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the arylstannane (S)-1b or the protected arylboronic ester
(S)-2b. These new developments suggest that fluorination using
unlabeled selectfluor could be favorably considered, after ade-
quate optimization, for the production of [18F]material.
We gratefully acknowledge the BBSRC and GE Healthcare
(ISRS), the Academy of Finland and the Finnish Centre of
Excellence in Molecular Imaging in Cardiovascular and Meta-
bolic Research (AK, SF), and the Lundbeck and Carlsberg
Foundations (CGJ) for generous funding.
Scheme 2 Synthesis of [18F]-6-fluoro-L-DOPA from (S)-1b.
Notes and references
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Scheme 3 Synthesis of [18F]-6-fluoro-L-DOPA from (S)-2b.
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Fig. 2 Statistical analysis of the RCYs of [18F]10 from (S)-1b or (S)-2b.
preparation of selectfluor bis(triflate) [18F]9. When 7.5 mmol of
precursor 8 was used to access [18F]9, the RCY was significantly
lower (6.8 ꢀ 1.8%). The specific activity (SA) of the final product
was consistently in the range of 3.4 ꢀ 0.1 GBq mmolꢁ1
.
The radiolabeling of (S)-2b was examined next (Scheme 3).
Unlike arylstannanes (S)-1a and (S)-1b, the transmetalation of
the arylboronic ester (S)-2b was performed prior to [18F]labeling.
Practically, the arylboronic ester (S)-2b was therefore converted to
the corresponding aryl Ag(I) complex (S)-5b prior to [18F]fluorina-
tion. The complex (S)-5b freshly prepared was labeled success-
fully within 20 minutes at room temperature using selectfluor
bis(triflate) [18F]9. Deprotection of [18F](S)-6b led to [18F]-6-
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¨
2.6 ꢀ 0.3 GBq mmolꢁ1. The efficiency of this process is compar-
W. Mohnike, T. Eberhard, F. Fuechtner, B. Lorenz-Depiereux and
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able to that of the best known protocol using [18F]F2.10
14 For selected fluorination of boronic acids (cold mode): (a) G. V.
In a statistical analysis, the yield of 6-fluoro-L-DOPA [18F](S)-10
from (S)-1b did not differ significantly from the yield obtained
when using (S)-2b (Fig. 2).
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In conclusion, we have extended the scope of [18F]selectfluor
bis(triflate) for [18F]radiochemistry. The demonstration that
the arylboronic ester (S)-2b is a competent substrate for
[18F]fluorination suggests that a plethora of arylboronic acid
derivatives can be radiolabeled using this new protocol. This
study demonstrates that [18F]selectfluor bis(triflate) is a suitable
15 T. Furuya and T. Ritter, Org. Lett., 2009, 11, 2860–2863.
alternative to [18F]F2 to access [18F]6-fluoro-L-DOPA from either 16 For details, see the ESI†.
c
This journal is The Royal Society of Chemistry 2013
1388 Chem. Commun., 2013, 49, 1386--1388