Tyrosine 656 in topoisomerase IIβ is important for the catalytic activity of the enzyme: Identification based on artifactual +80-Da modification at this site

Topoisomerase (topo) II catalyzes topological changes in DNA. Although both human isozymes, topo IIα and β are phosphorylated, site‐specific phosphorylation of topo IIβ is poorly characterized. Using LC‐MS/MS analysis of topo IIβ, cleaved with trypsin, Arg C or cyanogen bromide (CNBr) plus trypsin, we detected four +80‐Da modified sites: tyr656, ser1395, thr1426 and ser1545. Phosphorylation at ser1395, thr1426 and ser1545 was established based on neutral loss of H₃PO₄ (?98 Da) in the CID spectra and on differences in 2‐D‐phosphopeptide maps of ³²P‐labeled wild‐type (WT) and S1395A or T1426A/S1545A mutant topo IIβ. However, phosphorylation at tyr656 could not be verified by 2‐D‐phosphopeptide mapping of ³²P‐labeled WT and Y656F mutant protein or by Western blotting with phosphotyrosine‐specific antibodies. Since the +80‐Da modification on tyr656 was observed exclusively during cleavage with CNBr and trypsin, this modification likely represented bromination, which occurred during CNBr cleavage. Re‐evaluation of the CID spectra identified +78/+80‐Da fragment ions in CID spectra of two peptides containing tyr656 and tyr711, confirming bromination. Interestingly, mutation of only tyr656, but not ser1395, thr1326 or ser1545, decreased topo IIβ activity, suggesting a functional role for tyr656. These results, while identifying an important tyrosine in topo IIβ, underscore the importance of careful interpretation of modifications having the same nominal mass.     

Synthesis of anomeric sulfonamides and their behaviour under radical-mediated bromination conditions

O-Peracetylated methyl 3-(d-glycopyranosylthio)propanoates of β-d-gluco, and α- and β-d-galacto configurations were oxidized to the corresponding S,S-dioxides (sulfones) by Oxone^® or MCPBA. Oxidation of the β-d-gluco derivative with H₂O₂/Na₂WO₄ gave the corresponding S-oxide (sulfoxide). DBU-induced elimination of methyl acrylate from the β-d-gluco and β-d-galacto configured S,S-dioxides (sulfones) gave O-peracetylated β-d-glycopyranosyl-1-C-sulfinates which, on treatment with H₂NOSO₃H, furnished the corresponding β-d-glycopyranosyl-1-C-sulfonamides. Radical-mediated bromination of the protected methyl 3-(β-d-glycopyranosylthio)propanoate S,S-dioxides gave mixtures of 1-C- and 5-C-bromoglycosyl compounds. Similar brominations of the O-peracetylated β-d-glycopyranosyl-1-C-sulfonamides resulted in the formation of α-d-glycopyranosyl bromides and 1-C- and 5-C-bromoglycosyl sulfonamides. A rationale for these observations was proposed. Methyl 3-(β-d-glucopyranosylthio)propanoate, its S,S-dioxide, and β-d-glucopyranosyl-1-C-sulfonamide proved inefficient when tested as inhibitors of rabbit muscle glycogen phosphorylase b.     

The first synthesis,carbonic anhydrase inhibition and anticholinergic activities of some bromophenol derivatives with S including natural products

Starting from vanillin, known four benzyl bromides with Br were synthesized. The first synthesis of natural product 3,4-dibromo-5-((methylsulfonyl)methyl)benzene-1,2-diol (2) and 3,4,6-tribromo-5-((methylsulfonyl)methyl)benzene-1,2-diol (3) and derivatives were carried out by demethylation, acetylatilation, oxidation and hydrolysis reactions of the benzyl bromides. Also, these compounds were tested against some important enzymes like acetylcholinesterase and butyrylcholinesterase enzymes, carbonic anhydrase I, and II isoenzymes. The novel bromophenols showed Ki values of in range of 53.75 ± 12.54–234.68 ± 46.76 nM against hCA I, 42.84 ± 9.36 and 200.54 ± 57.25 nM against hCA II, 0.84 ± 0.12–14.63 ± 3.06 nM against AChE and 0.93 ± 0.20–18.53 ± 5.06 nM against BChE. Induced fit docking process performed on the compounds inhibiting hCA I, hCA II, AChE, and BChE receptors. Hydroxyl group should exist at the aromatic ring of the compounds for inhibition of the enzymes. The moieties reported in this study will be useful for design of more potent and selective inhibitors against the enzymes.     

Synthesis and paroxonase activities of novel bromophenols

Three novel bromophenols 10–12 were synthesized. Acylation of veratrole (4) with 2,3-dimethoxy benzoic acid (5) gave a kown diarylmethanone 6. Bromination of 6 with different equivalents of molecular bromine afforded new di and tribrominated compounds 7–9 which were converted to their corresponding bromophenols 10–12 via O-demethylation with BBr₃. Paraoxonase-1 (PON1) was purified from human serum with approximately 42% and 3584?U × mg^?1 specific activity. The synthesized compounds 6–12 showed inhibitory effects on paraoxonase-1 (PON1) which is an organophosphate (OP) hydrolyser and an antioxidant bioscavenger enzyme. IC₅₀ values were determined in the range of 0.123–1.212?mM.

