4aH-7a,15-endo-Oxiranonaphtho(2',3':4,5)cyclohepta(1,2-b)xanthene-4a-carboxylic acid, 6-chloro-2,3,4,7,8,13,15,17-octahydro-1,4,9,12,14,16-hexahydroxy-18-methyl-8,13,17-trioxo-, methyl ester, (4R-(4alpha,4abeta,7abeta,15beta,18R*,20S*))-