D. Medicinal chemistry

D. Medicinal chemistry

Core

D.1 Pharmaceutical products and drug action

Nature of science:

• Risks and benefits - medicines and drugs go through a variety of tests to determine their effectiveness and safety before they are made commercially available. Pharmaceutical products are classified for their use and abuse potential.

Understandings:

• In animal studies, the therapeutic index is the lethal dose of a drug for 50% of the population (LD50) divided by the minimum effective dose for 50% of the population (ED50).

• In humans, the therapeutic index is the toxic dose of a drug for 50% of the population (TD50) divided by the minimum effective dose for 50% of the population (ED50).

• The therapeutic window is the range of dosages between the minimum amounts of the drug that produce the desired effect and a medically unacceptable adverse effect.

• Dosage, tolerance, addiction and side effects are considerations of drug administration.

• Bioavailability is the fraction of the administered dosage that reaches the target part of the human body.

• The main steps in the development of synthetic drugs include identifying the need and structure, synthesis, yield and extraction.

• Drug–receptor interactions are based on the structure of the drug and the site of activity.

Applications and skills:

• Discussion of experimental foundations for therapeutic index and therapeutic window through both animal and human studies.

• Discussion of drug administration methods.

• Comparison of how functional groups, polarity and medicinal administration can affect bioavailability.

D.2 Aspirin and penicillin

Nature of science:

• Serendipity and scientific discovery - the discovery of penicillin by Sir Alexander Fleming.

• Making observations and replication of data - many drugs need to be isolated, identified and modified from natural sources. For example, salicylic acid from bark of willow tree for relief of pain and fever.

Understandings:

• Aspirin: Mild analgesics function by intercepting the pain stimulus at the source, often by interfering with the production of substances that cause pain, swelling or fever. Aspirin is prepared from salicylic acid. Aspirin can be used as an anticoagulant, in prevention of the recurrence of heart attacks and strokes and as a prophylactic.

• Penicillin: Penicillins are antibiotics produced by fungi. A beta-lactam ring is a part of the core structure of penicillins. Some antibiotics work by preventing cross-linking of the bacterial cell walls. Modifying the side-chain results in penicillins that are more resistant to the penicillinase enzyme.

Applications and skills:

• Aspirin: Description of the use of salicylic acid and its derivatives as mild analgesics. Explanation of the synthesis of aspirin from salicylic acid, including yield, purity by recrystallization and characterization using IR and melting point. Discussion of the synergistic effects of aspirin with alcohol. Discussion of how the aspirin can be chemically modified into a salt to increase its aqueous solubility and how this facilitates its bioavailability.

• Penicillin: Discussion of the effects of chemically modifying the side-chain of penicillins. Discussion of the importance of patient compliance and the effects of the over-prescription of penicillin. Explanation of the importance of the beta-lactam ring on the action of penicillin.

D.3 Opiates

Nature of science:

• Data and its subsequent relationships - opium and its many derivatives have been used as a painkiller in a variety of forms for thousands of years. One of these derivatives is diamorphine.

Understandings:

• The ability of a drug to cross the blood–brain barrier depends on its chemical structure and solubility in water and lipids.

• Opiates are natural narcotic analgesics that are derived from the opium poppy.

• Morphine and codeine are used as strong analgesics. Strong analgesics work by temporarily bonding to receptor sites in the brain, preventing the transmission of pain impulses without depressing the central nervous system.

• Medical use and addictive properties of opiate compounds are related to the presence of opioid receptors in the brain.

Applications and skills:

• Explanation of the synthesis of codeine and diamorphine from morphine.

• Description and explanation of the use of strong analgesics.

• Comparison of the structures of morphine, codeine and diamorphine (heroin).

• Discussion of the advantages and disadvantages of using morphine and its derivatives as strong analgesics.

• Discussion of side effects and addiction to opiate compounds.

• Explanation of the increased potency of diamorphine compared to morphine based on their chemical structure and solubility.

D.4 pH regulation of the stomach

Nature of science:

• Collecting data through sampling and trialling - one of the symptoms of dyspepsia is the overproduction of stomach acid. Medical treatment of this condition often includes the prescription of antacids to instantly neutralize the acid, or H2-receptor antagonists or proton pump inhibitors which prevent the production of stomach acid.

Understandings:

• Non-specific reactions, such as the use of antacids, are those that work to reduce the excess stomach acid.

• Active metabolites are the active forms of a drug after it has been processed by the body.

Applications and skills:

• Explanation of how excess acidity in the stomach can be reduced by the use of different bases.

• Construction and balancing of equations for neutralization reactions and the stoichiometric application of these equations.

• Solving buffer problems using the Henderson–Hasselbalch equation.

• Explanation of how compounds such as ranitidine (Zantac) can be used to inhibit stomach acid production.

