You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule [4-[(3R,3'aR,8'aR,8'bR)-1',2,3'-trioxospiro[1H-indole-3,4'-3a,6,7,8,8a,8b-hexahydropyrrolo[3,4-a]pyrrolizine]-2'-yl]phenyl] acetate into molecular formula.
user
C24H21N3O5
assistant