Graphical abstract

     

Bromonium ion-promoted glycosidic bond formation and simultaneous bromination of an activated aryl aglycon.

N-Bromosuccinimide (NBS) together with a catalytic amount of Me(3)SiOTf was found to be effective for the activation of thioglycosides. Concurrently with formation of the glycosidic bond, bromination took place on the activated aromatic ring of a 4-methoxyphenyl aglycon.     

Synthesis and biological evaluation of bromophenol derivatives with cyclopropyl moiety: Ring opening of cyclopropane with monoester

Trans-(1R*,2R*,3R*)-Ethyl 2-(3,4-dimethoxyphenyl)-3-methylcyclopropane-1-carboxylate (6) and its cis isomer 7 were obtained from the reaction of the methyl isoeugenol (5) with ethyl diazoacetate. The reduction and bromination reactions of the ester 6 and 7 together with the hydrolysis of all esters were carried out. Opening ring of cyclopropane was observed in the reaction of 7 with bromine. The opening of cyclopropane ring with COOR and synthesis of esters, alcohols and acids (6–26) are new. These obtained bromophenol derivatives (6–26) were effective inhibitors of the cytosolic carbonic anhydrase I and II isoforms (hCA I and II) and acetylcholinesterase (AChE) enzymes with Ki values in the range of 7.8 ± 0.9–58.3 ± 10.3 nM for hCA I, 43.1 ± 16.7–150.2 ± 24.1 nM for hCA II, and 159.6 ± 21.9–924.2 ± 104.8 nM for AChE, respectively. Acetylcholinesterase inhibitors are the most popular drugs applied in the treatment of diseases such as Alzheimer’s disease, Parkinson’s disease, senile dementia, and ataxia, among others.     

Remote site bromination via a cascade rearrangement involving two bridging dioxonium species during oxidative cleavage of a benzylidene acetal

Attempted cleavage of the benzylidene group of 3,5-O-benzylidene-2,6,7-tri-O-trimethylacetyl-D-glycero-D-gulo-heptono-1,4-lactone with N-bromosuccinimide led to the formation of a 7-bromo derivative with a benzoyl group in the 3-position and trimethylacetyl groups in the 5 and 6 positions. Analysis of the coupling constants in the proton NMR spectra indicated that both trimethylacetyl groups had participated to shift the crowded electron-deficient center formed at the 5-position by the decomposition of the bromobenzylidene group to the much more accessible 7-position. The net result of this cascade rearrangement was retention at both the C-5 and C-6 positions. This is an interesting example of a cascade rearrangement under strict entropic and stereo control the synthetic utility of which is being investigated.     

Synthesis of 3alpha-hydroxy-21-(1'-imidazolyl)-3beta-methoxyl-methyl-5alpha-pregnan-20-one via lithium imidazole with 17alpha-acetylbromopregnanone

The synthesis of biologically active 3alpha-hydroxyl-21-(1'-imidazolyl)-3beta-methoxymethyl-5alpha-pregnan-20-one was accomplished in six steps. The key steps were the improvement of stereoselectivity for acetyl isomers in C-17 and the introduction of imidazole into the core structure by use of lithium imidazole. This latter key step provided the desired product in 82% yield without the formation of 1,3-disubstituted imidazolium salt as impurity, which is generally observed in traditional method.     

The first synthesis of 4-phenylbutenone derivative bromophenols including natural products and their inhibition profiles for carbonic anhydrase,acetylcholinesterase and butyrylcholinesterase enzymes

The first synthesis of (E)-4-(3-bromo-4,5-dihydroxyphenyl)but-3-en-2-one (1), (E)-4-(2-bromo-4,5-dihydroxyphenyl)but-3-en-2-one (2), and (E)-4-(2,3-dibromo-4,5-dihydroxyphenyl)but-3-en-2-one (3) was realized as natural bromophenols. Derivatives with mono OMe of 2 and 3 were obtained from the reactions of their derivatives with di OMe with AlCl₃. These novel 4-phenylbutenone derivatives were effective inhibitors of the cytosolic carbonic anhydrase I and II isoenzymes (hCA I and II), acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with K_i values in the range of 158.07–404.16 pM for hCA I, 107.63–237.40 pM for hCA II, 14.81–33.99 pM for AChE and 5.64–19.30 pM for BChE. The inhibitory effects of the synthesized novel 4-phenylbutenone derivatives were compared to acetazolamide as a clinical hCA I and II isoenzymes inhibitor and tacrine as a clinical AChE and BChE enzymes inhibitor.