Carbon-14 labeling of hydrochlorothiazide via [14C]formaldehyde production from [14C]carbon dioxide at ambient temperature

Article abstract of DOI:10.1002/jlcr.2984

[¹⁴C]Formaldehyde was synthesized by reducing ¹⁴CO₂ at ambient temperature with Schwartz's reagent. The [¹⁴C]formaldehyde was then used in the radiosynthesis of high specific activity (2.1 GBq/mmol) [¹⁴C]hydrochlorothiazide via cyclization of 4-amino-5-chloro-1,3-benzenedisulfonamide. A synthesis of [ ¹⁴C]formaldehyde by reducing ¹⁴CO₂ at ambient temperature with Schwartz's reagent is described. The [¹⁴C] formaldehyde has been applied in the radiosynthesis of high specific activity (2.1 GBq/mmol) [¹⁴C]hydrochlorothiazide via cyclization of 4-amino-5-chloro-1,3-benzenedisulfonamide. Copyright

Full text of DOI:10.1002/jlcr.2984

Note
Received 14 August 2012,
Accepted 17 October 2012
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI: 10.1002/jlcr.2984
Carbon-14 labeling of hydrochlorothiazide via
1
4
4
[
[
C]formaldehyde production from
C]carbon dioxide at ambient temperature
1
Johan Sandell*
1
4
14
14
[
C]Formaldehyde was synthesized by reducing CO
hyde was then used in the radiosynthesis of high specific activity (2.1 GBq/mmol) [ C]hydrochlorothiazide via cyclization of
-amino-5-chloro-1,3-benzenedisulfonamide.
2
at ambient temperature with Schwartz’s reagent. The [ C]formalde-
14
4
Keywords: [14C]formaldehyde; Schwartz’s reagent; zirconocene hydrochloride; hydrochlorothiazide
ꢁ
and column oven at 40 C, coupled in series with a Packard Radiomatic
Introduction
Flow Scintillator 525TR, equipped with a solid scintillator (SolarScint) cell
C]Formaldehyde is a versatile labeled reagent readily available with a volume of 32 mL. The column used was an Waters Sverige AB (Sollen-
14
[
from commercial sources but with a limited storage lifetime due tuna, Sweden) and the flow rate was 0.8mL/min. A linear gradient was
applied, starting at 100% A (A: 0.1% TFA) and ending at 95% B (B: MeCN),
in 10 min.
to radiolytic decomposition and typically delivered as an aqueous
solution. One of the most frequently applied methods for prepara-
14
14
1
Mass spectra were recorded on a Waters Sverige AB (Sollentuna, Sweden)
consisting of an Alliance 2795 (LC), Waters PDA 2996, and a ZMD single
quadrupole mass spectrometer. The mass spectrometer was equipped
with an electrospray ion source operated in a positive or negative ion
mode. The capillary voltage was 3 kV and cone voltage was 30 V. The mass
spectrometer was scanned between m/z 100–600 with a scan time of 0.7s.
2
tion of [ C]formaldehyde is via reduction of CO with LiAlH4. This
method requires strict temperature control to optimize the yield
because it is very difficult to stop the reduction process at the stage
of formaldehyde. Instead, a mixture of formaldehyde, formic acid,
14
and methanol is formed. The optimized yield of [ C]formaldehyde
ꢁ
by this method has been reported to be 40–50% as determined by The column temperature was set to 40 C. The diode array detector was
an iodometric method.
scanned from 200 to 400 nm.
The H NMR spectrum was recorded on a Bruker BioSpin Scandinavia AB
1
Zirconocene hydrochloride, or Schwartz’s reagent, is mainly
used in organic synthesis for various transformations of alkenes
and alkynes via the process called hydrozirconation that formally
(
Solna, Sweden) and was referenced to the residual solvent peak.
1
4
results in the addition of the Zr–H bond across the C═C or [ C]Hydrochlorothiazide (2)
CꢀC bond. According to Gambarotta et al., two equivalents of
A solution of zirconocene chloride hydride (148 mg, 0.56mmol) in THF
Schwartz’s reagent (I) reduce carbon dioxide at room temperature
ꢁ
(
3mL) in a dry, 25-mL vial was cooled to À78 C, evacuated, and filled with
2
to form formaldehyde (Scheme 1). The formed formaldehyde
can either be trapped or reduced further by heating with
excess Schwartz’s reagent to form the methoxy complex III. No a microwave vial charged with 4-amino-6-chlorobenzene-1,3-disulfonamide
yields or optimized reaction conditions have been reported for (40mg, 0.14mmol). The reaction was heated at 140 C for 10min
14
CO
2
(1243 MBq, 0.56 mmol). The reaction mixture was stirred at room
ꢁ
temperature for 4h. The solution was cooled at À78 C and transferred to
ꢁ
this reaction.
by microwaves. The reaction mixture was filtered through a disc filter and
subjected to flash chromatography on silica using THF as eluent. The
product was isolated as a white solid with a radiochemical purity of 98.5%
(28.8mg, 0.1mmol). The specific activity was 2.1 GBq/mmol.
This note describes the application of Schwartz’s reagent to
14
14
14
generate [ C]formaldehyde from CO
2
, which affords [ C]formal-
14
dehyde in an anhydrous state. The generated [ C]formaldehyde
was used to label the drug [ C]hydrochlorothiazide.
14
LC/MS (M + 1): 295.8 (8.0%) 296.6 (0.7%) 297.8 (100%) 298.9 (8.7%) 299.8
1
(
44.3%) 300.8 (4.5%) 301.9 (3.5%) 302.6 (0.08%) 303.4 (0.16%). H NMR
(
1
600MHz, DMSO-d
H) 7.49 (s, 2H) 6.97 (s, 1H) 4.71 (dd, J = 8.11, 2.56 Hz, 2H).
6
) d ppm 8.00 (br s., 1H) 7.98 (s, 1H) 7.95 (t, J= 8.04 Hz,
Experimental
All solvents and starting material used were commercially available and of
analytical grade. Anhydrous solvents were used. The microwave reaction
1
4
was performed in a Biotage AB (Uppsala, Sweden). CO
CO
2
2
was handled in a
14
Isotope Chemistry, Screening and Profiling Global DMPK IM, AstraZeneca,
Research & Development, Södertälje, Sweden
mannifold system obtained from RC TRITEC AG, Teufen, Switzerland.
Flash column chromatography was performed on 12g rediSep silica
column (Teledyne Isco, Lincoln, Nebraska, USA).
W
*
Correspondence to: Johan Sandell, Isotope Chemistry, Screening and Profiling
HPLC radiochemical purity analyses were performed on an Agilent Tech-
nologies Sweden (Kista, Sweden) with a binary pump, auto-injector, DAD,
Global DMPK IM, AstraZeneca, Research & Development, Södertälje, Sweden.
E-mail: Johan.Sandell@novandi.se
J. Label Compd. Radiopharm 2012, 55 499–500
Copyright © 2012 John Wiley & Sons, Ltd.

