Synthesis and Evaluation of Simplified Cruentaren A Analogues

Abstract

The 90 kDa heat shock protein (Hsp90) belongs to a group of molecular chaperones that regulate homeostasis via the folding of nascent polypeptides into their biologically active proteins, many of which are involved in cancer development and progression. As a result, inhibition of Hsp90 is an exciting area of research for the treatment of cancer. However, most of the 18 Hsp90 N-terminal inhibitors evaluated in clinical trials exhibited deleterious side effects and toxicities. Cruentaren A is a natural product that manifests potent anticancer activity against various human cancer cell lines via disruption of interactions between Hsp90α and F 1 F O ATP synthase, which does not induce the pro-survival, heat shock response, a major limitation associated with current Hsp90 inhibitors. However, the development of cruentaren A as a new anticancer agent has been hindered by its complex structure. Herein, we systematically removed the functionalities present in fragment 2 of cruentaren A and incorporated some key structural modifications from previous work, which produced 12 simplified analogues. Our studies determined that all functional groups present in fragment 2 are essential for cruentaren A's anticancer activity.

CryoEM Structure with ATP Synthase Enables Late‐Stage Diversification of Cruentaren A

“…Furthermore, the macrocyclic ring is directed towards the C terminus of the β subunit and faces towards the solvent‐exposed region. Fragment 2 occupies the space between helix 1 of the C terminus in the α TP subunit and helix 4 of the C terminus in the β TP subunit, [8] wherein the distance between the C16 methyl group and α TP is 3.7 Å and the distance between the C18 methyl group and β TP is 3.9 Å, which might explain why fragment deletions are detrimental to cruentaren A's biological activity due to potential loss of hydrophobic interactions [7] …”

“…Fragment 2 occupies the space between helix 1 of the C terminus in the α TP subunit and helix 4 of the C terminus in the β TP subunit, [8] wherein the distance between the C16 methyl group and α TP is 3.7 Å and the distance between the C18 methyl group and β TP is 3.9 Å, which might explain why fragment deletions are detrimental to cruentaren A's biological activity due to potential loss of hydrophobic interactions. [7] Although previous SAR studies with cruentaren A have identified some inhibitors via diverted total syntheses, the interactions between cruentaren A and amino acids within the ATP synthase remained unknown. [7,9] During the course of our studies, it was determined that the methyl group at C16 interacts with α TP -Val369, α TP -Leu394, and α TP -Ala397, while the C18 methyl group interacts with the methylene of β TP -Phe424.…”

“…[7] Although previous SAR studies with cruentaren A have identified some inhibitors via diverted total syntheses, the interactions between cruentaren A and amino acids within the ATP synthase remained unknown. [7,9] During the course of our studies, it was determined that the methyl group at C16 interacts with α TP -Val369, α TP -Leu394, and α TP -Ala397, while the C18 methyl group interacts with the methylene of β TP -Phe424. Additionally, the hydroxy group at C17 forms a hydrogen bond with α TP -Lys393 (Figure 3c).…”

“…We recently reported the synthesis and evaluation of 12 cruentaren A analogues in an effort to establish preliminary SAR for simplification of the molecule (Figure 2). [7] However, all 12 compounds were significantly less active, resulting in minimal insight into this promising anticancer agent. Therefore, the structure of cruentaren A bound to ATP synthase is needed to rationally improve upon cruentaren A's promising anticancer activity.…”