Inhibition of Hsp90 with Resorcylic Acid Macrolactones: Synthesis and Binding Studies

Abstract

A series of resorcylic acid macrolactones, analogues of the natural product radicicol has been prepared by chemical synthesis, and evaluated as inhibitors of heat shock protein 90 (Hsp90), an emerging attractive target for novel cancer therapeutic agents. The synthesis involves acylation of an ortho-toluic acid dianion, esterification, followed by a ring-closing metathesis to form the macrocycle. Subsequent manipulation of the protected hydroxymethyl side chain allows access to a range of new analogues following deprotection of the two phenolic groups. Co-crystallization of one of the new macrolactones with the N-terminal domain of yeast Hsp90 confirms that it binds in a similar way to the natural product radicicol and to our previous synthetic analogues, but that the introduction of the additional hydroxymethyl substituent appears to result in an unexpected change in conformation of the macrocyclic ring. As a result of this conformational change, the compounds bound less favorably to Hsp90.

The G ProteinαChaperone Ric-8 as a Potential Therapeutic Target

“…HSP/C 70/90 are both attractive as therapeutic targets because they contain multiple sites amenable to drug targeting, including ATP cofactor-binding sites, client protein substrate sites, and protein-protein interfaces (PPIs), with cochaperones that facilitate client protein folding activity (Rérole et al, 2011;Assimon et al, 2013;Balaburski et al, 2013;Schlecht et al, 2013). Many HSP/C 90/70 inhibitors are indeed small molecule adenosine analogs that target the nucleotidebinding site (Chiosis et al, 2002;Dymock et al, 2004;Donnelly and Blagg, 2008;Williamson et al, 2009;Day et al, 2010;Budina-Kolomets et al, 2014). While the potential to target active sites in these chaperones is advantageous, limited therapeutic success has been achieved thus far because of the cytotoxic effects of pleotropic inhibition of protein folding (Banerji et al, 2005;Goetz et al, 2005;Grem et al, 2005).…”

Recent Advances in Macrocyclic Hsp90 Inhibitors

“…Similar to the epoxide analogues, inversion of the cyclopropyl group stereochemistry also gave a drop in activity. 57 Additionally, removal of the epoxide altogether, 104 or its replacement with rings such as a thiirane and cyclic carbonate 109 or other H-bonding moieties 110 gave much lower activity than radicicol itself, proposed to be due to the adoption of an alternative macrocycle conformation. 110 (1) and (c) radicicol (10) co-crystallised with yeast Hsp90.…”

“…57 Additionally, removal of the epoxide altogether, 104 or its replacement with rings such as a thiirane and cyclic carbonate 109 or other H-bonding moieties 110 gave much lower activity than radicicol itself, proposed to be due to the adoption of an alternative macrocycle conformation. 110 (1) and (c) radicicol (10) co-crystallised with yeast Hsp90. Images from the article by Pearl et al 59 Moody and Shinonaga have developed synthetic radicicol analogues in which the dienone moiety has been removed (12 and 13, Figure 2.9), 104,109,110 while Danishefsky has replaced the dienone of cycloproparadicicol with a triazole (14).…”

“…110 (1) and (c) radicicol (10) co-crystallised with yeast Hsp90. Images from the article by Pearl et al 59 Moody and Shinonaga have developed synthetic radicicol analogues in which the dienone moiety has been removed (12 and 13, Figure 2.9), 104,109,110 while Danishefsky has replaced the dienone of cycloproparadicicol with a triazole (14). 112 Moody has also incorporated a triazole into the macrocycle to give compound 15 in order to investigate the benefits of additional H-bonding potential.…”

Synthesis of macrolactam analogues of radicicol and their binding to heat shock protein Hsp90

“…Moody and Shinonaga have developed radicicol analogues with a C11 ketone and a either a saturated carbon chain from C7-C10 or an enone (4 and 5, respectively). [32][33][34] Additionally, Danishefsky has replaced the dienone of cycloproparadicicol with a triazole 6 35 and we have also incorporated a triazole into the macrocycle (compound 7) to investigate the benefits of additional H-bonding potential. 36 Unfortunately, it appears that the conformational constraints of RALs is important for binding to the Hsp90 N-terminal domain and, as such, all of the analogues showed a significant drop in activity compared to radicicol itself, although potencies commensurate with other important Hsp90 inhibitors were achievable.…”