616
HOW TO APPROACH EXAMINATION QUESTIONS: SELECTED PROBLEMS AND ANSWERS
(a) Identify the chiral centres in fluvastatin, and designate their configuration as R or S. Show the priorities
assigned to groups in establishing the configurations.
(b) Define the configuration of the double bond as E or Z. Show the priorities assigned to groups in establishing
the configuration.
(c) Draw the structure of the other component of racemic fluvastatin.
(d) Draw the structure of a diastereoisomer of fluvastatin.
(e) Fluvastatin can easily form a cyclic ester (lactone):
• Show the structures, including stereochemistry, of two possible lactone products.
• Indicate, giving reasons, which of the two lactones would be favoured.
• With an appropriate drawing, predict the most likely conformation of the favoured lactone.
• Give a mechanism for acid-catalysed formation of the lactone.
Answer 16.02
This problem shows a fairly complex structure, but asks relatively simple questions about it. It is important not
to be discouraged by the structure; simply apply standard procedures and reasoning.
(a) 3R and 5S.
CO 2 H
OH OH
3
aryl
priority 1
priority 2
priority 3
CO 2 H
OH OH
5
aryl
priority 1
priority 2
priority 3
chiral centres have four different groups attached
H
H
C
C
C
O
C
C
H
H
C
C
O
O
O
H
H
C
C
H
C
C
C
C
O
H
H
the sequence 1 → 2 → 3 looks anticlockwise
from front, but must be viewed from the rear
towards H; therefore it is clockwise: (R)
the sequence 1 → 2 → 3 looks clockwise
from front, but must be anticlockwise
looking from the rear towards H: (S)
H
don't put in the wedged
hydrogen like this: it is
more difficult to visualize
the stereochemistry
priority 4
priority 4
carbon-3
carbon-5
(b) E.
CO 2 H
OH OH
aryl
priority 1
priority 1
H
H
priority 2
priority 2
the high priority groups are on
opposite sides of double bond: (E)
HOW TO APPROACH EXAMINATION QUESTIONS: SELECTED PROBLEMS AND ANSWERS
(a) Identify the chiral centres in fluvastatin, and designate their configuration as R or S. Show the priorities
assigned to groups in establishing the configurations.
(b) Define the configuration of the double bond as E or Z. Show the priorities assigned to groups in establishing
the configuration.
(c) Draw the structure of the other component of racemic fluvastatin.
(d) Draw the structure of a diastereoisomer of fluvastatin.
(e) Fluvastatin can easily form a cyclic ester (lactone):
• Show the structures, including stereochemistry, of two possible lactone products.
• Indicate, giving reasons, which of the two lactones would be favoured.
• With an appropriate drawing, predict the most likely conformation of the favoured lactone.
• Give a mechanism for acid-catalysed formation of the lactone.
Answer 16.02
This problem shows a fairly complex structure, but asks relatively simple questions about it. It is important not
to be discouraged by the structure; simply apply standard procedures and reasoning.
(a) 3R and 5S.
CO 2 H
OH OH
3
aryl
priority 1
priority 2
priority 3
CO 2 H
OH OH
5
aryl
priority 1
priority 2
priority 3
chiral centres have four different groups attached
H
H
C
C
C
O
C
C
H
H
C
C
O
O
O
H
H
C
C
H
C
C
C
C
O
H
H
the sequence 1 → 2 → 3 looks anticlockwise
from front, but must be viewed from the rear
towards H; therefore it is clockwise: (R)
the sequence 1 → 2 → 3 looks clockwise
from front, but must be anticlockwise
looking from the rear towards H: (S)
H
don't put in the wedged
hydrogen like this: it is
more difficult to visualize
the stereochemistry
priority 4
priority 4
carbon-3
carbon-5
(b) E.
CO 2 H
OH OH
aryl
priority 1
priority 1
H
H
priority 2
priority 2
the high priority groups are on
opposite sides of double bond: (E)