Molecular conformation of prostaglandin A₁

The crystal and molecular structure of prostaglandin A₁ (PGA₁) has been determined by X-ray diffraction. (Space group P2₁2₁2₁, a = 18.10 A ̊A, b = 21.09 A ̊A, c = 5.42, Z = 4). Comparison of the structure of PGA₁ with that of PGF_1β (determined previously as the tribromobenzoate) indicates significant differences in the relative intramolecular side chain orientations. However, conformation and torsional angles within each side chain of PGA₁ are retained with little or no change in comparison with PGF_1β, indicating the presence of the C₁₅-bromobenzoate groups in the latter have had little effect in altering internal side chain conformation in the solid state. The overall differences in relative side chain orientation in PGA₁ are attributable to chemical and conformational changes in the substituted cyclopentane moiety (C₈-C₁₂).