Michihiro Ohno

Designed molecules reproducing the two conformations of teleocidins.

Abstract Tumor-promoting teleocidins are known to exist in an equilibrium between two conformational states, the twist form and sofa form, in solution. Benzolactam-Vs, in which the indole ring of indolactams was replaced with a benzene ring, were designed in an attempt to reproduce the active conformation of teleocidins, and synthesized. The 8-membered lactam (benzolactam-V8-310) exists only in the twist form in solution and the 9-membered lactam (benzolactam-V9-310) exists only in the sofa form in solution. The stronger biological activities of the 8-membered lactam than those of indolactam-V and the lack of activity of the 9-membered lactam clearly indicated that active conformation for tumor-promoting activity of teleocidins is close to the twist form.

TRA-418, a thromboxane A2 receptor antagonist and prostacyclin receptor agonist, inhibits platelet-leukocyte interaction in human whole blood

TRA-418, a compound with both thromboxane A2 receptor (TP receptor) antagonistic and prostacyclin receptor (IP receptor) agonistic activities, was synthesised in our laboratory as a new antithrombotic agent. In this study, we examined the effects of TRA-418 on platelet-leukocyte interactions in human whole blood. Platelet-leukocyte interactions were induced by U-46619 in the presence of epinephrine (U-46619 + epinephrine) or with thrombin receptor agonist peptide 1-6 (TRAP). Platelet-leukocyte interactions were assessed by flow cytometry, with examination of both platelet-neutrophil and platelet-monocyte complexes. In a control experiment, the TP receptor antagonist SQ-29548 significantly inhibited the induction of platelet-leukocyte complexes by the combination of U-46619 and epinephrine, but not TRAP-induced formation of platelet-leukocyte complexes. Conversely, the IP receptor agonist beraprost sodium inhibited platelet-leukocyte complex formation induced by both methods, although the IC50 values of beraprost sodium for U-46619 + epinephrine were at least 10-fold greater than for TRAP. Under such conditions, TRA-418 inhibited both U-46619 + epinephrine-induced and TRAP-induced platelet-leukocyte complex formation in a concentration-dependent manner, in a similar range. These results suggest that TRA-418 exerts its inhibitory effects on platelet-leukocyte interactions by acting as a TP receptor antagonist as well as an IP receptor agonist in an additive or synergistic manner. These inhibitory effects of TRA-418 on formation of platelet-leukocyte complexes suggest the compound is beneficial effects as an antithrombotic agent.

Chiral requirements for tumor promoters: conformations and activity of benzolactams

(−)-Benzolactam-V8-310 ((−)-1), which reproduces the twist conformation and biological activity of teleocidins, its antipode ((+)-1), and the epi-benzolactams ((−)-2 and (+)-2) were synthesized as optically pure forms. Structure-activity results indicate that the stereochemistry at C-5 plays a critical role in the binding to the receptor(s).