Ecteinascidin 745; (1'R,6R,6aR,7R,13S,16R)- 5-(Acetyloxy)-3',4',6,6a,7,13,14,16-octahydro-6',8-dihydroxy-7',9-dimethoxy-4,10,23-trimethyl-Spiro[6,16-(epithiopropanoxymethano)-7,13-imino-12H-1,3-dioxolo[7,8]isoquino[3,2-b][3]benzazocine-20,1'(2'H)-isoquinolin]-19-one,Trabectedin Impurity