Chirality of Biochemical Molecules

1. Chirality of Biochemical Molecules Group 8: The Chiral Crew

2. Focuses of our Project • Enzyme-Substrate Relationships • Effects on Tastes and Odors • Pharmaceutical Applications • As Seen in Living Organisms…

3. Introduction: What is Chirality?

4. Introduction: What is Chirality? • The geometric property of a molecule being non-superimposable on its mirror image; non-superimposable is not being able to place over or something. • When an atom has four non-equivalent atoms or groups attached to it, this is termed as the chirality center.

5. Introduction: What is Chirality? • Two Stereoisomers that differ only in their chirality = the arrangement of four different atoms or groups attached to a center atom typically a carbon, are called enantiomers. • Enantiomers are designated as R or S to signify whether they have a right-handed (R) or left-handed (S) configuration. • Active Learning: How do you determine if this molecule is the R-enantiomer or the S-enantiomer?

6. Introduction: What is Chirality? • Molecules that portray chirality or handedness may also be referred to as Levorotary (L=counterclockwise) or Dextrorotary (D=clockwise). • The L-configuration corresponds to the S-enantiomer while the D-configuration corresponds to the R-enantiomer. • This notation is often used to denote the chirality of many common biochemical molecules such as D-Fructose or L-Glyceraldehyde.

7. Introduction: When is a Molecule Achiral? • A molecule is achiral (non-chiral) if and only if it has an axis of improper rotation, that is, an n-fold rotation (rotation by 360°/n) followed by a reflection in the plane perpendicular to this axis maps the molecule on to itself.

8. Introduction:Guidelines for Chirality • You can determine if a molecule is chiral or achiral based on symmetry. • On the above model, you had a chiral reactant binding to a chiral reactant site where everything fits into place. • On the next model however, the enantiomer of the reactant below will not bind to the enzyme, so it will not react. • This leads to substrate specificity.

9. Enzyme-Substrate Relationships

10. Enzyme-Substrate Relationships Enzymes Macromolecules, mostly of protein nature, that function as (bio) catalysts by increasing the reaction rates. In general, an enzyme catalyses only one reaction type (reaction specificity) and operates on only one type of substrate.

11. Enzyme-Substrate Relationships Substrate • In an enzymatic reaction a substrate is the specific biochemical molecule that is acted upon by the enzyme to yield a specific product.

12. Enzyme-Substrate Relationships Substrate Specificity • A characteristic feature of enzyme activity in relation to the kind of substrate on which the enzyme or catalytic molecule reacts.

13. Effects on Tastes and Odors CHIRALITY AND ODOR

14. Effects on Tastes and Odors • The affect of chirality on bioactivity⋆ results in a variation in odor. • Each enantiomer has a different 3-D fit on odor receptors in the nose. • This phenomenon of specificity is not unlike that of enzyme- substrate relations. • The influence of this characteristic not only effects the specific odor, but also intensity of odor. • ⋆Note: Bioactivity is defined as: The effect of a given agent, such as a vaccine, upon a living organism or on living tissue. WHAT ACCOUNTS A DIFFERENCE IN ODOR PERCEPTION?

15. Effects on Tastes and Odors Why Do Lemons and Oranges Smell Differently?

16. Effects on Tastes and Odors • Found in both orange and lemon peels, Limonene is the molecule that is responsible for their characteristic odors. • Oranges contain the left-handed molecule, and lemons, the right-handed. • The same way your left foot fits only your left shoe, these molecules fit only into the appropriate left or right-handed receptors in your nose. • This is how the same molecule can cause the orange and the lemon to have different smells. Why Do Lemons and Oranges Smell Differently?

17. Effects on Tastes and OdorsEnantiomers of Limonene S-Limonene R-Limonene

18. Effects on Tastes and Odors Caraway Spearmint

19. Effects on Tastes and Odors Carvone • Carvone is a ketone that can be found in caraway, dill, and spearmint oils. • These oils are used for flavoring liqueurs and in perfumes and soaps. • (S)-carvone is a molecule with a caraway-like odor, while its mirror image molecule, (R)-carvone has a spearmint odor.

20. Effects on Tastes and OdorsEnantiomers of Carvone

21. Effects on Tastes and OdorsChirality and Food Flavor

22. Effects on Tastes and Odors WHAT ACCOUNTS FOR FOOD FLAVOR? • The major components of the food we eat, amino acids, proteins, carbohydrates, triacylglycerols and some vitamins, are all chiral. • This has a major impact on the perceived taste. • Chiral compounds can even be used to determine a products age, storage and handling procedures, and whether or not the food is of natural or synthetic origin.

