NTA Level 5 • Semester 2 • PST05210

Purine Alkaloids

Basic Pharmacognosy • Source Session/Topic 25

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Session 25: Purine Alkaloids

Total Session Time: 60 minutes

Prerequisites

• None

Learning Tasks

By the end of this session students are expected to be able to:

• Define purine alkaloids

• Explain natural sources and uses of alkaloids

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board and chalk/whiteboard markers

• LCD Projector and laptop

SESSION OVERVIEW

SESSION CONTENTS

STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)

READ or ASK students to read the learning tasks and clarify

ASK students if they have any questions before continuing.

STEP 2: Introduction to Purine Alkaloids (15 minutes)

• Purine alkaloids are derivatives of Xanthines

• They have amphoteric character

• They exhibit peculiar solubility in warm water and in chlorinated

solvents

• These alkaloids include caffeine (seeds of coffee plants, kola plants,

tea leaves and guarana seeds), theobromine (Theobroma cocao) and

theophylline (tea leaves and cola nuts)

• The stimulant action in beverages such as tea and coffee is due to the

purine alkaloids

• Caffeine (1, 3, 7-trimethylxanthine) stimulates CNS and has a weak

diuretic action.

• Theobromine (3,7-dimetylxanthine) produce opposite action to that of

Caffeine

• Theophylline (1,3-dimetylxanthine) relaxes involuntary muscles more

effectively than caffeine or theobromine

STEP 3: Natural Sources and Uses of Alkaloids (30 minutes)

• Cocoa

o Cocoa consists of seeds of Theobroma cacao, family sterculiaceae

o Cocoa is produced in South America (Ecuador, Columbia, Venezuela), West

Indies and West Africa (Nigeria, Ghana and Java)

o Cocoa kernels contain 0.9 – 3% theobromine and the husk 0.19- 2.98% of

this alkaloid

o The seed also contains 0.05 – 0.36% caffeine, cocoa fat/butter,

condensed tannins and volatile compounds

o Main constituents are Theobromine and Theophyllline

o Uses

▪ Theobromine is used

• As base for suppositories (cocoa butter)

• For heart and kidney tonic

• As a drink e.g. cocoa

• As flavouring agent e.g. chocolate

▪ Theophylline

• Relaxes bronchial smooth muscles

• Stimulates respiratory centre in the brain stem by increasing

sensitivity to CO2

• Stimulates the CNS

• Slightly inotropic

• Diuretic activity is stronger than that of caffeine

• Used for relief of cough (bronchodilator)

• Smooth muscle relaxant for symptomatic relief/prevention of

bronchial asthma

• Treatment of reversible bronchospasm associated with chronic

bronchitis and emphysema

• Coffee

o Coffee consists of seeds of coffea arabica and other species of coffee,

family rubiaceae

o Constituents:

▪ Caffeine, tannins, Nicotinic acid, fixed oils and chlorogenic acid

▪ Caffeine eenhances alertness, ffacilitates thought formation and

decreases the sensation of fatigue. At high doses caffeine induces

nervousness, insomnia and tremors.

o Another source of caffeine is Tea, which consists of prepared leaves of

Thea sinensis/Camellia sinensis

|Activity: Brainstorming (5 minutes) |

| |

|Ask students to brainstorm on the following question: |

| |

|What are the uses of Caffeine? |

| |

|ALLOW few students to respond |

| |

|WRITE their responses on the flip chart/ board |

| |

|CLARIFY and SUMMARISE by using the content below |

o Uses

▪ Coffee produce caffeine which is used in combinations with

antipyretics and analgesics, cold and flu medication (increases the

intestinal absorption of some of these drugs or to counteract

drowsiness)

▪ Caffeine is also used as an ingredient in non-alcoholic beverages

and “energizing” beverages

STEP 4: Key Points (5 minutes)

• Purine alkaloids are derivatives of xanthines

• Purine alkaloids exhibit peculiar solubility in warm water

• Main constituents of cocoa are Theobromine and Theophyllline

• Cocoa butter is used a suppository base

STEP 5: Evaluation (5 minutes)

• Mention the cardiovascular use of caffeine

• What are the pharmacological uses of Theophylline?

• What are the uses of Theobromine?

References

Trease, G. E., Evans, W. C., & Evans, D. (2009). Trease and Evans

pharmacognosy. London: Saunders.

Joanne Barnes et al (2002), Herbal medicines 3rd Edition: Pharmaceutical

Press

Wallis, T. E. (2005). Textbook of pharmacognosy. New Delhi: CBS.

Robbers, J. E., Speedie, M. K., Tyler, V. E., & Tyler, V. E. (1996).

Pharmacognosy and pharmacobiotechnology. Baltimore: Williams &

Wilkins.

Heinrich, M., Kinghorn, A. D., Maizels, D., Gibbons, S., & Phillipson, J.

D. (2012). Fundamentals of pharmacognosy and phytotherapy. Edinburgh:

Churchill Livingstone/Elsevier.

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