WORKED PROBLEMS
617
(c) The other component of racemic fluvastatin is its enantiomer.
CO 2 H
OH OH
aryl
H
H
change the configuration at both centres;
change dot-wedge representation rather
than trying to draw mirror image
(d) Diastereoisomers.
CO 2 H
OH OH
aryl
H
H
CO 2 H
OH OH
aryl
H
H
or
change the configuration at
just one of the chiral centres
(e) Make ester from acid plus one of the two alcohol groups.
CO 2 H
OH OH
aryl
O
aryl
OH
aryl
OH
HO 2 C
O
OH
favoured − 6-membered ring
O
aryl
H
O
OH
large group
equatorial
O
aryl
O
OH
H
a
b
OH O
aryl
O
unfavourable − 4-membered ring
a
b
for b, must rotate
about this bond
O
aryl
H
OH
O
large group axial
alternative,
unfavourable
conformer
preferred conformer
Acid-catalysed lactone (ester) formation.
OH
O
OH
OH
OH
OH
OH
O
H
OH
OH
O
OH 2
OH
O
O
O
H
O
O
acid
alcohol
H
+
− H +
H +
− H +
ester or
lactone
protonation
(using catalyst)
nucleophilic attack
loss of leaving
group
protonation to
improve leaving group