Dimethyl (2S,3aR,8aS)-(+)-hexahydro-8(phenylsulfonyl)pyrolo[2,3-b]indole-1,2-dicarboxylate; Pyrrolo[2,3-b]indole-1,2(2H)-dicarboxylic acid, 3,3a,8,8a-tetrahydro-8-(phenylsulfonyl)-, 1,2-dimethyl ester, (2S,3aR,8aS)-; α[¹¹C]Methyl-L-tryptophan precursor