Prostaglandin B₁: The L-shaped prostaglandin

The crystal and molecular structure of prostaglandin B₁ (PGB₁) has been determined. The conformation is L-shaped, with the α and ω side chains roughly perpendicular to one another. This arrangement differs from the "hairpin" or approximately parallel disposition of side chains observed for other prostaglandins. The w chain, which normally turns at the 15-hydroxyl back toward the α chain, is fully extended. The conformation is stabilized by the conjugation of the dienone chromophore. The 15-hydroxyl, which is normally directed away from the centroid of the prostaglandin in the hairpin model, is turned inward in L-shaped PGB ₁. The low biological activity of PGB₁ in many systems and especially its inhibition of the metabolizing enzyme 15-hydroxyprostaglandin dehydrogenase may be attributable directly to the observed L-shape conformation.