Chemistry Reference
In-Depth Information
SH
O
O
O
*NO
HO
H
OH
R
1
N-13 nitrosamines
S
NH
2
O
O
O
O
NH
R
2
R
1
*
HO
H
OH
NNO
13
NO
-
R
2
NH
2
O
Room
temperature
1 min
Ph
3
P/Br
2
R
1
, R
2
= Et, i-Pr or
cyclo-butane
[
13
N]S-nitrosoglutathione
NH
2
R
2
R
1
R
2
*N
R
1
=H or SO
3
H
R
2
= OH, NH
2
,
SO
3
H, N(CH
3
)
2
R
1
N
N-13 diazo compounds
scheme 4.32
[
13
N]nitrite a useful precursor for labelling nitrosothiols, nitrosamines and diazo compounds.
4.4
oxygen-15 chemIstry
Oxygen-15 is generally produced in target via the bombardment of nitrogen gas with deuterons
14
N(
d
,
n
)
15
O. A small
percentage of carrier oxygen is required in the target gas that results in low specific activities of [
15
O]O
2
. Oxygen-15 has the
shortest half-life (t
1/2
= 2.0 min) of the commonly used PET isotopes, which seriously prohibits its use in multistep chemical
syntheses. The majority of O-15 chemistry is therefore based on the production of small molecules either directly within the
cyclotron target or via one chemical transformation using high temperature gas phase methods. Despite the time challenges
of using O-15, some of the earliest PET scans in human were achieved using [
15
O]O
2
, [
15
O]CO, [
15
O]CO
2
, and [
15
O]H
2
O.
Oxygen-15 labelled water has been especially important for the measurement of regional cerebral blood flow [164-167].
The production of [
15
O]H
2
O for these studies has been achieved in several ways, most simply by the inhalation of [
15
O]CO
2
,
which is instantaneously converted into [
15
O]H
2
O in the lungs by carbonic anhydrase enzyme [168] and then transported
around the body in the bloodstream. [
15
O]H
2
O can be produced directly via the high temperature reduction
15
O
2
over platinum
[169] or palladium [170-172] catalysts (scheme 4.33).
Alternatively, [
15
O]H
2
O can be produced in target by bombardment of natural water with protons [173, 174] (scheme 4.33)
yielding [
15
O]H
2
O that can be administered intravenously. Early investigations of blood flow studies in brain and other
organ by PET relied on [
15
O]O
2
or [
15
O]H
2
O before other the PET isotopes became available [175-177]. [
15
O]CO can also
be used to measure regional blood volume and can be produced rapidly via the reduction of [
15
O]O
2
over carbon beads at
high temperature [169, 171, 178]. The number of other more complicated molecules labelled with O-15 is very limited.
[
15
O]H
2
O
16
O(
p
,
pn
)
15
O
carbon,
1025°C
[
15
O]CO
H
2
/Pt or
H
2
/Pd
14
N(
d
,
n
)
15
O
[
15
O]O
2
carbon,
400°C
B(n-butyl)
3
THF
[
15
O]CO
2
[
15
O]n-butanol
scheme 4.33
synthesis of major oxygen-15 compounds for PET.
