Synthesis of deuterium‐labeled analogs of the lipid hydroperoxide‐derived bifunctional electrophile 4‐oxo‐2(E)‐nonenal

Lipid hydroperoxides undergo homolytic decomposition into the bifunctional 4‐hydroxy‐2(E)‐nonenal and 4‐oxo‐2(E)‐nonenal (ONE). These bifunctional electrophiles are highly reactive and can readily modify intracellular molecules including glutathione (GSH), deoxyribonucleic acid (DNA) and proteins. Lipid hydroperoxide‐derived bifunctional electrophiles are thought to contribute to the pathogenesis of a number of diseases. ONE is an α,β ‐unsaturated aldehyde that can react in multiple ways and with glutathione, proteins and DNA. Heavy isotope‐labeled analogs of ONE are not readily available for conducting mechanistic studies or for use as internal standards in mass spectrometry (MS)‐based assays. An efficient one‐step cost‐effective method has been developed for the preparation of C‐9 deuterium‐labeled ONE. In addition, a method for specific deuterium labeling of ONE at C‐2, C‐3 or both C‐2 and C‐3 has been developed. This latter method involved the selective reduction of an intermediate alkyne either by lithium aluminum hydride or lithium aluminum deuteride and quenching with water or deuterium oxide. The availability of these heavy isotope analogs will be useful as internal standards for quantitative studies employing MS and for conducting mechanistic studies of complex interactions between ONE and DNA bases as well as between ONE and proximal amino acid residues in peptides and proteins. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis and selective 2H‐, 13C‐, and 15N‐labeling of the Tau protein binder THK‐523

A new synthetic route to the Tau binder, THK‐523, is disclosed herein, which can easily be adapted to ¹³C‐ and D‐isotope labeling. The synthesis proceeds via two key reactions, namely, a Pd‐catalyzed carbonylative Sonogashira coupling and a reductive ring‐closing step with hydrogen or deuterium gas. By carrying out these reactions in a 2‐chamber reactor we reported previously, ex situ–generated carbon monoxide and hydrogen/deuterium can be applied in stoichiometric quantities, thereby facilitating isotope labeling of this Tau‐binding compound. Iridium‐catalyzed hydrogen isotope exchange (HIE) reactions were performed on THK‐523 and its ¹³C‐labeled analog providing access to 4 additional analogues labeled with deuterium as well. Finally, by applying a Buchwald‐Hartwig coupling, we were able to prepare a ¹⁵N‐THK‐523 variant with the isotope label in the quinoline ring system.     

An overview of radio or stable isotope‐labeled cis‐neonicotinoid analogs

To support the metabolism and toxicology study of cis‐neonicotinoids, radio or stable isotope was introduced into different sites of the key intermediate 2‐chloro‐5‐((2‐(nitromethylene)imidazolidin‐1‐yl)methyl)pyridine (6‐Cl‐PMNI). [³H₂]‐ and [¹⁴C]‐label were successively prepared from initial materials NaB³H₄ and [¹⁴C]‐nitromethane, respectively. Similarly, [D₂]‐6‐Cl‐PMNI was prepared from NaBD₄ in four steps, with 52.6% overall isotopic yield, and dual‐labeled [D₂, ¹³C]‐target was obtained from NaBD₄ and [¹³C]‐nitromethane, affording overall isotopic yield of 42.5%. Moreover, [¹⁴C₂] was introduced from [U‐¹⁴C]‐ethylenediamine dihydrochloride in three steps, with a 58.3% overall chemical yield. Finally, typical labeled cis‐neonicotinoids paichongding and cycloxaprid were prepared and characterized. The methods were proved to have good generality in the synthesis of other cis‐neonicotinoids, and all results would be useful in metabolism studies of new cis‐neonicotinoids. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis of 3H‐, 14C‐, and stable‐isotope‐labelled galantamine

