Derivatives of fluorene. XXX. Rearrangement and antitumor activities of some 9-oxofluorene oximes. 6(5H)-Phenanthridinones. I

Palladium-catalyzed decarbonylative annulation of phthalimides with arynes: direct construction of phenanthridinones

A novel palladium-catalyzed decarbonylative annulation between phthalimides and arynes was well-established, affording phenanthridinone derivatives in moderate to good yields.

Synthesis and structural analysis of halogen substituted fibril formation inhibitors of Human Transthyretin (TTR)

Transthyretin (TTR), a β-sheet-rich tetrameric protein, in equilibrium with an unstable amyloidogenic monomeric form is responsible for extracellular deposition of amyloid fibrils, is associated with the onset of neurodegenerative diseases, such as senile systemic amyloidosis, familial amyloid polyneuropathy and familial amyloid cardiomyopathy. One of the therapeutic strategies is to use small molecules to stabilize the TTR tetramer and thus curb amyloid fibril formation. Here, we report the synthesis, the in vitro evaluation of several halogen substituted 9-fluorenyl- and di-benzophenon-based ligands and their three-dimensional crystallographic analysis in complex with TTR. The synthesized compounds bind TTR and stabilize the tetramer with different potency. Of these compounds, 2c is the best inhibitor. The dual binding mode prevalent in the absence of substitutions on the fluorenyl ring, is disfavored by (2,7-dichloro-fluoren-9-ylideneaminooxy)-acetic acid (1b), (2,7-dibromo-fluoren-9-ylideneaminooxy)-acetic acid (1c) and (E/Z)-((3,4-dichloro-phenyl)-methyleneaminooxy)-acetic acid (2c), all with halogen substitutions.

X-ray crystal structure and activity of fluorenyl-based compounds as transthyretin fibrillogenesis inhibitors

Transthyretin (TTR) is a 54 kDa homotetrameric protein that transports thyroxine (T4) and retinol (vitamin A), through its association with retinol binding protein (RBP). Under unknown conditions, it aggregates to form fibrils associated with TTR amyloidosis. Ligands able to inhibit fibril formation have been studied by X-ray crystallography. The use of polyethylene glycol (PEG) instead of ammonium sulphate or citrate has been evaluated as an alternative to obtain new TTR complexes with (R)-3-(9-fluoren-9-ylideneaminooxy)-2-methyl-N-(methylsulfonyl) propionamide (48R(1)) and 2-(9H-fluoren-9-ylideneaminooxy) acetic acid (ES8(2)). The previously described fluorenyl based inhibitors (S)-3-((9H-fluoren-9-ylideneamino)oxy)-2-methylpropanoic acid (6BD) and 3-((9H-fluoren-9-ylideneamino)oxy)propanoic acid (7BD) have been re-evaluated with the changed crystallization method. The new TTR complexes with compounds of the same family show that the 9-fluorenyl motif can occupy alternative hydrophobic binding sites. This augments the potential use of this scaffold to yield a large variety of differently substituted mono-aryl compounds able to inhibit TTR fibril formation.

Rat liver aryl sulfotransferase-catalyzed sulfation and rearrangement of 9-fluorenone oxime

The role of hepatic cytosolic aryl sulfotransferase (3'-phosphoadenylylsulfate:phenol sulfotransferase, EC 2.8.2.1) in the enzymic rearrangement of 9-fluorenone oxime to phenanthridone was investigated. 9-Fluorenone oxime was found to be an excellent substrate for a partially purified rat liver aryl sulfotransferase preparation. This compound was in fact superior to 2-naphthol, the standard assay substrate. This is the first reported observation of aryl oxime sulfation by the aryl sulfotransferases. 9-Fluorenone oxime sulfation exhibited pronounced substrate inhibition at high substrate concentrations. However, despite virtually complete conversion of 9-fluorenone oxime to the corresponding N-O-sulfate conjugate in enzyme incubation mixtures, only small amounts of rearrangement product were detected after long-term incubations. In addition, 9-fluorenone oxime-O-sulfonic acid was chemically synthesized and tested for stability. The results showed that rearrangement was pH-dependent and occurred slowly over several hours. It is therefore concluded that aryl sulfotransferase-catalyzed sulfation likely plays an important role in the in vitro and in vivo disposition of 9-fluorenone oxime. Moreover, sulfation facilitates the Beckmann-like conversion of 9-fluorenone oxime to phenanthridone. Sulfation alone, however, appears insufficient to account for all of the previously reported in vitro and in vivo rearrangement.

Metabolic conversion of fluorenone oxime to phenanthridinone by hepatic enzymes

Fluorenone oxime is converted to phenanthridinone by enzymes present in rat liver homogenates. The reaction is analogous to the chemical Beckman rearrangement. The oxime-amide rearrangement enzyme is localized primarily in the microsomes, with some activity in the cytosol. The reaction requires reduced nicotinamide adenine dinucleotide phosphate and observes Michaelis-Menten kinetics. The reaction is relatively slow (Vmax = 7.75 +/- 2.01 nmoles of phenanthridinone formed/100 mg of liver/15 min), but the enzyme reaches maximum velocity at relatively low substrate concentrations (Km = 3.90 +/- 1.85 x 10(-5) M). The reaction is strongly competitively inhibited by 1-decylimidazole (KI = 3.75 +/- 1.77 X 10(-7) M) and inhibited to a lesser extent by the chelating agents bipyridyl (KI = 1.33 +/- 0.21 X 10(-3) M) and ethylenediamine tetraacetate (KI = 1.00 +/- 0.28 X 10(-3) M) and the sulfhydryl binding agent p-chloromercuribenzoate (KI = 2.71 +/- 0.07 X 10(-4) M). Studies also suggest that the reaction mechanism does not involve initial enzymatic substrate esterification through acetylation, glucuronidation, phosphorylation, or sulfation.

Metabolic rearrangement of fluorenone oxime to phenanthridinone

Fluorenone oxime is metabolized in vivo in the rat to phenanthrifinone which is excreted in the urine. The structure of the metabolite has been determined by comparison of chromatographic and spectral properties of the metabolites with authentic phenanthridinone.