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The biochemistry of aromatic amines. II. The conversion of arylamines into arylsulphamic acids and arylamine-N-glucosiduronic acids
... However, many chemicals contain functional groups that allow them to form conjugates directly, without prior oxidation. For example, carcinogenic aromatic amines can form A'-glucuronides (11). Thus, A'-glucuronidation of aromatic amines can compete with A'-hydroxylation. ...
... The W-glucuronide was synthesized by modification of the methods of Boyland ei al. (11) and Lilienblum and Bock (12). Equal volumes of 400 mM D-glucuronic acid in ammonium acetate (100 mM) buffer, pH 7.4, and 20 mM benzidine free base in ethanol were mixed. ...
The mechanism by which benzidine induces bladder cancer in dog was evaluated by assessing me tabolism of [3H]benzidine by dog liver slices and microsomes. Slices incubated with 0.05 mM [3H]benzidine exhibited a 32.5 min peak, which was also produced when microsomal incubations were supplemented with UDP-glucuronic acid. In contrast to microsomes, very little of the 32.5 min peak was produced with the 100 000 g supernatant fraction. Microsomal metabolism was increased 5-fold by pretreatment with Triton X-100. Very little activity was observed with rat microsomes in either the presence or absence of Triton X-100. This metabolite was also generated by incubating benzidine with glucuronk add at 4°C for 3 days. Thermospray MS identified this metabolite as benzidine N -glucuronide. At 37°C, the t ½ stability of purified N -glucuronide was 99, 25 and 3 min in dog urine adjusted to pH 7.3, 6.3 and 5.3 respectively. The N -glucuronide was quite stable at pH 9.3, in dog plasma, and in aprotic solvents for 4 h at 37°C. Relative to benzidine, its N -glucuronide is weakly bound to plasma proteins but not more reactive with DNA. Thus, detoxification by liver provides a mechanism for accumulation of benzidine in acidic urine, uptake of benzidine into bladder epithelium, and activation of benzidine in bladder. The liver and N -glucuronidation play a potentially important role in the species specificity of benzidine carcinogenesis.
... Sodium (N-4-biphenyl-N-hydmoxy-D-glucumonosylamine) (Chart 1, Structure a) was synthesized by a reaction anabo gous to the synthesis of N-glucunonides from aromatic amines (7). D-Glucuronolactone (1.7 g) was dissolved in 15 ml H2O, and 0.81 g NaHCO3 was added. ...
... By a modification of the procedure of Boyland et a!. (7), utilizing tniethylamine as a catalyst and using sodium ascorbate as an antioxidant, we have succeeded in preparing small quantities of what we believe to be Corn pound a by direct condensation of glucuronic acid with NOH-4-ABP. This compound matches in every respect the chromatognaphic properties of the conjugate isolated from dog urine. ...
The glucuronic acid conjugate of N-hydroxy-4-aminobiphenyl (NOH-4-ABP) has been isolated in relatively pure form from the urine of dogs given 4-aminobiphenyl, utilizing molecular size, ion exchange, adsorption, and partition chromatography. This conjugate is an active mutagen in Salmonella typhimurium strains TA1538 and TA98 but not in TA1535 or TA1537. NOH-4-ABP and 4-nitrosobiphenyl are also highly active in TA1538 and TA98 and inactive in TA1535 and TA1537. These observations support the concept that this conjugate is the water-soluble carrier that delivers the active metabolite to the bladder. A substance of identical chromatographic and spectral properties to the conjugate isolated from dog urine has been synthesized in low yield by the direct condensation of NOH-4-ABP with glucuronic acid. This substance yields NOH-4-ABP on dilute acid hydrolysis. Sodium (N-4-biphenylhydroxylamino-beta-D-glucopyranosid) uronate, the N-O-C isomer, was also synthesized. It was found to have differing chromatographic and chemical properties to the natural conjugate. This evidence suggests that the urinary conjugate is the compound in which conjugation has occurred with the nitrogen atom of the hydroxylamine group rather than the oxygen atom.
... The data presented here demonstrate the enzymatic transfer of the glucuronosyl moiety of UDP-glucuronic acid to an amine acceptor. These observations suggest that this biosynthetic reaction may represent an important pathway for the metabolism of amino compounds and would explain the findings of others that the administration of amines results in the excretion of N-glucosyluronic acids (12,13). It appears likely, on the basis of the evidence presented by Dutton (5) and the current investigation, that a single enzyme catalyzes the transfer of glucuronic acid to phenolic, alcoholic, carboxylic, and amino acceptors, although a definitive answer must await purification of the enzyme. ...
... Thus, N-desulfated heparin is prepared under mild conditions that do not cause the hydrolysis of 0-sulfate groups in this polysaccharide (52). The instability of the N-sulfate linkage was also demonstrated for simpler sulfamates that are excreted after the administration of arylamines to mammals (24,196) and spiders (228). Authentic sulfate esters are known to differ in stability toward nonenzymic hydrolysis (i.e., the arylsulfates are easily hydrolyzed, whereas esters such as choline 0sulfate [232] and keratan sulfate [141] are reportedly resistant to autoclaving). ...
