2,6,10,14,18,22-Hexaazapentacosanedioic acid, 3,12,15,19-tetramethyl-7,23-bis(2-methylpropyl)-5,9,13,17,21-pentaoxo -, 1-(1,1-dimethylethyl) 25-(phenylmethyl) ester, (3S,7S,12R,15S,19S,23S)-