Reminyl^® is a newly approved drug, used in the treatment of mild to moderate Alzheimer disease. The active compound, galantamine, was initially isolated from the bulbs of certain Narcissus species, but is at the moment also produced synthetically. In the process leading to the final approval, the synthesis of tritium‐, carbon‐14‐ and stable‐isotope‐labelled galantamine for pharmacokinetic studies was required. Racemic (±)‐1‐bromonarwedine, a compound available as intermediate from the commercial synthesis, was transformed to racemic 1‐bromo‐galantamine. Catalytic bromo‐tritium exchange, followed by HPLC purification and resolution afforded tritium‐labelled galantamine. The [¹⁴C]‐label was introduced on the nitrogen as well as on the oxygen‐methyl position. This was achieved by N‐ and O‐demethylation of galantamine and reaction of the thoroughly purified intermediate with [¹⁴C]‐methyl iodide. Stable‐isotope‐labelled galantamine was obtained likewise by ¹³CD₃OD‐methylation of O‐demethylated galantamine under Mitsunobu conditions. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis of 19‐trideuterated ent‐testosterone and the GABAA receptor potentiators ent‐androsterone and ent‐etiocholanolone

19‐Trideuteromethyl enantiomers of androgens namely ent‐testosterone, ent‐androsterone and ent‐etiocholanolone were prepared by total synthesis. The isotope labeling at the C‐19 angular methyl group was achieved by using deuterated methyl iodide (99.5% d₃) for introduction of C‐19 before closure of the steroid A‐ring. This method yields 19,19,19‐trideuterated steroids without increasing the number of steps involved in the total synthesis of ent‐androgens. Analysis by mass spectrometry (MS) showed no loss of deuterium during incorporation of C‐19 into ent‐testosterone. The availability of the compounds will enable these ent‐androgens to be distinguished by MS from their natural enantiomers in future pharmacokinetic and metabolic studies. Copyright © 2008 John Wiley & Sons, Ltd.     

Design,Synthesis, and Antitumor Activity of (E,Z)‐1‐(dihydrobenzofuran‐5‐yl)‐3‐phenyl‐2‐(1,2,4‐triazol‐1‐yl)‐2‐propen‐1‐ones

A series of (E,Z)‐1‐(dihydrobenzofuran‐5‐yl)‐3‐phenyl‐2‐(1,2,4‐triazol‐1‐yl)‐2‐propen‐1‐ones ( C1 – C35 ) were designed and synthesized, and the structures of compounds (Z)‐ C27 and (Z)‐ C29 were confirmed by single‐crystal X‐ray diffraction. The antitumor activities of these novel compounds against cervical cancer (HeLa), lung cancer (A549), and breast cancer (MCF‐7) cell lines were evaluated in vitro. Majority of the title compounds exhibited strong antitumor activities and were much more promising than the positive control Taxol, which were also accompanied by lower cytotoxicity to normal cells. In particular, compounds (E,Z)‐ C24 exhibited the most consistent potent activities against three neoplastic cells with IC₅₀ values ranging from 3.2 to 7.1 μm . Further researches demonstrated that compounds (E,Z)‐ C24 could induce cell apoptosis and arrest cell cycle at the G2/M and S phases. Meanwhile, the structure–activity relationship between the configurations and cytotoxicity of the compounds was also investigated.     

Synthesis of 1‐(2′‐deoxy‐2′‐fluoro‐β‐D‐arabinofuranosyl)‐[Methyl‐11C]thymine ([11C]FMAU) via a Stille cross‐coupling reaction with [11C]methyl iodide

1‐(2′‐deoxy‐2′‐fluoro‐β‐D‐arabinofuranosyl)‐[methyl‐¹¹C]thymine ([¹¹C]FMAU) [¹¹C]‐ 1 was synthesised via a palladium‐mediated Stille coupling reaction of 1‐(2′‐deoxy‐2′‐fluoro‐β‐D‐arabinofuranosyl)‐5‐(trimethylstannyl)uracil 2 with [¹¹C]methyl iodide in a one‐pot procedure. The reaction conditions were optimized by screening various catalysts and solvents, and by altering concentrations and reaction temperatures. The highest yield was obtained using Pd₂(dba)₃ and P(o‐tolyl)₃ in DMF at 130°C for 5 min. Under these conditions the title compound [¹¹C]‐ 1 was obtained in 28±5% decay‐corrected radiochemical yield calculated from [¹¹C]methyl iodide (number of experiments=7). The radiochemical purity was >99% and the specific radioactivity was 0.1 GBq/μmol at 25 min after end of bombardment. In a typical experiment 700–800 MBq of [¹¹C]FMAU [¹¹C]‐ 1 was obtained starting from 6–7 GBq of [¹¹C]methyl iodide. A mixed ¹¹C/¹³C synthesis to yield [¹¹C]‐ 1 /(¹³C)‐ 1 followed by ¹³C‐NMR analysis was used to confirm the labelling position. The labelling procedure was found to be suitable for automation. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis of stable isotopically labelled 3‐methylfuran‐2(5H)‐one and the corresponding strigolactones

