ELM 3.1

Question 1

What is ‘the pharmacophore’?

Answer 1

The arrangement of chemical groups within a molecule that is necessary for biological activity

Question 2

What are optical isomers?

Answer 2

Optical isomers are compounds in which there is a different three dimensional arrangement of functional groups about one or more atoms.

Question 3

What two types of optical isomers are there?

Answer 3

enantiomers: pairs of molecules that are non-superimposable mirror images of each other
diastereoisomers: molecs that are not mirror images but which differ in orientation of one or more chiral centres

Question 4

How do enantiomers rotate polarized light?

Answer 4

d- (+): rotate light in a clockwise direction
l- (-): rotate light in an anticlockwise direction

Question 5

What is the D/L system used for?

Answer 5

Used for monosaccharides (sugars) and amino acids

Question 6

How does the D/L system work?

Answer 6

molecules whose structure can be “related back” to the (+) enantiomer of glyceraldehyde (right) are classified as D and those that can be related back to the (-) enantiomer of glyceraldehyde are termed L

• All naturally occurring amino acids (except glycine) are in the L configuration

Question 7

How does that Cahn-Ingold-Prelog (R/S) system work?

Answer 7

1. Identify the chiral centre. Usually, it will be a carbon with four different substituents.
2. Prioritise the substituents according to the atomic number of the atom connected to the chiral centre.
3. If two substituent atoms have the same atomic number, work your way out concurrently along the two chains until a point of difference is found. The priorities are then assigned at that point of difference. At the point of difference, priority is assigned on the basis of the highest atomic number. For example:
   -CH2-Cl has higher priority than CH2-CH2-CCl3 because at the first point of difference, Cl has a higher atomic number than C.
4. If a double bond is present, treat it as two single bonds to the same type of atom
5. If when you make the comparison, an atom (A) is bonded to two or more atoms of the same type e.g. a carbon bonded to two or three other carbons in a branched structure, then when you compare to its competing atom (B) you look to see if any of the substituents on the B have a higher atomic number than the substituents on A. If this is not the case, then A takes priority. For example, a -CH=CH2 group would beat -CH2-CH2-Cl chain because at the first point of difference we have a carbon bonded to the equivalent of two carbons (see rule 4). Its competitor is a carbon that is bonded to two hydrogens and one carbon. As there is no higher atomic number substituent on B, A wins by virtue of being bonded to two carbons.
6. Once priorities have been assigned, orient the molecule so that the lowest priority group faces away from you.
7. If the other groups are arranged in clockwise descending order of priority, the chiral centre is in the R configuration.
8. If the other groups are arranged in an anticlockwise descending order of priority, the chiral centre is in the S configuration.

Question 8

The R version of noradrenaline binds to __ adrenoreceptors around __x tighter than does the S version

Answer 8

beta 2
45
(remember that R noradrenaline has higher affinity than S noradrenaline - therefore is the naturally occurring enantiomer)

Question 9

Which classification systems is based on the direction a molecule rotates polarised light when in solution?

Answer 9

(+)/(-)

Question 10

What is the method of classifying the stereochemistry of a molecule, that relates the molecule’s structure to that of glyceraldehyde:

Answer 10

D/L - used most commonly with amino acids.

Question 11

Chiral centres

Answer 11

Carbons bonded to 4 dif things