You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
tert-butyl 3-[(6-amino-8-bromo-2-butoxypurin-9-yl)methyl]piperidine-1-carboxylate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H31BrN6O3
assistant