I-hyoscyamine

A comparison of the activities of these three alkaloids lias been made by Graliam and Gunn using their antagonism to the effects of carbamjd-choline chloride on isolated mammalian intestine. The relative activities found were, atropine sulphate 1 I-hyoscyamine sulphate 2-4 hyoscine hydro bromide 1-5. The results of previous authors are discussed and reasons suggested for some of the differences found. 

The alkaloids of this group are derived from a combination of a piperidine and a pyrrolidine ring, designated as tropane (Figure 14.2). The 3-hydroxy derivative of tropane is known as tropine and is the basic component of atropine. When atropine is hydrolyzed, it forms tropine and tropic acid (a-phenyl-p-hydroxy-propionic acid). Atropine is the tropic acid ester of tropine. It has been prepared synthetically. Tropic acid contains an asymmetric carbon atom. The racemic compound (atropine) as obtained naturally or as synthesized may be resolved into its optically active components, d- and /-hyoscyamine. Atropine is racemic hyoscyamine that is, it consists of equal parts of /-hyscyamine and plant cells and also in the process of extraction, so that the relative proportion of the isomers in the plants and in the preparations varies. However, atropine itself does exist in small amounts in the plants, although most of it is formed from the /-hyoscyamine in the process of extraction. 

N. tfibacuTn of nomicotine in N. glutinosa and of anabasine in N. glauca. In the tropane group, i-hyoscyamine predominates in A. belladonna and f-hyoscine in Datura metel L. (68). The distribution of the alkaloids in a graft whose stock and scion produce different kinds may thus prove illuminating. 

On Datura stramonium stocks similar results have been obtained, and i-hyoscyamine has been isolated from the tomato scions as the aurichloride (76). The fruits when eaten by humans caused dryness of the mouth, dilation of the pupils and other signs of hyoscyamine poisoning according to Krajevoj and Nachev (75) but Vincent and Dulucq-Mathou (80a) were able to find mydriatic alkaloids only in the leaves. Ripe fruits gave none. 

In many instances a useful purpose is served by presenting the chemistry of the alkaloids according to their occurrence in various plant families, genera and species (254). However, it is the opinion of the author that a more direct route to a knowledge of the chemistry of the tropane alkaloids is through (1) the presentation of the chemistry of the alkaloids whose structure is known with certainty (e.g., atropine, i-cocaine, i-hyoscyamine All R groups in formula I will be considered to be hydrogen unless otherwise stated. 

The isolation of the levorotatory hyoscine from the mother liquors from the preparation of i-hyoscyamine from Hyoecyamus muticu L. was reported in 1881. From early analyses (20) the new base was assigned the formula CitHjsOjN but this was subsequently revised to Ci7H2i04N (25, 52). In 1892 a second alkaloid, scopolamine (52), with the formula Ci7Hji04N, was isolated from Scopolia atropoides Bercht and Presl. However, the conversion of hyoscine and scopolamine to the same hydrobromide (25) established that they were one and the same base. 

The military mass intoxications mentioned above were mostly accidental. But in his review, Goodman also includes a history of the deliberate military use of atropine and atropine-like substances, i.e., hyoscyamine (atropine) and hyoscine (scopolamine), both obtainable from plant sources. In one instance ... 

Figure 3. Solubilities of hyoscyamine (I) and scopolamine (2) free bases in supercritical CO, [39]. Reprinted from J. Chromatogr. A, 863, Y. H. Choi et al., Strategies for supercritical fluid extraction of hyoscyamine and scopolamine salts using basified modifiers, 47-55 (1999), with permission from Elsevier Science.

The quantitative racemization of hyoscyamine to atropine was achieved16 by refluxing the methanolic or butanolic solution (catalysed by a base) or, even better, by refluxing in diethylamine. The partial racemization, i.e. epimerization at C-2, of (—)-cocaine to (+)-pseudococaine was effected by strong bases in methanol followed by re-benzoylation of C-3 in pseudoecgonine methyl ester. This interconversion17 allows the detection of small amounts of cocaine in forensic medicine. 

