Atropine hydrolysis

An antiserum was raised by immunization of rabbits with an immunogen prepared by coupling hyoscyamine to human serum albumin and using [3H]-atropine as tracer. Atropine and hyoscyamine reacted to equal extents with the antibodies. Some structurally related drugs e.g. homatropine or scopolamine as well as atropine hydrolysis products (tropine and tropic acid) did not interfere in the assay. 

Hyoscyamine, Ci,H2303N. This, the most commonly occurring alkaloid of the oup, was obtained by Geiger and Hesse from henbane. Ks hydrolysis into a base and an acid was observed by Hohn and Reichardt. The accepted, empirical formula is due to Ladenburg, who s owed that it was a physical isomeride of atropine. Hyoscyamine... 

When heated with acids or alkalis, hyoscyamine undergoes hydrolysis into tropine and dZ-tropic acid probably via conversion into atropine, and it is this alkaloid which is hydrolysed. According to Gadamer, when hyoscyamine is hydrolysed with cold water the products are inactive tropine and Z-tropie acid. Amenomiya has shown that Ladenburg and Hundt s partially synthetic d- and Z-atropines were probably mixtures of atropine with d- and Z-hyoscyamines. He resolved dZ-tropic acid into the d- and Z- forms, esterified these with tropine in 5 per cent, hydrochloric acid, and so obtained d- and Z-hyoscyamines, the latter identical with the natural alkaloid, d- and Z-Hyoscyamines have also been obtained by Barroweliff and Tutin by the resolution of atropine by means of d-camphorsulphonic acid. 

Reduction of tropanone affords the alcohol epitropanol (13), epimeric with the alcohol obtained on hydrolysis of atropine. 

Several drugs, in particular neuropharmacological agents, feature a car-boxylate group esterified to an aminoalkyl moiety. As a rule, such lipophilic compounds are good substrates for hydrolases, and their duration of action is influenced by their rate of hydrolysis (see also Sect. 7.3.4). A simple example is that of procaine (7.56), which is rapidly inactivated by hydrolysis [41] [76a], Various hydrolases catalyze the reaction, in particular plasma cholinesterase and cellular carboxylesterases. As often reported, atropine and scopolamine are rapidly hydrolyzed by plasma carboxylesterases in rabbits (with very large differences between individual animals), but are stable in human plasma [1] [75] [76a] [110]. 

Both atropine and scopolamine are tertiary amines that cross biological membranes readily. They are well absorbed from the gastrointestinal tract and conjunctiva and can cross the blood-brain barrier. After the intravenous injection of atropine (oL-hyoscyamine), the biologically inactive isomer, D-hyoscyamine, is excreted unchanged in the urine. The active isomer, however, can undergo dealkylation, oxidation, and hydrolysis. 

Diphenoxylate (marketed in combination with atropine as Lomotil in the United States) is chemically related to both analgesic and anticholinergic compounds. It is as effective in the treatment of diarrhea as the opium derivatives, and at the doses usually employed, it has a low incidence of central opioid actions. Diphenoxylate is rapidly metabolized by ester hydrolysis to the biologically active metabolite difenoxylic acid. Lomotil is recommended as adjunctive therapy in the management of diarrhea. It is contraindicated in children under 2 years old and in patients with obstructive jaundice. Adverse reactions often caused by the atropine in the preparation include anorexia, nausea, pruritus, dizziness, and numbness of the extremities. 

After administration, the elimination of atropine from the blood occurs in two phases the t1/2 of the rapid phase is 2 hours and that of the slow phase is approximately 13 hours. About 50% of the dose is excreted unchanged in the urine. Most of the rest appears in the urine as hydrolysis and conjugation products. The drug s effect on parasympathetic function declines rapidly in all organs except the eye. Effects on the iris and ciliary muscle persist for s 72 hours. 

The metabolism of atropine (227) by rat and guinea pig liver microsomes has been studied (197-199). French workers noted the formation of nora-tropine (229), apoatropine (233), and a phenolic metabolite formulated as the ortho-phenol 230 (197, 198) by liver microsomes from the rat, and they reported that hydrolysis of the ester function of 227 did not occur with enzymes from this source (197, 198). The structure of 229 was determined by TLC comparisons of the metabolite with an authentic sample and by correlation of the formation of the metabolite with the release of formaldehyde in the incubation mixture. The structure of 233 was deduced by TLC and UV spectral comparisons of isolated metabolite with authentic sample, and the phenol 230 was identified by TLC color reactions and by comparison with a phenolic sample obtained by Udenfried oxidation of atropine. In the absence of more definitive data on the phenolic products of this reaction, the structure 230 proposed for the phenolic metabolite of atropine... 