Arylamines and nitroarenes are intermediates in the production of pharmaceuticals, dyes, pesticides, and plastics and are important environmental and occupational pollutants. N-Hydroxyarylamines are the toxic common intermediates of arylamines and nitroarenes. N-Hydroxyarylamines and their derivatives can form adducts with hemoglobin (Hb-adducts), albumin, DNA, and tissue proteins in a dose-dependent manner. Most of the arylamine Hb-adducts are labile and undergo hydrolysis in vitro, by mild acid or base, to form the arylamines. According to current knowledge of arylamine adduct-formation, the hydrolyzable fraction is derived from the reaction products of the arylnitroso derivatives that yield arylsulfinamide adducts with cysteine. Hb-adducts are markers for the bioavailability of N-hydroxyarylamines. Hb-adducts of arylamines and nitroarenes have been used for many biomonitoring studies for over 30 years. Hb-adducts reflect the exposure history of the last four months. Biomonitoring of urinary metabolites is a less invasive process than biomonitoring blood protein adducts, and urinary metabolites have served as short-lived biomarkers of exposure to these hazardous chemicals. However, in case of intermittent exposure, urinary metabolites may not be detected, and subjects may be misclassified as nonexposed. Arylamines and nitroarenes and/or their metabolites have been measured in urine, especially to monitor the exposure of workers. This review summarizes the results of human biomonitoring studies involving urinary metabolites and Hb-adducts of arylamines and nitroarenes. In addition, studies about the relationship between Hb-adducts and diseases are summarized.
Biological product of sulfisoxazole excreted in the urine after its oral administration was examined chiefly through paper chromatography and paper electrophoresis. It was thereby found that the substances excreted are sulfisoxazole, acetylsulfisoxazole, sulfanilamide, sulfisoxazole-N-sulfonate, and sulfisoxazole-N-glucuronide. Isolation of the substances excreted into the urine was carried out and sulfisoxazole, acetylsulfisoxazole, and an unknown substance were isolated. Other substances were in too minute a quantity or too labile to be isolated.
1-Arylamino-1-deoxy-D-glucuronamide was prepared from D-glucuronamide and arylamine and 1-arylamino-1-deoxy-2, 3, 4-tri-O-acetyl-D-glucuronamide (III) obtained by its acetylation was found to be the same as that obtained from 1, 2, 3, 4-tetra-O-acetyl-D-glucuronamide (α- and β-forms) (IV) and 1-bromo-l-deoxy-2, 3, 4-tri-O-acetyl-α-D-glucuronamide (V). It was revealed from these facts that (II) is an N-glucopyranoside with a pyranose ring.
Examinations were made on the formation of sulfisoxazole N-glucuronide, one of the biological metabolites of sulfisoxazole. The increased excretion of N-glucuronide into the urine after oral administration of sulfisoxazole and further increase in the N-glucuronide by the combined use of glucuronolactone were observed. Formation of sulfisoxazole N-glucuronide was recognized in the aqueous solution, blood, and urine when allowed to stand at 37° for 8 hours after addition of sulfisoxazole and glucuronic acid. It was also found that addition of sulfisoxazole to normal urine and allowing this to stand at 37° for 8 hours resulted in increased formation of the N-glucuronide and this was accompanied with the corresponding decrease of approximately equal amount of free glucuronic acid. From these results, it is pointed out that bioformation of sulfisoxazole N-glucuronide is non-enzymatic as well as being enzymatic, and the effect of (administered) glucuronolactone on detoxication of sulfisoxazole is chiefly acceleration of N-glucuronide-type detoxication process.
Reaction of methyl 1-bromo-1-deoxy-2, 3, 4-tri-O-acetyl-α-D-glucopyranuronate (I) and 1-bromo-1-deoxy-2, 3, 4-tri-O-acetyl-α-D-glucopyranuronamide (VIII) with potassium thiocyanate in acetone afforded the corresponding thiocyanates, (II) and (IX), and their rearrangement by heating gave the corresponding isothiocyanates, (III) and (X). Treatment of (III) and (X) with ammonia in methanol resulted in the formation of identical 1-deoxy-1-thioureido-β-D-glucopyranuronamide (IV), while the reaction with ammonia in dioxane gave methyl 1-deoxy-1-thioureido-2, 3, 4-tri-O-acetyl-β-D-glucopyranuronate (V) and the corresponding uronamide (XI). Treatment of (V) with barium hydroxide afforded barium 1-deoxy-1-thioureido-β-D-glcopyranuronate (VII) and its reaction with hydrazine hydrate gave 1-deoxy-1-thioureido-β-D-glucopyranuronic acid hydrazide (VI). (IV) is much more stable than N-glucuronide of amines in general. Infrared absorption of thioureido group in (V) and (XI) appeared at around 1530-1550cm⁻¹.
o-Aminophenol was given orally to a rabbit and substances in the urine originating from the aminophenol were examined. The presence of o-aminophenol, o-amino-phenyl glucosiduronic acid, o-aminophenyl hydrogensulfate, and o-acetamidophenol were confirmed by individual isolation. 1-o-Hydroxyanilino-1-deoxyglucuronic acid was not isolated directly but its presence was proved indirectly, while o-hydroxy-phenylsulfamic acid and 3-aminophenoxazin-2-one were not detected. Quantitative examination of these substances in the urine after oral administration of 1g. of o-aminophenol showed that approximately 7.6% of the administered aminophenol was excreted per se, 26% as o-aminophenyl glucosiduronic acid, 18% as o-aminophenyl hydrogensulfate, and 1.2% as o-acetamidophenol.
