You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
5-[[5-(carboxymethyl)-5-hydroxy-4,7-dioxo-1,3,2-dioxalumepan-2-yl]oxy]-3-[[5-(carboxymethyl)-5-hydroxy-4,7-dioxo-1,3,2-dioxalumepan-2-yl]oxycarbonyl]-3-hydroxy-5-oxopentanoic acid is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H18Al2O21
assistant