(1'R,6R,6aR,7R,13S,16R)-5-(Acetyloxy)-3',4',6,6a,7,12,13,16-octahydro-6',8-dihydroxy-7',9-dimethoxy-4,10,23-trimethylspiro[6,16-(epithiopropanoxymethano)-7,13-imino-14H-1,3-dioxolo[7,8]isoquino[3,2-b][3]benzazocine-20,1'(2'H)-isoquinoline]-14,19-dione,Trabectedin Impurity