D.7 Taxol - a chiral auxiliary case study
Written specifically for students to provide help and support for the IB Diploma chemistry programme this page provides full coverage of the syllabus content of Option D - sub topic D.7. It encourages you to think critically and provides many questions with full worked answers so that you can monitor and improve your knowledge and understanding.
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Learning outcomes
After studying this topic you should be able to:
Understand:
- Taxol is a medicament that is commonly used to treat several different forms of cancer.
- Taxol occurs naturally in certain types of yew tree but it is now commonly produced synthetically.
- Chiral auxiliaries are optically active substances that are incorporated temporarily into organic syntheses so that they can be carried out asymmetrically to selectively produce a single enantiomer.
Apply your knowledge to:
- Explain how paclitaxel (Taxol is the trademark name) is obtained and used as a chemotherapeutic agent.
- Describe the use of chiral auxiliaries to form the desired enantiomeric product.
- Explain how a polarimeter can be used to identify enantiomers.
Relationships & vocabulary
Nature of science
The demand for certain drugs is greater than the supply of natural substances required to synthesize them. However, due to advances in technology, many natural substances can now be produced in laboratories in large enough amounts to meet the demand.International-mindedness
he availability and distribution of certain medicines and drugs around the world is unequal.Vocabulary
| Taxol | paclitaxel | chiral auxiliary | chemotherapeutic agent | polarimeter |
Learning slides
You can use this slide gallery for learning or for reviewing concepts and information. It covers all the key points in the syllabus for this sub-topic.
Taxol - a chiral auxiliary case study:
Taxol - a chiral auxiliary case study:
Taxol - a chiral auxiliary case study:
Taxol - a chiral auxiliary case study:
Taxol - a chiral auxiliary case study:
Taxol - a chiral auxiliary case study:
Taxol - a chiral auxiliary case study:
Taxol - a chiral auxiliary case study:
Taxol - a chiral auxiliary case study:
Taxol - a chiral auxiliary case study:
Something to think about
Paclitaxel, (which has the trade name of Taxol) is an incredibly complex molecule with no fewer than eleven chiral centres. It is possible to get side-tracked into some very complicated chemistry when learning this topic so it helps to keep clear in your mind exactly what this topic is covering. The following checklist may help.
1. Natural source of taxol
Taxol is an effective chemotherapeutic agent that occurs naturally, mainly in the Pacific yew tree, but only in very small amounts. Even if this tree is grown commercially it cannot produce all the taxol required for therapeutic use.
2. Structure of taxol
A molecule of taxol contains 11 chiral centres.
3. Chemotherapeutic properties of taxol
It is effective against several different types of cancer (e.g. ovarian, breast, lung and pancreatic cancers). It works by interfering with tumour cell division by binding to certain proteins called tubulins.
4. Semi-synthesis of taxol
It can be semi-synthesised from Baccatin III, a precursor of taxol which is also found in yew trees.
Baccatin III
To obtain the correct stereochemical configuration in the side chains of taxol, use of chiral auxiliaries is made.
5. Chiral auxiliaries
A chiral auxiliary is a specific enantiomer of a reagent, which can be attached to the starting material to create the stereochemical conditions necessary for only the desired enantiomeric product to be formed. After the product has been formed the chiral auxiliary is removed and recycled.
trans-2-phenylcyclohexan-1-ol - a chiral auxiliary used in the synthesis of taxol
6. Test for purity using a polarimeter
A pure enantiomer will rotate the plane of plane-polarized light either clockwise or anti-clockwise by a fixed number of degrees. By using a polarimeter and measuring the angle of rotation the percentage purity of the desired enantiomer in the product can be determined.
Test your understanding of this topic
(Note that your teacher may have restricted your access to some or all of these questions and worked answers if they are going to use them as a class test or set them as an assignment.)
For ten 'quiz' questions (for quick testing of knowledge and understanding with the answers explained) see MC test: Taxol - a chiral auxiliary case study.
For short-answer questions see Taxol questions together with the worked answers on a separate page Taxol answers.
More resources
1. A life science video from ScienceOnline showing that Taxol can also be obtained from Canada yew as well as Pacific yew.
2. Although you are not required to know in detail how Taxol works as a chemotherapeutic agent in the body it is probably good that you do have some idea. One way in which Taxol is delivered is a by binding it to albumin nanoparticles. The following video by the European Fellowship for Pharmacists explains clearly how Taxol works when bound to albumin.
Mechanism of action of taxol (paclitaxel)
3. A video you might like by Richard Thornley on how chiral auxiliaries only give the desired enantiomer. It was actually made for the old programme but is still relevant to this sub-topic.
4. A simple but effective demonstration of the principle of polarimetry.