1'-acetyl-2'-oxo-1',2'-dihydrospiro[cyclohexane-1,3'-indole]-2-carboxylic acid InChI=1/C16H17NO4/c1-10(18)17-13-8-3-2-6-11(13)16(15(17)21)9-5-4-7-12(16)14(19)20/h2-3,6,8,12H,4-5,7,9H2,1H3,(H,19,20 spiro[cyclohexane-1,3'-[3H]indole]-2-carboxylic acid, 1'-acetyl-1',2'-dihydro-2'-oxo-