You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule pentyl (2S)-2-[[(5S)-5-[(6-aminopurin-9-yl)methyl]-2-oxo-1,4,2lambda5-dioxaphosphinan-2-yl]amino]-4-methylpentanoate into molecular formula.
user
C20H33N6O5P
assistant