(3S,10S,31S,2R,12R,20R,28R)-31-Hydroxy-28-methoxy-2,3,18,20,29-pentamethyl-9,13,17,26-tetraoxaspiro[2H-3,4,5,6-tetrahydropyran-6,6'-pentacyclo[16.6.1.1<4,8