23. Effects on Tastes and Odors Aspartame Molecule

24. Effects on Tastes and Odors • Aspartame is a sugar substitute composed of aspartic acid and phenylalanine. • Found in Equal and Nutrasweet, aspartame is very low in calories compared to sucrose (table sugar). • Although it is 100-200x sweeter than sugar, its stereoisomer is bitter.

25. Effects on Tastes and Odors FAST FACTS • There are more than 285 enantiomeric pairs (570 enantiomers) that are known to demonstrate odor differences or odor intensity differences. • Until the mid-1970’s to 1980’s, the idea that optical enantiomers could have different odors was not generally accepted by academics. • 8-10% of the population cannot distinguish between R-carvone and S-carvone. • In 1848, French scientist, Louis Pasteur, discovered the chirality in the spin of molecules while examining salt of tartaric acid.

26. Pharmaceutical Applications Chirality and Pharmaceutical Drugs • Most drugs derived from natural sources are chiral and are almost always obtained as a single enantiomer whereas approximately 80% of synthesized drugs are composed of a 50:50 racemic mixture. • Receptors and enzymes in the body are very stereo selective and only react with one of the enantiomers of a chiral molecule in a process called chiral recognition • As a result, one enantiomer has the desired effect on the body, while the other may have no effect or an adverse effect.

27. Pharmaceutical Applications In Vivo Effect of Enantiomers • Both enantiomers exhibit similar therapeutic properties (e.g. Promet-hazine, Flecainide) • Only one isomer shows pharmacological activity (S-propranolol is a beta blocker) while the other one is inactive (R-propranolol) • One type of isomer may show one type of pharmacological activity (S-penicillamine) and the other one shows toxicity (R-penicillamine) • One type of isomer may show one type of pharmacological activity (R- methylphenylpropyl barbituric acid – anesthetic) and the other type shows a convulsant effect

28. Pharmaceutical Applications Thalidomide - C13H10N2O4

29. Pharmaceutical Applications Thalidomide • Drug that was used in Europe during the period 1959 – 1962 to combat morning sickness in pregnant women. • ( R ) – thalidomide contained the properties that made it useful as a sedative and antinausea drug. • ( S ) – thalidomide was responsible for many birth defects such as phocomelia. • Even if thalidomide were purified to only the ‘R’- isomer, the pH of blood would cause rapid racemization into roughly equal amounts of both isomers.

30. Pharmaceutical Applications Birth Defects Caused by Thalidomide “Thalidomide Babies”

31. Pharmaceutical Applications Enantiomers of Thalidomide 'S' Optical isomer 'R' Optical Isomer

32. Pharmaceutical Applications Advantages of using the more active isomer of a drug • It leads to opportunities for “racemic switching” • Increase in production capacity • Less waste • Dose will be halved • Less likelihood of side effects

33. As seen in living organisms… • The Chirality of biochemical molecules greatly affects their functions in living organisms. • Many Organisms can use only the D-configuration or the L-configuration of a specific molecule. • A specific enantiomer may be produced by one organism and passed on to another for further use. • Many major biochemical molecules present even in our own bodies are chiral. • Typically in nature…

34. As seen in living organisms… D-Galactose Monosaccharide are found in the D-configuration D-Glucose In what foods would you find these monosaccharide?

35. As seen in living organisms… • D-Galactose is commonly referred to as milk sugar because it is found in dairy products such as milk, cheese and yogurt. • D-Glucose is found in a wide variety of foods from vegetables to baked goods. • D-Glucose molecules are synthesized by plants to store energy collected from the sun through the reactions of photosynthesis. • The D-Glucose we consume is oxidized within our cells to release this stored energy as heat and ATP.

36. As seen in living organisms… While Amino Acids are found in the L-Conformation L-Cysteine L-Serine What Amino Acid is Achiral?

37. As seen in living organisms… The Amino Acid Glycine is Achiral because it has 2 Hydrogen atoms attached to its central Carbon Atom.

38. As seen in living organisms… • A major exception to the generalization that amino acids in nature exist in the L-Configuration is found in the cell walls of bacteria • Bacterial cell walls are consist of a Peptidoglycan layer. • The Peptidoglycan layer is made up of chains of the sugar units NAM (N-acetylmuramic acid) and NAG (N-acetylglucosamine). • Amino acids are attached to the NAM units and are cross linked together between the sugar unit chains.

