Synthesis of carbon‐14 labeled LTD 4 antagonist MK‐571

The synthesis of (E)‐5‐(3‐(2‐(7‐chloroquinolin‐2‐yl)ethenyl)‐ phenyl)‐[5‐ 14 C]‐4,6‐dithianonane dicarboxylic acid N, N‐dimethylamide ([ 14 C]MK‐571), a high‐affinity LTD 4 antagonist, from sodium [ 14 C]cyanide via a five step sequence is described. Condensation of 3‐[ 14 C]cyanobenzaldehyde with 7‐chloroquinaldine followed by nitrile reduction provided the [ 14 C]aldehyde 2. The pivotal formation of the penultimate unsymmetrical dithioacetal intermediate was accomplished in a selective manner from aldehyde 2 by way of an O‐trimethylsilyl hemiacetal intermediate. Subsequent ester hydrolysis afforded [ 14 C]MK‐571 in 14% overall radiochemical yield.