Fig. 3 Chiral separation of atropine (racemic mixture of S- and //-hyoscyamine). Analysis of buffered serum dilution was performed according to John et al. [49] using two consecutively coupled AGP columns (150 mmx2.0 mm I.D., 5 pm) in isocratic mode with solvent A (0.01 M NH4FA, pH 8.0) and solvent B (0.01 M NH4FA in 25 % v/v ACN, pH 8.0) in 85 15 ratio at 300 pi/ min and 40 °C. Detection was done by positive ESI MS/MS in MRM mode...

The second chiral method was presented by John et al. [49], Distinction of hyoscyamine variants from rabbit serum dilutions was enabled on two consecutive AGP columns (each 150 mmx2 mm I.D., 5 pm, ChromTech) coupled to +ESI-MS/... 

The enantioselective procedure of John et al. was also originally applied to monitor concentration-time profiles of atropine and hyoscyamine variants in a PK study in healthy swine (Table 5) [47], Mass spectrometric characteristics with respect to precursor and product ions of atropine and hyoscyamine are summarized in Table 9. Following single i.v. administration of 100 ug/kg, maximum plasma concentrations were found to be 48 ng/ml for atropine and 24 ng/ml for both enantiomers, the dis-tomer /Miyoscyamine and the eutomer. S -hyoscyamine, In contrast to data in human, no stereoselective preference for elimination was found in swine thus substantiating the assumption that hyoscyamine kinetics in man differ from that in swine. 

Fig. 6 Concentration-time profile of antidotal atropine and its enantiomers S- and / -hyoscyamine in plasma of an in vivo swine study. Swine were topically exposed to the nerve agent VR (302 pg/ kg, t0) followed by administration of atropine sulphate (30 pg/kg) and the reactivating oxime HI 6 (12.8 mg/kg) via three i.m. injections into the rear leg at 30 (I), 180 (II) and 330 min (III). Blood samples were collected at distinct time points to generate EDTA plasma. Maximum concentrations were found 4 min after drug administration each. No differences of S- and R-Hyo concentrations were evident underlining similar elimination kinetics for both enantiomers. Data are mean and SD from duplicate measurement using the enantioselective LC-MS/MS approach of John et al. [47,49]. Black circles, total hyo grey circles, S-hyo grey triangles, R-hyo...

Spectra for the diastereoisomeric pairs quinine-quinidine, cinchonine-cinchonidine alkaloids are mirror images of each other and mixtures have been determined using CD detection [57]. Spectra for the pilocarpine-isopilocarpine pair were such low quality that they could be used only for qualitative distinction. CD detection combined with UV detection was used to measure enantiomeric excesses in mixtures of L-hyoscyamine and atropine, i.e. racemic hyoscyamine. This subject is returned to in greater depth later. 

A GC-MS method was developed for the determination of hyoscyamine and scopolamine in blood semm [91,92]. Extraction was carried out using aqueous basic solution followed by a purification step on an Extrelut column. Derivatization was done with N,0-bis(trimethylsilyl)trifluoroacetamide/trimethylchlorosilane (99 1). GC-MS was performed on a HP-5 MS column (30m x 0.25 mm i.d. with a 0.25 p,m film thickness). The linearity was good between 10 and 5000ng/mL. The limit of detection (LOD) was 5ng/mL for each compound. 

Siluk, D., Mager, D.E., Gronich, N., Abemethy, D., Wainer, I.W. HPLC-atmospheric pressure chemical ionization mass spectrometric method for enantioselective determination of R, S-propranolol and R,S-hyoscyamine in human plasma. J. Chromatogr. B 859, 213-221 (2007)... 

Tropanone then is reduced via an NADPH-dependent reductase to tropine that has been cloned from Hyoscyamus niger (149, 150). All tropane-producing plants seem to contain two tropinone rednctases, which create a branch point in the pathway. Tropinone reductase I yields the tropane skeleton (Fig. 3b), whereas tropinone rednctase II yields the opposite stereocenter, pseudotropine (151). Tropane is converted to scopolamine or hyoscyamine, whereas the TRII product pseudotropine leads to calystegines (152). These two tropinone reductases have been crystalhzed, and site-directed mutagenesis studies indicate that the stereoselectivity of the enzymes can be switched (153, 154). 

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