2'-oxo-1',2'-dihydrospiro[bicyclo[2.2.2]oct-5-ene-2,3'-indole]-3-carboxylic acid InChI=1/C16H15NO3/c18-14(19)13-9-5-7-10(8-6-9)16(13)11-3-1-2-4-12(11)17-15(16)20/h1-5,7,9-10,13H,6,8H2,(H,17,20)(H,18,19 spiro[bicyclo[2.2.2]oct-5-ene-2,3'-[3H]indole]-3-carboxylic acid, 1',2'-dihydro-2'-oxo-