E. Hyoscyamine
Synonyms l-Tropine Tropate; Daturine; Duboisine; l-Hyoscyamine; Cystospaz; Levsin; l-Tropic acid ester with Tropine; 3α-Tropanyl S-(–)-Tropate.
Biological Sources It is obtained from the roots and leaves of Atropa bella-dona L. (Solanaceae) (0.21%) (Thorn Apple); fruits, roots and leaves of Datura metel L. (Solanaceae) (Unmatal, Metel, Hindu Datura); leaves and seeds of Datura stramonium L. (Solanaceae) (Jimson Weed, Thorn Apple, Stramonium); root bark of Duboisia myoporoides R. Br. (Solanaceae) (Pituri, Corkwood Tree); young plants of Hyoscyamus niger L. (Solanaceae) (Henbane, Henblain Jusquaime); seeds of Lactuca virosa L. (Asteraceae) (Bitter Lettuce, Wild Lettuce); and the herb Mandragora officinarum L. (Solanaceae) (Mandrake, Loveapple).
Chemical Structure
1αH, 5αH-Tropan-3α-ol (–)-tropate (ester); (C17H23NO3).
Isolation Hyoscyamine may be isolated from the Belladona leaves by adopting the following steps sequentially:
1. The finely powdered and sieved Belladona leaves is extracted with 95% (v/v) ethanol in a Soxhlet Apparatus till no more alkaloids come out from the marc. The ethanolic extract is concentrated to a syrupy residue under vaccuo and subsequently treated with dilute HCl. The resinous matter is separated by filtration and the resulting solution is further purified by shaking out with petroleum ether (40-60°C) several times.
2. The purified acidic solution thus obtained is made alkaline with ammonia solution (dilute) carefully and extracted with chloroform successively. The combined chloroform layer is once again shaken with dilute HCl, and the acidic solution made alkaline with dilute ammonia solution and extracted with chloroform successively.
3. The combined chloroform layer is removed by distillation under reduced pressure. The crude alkaloids thus obtained is neutralized with oxalic acid. The oxalates of atropine and hyoscyamine may be separated by fractional crystallization from acetone and ether wherein the hyoscyamine oxalate being more soluble gets separated as the second crop.
Characteristic Features
1. Hyoscyamine is obtained as silky tetragonal needles from evaporating ethanol having mp 108.5°C.
2. The physical parameters are: [α]D20 -210 (ethanol); and dissociation constant K at 19° is 1.9 ×10–12.
3. Solubility Profile: 1 g dissolves in 281 ml water (pH 9.5), 69 ml ether, 150 ml benzene, and 1ml chloroform. It is freely soluble in dilute mineral acids and ethanol.
Identification Tests The various identification tests for hyoscyamine are, namely:
1. Gerrard Reaction: Hyoscyamine (and also atropine) responds to the Gerrard Reaction wherein about 5-10 mg of it reacts with mereuric chloride solution (2% w/v) in 50% ethanol to give rise to an instant red colouration without warming.
2. Schaer’s Reagent: A few mg of hyoscyamine when made to react with a few drops of the Schaer’s Reagent i.e., 1 volume of 30% H2O2 mixed with 10 volumes of concentrated sulphuric acid, produces a distinct green colouration.
3. Vitali-Morin Colour Reaction: A few mg of hyoscyamine (and also atropine) is treated with about 0.2 ml of fuming HNO3, evaporated to dryness on the water-bath. To the residue is then added 0.5 ml of a 3% (w/v) solution of KOH in methanol, it gives a bright purple colouration, that changes to red and finally fades to colourless.
Note: (a) The 3% solution of KOH must be freshly prepared.
(b) The reaction is very sensitive i.e., upto 0.0001 mg of any of the alkaloids viz., strychnine, apomorphine, veratrine, physostigmine etc. give a positive test.
4. para-Dimethylaminobenzaldehyde Reagent: [Prepared by dissolving 2 g of
p-Dimethylaminobenzaldehyde in 6 g of H2SO4 to which 0.4 ml of water is added previously]. Add to 5-10 mg of hyoscyamine in an evaporating dish 2-3 drops of this reagent and heat on a boiling water-bath for several minutes. A distinct red colouration is produced that ultimately gets changed to permanent cherry red upon cooling.
5. Hyoscyamine Hydrobromide (C17H23NO3.HBr): It is obtained as deliquescent crystals having mp 152°C; very soluble in water; 1 g dissolves in 3 ml ethanol; 1.2 ml chloroform and 2260 ml ether.
6. Hyoscyamine Hydrochloride (C17H23NO3.HCl): The crystals have mp 149-151°C; and freely soluble in water and ethanol.
7. Hyoscyamine Methyl Bromide (C17H23NO3.CH3Br) (N-Methylhyo-scyaminium bromide): The crystals have mp 210-212°C; and freely soluble in water, dilute ethanol; and slightly soluble in absolute ethanol.
8. Hyoscyamine Sulphate Dihydrate [(C17H23NO3)2.H2SO4.2H2O] (Egacene, Peptard, Egazil Duretter): It is obtained as needles from ethanol having mp 206°C (when dry); [α]D15 -290 (C = 2); pH 5.3 (1 in 100); 1 g dissolves in 0.5 ml water and about 5.0 ml ethanol; and very slightly soluble in ether and chloroform.
Uses
1. It is mostly employed as an anticholinergic drug.
2. It exerts relaxation of bronchial and intestinal smooth museles (i.e., antispasmodic action).
3. It also inhibits contraction of the iris muscle of the eye to produce mydriasis.
4. It decreases significantly decreases the sweat gland and salivary gland secretions.
Biosynthesis of Hygrine, Cuscohygrine, Cocaine, Cinnamoyl Ecgonine (Methylecgonine) and Hyoscyamine The pyrrolidine ring system, present in hygrine and cuscohygrine, is formed initially as a ∆1-pyrrolinium cation. The extra C-atoms required for hygrine formation are derived from acetate via acetyl-CoA; and the sequence appears to involve stepwise addition of two acetyl-CoA units as shown below:
These two steps may be explained as under:
(a) The enolate anion from acetyl-CoA serves as nucleophile for the pyrrolinium ion in a Mannichlike reaction, that may give rise to products having either R or S stereochemistry.
(b) An addition is caused by virtue of a Claisen condensation which essentially extends the sidechain, and the product is 2-substituted pyrrolidine, thereby retaining the thioester moiety of the second acetyl-CoA.
It has been observed that Hygrine and most of the naturally occurring tropane alkaloids is devoid of this specific C-atom, which is subsequently eliminated by suitable decarboxylation hydrolysis reactions. Interestingly, the genesis of the bicyclic structure of the tropane skeleton existing in either cocaine or hyoscyamine is accomplished due to the repeatation of the Mannich-like reaction stated above. These reactions are summarized in the description given under.
