N-[9-[(2′S,6aR,8R,9aR)-Dihydro-2,2,4,4-tetrakis(1-methylethyl)spiro[6H-furo[3,2-f]-1,3,5,2,4-trioxadisilocin-9(8H),2′-oxiran]-8-yl]-6-(2-propen-1-yloxy)-9H-purin-2-yl]-2-methylpropanamide