You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Under IUPAC nomenclature, a molecule named (3'R,4'S,5'R,7S)-5'-[[[[(2R,3R,4R,5S)-5-[6-(dioxaziridin-3-yl)purin-9-yl]-3-hydroxy-4-phosphonooxyoxolan-2-yl]methoxy-hydroxyphosphoryl]oxy-hydroxyphosphoryl]oxymethyl]-3',4'-dihydroxyspiro[1-azabicyclo[4.1.0]hepta-2,5-diene-7,2'-oxolane]-3-carboxylic acid is given. What is its corresponding molecular formula?
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C21H25N6O20P3
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