A New Method for Radiosynthesis of 11C-Labeled Carbamate Groups and its Application for a Highly Efficient Synthesis of the Kappa-Opioid Receptor Tracer [11C]GR103545

Table 1: Radiochemical Yield^a of N-benzyl-[¹¹C]methyl Carbamate (2)^b,^c

Phase-Transfer Catalyst	Methylation Agent	T (°C)	Reaction Time (min)	RCY^a
TBAI	[¹¹C]MeI	25	5	36 ± 7
TBAI	[¹¹C]MeI	40	5	27 ± 6
TBAI	[¹¹C]MeI	50	5	21 ± 3
TBAI	[¹¹C]MeI	70	5	18 ± 4
TBAOTf	[¹¹C]MeOTf	25	2	69 ± 8
TBAOTf	[¹¹C]MeOTf	25	5	78 ± 6
TBAOTf	[¹¹C]MeOTf	35	2	82 ± 4
TBAOTf	[¹¹C]MeOTf	40	2	91 ± 5

^a Determined by analytical radio-HPLC

^b Results represent the mean ± sd, n = 4

^c To a solution of benzylamine (1) (2 mg, 18.6 µmol) in anhydrous DMF (500 µl) was added 3 molar equivalents of the TBA-reagent and 3 molar equivalents of Cs₂CO₃. CO₂ gas (20 ml/min) was bubbled through the suspension for 1 h at room temperature. The ¹¹C-alkylating agent was swept trapped in the reaction vial and allowed to react for the desired period of time.