Structural Elucidation and Synthesis of Eudistidine A: An Unusual Polycyclic Marine Alkaloid that Blocks Interaction of the Protein Binding Domains of p300 and HIF-1α

Abstract

Low oxygen environments are a hallmark of solid tumors, and transcription of many hypoxia-responsive genes needed for survival under these conditions is regulated by the transcription factor HIF-1 (hypoxia-inducible factor 1). Activation of HIF-1 requires binding of its α-subunit (HIF-1α) to the transcriptional coactivator protein p300. Inhibition of the p300/HIF-1α interaction can suppress HIF-1 activity. A screen for inhibitors of the protein binding domains of p300 (CH1) and HIF-1α (C-TAD) identified an extract of the marine ascidian Eudistoma sp. as active. Novel heterocyclic alkaloids eudistidines A (1) and B (2) were isolated from the extract, and their structures assigned by spectroscopic analyses. They contain an unprecedented tetracyclic core composed of two pyrimidine rings fused with an imidazole ring. Eudistidine A (1) was synthesized in a concise four-step sequence featuring a condensation/cyclization reaction cascade between 4-(2-aminophenyl)pyrimidin-2-amine (3) and 4-methoxy-phenylglyoxal (4), while eudistidine B (2) was synthesized in a similar fashion with glyoxylic acid (5) in place of 4. Naturally occurring eudistidine A (1) effectively inhibited CH1/C-TAD binding with an IC50 of 75 μM, and synthetic 1 had similar activity. The eudistidine A (1) scaffold, which can be synthesized in a concise, scalable manner, may provide potential therapeutic lead compounds or molecular probes to study p300/HIF-1α interactions and the role these proteins play in tumor response to low oxygen conditions. The unique structural scaffolds and functional group arrays often found in natural products make these secondary metabolites a rich source of new compounds that can disrupt critical protein-protein binding events.

Marine natural products

“…The eighteen new tunicate-derived natural products presented in this review is the second lowest annual count since 2002. The metabolites reported included a meroterpenoid 1317, 934 940 Noteworthy were the isolation, structure elucidation, synthesis and biological evaluation of eudistidines A 1333 and B 1334 (Eudistoma sp., Palau). 940 A fourstep condensation/cyclisation reaction sequence afforded both natural products, allowing conrmation of their structures.…”

“…The metabolites reported included a meroterpenoid 1317, 934 940 Noteworthy were the isolation, structure elucidation, synthesis and biological evaluation of eudistidines A 1333 and B 1334 (Eudistoma sp., Palau). 940 A fourstep condensation/cyclisation reaction sequence afforded both natural products, allowing conrmation of their structures. Eudistidine A was found to inhibit an essential protein-protein interaction (p300-HIF-1a) required for HIF-1a (hypoxiainducible factor 1) activation: such inhibitors could nd therapeutic use as antitumour agents by acting to down-regulate the expression of hypoxia-selective genes.…”

Biologically active quinoline and quinazoline alkaloids part II

“…In 2015, novel heterocylic alkaloids eudistidines A ( 75 ) and B ( 76 ) (Figure ) were isolated from Eudistoma sp. in a screen for inhibitors of the binding interaction between HIF‐1α and the transcriptional coactivator p300, which plays an important role in the survival of solid tumors in low oxygen environments and involves the C‐terminal transactivation domain (C‐TAD) and cysteine histidine‐rich domain 1 (CH1), respectively, of the two proteins . The former compound effectively inhibited CH1/C‐TAD binding with an IC 50 of 75 μM.…”

Targeting Protein–Protein Interactions in the HIF System

“… Small‐molecule inhibitors of HIF protein–protein interactions. A selection of compounds modulating HIF protein–protein interactions are shown, including those targeting 1) the HIF‐α,β dimer: acriflavine, 0X3, and cyclo‐CLLFVY; 2) HIF‐α:pVHL interactions: Ligand 51 and Ligand 7 ; 3) HIF‐α:CBP/p300 interactions: KCN1, Chetomin, Eudistidine A, Quinone 1 and the peptidomimetic inhibitors OHM1, Compound 3 , and HBS1 …”

“…A high‐throughput screen of natural products also led to the identification of quinones and indandiones that cause loss of structural zinc from CH1 . Eudistidine A, a marine alkaloid with an unusual tetracycline core comprised of two fused pyrimidine and imidazole rings (Figure ) has also been reported to inhibit the CH1 CAD interaction …”