Chen et al. used MeOH for precipitation of rat plasma in a 3 1 volume ratio to investigate a broad spectrum of biotransformation products generated from ani-sodine [5], anisodamine [6], atropine [52] and scopolamine [87], Biotransformation products covered a broad spectrum of polarity including sulfo- and glucuronide conjugates, oxidized, hydroxylated, methoxylated and demethylated metabolites of the parent drug as well as its hydrolysis products. Unfortunately, recoveries were not reported (Table 2). 

Fig. 4 Scheme of enzymatic plasma sample preparation for enantioselective analysis of S- and fChyoscyamine. Atropine-containing plasma samples are mixed either with human serum (procedure A) or with rabbit serum (procedure B). The latter one contains atropinesterase (AtrE) whereas human serum does not. AtrE catalyses the stereoselective hydrolysis of S-Hyo, whereas f -Hyo remains unaffected. 

Anticholinergics, such as atropine and oxyphenonium bromide, which are esters of carboxylic acids, were analysed in plasma and urine as pentafluorobenzyl esters [541,542], The method involves ion-pair extraction of the material under analysis, hydrolysis of esters and derivatization of the acid moiety. The minimal detectable amount was found to be 0.15 pg with the use of an ECD. 

Disposition in the Body. Rapidly absorbed after oral administration but it is usually administered together with a small quantity of atropine and this may delay absorption, especially with high doses. It is extensively metabolised by hydrolysis, hydroxylation, and conjugation with glucuronic acid. The major metabolites are diphenoxylic acid (difenoxin), which is active, and hydroxy-diphenoxylic acid in both free and conjugated forms. About 14% and 50% of a dose, respectively, is excreted in the urine and faeces in 96 hours less than 0.1% of a dose is excreted in the urine as unchanged drug in 24 hours. 

Enzymatic hydrolysis is a primary route for elimination of nerve agents. Specifically, treatment for OP intoxication includes atropine, a muscarinic receptor antagonist, an anticonvulsant such as diazepam, and a cholinesterase reactivator, an oxime. It has been found that drag-induced inhibition of ACh release and accumulation in the synaptic cleft, such as adenosine receptor antagonist early in the OP intoxication, improves the chances of survival. Some AChE reactivators, such as bispyridinum oximes, HI 6 and HLo 7 with atropine, are quite effective. 

The failure to find C02 In the expired air of the mice Indicates that the tropic acid moiety in the atropine molecule Is not metabollzed ln accord with the finding that labeled tropic acid Itself was excreted without loss In the urine. The finding of atropine but no tropic acid In the urine of the mice Indicates that hydrolysis of the ester did not occur rapidly. The latter finding was somewhat unexpected because an esterase capable of hydrolysing atropine is present In the livers of many vertebrate species, although It or a similar enzyme appears In the sera of only a few species (93-95). This enzyme Is also able to hydrolyze L hyoscyamine, troplnyl benzoate, and caramlphen (95). 

Their general conclusion was that, although various species differed quantitatively in the relative amounts of particular end products of atropine metabolism, the chemical changes undergone by the molecule In the various species were the same hydrolysis of the ester linkage, hydroxylatlon of the benzene nucleus, glucuronldatlon, and oxidation to C02 ... 

Two fairly recent papers on the metabolic face of atropine In man have been published (104,105) an excellent summary of the work was presented by Kaiser (106). The two subjects In the first of these papers excreted within 24 h 85% of an Intramuscularly Injected dose of 2 mg of alpha-[ C]atroplne. A urine saaq>le collected from one of the subjects between 1.5 and 4 h after injection contained substances that produced four small. Interconnected peaks of radioactivity on a paper chromatogram that were apparently removed by Incubation of the urine with bacterial beta-glucuronldase. Only three clear peaks of radioactivity appeared on the paper chromatograms of this urine after It had been exposed to glucuronidase. Two of these had Rfs chat agreed with those for atropine (the major peak) and for tropic acid (a small peak). The Identity of the third peak, with an Rf below that for atropine, was not determined. After alkaline hydrolysis of this sample of urine, the only radioactive substance detected In the chromatogram had an Rf similar to that of tropic acid thus, the tropic acid... 

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