Syntheses of two isotopically labeled CB1 receptor antagonists

Synthesis of deuterium‐labeled CB₁ receptor antagonist 2‐d₉ was accomplished in three steps by alkylation of 2‐nitrophenylacetonitrile with cyclopentyl‐d₉ bromide, reductive cyclization of the resulting secondary nitrile into the 3‐cyclopentyl indole‐d₉ and its N‐sulfonylation with corresponding p‐amidosulfonyl chloride. Another, structurally related, CB₁ receptor antagonist 1 was radiolabeled with carbon‐14 by oxidative cleavage of 3‐cyclopentyl indole followed by the ring closure of o‐acyl substituted N‐formylaniline with potassium cyanide‐[¹⁴C], in situ reduction‐elimination of the intermediate amino alcohol, and N‐sulfonylation of the resulting 3‐cyclopentyl indole‐2‐[¹⁴C].