(5e,7e,21e)-4-ethyl-11,12,15,17,19-pentahydroxy-6'-(2-hydroxypropyl)-5',10,12,16,18,20,26,29-octamethylspiro[24,28-dioxabicyclo[23.3.1]nonacosa-5,7,21-triene-27,2'-oxane]-13,23-dione