J. Sandell
3
O
previously. The limited options to label hydrochlorothiazide
2
Cp Zr(H)(Cl)+ CO
CH O
2
2
2
Cp (Cl)Zr
Zr(Cl)Cp2
+
2
14
in the benzene ring made labeling with [ C]formaldehyde an
attractive option, and this placement of label was deemed to be
adequate for this study.
I
II
The experimental conditions described by Gambarotta et al.
OMe
14
Cp Zr
were directly applied to the synthesis of [ C]formaldehyde, which
Cp Zr(H)(Cl)
+
CH O
2
2
2
1
4
Cl
III
utilized an excess1 CO relative to the Schwartz’s reagent. After
2
4
I
reduction of the CO , half an equivalent of the substrate 1 was
2
directly added to the reaction mixture and the solution was heated
Scheme 1. Reduction of carbon dioxide to formaldehyde by Schwartz’s reagent (I)
and further reduction to a methoxy complex (III) by excess I according to Gambarotta at elevated temperature by microwaves (Scheme 2).
2
14
et al.
After workup, the chemical yield of [ C]hydrochlorothiazide
2
was 69% as calculated from substrate 1 or 36% as calculated
from the Schwartz’s reagent. The yield as calculated from the
14
excess CO was 18%. This yield was achieved without systematic
2
[14
C]CO2
optimization of the reaction conditions. Mass spectroscopy
Schwartz´s reagent
THF
Ambient temperature
14
indicated that no [ C]formic acid was formed because the
14
corresponding [ C]chlorothiazide product could not be detected.
14
[
C]Hydrochlorothiazide 2 was prepared with a specific activity of
2.1 GBq/mmol and a radiochemical purity of 98.5%.
In conclusion, the simple setup and that this reaction can be
carried out at ambient temperature should make this a useful
alternative for synthesis of [ C]formaldehyde from CO .
2
O
14
14
O
S
O
O
S
O
H N
O
H N
2
O
2
S
S
H
H
NH
NH2
NH2
*
O
O
1
4
CH2
Acknowledgements
Cl
Cl
N
MW 140°C 10min
THF
H
1
2
I would like to thank Stefan Elofsson for the analysis of radiolabeled
compounds and Alexandra Bernlind for assistance with NMR.
Conflict of Interest
1
4
Scheme 2. Synthesis of [ C]hydrochlorothiazide (2) via cyclization of 4-amino-5-
1
4
chloro-1,3-benzenedisulfonamide (1) with [ C]formaldehyde.
The author did not report any conflict of interest.
Results and discussion
References
Hydrochlorothiazide is a diuretic drug of the thiazide class that
acts by inhibiting the kidneys’ ability to retain water. For an
environmental fate study, hydrochlorothiazide was needed in C-14
labeled form. A convenient cyclization of analogous 4-amino-1,
[
1] S. Mlinkó, J. Szammer, J. Radioanal. Nucl. Chem. Lett. 1993, 176,
91–496.
4
[
2] S. Gambarotta, S. Strologo, C. Floriani, A. Chiesi-Villa, C. Guastinig,
J. Am. Chem. Soc. 1985, 107, 6278–6282.
3
-benzenedisulfonamides with formaldehyde has been described [3] J. H. Short, U. Biermacher, J. Am. Chem. Soc. 1960, 82, 1135–1138.
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Copyright © 2012 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2012, 55 499–500