You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the molecule 7-[(2R,3R,4S,5R)-3,4-dihydroxy-5-methoxy-6,6-dimethyloxan-2-yl]oxy-4-hydroxy-3-(N-methoxy-C-methylcarbonimidoyl)-5-methylchromen-2-one ?
user
C21H27NO9
assistant