2H-Cyclobuta(4'',5'')pyrano(3'',2'':5',6')benzofuro(3',2':3,4)cyclobuta(1,2-d)pyrimidine-3,8,10(1H,6aH,9H)-trione, 7-(2-deoxy-beta-D-erythro-pentofuranosyl)-2a,6b,7,10a,10b,11b-hexahydro-5-methoxy-1,1,2,2,10a-pentamethyl-, (2S-(2alpha,5alpha,6beta(S*)))-