You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[(2S,6S,7S,9R)-4,4-dimethyl-13-oxo-3,5,18,20-tetraoxa-14-azapentacyclo[13.7.0.02,6.07,14.017,21]docosa-1(22),11,15,17(21)-tetraen-9-yl] acetate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H23NO7
assistant