(S)-2-((2-amino-6-oxo-1H-purin-9(6H)-yl)methoxy)ethyl 3-methyl-2-((((6-oxo-6,9-dihydro-1H-purin-2-yl)amino)methyl)amino)butanoate
(S)-2-((2-amino-6-oxo-1H-purin-9(6H)-yl)methoxy)ethyl 3-methyl-2-((((6-oxo-6,9-dihydro-1H-purin-2-yl)amino)methyl)amino)butanoate