((3S,7S,13S,15S,2R,20R,27R)-15-Hydroxy-13-methoxy-2,3,12,20,22-pentamethyl-8,26-dioxa-9-oxospiro[2H-3,4,5,6-tetrahydropyran-6,21'-tricyclo[17.3.1.0<4,9