Synthesis and Biological Activities of New Conformationally Restricted Analogues of (−)-Indolactam-V:  Elucidation of the Biologically Active Conformation of the Tumor-Promoting Teleocidins

Abstract

The tumor-promoting teleocidins and their core structure (−)-indolactam-V (1) exist in two stable conformers in solution at room temperature. The cis amide assumes a twist conformation while the trans amide exists in a sofa form. In order to identify the biologically active conformation of the teleocidins, we have synthesized new twist-restricted analogues 5a and 6 based on an aza-Claisen rearrangement of (−)-N 13-desmethyl-N 13-allylindolactam-V (3) and a sofa-restricted analogue, (−)-5-methylindolactam-V (22). The activities of these new compounds were evaluated in three in vitro bioassays associated with in vivo tumor-promoting activity: binding to the protein kinase C regulatory domain, induction of the Epstein−Barr virus early antigen, and stimulation of radioactive inorganic phosphate incorporation into phospholipids of HeLa cells. These three biological activities correlated well for each derivative. Twist-restricted analogues 5a and 6 showed significant activities in the three assays, comparable to 1 itself. In contrast, sofa-restricted 22 showed little activity related to tumor promotion. Introduction of a prenyl group into position 7 or 18 of 5a and 6 significantly enhanced the activity while sofa-restricted (−)-5-prenylindolactam-V (23) showed only very weak activity. These results indicate that the active conformation of the teleocidins and 1 is close to the twist form. This is the first evidence bearing on the active conformation of the teleocidins based on conformationally restricted analogues with an intact indolactam skeleton and is in accord with conclusions reported for benzolactams, analogues without the pyrrole moiety. This study also describes the synthesis of new biologically active compounds (26a, 26b, 28) based on inactive (+)-epiindolactam-V (24), involving a further application of the aza-Claisen rearrangement. Bridge formation between positions 5 and 13 of indolactam derivatives represents a particularly effective analogue design strategy, allowing for the remote control of the conformation of this ring system and for the introduction of a wide range of structural variations, as required for the development of new protein kinase C activators with high isozyme selectivity.

Binding Selectivity of Conformationally Restricted Analogues of (−)-Indolactam-V to the C1 Domains of Protein Kinase C Isozymes

“…The Ki values of the twistrestricted analogue (2) were similar to those of 1, supporting the active conformation of 1 being in the twist form of the cis amide. 8) The K i values of 1 for the conventional PKC C1A peptides and those for the novel PKC C1B peptides were in good agreement with those for the whole PKC isozymes reported by Kazanietz et al 9) The sofa-restricted analogue (3), which was almost inactive in several in vitro bioassays related to tumor promotion, 8) bound only to the C1B domains of all novel PKCs with similar potency to that of 1. It is especially noteworthy that the binding a‹nity of 3 to the conventional PKC C1A domains was over 100 times weaker than that of 1 or 2 (Fig.…”

Synthesis and biological activities of the amide derivative of aplog-1, a simplified analog of aplysiatoxin with anti-proliferative and cytotoxic activities

“…37,38) Side chains at C-11 were attached to them and dihedral angles in the side chain were manually rotated to search for an energetically stable orientation, in which the 18-OH group is involved in intramolecular hydrogen bonding as suggested by its sharp 1 H NMR signal in CDCl 3 . The candidate structures were pre-optimized using the molecular mechanics method with the MMFF94s force field, and the final DFT geometry optimizations were then performed at the ωB97X-D/6-31G* level of theory.…”

Synthesis and Biological Activities of Indolactone-V, the Lactone Analogue of the Tumor Promoter (–)-Indolactam-V

“…8, 13.14) Binding affinity was evaluated by the binding constant (K j ), which was calculated from Ie 50, the concentration required to cause 50% inhibition of the specific [3HJPDBu binding, by the method of Blumberg. 15) The binding affinity of 2 was quite similar to that of sofa-restricted (-)-5-methylindolactam-V, 8) and far weaker than that of 1. Indolactone-V (2) was also inactive in the EBV-EA induction test even at 10 flM.…”

“…To clarify this, it is necessary to synthesize a twist-like-fixed analogue of 2. We have recently succeeded in synthesizing the twist-restricted analogues of 1 by the aza-Claisen rearrangement of (-)-N 13 -desmethyl-N 13 -allylindolactam-V. 8) The application of this reaction to the synthesis of the twist-like-fixed analogue of2 is in progress.…”