Option D : Medicinal Chemistry SL & HL

Click Here: Chemistry Guide

This is a revision guide for IBDP Chemistry SL & Chemistry HL students, as I always feel like there aren't many study resources on topics in Option D.

The [ Related Pastpaper ] and [  Typical Exam Question ! ] section may aid you through the learning process, and let you know the importance of the topic in Exam. However, for your revision purpose, I will ONLY show you SOME of the past papers from 2016-2018.

The [ Exam Tips ! ] section reminds you of the points that need to be revised.

Good Luck!

D.1 Pharmaceutical Products and Drug Action

[ Exam Tips ! ]
- Please remember some of the side-effects of drugs (ie. symptoms an addict may experience)
- Remember the Definitions (ie. Bioavailability, Therapeutic Window)

Method of administration Drugs 

1. Oral - taken by mouth i.e Tablets, pills, capsules (usually drug water-soluble)

2. Inhalation - vapour breath in ie. medication for asthma 

3. Parenteral by injection - intramuscular/intravenous/subcutaneous ie. vaccines

4. Eye / Ear drop - liquid deliver to the opening i.e. medication for ear infection

5. Suppositories - insert into the rectum i.e. treatment of digestive illnesses and haemorrhoids

6. Skin Patches - Absorption by the skin and enters to the blood i.e. hormone treatment

*(Usually use for medication that requires Non-polar Drugs only)

Bioavailability    

Definition: The fraction of the administered dosage that enters the bloodstream (reaches to the target organs).

Bioavailability of a drug, by definition, affects the rate of absorption and dispersion. Oral administrated drugs have low bioavailability as the drug is being digested and pass to the liver, where the metabolic breakdown of chemical reaction occurs.  In contrast, Intravenous administration has high bioavailability as it is directly injected to the bloodstream.

 Factors that affect Bioavailability
- Administrative Method
- Functional Group of the Drug 
- Polarity of the Drug

Therapeutic Window 

Definition: Therapeutic window is the range of dosage between the min. amount of drug that will provide the desired effect and a medically unacceptable adverse effect. 

[ Note !]

High Therapeutic Index => safer (wide margin between producing effective and toxic effect)
Low  Therapeutic Index => slight change in the dose may not have the desired effect or unacceptable effect.

Definition: LD50 is the amount/dose that kills 50% of the population, used in animal studies

Definition: TD50 is the amount/dose that negatively affects/produces toxic effects in 50% of the population, used in human studies

[ Related Pastpaper ]
- Question 19 - 2 Marks: M18/4/CHEM/HP3/ENG/TZ2/XX
- Question 24 (a) - 1 Marks : M16/4/CHEM/HP3/ENG/TZ0/XX (May)
- Question 24 (a) - 1 Marks: M17/4/CHEM/HP3/ENG/TZ2/XX

D.2 Aspirin and Penicillin

[ Exam Tips ! ]
- Explain the function of Asprin and Penicillin (and how they work)
- Explain the synthesis of Asprin and its conditions required
- Explain When to use Asprin and Penicillin
- Explain Why antibiotics shouldn't always be used - environmental impact, viral infection etc.
- *Explain the process of recrystallization

* indicates the points that I have not covered because it is not being asked very often but you should know this.

Aspirin

Aspirin is a mild analgesic that intercepts the pain stimulus at the source, and often interferes with the production of pain sensitizing substances (prostaglandins) that cause pain, swelling or fever at site of pain.

Synthesis of Asprin 

*Acetylsalicylic acid is also known as Asprin, is prepared through esterification (condensation reaction).

Required Conditions 
- Warm Gently 
- Conc. H2SO4 or H3PO4 added



The Asprin's benzene ring structure makes the molecule non-polar, despite the existence of carboxyl functional group (COOH). Therefore, by neutralizing Asprin with NaOH or NaHCO3 is added to increase its aqueous solubility, hence marginally increase the bioavailability- rate of dispersion and absorption of the drug.


[ Note ! ] Reaction of  NaOH or NaHCO3 with Asprin is a neutralization reaction.


[ Related Pastpaper ]

- Question 20 (b)(i)(ii) - 2 Marks: M17/4/CHEM/HP3/ENG/TZ2/XX

Purity 

The purity of product ie. Asprin can be confirmed by 

- melting points (pure substance/literature value should have every small difference / small range of values)

- Mass Spectrometry

- X-ray crystallography

- High-performance liquid Chromatography  

- Infra spectra (arguably an accepted answer)

[ Related Pastpaper ]

- Question 25 (c) - Marks 1 : M16/4/CHEM/HP3/ENG/TZ0/XX (May)

Physiological effect of Asprin

Aspirin can be used as an anticoagulant in the prevention of the recurrence of heart attack and stroke. However, alcohol has a synergistic effect with aspirin that causes increase bleeding of the stomach lining and increased the risk of ulcer. 

