(1R)-1-[(4E,9R,10E,12Z,16R,16aS,18R,19aR,23aR)-5,16a,21-trimethyl-3,14-dioxo-6,7,9,14,16,16a,22,23-octahydro-3H,18H,19aH-spiro[16,18-methano[1,6,12]trioxacyclooctadecino[3,4-d]chromene-17,2'-oxiran]-9-yl]ethyl acetate