It is a well-known fact that at the time of administration of sulfadrug to normal subjects, its metabolism is done mostly in liver and kidney. From my experimental results, I confirmed the exsistence of autonomous sulfadrug metabolism in the skin like liver and kidney.
Results:
1) After oral administration of p-aminobenzoic acid (PABA) to rabbit, acetyl-PABA was measured quantitativly in the skin and other 10 organs, and the ratio of acetylation in the skin showed the smallest level of all 11 organs.
2) In injured and normal skin, each ratio of acetylation was almost the same.
3) Quantitative analysis of gurucuronic acid in normal skin showed 0.98 mg/100g by modified Fishman's method.
4) Qualitative experiments using paper chromatography and thin layer chromatography showed that metabolized sulfadrug (Sulfathiazole) was identified in spots Rf 0.55, 0.09, after incubating Sulfathiazole in the skin homogenate 2 hrs., at 37°C. Then, both metabolites seem to be N⁴-acetylsulfathiazole and Sulfathiazole-N⁴-gurucosidouronate.
Sodium glutamate and histamine hydrochloride were each administered to man and rabbit and the urine, after lyophilization, was submitted to circular paper chromatography, comparing the results with in vitro experiments. It was thereby found that a ring spot coloring both to ninhydrin and anisidine hydrochloride appeared in both cases and indicated that these amines form N-glucuronide in vivo.
In biochemistry the term ’sulphate ester’ means an ion having the structure RO.SO3. These compounds are therefore half-esters of sulphuric acid (not to be confused with the fully covalent diesters, R.OSO2O.R′, e.g. dimethyl sulphate) and are usually isolated or prepared as the corresponding potassium salts although other cations may confer useful properties. In the following discussion the compound called, for example, phenyl sulphate should therefore strictly be named potassium phenyl sulphate, trimethylammonium phenyl sulphate, etc. as appropriate. In metabolic experiments the nature of the cation is unimportant, except in so far as it itself may have biological effects, because the sulphate esters are salts of strong acids and so are fully ionised at any pH likely to be encountered in biological systems. The corresponding free acids, for example phenyl hydrogen sulphate, C6H5O.SO3H, are unstable and cannot normally be isolated. The preparation and some properties of various types of sulphate ester have recently been summarised by Roy and Trudinger (1970).
1. The production of sulfate conjugates is a well-known and established pathway within the field of xenobiotic metabolism. In addition to the usual attachment of a sulfonate grouping via an oxygen atom (O-sulfonates) to yield a sulfate conjugate, so-called ‘N-sulfates’ (N-sulfonates) have been reported and ‘S-sulfates’ (S-sulfonates) mooted to exist.
2. The few examples cited in the literature where the sulfur atom of the sulfonate group was attached directly to a carbon atom of the xenobiotic (C-sulfonates) and subsequently excreted as a metabolite have been collated, examined and reviewed.
3. The potential mechanisms of formation of these C-sulfonates are discussed, both biological and chemical, the potential rôle of the gut microbiome raised and hopefully by highlighting this curiosity further fruitful investigation will be stimulated.
This chapter focuses on the history of the discovery of the conjugation mechanisms. The majority of the biochemical reactions called conjugations were discovered during the 19th century, largely through the study of the composition of normal and pathological urines. Conjugates are the end products of the metabolism of many natural and foreign chemicals, and it seems logical in view of the methods then used that they should have been found before the oxidation, reduction, and hydrolysis products of foreign compounds that are usually intermediates in the formation of conjugates. The terms conjugated, conjugation, and conjugate have arisen from the use of the German word gepaart to describe the indigo-forming substances in urine. At the present time, two variants of this word are used, namely, detoxication and detoxification with possibly a shade of difference in meaning, the former being the process of reducing toxicity and the latter the capacity for reducing toxicity. Nearly all the enzyme systems involved in conjugation reactions have natural substrates, and all the conjugating agents have roles in normal intermediary metabolism apart from those involving foreign compounds. The major conjugation reactions are relatively few in number, and the conjugating agents are derived mainly from the animal's carbohydrate and amino acid sources.
Die Fähigkeit, aus der Umwelt aufgenommene Substanzen unter Angleichung zum eigenen Aufbau zu benutzen (Stoffwechsel und Wachstum, Bedingungen des individuellen Lebens) und die eigene Art durch Bildung neuer, gleichartiger Lebewesen zu erhalten und zu vermehren (Fortpflanzung, Bedingung des Lebens der Art), ist allen belebten Organismen gemeinsam. Wir finden sie beim primitivsten Einzeller nicht weniger als bei Pflanze, Tier und Mensch. Diese „vegetativen Funktionen“ gelten deshalb mit Recht als Kriterium des Lebens.
