senecivernine
senkirkine
senecionine
erucifoline
acetylerucifoline
f
otosenine
Jacobine
jacoline
jacozine
b
d
e b,e
jaconine dehydrojaconine
deacetyldoronine
doronine
florosenine
floridanine
f
f
f
d
e
onetine
Integerrimine
seneciphylline
retrorsine
usaramine
spartioidine
a
a
b
c
a,c
1
2
2
senecivernine
a
b
senkirkine
senecionine
erucifoline
acetylerucifoline
f
otosenine
Jacobine
jacozine jacoline
jaconine
dehydrojaconine
deacetyldoronine
doronine
florosenine
floridanine
b
d
e
e
onetine
f
Integerrimine
seneciphylline
retrorsine
usaramine
spartioidine
a
a
b
c
a,c
1
2
2
f
f
1
1
1
Fig. 2 Putative biosynthetic pathways for diversification of PAs in the Jacobaea section. With the
exception of senecivernine, senecionine is the common precursor of all other PAs. Since the
substrate specificity of the enzymes involved is not known, two scenarios are illustrated:
(a) = senkirkine is assumed to be a common precursor of all otonecine derivatives; (b) = the
otonecine derivatives originate independently from the respective retronecine derivatives. Two
main reactions exist: conversion of retronecine to otonecine (reaction 1) and site-specific epoxide
formation (reaction 2). Further structural diversification requires six simple one-step reactions
marked by letters a–f: (a) Z/E isomerization at C20; (b) 13, 19-dehydrogenation; (c) site-specific
hydroxylations; (d) hydrolysis of 15,20-epoxide; (e) chlorolysis of 15,20-epoxide; and (f) sitespecific O-acetylations. (Adapted from Pelser et al. [30])
254
D. Cheng
senkirkine
senecionine
erucifoline
acetylerucifoline
f
otosenine
Jacobine
jacoline
jacozine
b
d
e b,e
jaconine dehydrojaconine
deacetyldoronine
doronine
florosenine
floridanine
f
f
f
d
e
onetine
Integerrimine
seneciphylline
retrorsine
usaramine
spartioidine
a
a
b
c
a,c
1
2
2
senecivernine
a
b
senkirkine
senecionine
erucifoline
acetylerucifoline
f
otosenine
Jacobine
jacozine jacoline
jaconine
dehydrojaconine
deacetyldoronine
doronine
florosenine
floridanine
b
d
e
e
onetine
f
Integerrimine
seneciphylline
retrorsine
usaramine
spartioidine
a
a
b
c
a,c
1
2
2
f
f
1
1
1
Fig. 2 Putative biosynthetic pathways for diversification of PAs in the Jacobaea section. With the
exception of senecivernine, senecionine is the common precursor of all other PAs. Since the
substrate specificity of the enzymes involved is not known, two scenarios are illustrated:
(a) = senkirkine is assumed to be a common precursor of all otonecine derivatives; (b) = the
otonecine derivatives originate independently from the respective retronecine derivatives. Two
main reactions exist: conversion of retronecine to otonecine (reaction 1) and site-specific epoxide
formation (reaction 2). Further structural diversification requires six simple one-step reactions
marked by letters a–f: (a) Z/E isomerization at C20; (b) 13, 19-dehydrogenation; (c) site-specific
hydroxylations; (d) hydrolysis of 15,20-epoxide; (e) chlorolysis of 15,20-epoxide; and (f) sitespecific O-acetylations. (Adapted from Pelser et al. [30])
254
D. Cheng