You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Please write the molecular formula of the molecule (1R,2R,5R)-2-hydroxy-3'-[(5R)-5H-imidazo[5,1-a]isoindol-5-yl]spiro[3-azabicyclo[3.2.1]octane-8,1'-cyclobutane]-3-carboxylic acid .
user
C21H23N3O3
assistant