Drug molecules contain a vast array of structural moieties that can undergo a variety of biotransformation reactions. When studying the biotransformation of a new chemical, the first step is to examine the structure of the molecule and list the possible reaction types it could undergo and the drug metabolizing enzymes that can catalyze those reactions. This can direct the investigator to the experimental approaches best suited to study the metabolism of the new compound. In this article, drug metabolism reactions are described, organized by the chemical substituents frequently present in drug molecules. Mechanisms of these biotransformation reactions are described and illustrated with examples.
carcinogenesis;cancer;aromatic amines;chemical workers;experimental animals
The duration of drug action is generally limited by the rate of conversion of therapeutic agents to inactivate metabolites, since most drugs must be metabolized before they are excreted in urine, air or bile. Without mechanisms for the metabolism of foreign compounds, little of our present drug therapy would be possible, for many therapeutic agents would evoke their effects for too long a time; in fact, many drugs like chlorpromazine or thiopental would act for virtually a lifetime.
The main factors which affect the duration and intensity of drug action are absorption, distribution, excretion, and metabolism; in this chapter attention will be focused on one important factor, the metabolism of antineoplastic agents. The metabolism of a drug can lead to an increase, a decrease, or no change in the pharmacologic or toxicologic activity of that drug. The catabolic reactions which are usually directed toward enhancing the elimination of a drug are emphasized in this and the preceding chapter. The anabolic processes by which conversion of drugs to more complex forms, and, in some cases, incorporation into body constituents occurs, have been discussed (Johns, Chapt. 14, this volume). In the latter case assimilation can occur only when the enzymes involved in intermediary anabolism cannot distinguish the antineoplastic compound from endogenous substrates because of a close resemblance in structural and/or physicochemical properties. Such a substitution of a drug for a natural metabolite is defined by the term “parametabolite” where substitution in a morphological, as well as a functional sense can occur. When the drug substitutes for the natural metabolite only in a morphological sense, with a resultant blockage in the normal biochemical process, the drug is called an antimetabolite.
This chapter focuses on sulfoconjugation and sulfohydrolysis. Sulfur has played an important biological role since the beginnings of life on Earth. It is an extremely reactive element and participates in an extraordinary range of chemical linkages in a wide variety of biological compounds. Sulfoconjugates constitute a very diverse and widespread group of compounds, representatives of which are to be found in microorganisms, lower and higher plants, and throughout the animal world. They are so diverse in their distribution and in their chemical nature that very few laboratories have ever considered the group as a whole. Thus, in the field of drug metabolism, the term sulfoconjugate is generally synonymous with the sulfoconjugates of steroids and phenols, whereas the connective tissue biochemist would regard the term as synonymous with the acidic glycosaminoglycans. There have been no reports of sulfohydrolases being active toward arylamine sulfamates, but the spleen enzyme that liberates the N-sulfate groups from heparin is without activity toward phenyl sulfamate, although the latter compound inhibits the activity of the enzyme toward heparin.
Thirty one new sodium heterosulfamates, RNHSO 3 Na, where the R portion contains mainly thiazole, benzothiazole, thiadiazole and pyridine ring structures, have been synthesized and their taste portfolios have been assessed. A database of 132 heterosulfamates (both open-chain and cyclic) has been formed by combining these new compounds with an existing set of 101 heterosulfamates which were previously synthesized and for which taste data are available. Simple descriptors have been obtained using (i) measurements with Corey-Pauling-Koltun (CPK) space-filling models giving x, y and z dimensions and a volume V CPK , (ii) calculated first order molecular connectivities (1 χ v) and (iii) the calculated Spartan program parameters to obtain HOMO, LUMO energies, the solvation energy E solv and V SPARTAN . The techniques of linear (LDA) and quadratic (QDA) discriminant analysis and Tree analysis have then been employed to develop structure-taste relationships (SARs) that classify the sweet (S) and non-sweet (N) compounds into separate categories. In the LDA analysis 70 % of the compounds were correctly classified (this compares with 65 % when the smaller data set of 101 compounds was used) and in the QDA analysis 68 % were correctly classified (compared to 80 % previously). TheTree analysis correctly classified 81 % (compared to 86 % previously). An alternative Tree analysis derived using the Cerius2 program and a set of physicochemical descriptors correctly classified only 54 % of the compounds.
The effect on taste of introducing a heteroatom(s) in place of a carbon atom(s) in sulphamate tastants has been examined in this work. Seventy sets of heterosulphamates and their corresponding carbon analogues (130 compounds in total) were examined. This interesting database was assembled by bringing together series of heterocompounds and suitable nonhetero analogues from the literature, by the synthesis in this work of 15 new heterosulphamates and two new carbosulphamates, which was necessary “to match up” with known carbosulphamate analogues and by making taste predictions for ten carbosulphamates which are unknown, using existing well-established structure-taste relationships (SARs). A sulphur atom replaced a carbon atom in 18 cases, either oxygen or an –OH group replaced carbon in 16 cases, and there are 29 examples where a nitrogen atom or an –NH group replaced carbon. Finally, there are six instances of a “double carbon–carbon, nitrogen–nitrogen substitution” and one of a treble carbon, nitrogen substitution. The overall picture shows that in 33 instances no change in taste was found when substitution occurred, in 29 instances sweet taste (S) was removed giving a nonsweet compound (N), and in eight instances a nonsweet material (N) became sweet (S). Replacement of oxygen by sulphur resulted in the introduction of sweetness in three cases out of four examined. Several important findings were made and a number of new structure-taste relationships have been derived for heterosulphamates.
