, however, should not function during long-term exposure to repetitive low doses of such o-aminophenols.

Some new aspects of the metabolism of phenacetin in the rat

1. Four new metabolites of phenacetin in the urine of the rat are described; these are (i) N-acetyl-S-ethylcysteine, (ii) quinol, (iii) acetamide and (iv) probably N-acetyl-S-2-(4-ethoxyacetanilido)cysteine S-oxide. 2. Metabolites (i), (iii) and (iv) were characterized and estimated by g.l.c., by t.l.c., by paper chromatography, by chemical reactions or by radioactive techniques after administration to rats of [ethyl-(14)C]phenacetin and [acetyl-(3)H]phenacetin; metabolite (ii), which was excreted mainly as conjugates of sulphuric acid and glucosiduronic acid, was measured by paper chromatography and characteristic colour reactions after enzymic and chemical hydrolysis of the conjugates. 3. Small amounts of azoxy-4-[ethyl-(14)C]ethoxybenzene and an unknown metabolite were also found in the urine of rats after administration of [ethyl-(14)C]phenacetin. 4. The likely mechanisms and some biological implications of these metabolic reactions are discussed.