You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(1R,3R,3aR,6aR)-1-(5-bromo-2-hydroxyphenyl)-5-butyl-3-(2-methylpropyl)-4,6-dioxo-1,2,3a,6a-tetrahydropyrrolo[3,4-c]pyrrole-3-carboxylic acid The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H27BrN2O5
assistant