Chemistry Reference
In-Depth Information
(a)
OH
O
O
O
O
O
O
Ladder A
Ladder B
OH
syn
O
O
O
O
O
HH
O
O
HO
O
O
trans
O
O
O
O
n
HH
OH
n
= 1-4
HO
O
HO
(b)
Ladder D
NaO
3
SO
OH
OH
O
HO
OH
OH
O
O
O
O
HO
K
J
O
OH
O
OH
O
OH
O
O
O
O
O
A
O
OH
OH
OH
OH
HO
O
OH
Ladder C
HO
OSO
3
Na
HO
OH
OH
OH
OH
16 Maitotoxin
OH
(c)
H
HO
HO
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Shimizu/Nakanishi
O
HO
O
O
O
O
O
HO
O
13 Brevetoxin A
O
O
OH
O
O
O
O
O
O
Gallimore/Spencer
O
O
X
O
(d)
1. asymmetric epoxidation
2. substrate released
OH
O
m
m
Repeat
m
m
OH
m
m
O
Monooxygenase
Epoxide Hydrolas
e
n
−
1
O
O
OH
(i)
OH
m
n
m
m
m
m
n
−
2
n
Repeat
(ii)
Monooxygenase
m
1. asymmetric epoxidation
2. Substrate released
O
O
m
m
H
m
n
O
O
m
m
n
−
2
m
= 0,1,2,3,4
MO-bound transition state
Figure 8.4
(a) Maitotoxin. (b) Common structure feature of marine polyether ring junc-
tions (3). (c) Brevetoxin A biosynthesis as proposed by 1) Shimizu/Nakanishi (24, 25)
and 2) Gallimore and Spencer from all (
S,S
)-
trans
epoxides (3). (d) Possible enzymatic
routes to a fused polyether using 1) a mono-oxygenase and an epoxide hydrolase or 2) a
monooxygenase only (3).
(cf. MonB in monensin biosynthesis) to the polycyclic ether, because of the reac-
tivity of the polyepoxide intermediate (which may contain in excess of 20 reactive
epoxide groups), this seems unlikely. An alternative mechanism is for the epox-
idation and cyclization steps to be coupled in an iterative process whereby the
production of an epoxide is followed by ring closure (Fig. 8.4d). Gallimore and
Spencer (3) suggest that it may be possible for this process to be affected by the
