Crystal structure and absolute configuration of 2′-bromopodophyllotoxin–0.5 ethyl acetate

Abstract

The crystal structure of the title compound (I; R = Br) has been determined in order to provide conclusive evidence for the absolute configuration of podophyllotoxin (I; R = H) and related lignans. The structure was determined from diffractometer data by the heavy-atom method and refined by least-squares techniques to R 0·098 for 2043 observed reflections. Crystals are monoclinic, space group P2₁, with Z= 4 in a unit cell of dimensions a= 1321(4), b= 1558(2), c= 1168(5) pm, β= 102·0(2)°.