Atropine

Properties of atropine are:

• Melting Point: 115-116°C.

• optically: Inactive.

• Taste: sharp bitter.

• Used in Opthalmology due to dilating action on the eye pupils.

• It has stimulative and depression action on the CNS on internal administration.

• It is the racemic modification of the laevo-rotatory hyoscyamine.

• Atropine does not exist naturally but is formed during the isolation of hyoscyamine.

• Atropine and hyoscyamine have similar physiological activity; however, the activity of the latter on the peripheral nerves is more than that of atropine.

• Method 1

• Species for isolation : Hyoscyamus muticus

  • It contains high alkaloidal content than other sources like Datura stramonium.

  • The powdered drug is moist with an aqueous solution of sodium carbonate and extracted with ether or benzene.

  • The free alkaloidal bases are extracted from the dilute solvent and acidified with acetic acid.

  • The acidic solution is shaken with ether solvent which separates colouring matter.

  • The alkaloids get precipitated with sodium carbonate which is filtered, washed and dried.

  • The dried residue is dissolved in ether/acetone and dehydrated with anhydrous sodium sulphate.

  • This all treatment should be done before filtration.

  • The filtrate is concentrated and cooled.

  • This process will yield crystals of hyoscyamine and atropine.

  • The crystalline mass is separated and dissolved in alcohol. Then sodium hydroxide solution is added and mixture is kept for some time.

  • The hyoscyamine will completely be racemized into atropine.

  • The purification of crude atropine should be done by crystallization with acetone.

  • Atropine sulphate is the most important salt of atropine which occurs in colourless crystalline powdered form.

  • It has a solubility in water and alcohol and insolubility in ether and chloroform.

Thin layer chromatography of Atropine:

• Atropine solution (1%) is dissolved in 2N acetic acid and it is spotted over silica gel-G plate and eluted into solvent system strong ammonia solution: methanol (1.5:100).

• The TLC plates are spread with acidified iodoplatinate solution.

• It gives Rf value 0.18.

• Atropine sulphate gives Rf value 0.70 in solvent system acetone: sodium chloride with Dragendorff reagent as spraying agent.

Identification Test:

• Vitali-Morin reaction:

  • Dilute solution of atropine is treated with concentrated nitric acid.

  • The mixture is evaporated to dryness which produces pale yellow residue.

  • A violet colour appears when a drop of potassium hydroxide solution is added in the residue.

Atropine can be analysed by the following techniques:

1) GC/MS Analysis:

• 0.5ml sample, 5µl IS (Internal Standard) solution and 1.0ml borate solution (0.1M, pH 9.3) are mixed in a test tube and poured into an Extrelut column.

• After 15 minutes, the target compounds are eluted with 4ml dichloromethane.

• The obtained eluate is evaporated to dryness under nitrogen stream.

• The residue is mixed with 50µl of N,O-bis(trimethylsilyl) trifluoroacetamide : trimethylchlorosilane (BSTFA:TMCS) in 99:1 ratio and warmed at 45°C temperature for 20 minutes for TMS derivatisation in a glass vial with a teflon cap.

• The solution obtained is mixed with 100 µl dichloromethane, and a 1µl aliquot of it is injected into GC/MS for analysis.

2) HPLC Analysis:

• 0.5ml sample is poured into an activated HLB cartridge, which is washed with 1ml of 5% methanol.

• The target compounds are eluted with 1ml methanol.

• The obtained eluate is evaporated to dryness under reduced pressure.

• The residue is dissolved in 100µl of the mobile phase, and a 10µl aliquot of it is injected into HPLC for analysis