1H-Pyrrolo(1,2,3-de)quinoxaline-6-carboxylic acid, 2,3-dihydro-1-(2-(diethylamino)ethyl)-5-methyl-2-oxo-, ethyl ester, (R-(R*,R*))-2,3-dihydroxybutanedioate (2:1) 67918-90-5