Chemistry Reference
In-Depth Information
O
O
O
OH
HN
O
HO
O
OH
OCH
3
OH
O
O
O
16
O
OH
12
OH
OH
9 -
Mupirocin
10 -
Myxovirescin A
O
COOH
OCH
3
H
OCH
3
HO
OH
O
H
2
N
NH
O
OH
O
O
N
O
N
OH
NH
O
OCH
3
O
OCH
3
O
O
O
11 -
Onnamide
12 -
Pederin
O
P(OH)
2
3
OH
O
OH
O
OH
2
O
HO
15
O
12
O
O
O
O
OH
O
H
2
N
13 -
Phoslactomycin
14 -
Tautomycetin
O
OH
H
O
O
O
N
O
O
N
15 -
Virginiamycin M
Figure 7.4
(
Continued
)
account for the infrequent occurrence of this double bond configuration. One
explanation is that an isomerization event occurs that converts a
trans
double
bond into a
cis
double bond. This isomerization activity could be specified by
the PKS elongation module, much like previously identified epimerization activ-
ities that are known to exist in some PKS and NRPS modules. Alternatively,
the combined activity of KR-DH domains within certain modules could directly
establish the
cis
double bond. Finally, it is possible that after reduction of the
β
-
keto functionality, a
trans
acting DH could catalyze dehydration to form a (
Z
)-
cis
double bond. This
trans
activity might derive from a discrete enzyme encoded