Biochemical processes of conjugation include the formation of glucuronides, sulphuric esters, sulphamates, phosphoric esters and mercapturic acid derivatives. A result of the conjugation is the production of compounds more ionized and more water soluble than parent compounds. The significance of these substances in the animal kingdom is pointed out. Mercapturic acid formation from naphthalene as well as the general significance of conjugation processes in detoxication are discussed.
The metabolic fate of 2-amino-3,8-dimethylimidazo[4,5- f ] quinoxaline (MeIQx), a carcinogen formed in cooked meat and fish, has been investigated in male Sprague-Dawley rats. Five metabolites were recovered from bile of animals given an intragastric dose of {2- ¹⁴ C]MeIQx. These accounted for nearly all of the radioactivity in bile. The chemical structures of these metabolites were elucidated by proton NMR, UV and mass spectroscopy. Three structures may be assigned unambiguously: two sulfamates, N -(3,8.dimethylimidazo [4,5 f ]quinoxalin-2-yl)sulfamic acid and N -(8-hydroxymethyl-3-methylimidazo[4,5 f ]quinoxalin-2-yl) sulfamic acid, and N -(8-one glucuronide, N ² (β-1-glucosiduronyl)-2-amino-3,8-dimelhyliinidazo [4,5 f ]quinoxaline In addition, an acetyl and a glucosiduronyl conjugate of 5-hydroxy-MeIQx were observed. The spectral evidence did not allow an unambiguous assignment of the site of conjugation. The two glucuronides were excreted in urine and the sulfamate of MeIQx was found in feces as well as urine. All five metabolites were found to be non-mutagenic to Salmonella typhimurium TA98 with or without metabolic activation. The glucuronide conjugates were found also to be non-mutagenic when β- glucuronidase was incorporated with S-9 mixture in the mutation assay, and thus all appear to be detoxification products. The previously reported metabolite, 2-amino-8-hydroxymethyl-3-methylimidazo[4,5 f ]quinoxaline which is mutagenic to Salmonella typhimurium TA98 with metabolic activation, was identified as a minor component in both urine and feces.
(A) A series of sulfur trioxide complexes have been employed in the sulfation of alcohols. There are many examples extensively documented in the literature; tert-butyl alcohol and 3-methyl-3-pentanol were successfully converted to their sulfate ester salts by reaction with SO3-pyridine or SO3-Et3N. (B) Sulfonation proceeds via oxidation of hydrocarbons resulting in carbocation formation. Saturated aliphatic hydrocarbons possessing a carbonyl component are sulfonated upon the carbon adjacent to this entity. Unsaturated hydrocarbons are sulfonated quite easily forming a β-sultone or a solvated carbenium ion. However, (2SO 3)-pyridine sulfonates butyric acid quantitatively. (C) Sulfonation is also achieved via insertion of SO3 into a carbon-metal bond. Organometallic compounds treated with SO3-Me3N, a mild reagent, react to produce the corresponding sulfonic acids - a process suitable for both aliphatic and aromatic hydrocarbons. (D) 2% Cross-linked p-bromopolystyrene, may also be converted to its corresponding aromatic polystyrenesulfonic acid via sulfonation of its lithium derivative. (E) Initially amines were sulfamated by treatment with chlorosulfonic acid. Both mono- and disubstituted sulfamates may be prepared with ease. SO 3-Pyridine is used extensively in the sulfamation of primary amines. The amine salt formed is treated with hydroxide and the alkali sulfamate extracted and recrystallised finally from 95% ethanol. (F) Electron donating groups, for example methyl, ethoxy etc., promote sulfamation however electron-withdrawing groups such as nitro substitutents hinder the reaction. Utilizing α-picoline (2-methylpyridine) however overcomes this problem and the resulting sulfamate may be extracted in good yield. (F) SO 3-amine adducts, such as SO3-pyridine, may be affectively utilized in the reduction of aromatic (diphenyl sulfoxide) and aliphatic sulfoxides at room temperatures resulting in quantitative yields of the corresponding sulfide.
The photolysis (254 nm) of a series of para-substituted phenylsulphamates, XC6H4NHSO3Na [XH (1a), CH3(1b), F (1c), Cl (1d), Br (1e) and NO2(1f)] in degassed methanolic solutions has been examined. For 1a and 1b photo-Fries type rearrangements to sulphonic acids and photodegradation to anilines have been observed. The halogenosulphamates 1c–1e do not rearrange but degrade to anilines and are photosolvolysed to p-methoxyphenylsulphamic acid. No notable spectral changes took place during the irradiation of 1f over a relatively long period. Substrate concentration studies, radical scavenging and sensitization and quenching experiments on 1b indicate that, as previously found for 1a, its photolysis involves an intramolecular radical mechanism with the participation of two triplet states.