Penicillin 

[  Typical Exam Question ! ]

The Ring strain (beta-lactam ring) in the penicillin structure - 90 unusual bond angle in the Penicillin makes the ring easy to break and bind with the enzymes, which are responsible for the formation of cell-wall. Therefore, the binding prevents the bacteria to form a cell-wall and can not reproduce, eventually causing it to absorb water AND burst.

To combat antibiotic-resistant bacteria, modifying the side-chains in penicillin will prevent the penicillin to bind with the resistant bacteria enzyme, hence prevent the ring from cleavage before it finds its target.

[ Related Pastpaper ]

- Question 20 (a) (i) (ii) - 3 Marks : M18/4/CHEM/HP3/ENG/TZ2/XX

- Question 23 (a) (i) (ii) (b) (i) - 3 Marks : M16/4/CHEM/HP3/ENG/TZ0/XX (Nov)

- Question 22 (a) - 3 Marks : M16/4/CHEM/HP3/ENG/TZ0/XX (May)

D.3 Opiates

[ Exam Tips ! ]

 - Explain how strong analgesics works 

 - Compare the differences of Morphine, Codeine and Diamorphine in terms of polarity, structure, potency, side-effects, medical usage, therapeutic effects and how the drug can be made (reactants and type of reaction). 

Strong analgesics (i.e. Morphine, codeine and diamorphine) works by temporary bind to the pain receptor (opioid receptors) in the human brain, therefore, prohibits the transmission of pain impulses within the Central Nervous System, CNS.

Please refer to the data booklet for the structure of morphine, codeine and diamorphine. 

[  Typical Exam Question ! ]

The following is a comparison of morphine, codeine and diamorphine. 

Morphine 

- the most polar molecule  (more soluble in blood plasma)

- greater potency than codeine, but not as strong as diamorphine

- synthesis and obtained from raw opium

Codeine 

- Moderately polar molecule  (more polar than morphine, but the least polar)

- the least potency 

- synthesis from methylation (Reaction Type : Nucleophilic substitution of morphine), reacting morphine with methyl iodide. 

Diamorphine 

- Least polar molecule (greater solubility in lipids and more able to cross the blood-brain carrier)

- the greatest potency with the greatest side-effect

- synthesis from diestification (Reaction Type : condensation) by reacting morphine with ethanoic acid. However, water is also be produced as side-product.

 

D.4 pH Regulation of the stomach

[ Exam Tips ! ]

 - Explain how Antacids, Zantac and Proton Pump Inhibitors (Prilosec and Nexium) works

 - Explain the difference between Antacids, Zantac and Proton Pump Inhibitors (Prilosec and Nexium)

 - Explain the medical use of Antacids, Zantac and Proton Pump Inhibitors (Prilosec and Nexium)

The function of HCl in the stomach

1. denature proteins and provide the optimum pH for digestive enzymes in the gastric juice

2. Killing bacteria of the food ingested

*pH value of HCl ranges from 1 to 2.5, with 0.003 to 0.1M of concentration.

Antacids

Antacids are usually weak bases - reducing the pH of the stomach by neutralization. 

e.g. Mg(OH)2, Al(OH)3, Na2CO3 and NaHCO3

[  Typical Exam Question ! ]

Unique features of Antacids include...

 - neutralizing excess acid

 - short-term effect only

 - affects ionic balance in the body

Zantac

[  Typical Exam Question ! ]

Zantac works by inhibits the histamine for binding to the H2 receptors in order to reduce stomach acid secretion.

Unique features of Zantac includes...

 - Used to treat Ulcers

 - takes time to provide relief

 - short-term effect ONLY

Proton Pump Inhibitors

[  Typical Exam Question ! ]

Proton Pump inhibitors inhibit enzyme which secretes H+ ions into gastric juice, in the proton pump (site of action of the drug).

Unique features of Proton Pump inhibitors include...

 - can be used to treat Ulcers

 - takes longer to provide relief

 - Prevent Long term damage from the overproduction of acid

 - Has a long-lasting effect 

The similarity of Antacids, Zantac and Proton Pump Inhibitors

[  Typical Exam Question ! ]

- All 3 cause diarrhoea (side-effect)

- relieve symptoms of acid reflux/heartburn/indigestion

- reduce the stomach acidity

D.5 Antiviral Medication

[  Typical Exam Question ! ]

Difficulties of treating viral infections 

Reason 1: Lack of a cell structure, hard to target

Reason 2: Multiply too quickly

Reason 3: Tendency to mutate rapidly

The function of Anti-Viral Drug

[  Typical Exam Question ! ]

 The anti-viral drug inhibits the viral enzyme, and prevents the virus from leaving the host cell, therefore cannot infect other cells. 

D.6 Environmental Impact of some medication