You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
methyl 3-[(7R,8aR)-7-hydroxy-2-(3-hydroxypropanoyl)spiro[1,3,6,7,8,8a-hexahydropyrrolo[1,2-a]pyrazine-4,3'-azetidine]-1'-carbonyl]benzoate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H27N3O6
assistant