A data set of 101 hetero- (both cyclic and open chain) sulfamate sodium salts, whose taste data are known, have been assembled and divided into sweet (S) (20 compounds) and non-sweet (N) (81 compounds) categories. The data set is made up of 56 compounds reported earlier, 32 synthesised in this work and another 13 reported since the earlier publications. Using the parameters x, y and z (measured for the RNH portion of RNHSO3Na using CPK models) and first order molecular connectivity, 1χν it has been possible to achieve a correct classification rate of approximately 65% using linear discriminant analysis (LDA): a compound is N if −3.285 + 0.439x + 0.662y + 0.236z − 1.27 1χν > 0 otherwise it would be S. Using quadratic discriminant analysis (QDA) the classification rate increased to approximately 80%. Finally a Tree-based analysis gave an 86% classification rate but performed poorly in classifying correctly the S group of compounds.
A phenolate anion reacts with persulfate ion in alkaline solution to yield a product in which a sulfate group enters the ring para or ortho to the phenolic group. Para substitution predominates. Subsequent acid‐catalyzed hydrolysis yields the dihydric phenol.
The reaction was discovered by Karl Elbs in 1893 and named the Elbs persulfate oxidation . The reaction is generally applicable to ortho ‐, meta ‐, and para ‐substituted phenols with isomer distributions. The yields are not very high, particularly from para ‐substituted phenols, but the major contaminant is usually unchanged starting material that can be separated easily from the intermediate sulfate ester by solvent extraction. Other generally oxidizable groups such as an aldehyde or a double bond are usually not affected under the reaction conditions. The reaction was last thoroughly reviewed in 1951. T. R. Seshadri has made major contributions to the development of the Elbs oxidation. Nearly 30% of the references in this chapter are due to him and his colleagues.
By analogy with the Elbs persulfate oxidation of phenols, it might be expected that aromatic amines would react with persulfate to give p ‐aminoaryl sulfates. Although the Elbs reaction had been known since 1893, it was not until 60 years later that Boyland et al. reported the extension of this reaction to aromatic amines. In accordance with expectations, aminoaryl sulfates were indeed the major products of the reaction, but, unexpectedly, the substitution took place exclusively ortho to the amino group rather than predominantly in the para position as in the phenol oxidation. Para substitution takes place only if the ortho positions are occupied by substituents other than hydrogen. Boyland and Sims explored the preparative aspects of this reaction in a series of papers. It seems appropriate to name the reaction the Boyland–Sims oxidation. Primary, secondary, and tertiary aromatic amines are all converted to the corresponding o ‐aminoaryl sulfates under conditions similar to those used for the Elbs oxidation, that is, room temperature or below, aqueous alkali, and equimolar quantities of amine and persulfate.
The aminolysis and hydrolysis of several sulphamate esters, RNHSO2ONp (R = PhCH2, Ph, 4-MeC6H44, 3-MeC6H4, 4-FC6H4, 4-ClC6H4, 3-ClC6H4, H; Np = 4-NO2C6H4) were been studied in 50% (v/v) aqueous acetonitrile at various temperatures. Reaction of the esters with an amine (R1NH2) gives −ONp and both sulphamide, (RNHSO2NHR1) and sulphamate (RNHSO2O−R1NH3+) products. First-order rates were determined by the appearance of −ONp and sometimes also by the disapperance of ester. The reaction was found to be independent of amine type and concentration and at the high pHs that obtain the substrate esters are fully ionized. A Hammett ρacyl of −;1·8 was obtained for the decomposition of the sulphamate anions and this is consistent with substantial NS bonding in the transition state leading to N-sulphonylamine, RNSO2. This intermediate then partitions very rapidly, reacting with R1NH2 and H2O respectively. ΔH‡, ΔS‡ and a deuterium solvent isotope effect were determined and were also interpreted in favour of the proposed mechanism. The dimethyl sulphamate ester (Me2NSO2ONp) does not react under the conditions used.
A cDNA of amine sulfotransferase-RB1 (AST-RB1), which efficiently catalyzes 4-phenyl-1,2,3,6-tetrahydropyridine (PTHP) sulfation, has been isolated by immunoscreening of a rabbit liver cDNA library. The cDNA consisted of 1,117 base pairs and encoded a protein of 301 amino acids with a molecular weight of 35,876. The deduced amino acid sequence matched at six positions those of peptide fragments obtained from purified AST-RB1 protein. The sequence had less than 38% identity at the amino acid level with cytosolic sulfotransferases in mammals, although high degrees of similarity were observed with regions conserved throughout mammalian sulfotransferases. These results indicate that AST-RB1, arbitrarily named sulfotransferase 3A1 (ST3A1), constitutes a new and third gene family of cytosolic sulfotransferases in mammals. ST3A1 expressed in Escherichia coli as a fused protein catalyzed sulfation of amines such as PTHP, aniline, 4-chloroaniline, 2-naphthylamine, and desipramine, but barely O-sulfation of typical aryl and hydroxysteroid sulfotransferase substrates. These data unequivocally demonstrate the existence of a cytosolic sulfotransferase showing a high selectivity for amine substrates, and indicate that multiple forms of sulfotransferase mediate sulfation of xenobiotics in mammalian livers.