• Explanation of how compounds like omeprazole (Prilosec) and esomeprazole (Nexium) can be used to suppress acid secretion in the stomach.

D.5 Antiviral medications

Nature of science:

• Scientific collaboration - recent research in the scientific community has improved our understanding of how viruses invade our systems.

Understandings:

• Viruses lack a cell structure and so are more difficult to target with drugs than bacteria.

• Antiviral drugs may work by altering the cell’s genetic material so that the virus cannot use it to multiply. Alternatively, they may prevent the viruses from multiplying by blocking enzyme activity within the host cell.

Applications and skills:

• Explanation of the different ways in which antiviral medications work.

• Description of how viruses differ from bacteria.

• Explanation of how oseltamivir (Tamiflu) and zanamivir (Relenza) work as a preventative agent against flu viruses.

• Comparison of the structures of oseltamivir and zanamivir.

• Discussion of the difficulties associated with solving the AIDS problem.

D.6 Environmental impact of some medications

Nature of science:

• Ethical implications and risks and problems - the scientific community must consider both the side effects of medications on the patient and the side effects of the development, production and use of medications on the environment (ie disposal of nuclear waste, solvents and antibiotic waste).

Understandings:

• High-level waste (HLW) is waste that gives off large amounts of ionizing radiation for a long time.

• Low-level waste (LLW) is waste that gives off small amounts of ionizing radiation for a short time.

• Antibiotic resistance occurs when micro-organisms become resistant to antibacterials.

Applications and skills:

• Describe the environmental impact of medical nuclear waste disposal.

• Discussion of environmental issues related to left-over solvents.

• Explanation of the dangers of antibiotic waste, from improper drug disposal and animal waste, and the development of antibiotic resistance.

• Discussion of the basics of green chemistry (sustainable chemistry) processes.

• Explanation of how green chemistry was used to develop the precursor for Tamiflu (oseltamivir).

Additional higher level

D.7 Taxol - a chiral auxiliary case study

Nature of science:

• Advances in technology - many of these natural substances can now be produced in laboratories in high enough quantities to satisfy the demand.

• Risks and problems - the demand for certain drugs has exceeded the supply of natural substances needed to synthesize these drugs.

Understandings:

• Taxol is a drug that is commonly used to treat several different forms of cancer.

• Taxol naturally occurs in yew trees but is now commonly synthetically produced.

• A chiral auxiliary is an optically active substance that is temporarily incorporated into an organic synthesis so that it can be carried out asymmetrically with the selective formation of a single enantiomer.

Applications and skills:

• Explanation of how taxol (paclitaxel) is obtained and used as a chemotherapeutic agent.

• Description of the use of chiral auxiliaries to form the desired enantiomer.

• Explanation of the use of a polarimeter to identify enantiomers.

D.8 Nuclear medicine

Nature of science:

• Risks and benefits - it is important to try and balance the risk of exposure to radiation with the benefit of the technique being considered.

Understandings:

• Alpha, beta, gamma, proton, neutron and positron emissions are all used for medical treatment.

• Magnetic resonance imaging (MRI) is an application of NMR technology.

• Radiotherapy can be internal and/or external.

• Targeted Alpha Therapy (TAT) and Boron Neutron Capture Therapy (BNCT) are two methods which are used in cancer treatment.

Applications and skills:

• Discussion of common side effects from radiotherapy.

• Explanation of why technetium-99m is the most common radioisotope used in nuclear medicine based on its half-life, emission type and chemistry.

• Explanation of why lutetium-177 and yttrium-90 are common isotopes used for radiotherapy based on the type of radiation emitted.

• Balancing nuclear equations involving alpha and beta particles.

• Calculation of the percentage and amount of radioactive material decayed and remaining after a certain period of time using the nuclear half-life equation.

• Explanation of TAT and how it might be used to treat diseases that have spread throughout the body.

D.9 Drug detection and analysis

Nature of science:

• Advances in instrumentation - advances in technology (IR, MS and NMR) have assisted in drug detection, isolation and purification.

Understandings:

• Organic structures can be analysed and identified through the use of infrared spectroscopy, mass spectroscopy and proton NMR.

• The presence of alcohol in a sample of breath can be detected through the use of either a redox reaction or a fuel cell type of breathalyser.

Applications and skills:

• Interpretation of a variety of analytical spectra to determine an organic structure including infrared spectroscopy, mass spectroscopy and proton NMR.

• Description of the process of extraction and purification of an organic product. Consider the use of fractional distillation, Raoult’s law, the properties on which extractions are based and explaining the relationship between organic structure and solubility.

• Description of the process of steroid detection in sport utilizing chromatography and mass spectroscopy.

• Explanation of how alcohol can be detected with the use of a breathalyser.