XT1 xt1 (2R)-3-[(2S,5R,6R,8S)-8-{(1R,2E)-3-[(2R,4a'R,5R,6'S,8'R,8a'S)-6'-{(1S,3S)-3-[(2S,3R,6R,11R)-3,11-dimethyl-1,7-dioxaspiro[5.5]undec-2-yl]-1-hydroxybutyl}-8'-hydroxy-7'-methylideneoctahydro-3H,3'H-spiro[furan-2,2'-pyrano[3,2-b]pyran]-5-yl]-1-methylprop-2-en-1-yl}-5-hydroxy-10-methyl-1,7-dioxaspiro[5.5]undec-10-en-2-yl]-2-hydroxy-2-methylpropanoic acid XT1