Aromatic amines and heterocyclic aromatic amines (HAAs) are structurally related classes of carcinogens that are formed during the combustion of tobacco or during the high-temperature cooking of meats. Both classes of procarcinogens undergo metabolic activation by N-hydroxylation of the exocyclic amine group to produce a common proposed intermediate, the arylnitrenium ion, which is the critical metabolite implicated in toxicity and DNA damage. However, the biochemistry and chemical properties of these compounds are distinct, and different biomarkers of aromatic amines and HAAs have been developed for human biomonitoring studies. Hemoglobin adducts have been extensively used as biomarkers to monitor occupational and environmental exposures to a number of aromatic amines; however, HAAs do not form hemoglobin adducts at appreciable levels, and other biomarkers have been sought. A number of epidemiologic studies that have investigated dietary consumption of well-done meat in relation to various tumor sites reported a positive association between cancer risk and well-done meat consumption, although some studies have shown no associations between well-done meat and cancer risk. A major limiting factor in most epidemiological studies is the uncertainty in quantitative estimates of chronic exposure to HAAs, and thus, the association of HAAs formed in cooked meat and cancer risk has been difficult to establish. There is a critical need to establish long-term biomarkers of HAAs that can be implemented in molecular epidemioIogy studies. In this review, we highlight and contrast the biochemistry of several prototypical carcinogenic aromatic amines and HAAs to which humans are chronically exposed. The biochemical properties and the impact of polymorphisms of the major xenobiotic-metabolizing enzymes on the biological effects of these chemicals are examined. Lastly, the analytical approaches that have been successfully employed to biomonitor aromatic amines and HAAs, and emerging biomarkers of HAAs that may be implemented in molecular epidemiology studies are discussed.
A total of 28 new five-membered aromatic ring thiazolyl-, benzothiazolyl-, and thiadiazolylsulfamates, as their sodium salts, have been synthesized and combined with 30 known similar heterocyclic sulfamates to create a database for the study of structure-activity (taste) relationships (SARs) in this heterocyclic subgroup, which is known to contain a somewhat disproportionate number of sweet compounds compared to other groups of tastants. A series of nine parameters (descriptors) to describe the properties of the sulfamate anions were calculated in Spartan Pro and HyperChem programs. These are the highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), length of the molecule, dipole moment, area, volume, E(solv), sigma (from the literature), and log P. The taste data for all 58 compounds were categorized into three classes, namely, sweet (S), nonsweet (N), and nonsweet/sweet (N/S). Discriminant analysis only classified 44 of the 58 compounds correctly. Classification and regression tree analysis (CART) using the S_ Plus program proved highly effective, in that the derived tree correctly classified 46 compounds from a training set of 48 and, from a computer randomly selected test set of 10 compounds, 7 had their taste correctly predicted. A second tree was grown using the additional taste category N/S, and this tree also performed extremely well, with 8 of the 10 compounds in the test set correctly classified. These trees should be very reliable for predicting the tastes of other heterocyclic sulfamates, which belong to the subset used here.
Uridine 5'-diphosphoglucuronic acid-fortified hepatic microsomes from dogs, rats, or humans rapidly metabolized [3H]-N-hydroxy-2-naphthylamine (N-HO-2-NA) to a water-soluble product that yielded 98% of the parent N-hydroxy amine upon treatment with beta-glucuronidase. The metabolite was identified as N-(beta-1-glucosiduronyl)-N-hydroxy-2-naphthylamine from ultraviolet, infrared, and mass spectral analyses of the glucuronide and its nitrone derivative. Incubation of N-hydroxy-1-naphthylamine (N-HO-1-NA), N-hydroxy-4-aminobiphenyl (N-HO-ABP), or the N-hydroxy derivatives of 2-aminofluorene, 4-aminoazobenzene, or N-acetyl-2-aminofluorene with uridine 5'-diphosphoglucuronic acid-fortified hepatic microsomes also yielded water-soluble products. beta-Glucuronidase treatment released 80 to 90% of the [3H]-NHO-1-NA and [3H]-N-HO-ABP conjugates as tritiated ether-extractable derivatives. N-HO-1-NA, N-HO-2-NA, and N-HO-ABP and the glucuronides of these N-hydroxy arylamines were relatively stable and nonreactive near neutral pH. At pH 5, the N-glucuronide of N-HO-2-NA and the presumed N-glucuronides of N-HO-1-NA and N-HO-ABP were rapidly hydrolyzed to the N-hydroxy arylamines that were then converted to reactive derivatives capable of binding covalently to nucleic acids. These data support the concept that arylamine bladder carcinogens are N-oxidized and N-glucuronidated in the liver and that the N-glucuronides are transported to the urinary bladder. The hydrolysis of the glucuronides to N-hydroxy arylamines and the conversion of the latter derivatives to highly reactive electrophilic arylnitrenium ions in the normally acidic urine of dogs and humans may be critical reactions for tumor induction in the urinary bladder.
