You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(18S,21S)-4,26-dimethoxy-14-(2-methoxy-2-methylpropanoyl)-21-methyl-18-(2-phenylethyl)-2-oxa-9,14,17,20,23-pentazatricyclo[23.2.2.13,7]triaconta-1(27),3,5,7(30),25,28-hexaene-8,16,19,22-tetrone is the IUPAC name of a molecule. Please give its molecular formula.
user
C40H51N5O9
assistant