39. As seen in living organisms… Diagram of Gram-Negative Bacterial Cell Wall

40. As seen in living organisms… • In Gram-Positive Bacteria the Peptidoglycan layer is very thick. • The 4th Amino Acid in each chain is cross-linked to the 3rd Amino Acid in the adjacent chain directly or by a bridge of multiple amino acids. • The amino acids attached to the NAM units in the NAG-NAM chains are: 1) L-Alanine 2) D-Glutamic Acid 3) L-Lysine 4) D-Alanine

41. As seen in living organisms… Amino Acid Bridge in Cell Wall of Gram Positive Bacteria

42. As seen in living organisms… • In Gram-Negative Bacteria the Peptidoglycan layer is not as thick, but an outer membrane is present to help protect the cell. • The cell walls of Gram-Negative Bacteria differ in their amino acid chains in the 3rd position there is Meso-Diaminopimelic acid (DAP) instead of the L-Lysine found in Gram-Positive. • The Peptidoglycan layers of Gram Negative Bacteria also lack interpeptide bridges; their amino acid chains are connected by direct bonding between the 3rd and 4th amino acids only.

43. As seen in living organisms… Direct Amino Acid linkages in Gram-Negative Bacteria

44. Conclusion: Active Learning 3.* (1996 F 4) Vitamin E is a fat soluble vitamin essential for muscle development. Two Chemistry 32 students take Vitamin E; Fred gets his vitamin from a discount drug store; Sara believes in "natural foods“ and so she buys her Vitamin E from a health food store. Fred’s Vitamin E is made in a factory; Sara’s Vitamin E is derived from soybeans. Fred and Sara compared their Vitamin E samples by taking a melting point and measuring the 1H NMR spectrum of each. The melting points are different!!

45. Conclusion: Active Learning A. What is the difference between Fred and Sara's samples? B. What additional experiment would clarify the difference between Fred and Sara's Vitamin E? C. Would the NMR spectra of the two samples be the same? D. What do you advise Fred and Sara about taking the synthetic versus natural Vitamin E?

46. Conclusion: Active Learning A. What is the difference between Fred and Sara's samples? Natural compounds, such as Sara's sample, occur as one enantiomer. Vitamin E has 3 chiral centers, so there are 23=8 possible stereoisomers, many of which are probably contained in the synthetic analog that Fred bought.

47. Conclusion: Active Learning B. What additional experiment would clarify the difference between Fred and Sara's Vitamin E? Because Fred's sample is a mixture of diastereomers and Sara's sample is one pure enantiomer, the samples will have different physical and light-rotating properties. Chromatography or solubility experiments could clarify the differences in physical properties. NMR might elucidate how the structures differ. In addition, the optical activity of the samples could be checked. (Fred's sample is probably racemic.)

48. Conclusion: Active Learning C. Would the NMR spectra of the two samples be the same? They would be different. Fred's NMR would be complex because he has a mixture of diastereomers, which would be present in unpredictable ratios; Sara's would be simpler.

49. Conclusion: Active Learning D. What do you advise Fred and Sara about taking the synthetic versus natural Vitamin E? Biological receptors are often stereospecific, so only the proper enantiomer would be effective. Fred's Vitamin E probably has only 1/8 of the proper compound and probably contains other diastereomers that may be harmful. Sara's Vitamin E is a pure sample of the proper, natural compound and would be well received in the body.

50. For More Information see…(References) • Carey, Francis A. Organic Chemistry. 5th ed. New York: McGraw-Hill, 2000 • Dr. Gilmer’s Chapter 19 lecture • EXPERIMENT # 3: Essential Oils (EO). EO-1. MASSACHUSETTS INSTITUTE OF TECHNOLOGY Department of Chemistry. 5.310 Laboratory Chemistry. EXPERIMENT #3 ESSENTIAL OILS. http://web.mit.edu/5.310/www/Essential_oils.pdf • http://en.wikipedia.org/wiki/Image:D-glucose.png • http://en.wikipedia.org/wiki/Image:D-galactose_Fischer.png • http://orion.math.iastate.edu/mathnight/activities/modules/Mirror/leftpanel.pdf • http://web.mit.edu/5.310/www/Essential_oils.pdf