D.8.1: Describe the importance of geometrical isomerism in drug action Recall in Topic 20 you learned about geometric isomerism. What is a geometric isomer? Two different geometric isomers may have very biological different effects. For example, diamminedichloroplatinium (II). This compound has a formula of Pt(NH3)2Cl2 has a cis- and a trans- isomer due to the square planar structure. The cis- isomer is highly effective in the treatment of testicular and ovarian cancers, as well as other forms of cancer. The trans- isomer is not an effective anti-cancer drug.

D.8.2: Discuss the importance of chirality in drug action Drug molecules that process a chiral carbon atom will exist in two different enantiomeric forms. Thalidomide alleviates the symptoms of morning sickness in pregnant woman; the other causes severe deformities in the limbs of the baby.

D.8.3: Explain the importance of the beta-lactam ring action of penicillin All penicillins contain a 4-membered beta-lactam ring. The ring contains 2 carbon atoms that are sp3 hybridized, a nitrogen atom that is sp3 hybridized, and a carbon atom that is sp2 hybridized. Penicillin Because of the restrictions of the ring, the normal bond angles of 109.5 and 120 are not able to be obtained, and so the ring becomes strained. This makes the amide highly reactive. The ring opens so that the penicillin can become covalently bonded to the enzyme that synthesizes the cell walls of the bacterium, thus blocking its action.

D.8.4: explain the increased potency of diamorphine (heroin) compared to morphine Heroin is stronger than morphine. This can be explained due to the difference in polarity of the two substances. Morphine molecules contain two polar hydroxyl groups; in heroin, these molecules are replaced by ethanoate groups. These two ester groups make it much less polar than morphine and more soluble in lipids, which are non-polar. Morphine Heroin Much less Polar group Polar group