13 C‐ and 14 C‐labelling of N ‐[1‐(4‐chlorophenyl)‐1H‐pyrrol‐2‐yl‐methyleneamino] guanidinium acetate

N ‐[1‐(4‐chlorophenyl)‐1H‐pyrrol‐2‐yl‐ 13 C 4 ‐methyleneamino]guanidinium acetate has been synthesized by a four‐step procedure. This involved reduction of the Weinreb amide N , N′ ‐dimethyl‐ N , N′ ‐dimethyloxybutane‐1,4‐diamide‐1,2,3,4‐ 13 C 4 by Dibal‐H to give the corresponding unstable dialdehyde which is reacted in situ with 4‐chloroaniline to form 1‐(4‐chlorophenyl)‐1H‐pyrrole‐ 13 C 4 . This pyrrole analogue underwent a Vilsmeyer acylation with POCl 3 /DMF followed by final reaction with aminoguanidine bicarbonate to produce the desired labelled compound with 99% atom 13 C. By using DMF [ α ‐ 14 C] a radio‐labelled analogue was synthesized with a specific activity of 60 mCi/mmol. Copyright © 2005 John Wiley & Sons, Ltd.