[11C]cyanogen bromide in the synthesis of 1,3‐di(2‐tolyl)‐[11C]guanidine

Abstract The title compound was 11C‐labelled in a one‐pot procedure using [11C]cyanogen bromide as the key intermediate. Synthesis time was 31–33 min counted from the end of bombardment, affording 1,3‐di(2‐tolyl)‐[11C]guanidine (6) in 87 % decay‐corrected radiochemical yield counted from [11C]cyanogen bromide. The specific radioactivity of the product at the end of synthesis was 118 GBq μmol−1 (3.2 Ci μmol−1). Autoradiographic studies on slide‐mounted rat brain sections showed specific binding of guanidine (6), but when injected intravenously into Rhesus monkey, brain uptake was very low, indicating that the 1,3‐di(2‐tolyl)‐[11C]guanidine did not cross the blood‐brain barrier.