Synthesis and biological activities of turkesterone 11alpha-acyl derivatives.

Turkesterone is a phytoecdysteroid possessing an 11alpha-hydroxyl group. It is an analogue of the insect steroid hormone 20-hydroxyecdysone. Previous ecdysteroid QSAR and molecular modelling studies predicted that the cavity of the ligand binding domain of the ecdysteroid receptor would possess space in the vicinity of C-11/C-12 of the ecdysteroid. We report the regioselective synthesis of a series of turkesterone 11alpha-acyl derivatives in order to explore this possibility. The structures of the analogues have been unambiguously determined by spectroscopic means (NMR and low-resolution mass spectrometry). Purity was verified by HPLC. Biological activities have been determined in Drosophila melanogaster B(II) cell-based bioassay for ecdysteroid agonists and in an in vitro radioligand-displacement assay using bacterially-expressed D. melanogaster EcR/USP receptor proteins. The 11alpha-acyl derivatives do retain a significant amount of biological activity relative to the parent ecdysteroid. Further, although activity initially drops with the extension of the acyl chain length (C2 to C4), it then increases (C6 to C10), before decreasing again (C14 and C20). The implications of these findings for the interaction of ecdysteroids with the ecdysteroid receptor and potential applications in the generation of affinity-labelled and fluorescently-tagged ecdysteroids are discussed.

Ecdysteroid 7,9(11)-dien-6-ones as potential photoaffinity labels for ecdysteroid binding proteins.

Three ecdysteroid 7,9(11)-dien-7-ones (dacryhainansterone, 25-hydroxydacryhainansterone and kaladasterone) were prepared by dehydration of the corresponding 11a-hydroxy ecdysteroids (ajugasterone C, turkesterone and muristerone A, respectively). The biological activities of the dienones in the Drosophila melanogaster B(II) cell bioassay, which reflect the affinity for the ecdysteroid receptor complex, showed that the dienones retain high biological activity. Irradiation at 350 nm of the ecdysteroid dienones (100 nM) with bacterially-expressed dipteran and lepidopteran ecdysteroid receptor proteins (DmEcR/DmUSP or CfEcR/CfUSP), followed by loading with [(3)H]ponasterone A revealed that irradiation of dacryhainansterone or kaladasterone resulted in blocking of >70% of the specific binding sites. Thus, ecdysteroid dienones show considerable potential as photoaffinity analogues for ecdysteroid binding proteins.