3-[2-[[4-(2-carboxyethyl)-5-[[4-(2-carboxyethyl)-5-[[4-(2-carboxyethyl)-3-(carboxymethyl)-1H-pyrrol-2-yl]methyl]-3-(carboxymethyl)-1H-pyrrol-2-yl]methyl]-3-(carboxymethyl)-1H-pyrrol-2-yl]methyl]-4-(carboxymethyl)-5-(hydroxymethyl)-1H-pyrrol-3-yl]propanoic acid