You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 2-[6-[1-(1,3-benzothiazol-2-ylsulfanyl)propan-2-ylamino]-2-chloropurin-9-yl]-5-(hydroxymethyl)oxolane-3,4-diol by IUPAC nomenclature, provide its molecular formula.
user
C20H21ClN6O4S2
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