Crystal and Molecular Structure of the Orthorhombic Form of Prostaglandin A₁

The crystal and molecular structure of the orthorhombic polymorph of the renal antihypertensive prostaglandin A] [15(S)-hydroxy-10,13-dien-9-ketoprostanoic acid, structure A], C₂₀H₃₂O₄, has been determined by X-ray diffraction techniques. The compound crystallizes in the orthorhombic space group P2₁2₁2₁, with cell constants a = 18.106 (3), b = 21.091 (4), and c = 5.420 (1) Å Z = 4, d_calcd = 1.086 g cm ^-3. The structure was solved by direct methods employing calculated values for the cosines of the seminvariant 2 triples. The refinement by F²-based full-matrix least squares led to final agreement factors of R(F) = 0.098 [R_w = 0.109; S = 1.14, Σw(F_o-sF_c) = 1312] for 1002 intensities measured on a G.E. XRD-5 single-crystal orienter using the stationary counter-stationary crystal technique. The molecular structure is characterized by extensions of the two side chains in the same direction away from the cyclopentenone ring. The crystal structure is stabilized by an infinite helical hydrogen-bonding network paralleling c, which does not involve the cyclopentenone moiety.