ANTICANCER AGENT DEVELOPMENT .5. X-RAY STRUCTURE AND H-1-NMR SPECTRAL-ANALYSIS OF (1-ALPHA,2-ALPHA,5-ALPHA,6-ALPHA)-2,6-BIS(3,4-METHYLENEDIOXYPHENYL)-3,7-DIOXABICYCLO[3.3.0]OCTANE-4,8-DIONE

The title compound, C20H14O8, Mr=382.3, crystallized from chloroform in the centric space group P-1 with a=6.516(4), b=6.798(3), c=9.545(7) Å, α=85.31(5), β=73.87(5), γ=79.59(4)°, V=399.2 Å3, and Dcalc=1.59 g cm-3 for Z=1. Least-squares refinement of 1035 observed [Fo≥5 σ(Fo)] reflections led to the final agreement index of R=0.074. The molecule resides on a crystallographic center of inversion and is disordered into two different conformations. This manifests itself as a 50/50 disorder at O(4), C(2), and C(3). The observed structure reveals a cis relationship between the bridgehead hydrogen atoms and the aryl rings. The 90 MHz1H nmr spectrum of the title compound exhibits an AA′XX′ spin system with a H(1)C(2) to H(1)C(3) and H(1)C(2)′ to H(1)C(3)′ coupling constant of 2.8 Hz. Computer spectral simulation and Karplus equation analysis are utilized to illustrate a relaxation of the torsion angles between H(1)C(2) and H(1)C(3), and H(1)C(2)′ and H(1)C(3)′ is solution. © 1990 Plenum Publishing Corporation.