Nucleophilic enantioselective synthesis of 6-[18F]Fluoro-l-dopa via two chiral auxiliaries

Nucleophilic substitution of nitro groups by [18F]fluoride in methoxy-substituted ortho-nitrobenzaldehydes—A systematic study

“…The poor RCY is to be understood in terms of the strong +M-effect of the CH 3 O-substitutent p-oriented to the leaving group. Compared to this result, the radiochemical yields obtained for 4,5-dimethoxy-2-nitrobenzaldehyde (25-55%) as labelling precursor [8,9] are considered to be unexpectedly high. That prompted us to a systematic study about the dependence of the RCY on the number and positions of methoxy substituents present in o-nitrobenzaldehydes.…”

Radiosynthesis of 4-[ 18 F]fluoro- l -tryptophan by isotopic exchange on carbonyl-activated precursors

“…In previous studies this was done using concentrated HBr or HI and temperatures as high as 150°C or even 200°C. 17,30 In another work concentrated HCl and heating to 150°C for 30 min proved sufficient for the hydrolysis of the Bocprotected derivative of Seebach's auxiliary. 21 In the study here, those conditions were adapted to give a RCY of [ 18 F]18 of approximately 34% for this deprotection reaction.…”

Methods for 11C‐ and 18F‐labelling of amino acids and derivatives for positron emission tomography imaging

“…In initial studies, the aldehyde function was directly used for coupling by a condensation reaction using the Erlenmeyer–Plochl azlactone synthesis . In this way, 4‐[ 18 F]fluorophenylalanine has been synthesized using nucleophilic displacement of the activated nitro group of p ‐nitrobenzaldehyde by n.c.a.…”

“…In later attempts, the 18 F‐labelled aldehyde was first converted into [ 18 F]fluorobenzyl bromide or iodide derivatives that were coupled with the chiral amino acid auxiliaries (1R,2R,5R)‐[(+)‐2‐hydroxypinanyl‐3‐idene]glycine tert ‐butyl ester, to obtain 6‐[ 18 F]fluoro‐ l ‐dopa, or (S)‐(−)‐1‐boc‐2‐tert.‐butyl‐3‐methyl‐4‐imidazolidinone, to obtain 6‐[ 18 F]fluoro‐ l ‐dopa, α‐methylated derivatives, and 4‐chloro‐2‐[ 18 F]fluoro‐α‐methyl‐ l ‐phenylalanine . This latter method gave a higher enantiomeric excess of the aromatic amino acids.…”