Carbon-13 relaxation and proton nuclear magnetic resonance studies of prostaglandin F2alpha

Conformations of prostaglandin F 2alpha and recognition of prostaglandins by their receptors

The conformation of prostaglandin F 2alpha (PGF 2alpha) has been determined by x-ray diffraction techniques. Two independent conformers of PGF 2alpha, studied as the tris(hydroxymethyl)methylamine salt, are observed to adopt the familiar "hairpin" conformation with the alpha and omega chains aligned roughly parallel. The conformers differ in ring conformation and at the C(17)-C(18) bond, one adopting a C(9) envelope ring conformation and a trans geometry at the C(17)-C(18) bond, while the other adopts a C(8) envelope ring conformation and a novel gauche geometry about C(17)-C(18). Comparison of the conformation of PGF 2alpha with that of prostaglandin E2 suggests a recognition mechanism which would permit PGF 2alpha and prostaglandin E receptors to distinguish between the two potent prostaglandins. The recognition model explains much of the binding data for the PGF 2alpha receptor in the corpus luteum and predicts the existence of an interesting PGF 2alpha analog.

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 alpha and omega 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 omega chain, which normally turns at the 15-hydroxyl back toward the alpha 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 PGB1. 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.