1. 2,4-Diamino[ring-U-14C]anisole.2HCl administered intraperitoneally to rats is excreted chiefly via the urine (79 and 85% of the dose in 24 and 48 h, respectively). The isotope in the faeces was 2.1 and 8.9% of the dose at 24 and 48 h. 2. The major metabolic pathway was acetylation of the amine groups(s), resulting in 4-acetylamino-2-aminoanisole and 2,4-diacetylaminoanisole. 3. Oxidate pathways yielded 2,4-diacetylaminophenol (O-demethylation), 5-hydroxy-2,4-diacetylaminoanisole (ring hydroxylation), and 2-methoxy-5-(glycol-amido)acetanilide or its isomer (omega-oxidation). 4. These major metabolites were excreted in the urine both as free and glucuronic acid conjugates.
The metabolism and disposition of intravenously infused radioactive 3,4,4′-trichloro[14C]carbanilide (TCC) in the adult and newborn rhesus monkey have been evaluated. In adult animals the major metabolic reactions were N-glucuronide formation or ring hydroxylation followed by conjugation to glucuronic acid or sulfuric acid. Removal of 14C from the plasma was biphasic; TCC and the N-glucuronides accounted for the fast phase, and the O-sulfate conjugates accounted for the slow phase. The major urinary metabolites were the N-glucuronides of TCC. The tissue residue of 14C was low in the monkeys and was limited primarily to tissues that are active in drug metabolism (liver, kidneys, and lungs). The bile was the major route of elimination with glucuronide conjugates as the major radioactive component. Enterohepatic circulation was extensive but did not affect the plasma concentrations or the elimination kinetics of TCC-derived material from the plasma. The newborn monkey also metabolized TCC by ring hydroxylation or N-glucuronidation. The plasma kinetics were similar to those observed in adults as was the tissue distribution. Unlike the adult, there were only very low amounts of O-glucuronides and, instead, high amounts of O-sulfate conjugates. It is concluded that the infant monkey can readily metabolize and eliminate TCC.
1. Urinary excretion of the radioactivity in 24 h after oral administration of [14C]tiaramide hydrochloride was 67% of the dose in mice, 59% in rats, 41% in dogs and 74% in monkeys. 2. The serum half-lives of tiaramide after intravenous administration were approximately 0-2 h in mice, 0-8 h in rats and 0-5 h in dogs. 3. Marked species variations were noted in the composition of metabolites in the serum and urinary radioactivity. The major metabolites found were 1-[(5-chloro-2-oxo-3(2H)-benzothiazolyl)acetyl]-piperazine (DETR) and 4-[(5-chloro-2-oxo-3(2H)-benzothiazolyl)acetyl]-1-piperazineacetic acid (TRAA) in mice, TRAA and 4-[(5-chloro-2-oxo-3(2H)-benzothiazolyl)acetyl]-1-piperazineethanol 1-oxide (TRNO) in rats, TRNO and tiaramide-O-glucuronide (TR-O-Glu) in dogs, and TRAA and TR-O-Glu in monkeys. 4. The binding of tiaramide to plasma protein of the various species of animals and human was about 24-34% and the extent of the binding of tiaramide to human plasma protein was independent of drug concentration within the range of 1-100 micron.
The absorption, distribution and excretion of 6-aminochrysene-5, 6-14C were investigated in rats. The highest concentration of radioactivity in the organs at 48 hr after an i. p. dose were in the liver and kidneys. Only 12% of the administered radioactivity was recovered in the urine and 56% from the feces during a ten day period. Up to 42% of the dose was excreted in the bile during 48 hours. The major biliary metabolite of 6-aminochrysene was the N-glucuronide of 6-aminochrysene. 12-Hydroxy-6-acetylaminochrysene was present in the urine as a glucuronide and in unconjugated form in the feces.
1. The metabolism of [14C]aniline in the cattle tick, Boophilus microplus (Canestrini) at 40 and 300 mug per animal) and in the spider, Nephila plumipes (at 40 mug per 100 mg) were studied. 2. In both species hydroxylation occurred yielding both free and conjugated o-and p-aminophenols. 3. The water-soluble metabolites affording aniline on acid hydrolysis were examined, and gamma-glutamylanilide (23% of dose) was identified as a tick metabolite (40 mug dose). This metabolite was not found in extracts of dosed spiders.
Urine samples from workers exposed to 4,4'-methylenebis (2-chloroaniline) (MbOCA) contain a labile metabolite(s) that, on hydrolysis, yields the parent compound at concentrations two to three times those of free MbOCA. Evidence has now been obtained that the major labile metabolite is an N-glucuronide of MbOCA. The N-glucuronide of MbOCA was synthesised chemically, characterised by thermospray mass spectrometry, and found to have a pseudomolecular (M + 1) ion at m/z 443/445. MbOCA and [14C] uridine diphosphoglucuronic acid [( 14C]UDPGA) were incubated with liver microsomes from rats induced with polychlorinated biphenyls. The stoichiometry of the reaction product was about 1:1 (MbOCA:UDPGA). This product, the chemically synthesised glucuronide, and the labile urinary metabolite had identical chromatographic and hydrolytic (heat and beta-glucuronidase) properties. These studies show that the major labile conjugate of MbOCA in the urine of workers exposed to this compound is probably the mono N-glucuronide. In view of the lability of this compound and the fact that its concentration in urine is two to three times that of free MbOCA, it is essential that any strategy for the biological monitoring of exposed workers takes into account the N-glucuronide.
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