You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Please write the molecular formula of the molecule methyl (4R,7S)-2-methyl-4-(5-methylfuran-2-yl)-5-oxo-7-thiophen-2-yl-4a,6,7,8-tetrahydro-4H-quinoline-3-carboxylate .
user
C21H21NO4S
assistant