Conventional synthetic procedures of strigolactones (SLs) involve the independent synthesis of ring ABC and ring D, followed by a coupling of the two fragments. Here we prepared three kinds of stable, isotopically labelled D‐ring analogues productively using a facile protocol. Then, a coupling of the D‐rings to ring ABC produced three isotope‐labelled SL derivatives. Moreover, (+)‐D₃‐2′‐epi‐ 1A and (?)‐ent‐D₃‐2′‐epi‐ 1A with high enantiomeric purity were obtained via chiral resolution.     

Design,syntheses, and evaluation of 2,3‐diphenylcycloprop‐2‐en‐1‐ones and oxime derivatives as potential cyclooxygenase‐2 (COX‐2) inhibitors with analgesic‐antiinflammatory activity

A group of 2,3‐diphenylcycloprop‐2‐enes having a variety of substituents at the para‐position of the C‐2 phenyl ring (H, F), and C‐3 phenyl ring (H, F, SMe, SOMe, SO₂Me), in conjunction with either a C‐1 carbonyl, oxime, oxime acetate, benzoyl hydrazone, or hydrogen substituent were synthesized for in vivo evaluation as analgesic and antiinflammatory (AI) agents, and as potential selective cyclooxygenase‐2 (COX‐2) inhibitors. This group of cycloprop‐2‐ene compounds exhibited significant analgesic activity, since 4% NaCl‐induced abdominal constriction was reduced by 43–90% at 30 min, and 41–100% at 60 min, after drug administration relative to the reference drugs aspirin and celecoxib (58% and 32% inhibition at 30 min after drug administration) for a 50 mg/kg intraperitoneal dose. AI activities, determined using the carrageenan‐induced rat paw edema assay, showed that this class of cycloprop‐2‐ene compounds exhibited AI activities in the inactive‐to‐modest activity range (0–26% inhibition) for a 50 mg/kg oral dose. The AI potency order for a group of 2,3‐diphenylcycloprop‐2‐enes with respect to the C‐1 substituent was oxime>hydrogen>carbonyl>benzoyl hydrazone. 2,3‐Diphenylcycloprop‐2‐en‐1‐one oxime ( 20 ) was the most active AI agent, inducing a 26% reduction in inflammation, relative to the reference drugs ibuprofen and celecoxib, which showed 52% and 58% reductions in inflammation, at 5 h after drug administration. In vitro COX‐1 and COX‐2 inhibition studies showed that 2,3‐diphenylcycloprop‐2‐en‐1‐one oxime ( 20 ) is a selective COX‐2 inhibitor (COX‐1 IC₅₀>100 μM; COX‐2 IC₅₀=2.94 μM; COX‐2 selectivity index>34). A molecular modeling study that docked the oxime ( 20 ) in the active site of the human COX‐2 isozyme showed that it binds in the vicinity of the mouth of the COX‐2 binding site with the O‐atom of the oxime (=N–OH) moiety separated from the NH₂ group of Arg¹²⁰ by about 3.65 Å. This orientation of the oxime compound ( 20 ) in the COX‐2 binding site could be due to a potentially strong ionic interaction between the =NOH oxime moiety and the guanidinium moiety of Arg¹²⁰. Drug Dev. Res. 57:6–17, 2002. © 2002 Wiley‐Liss, Inc.     

α‐Substitution Effects on the Ease of S→N‐Acyl Transfer in Aminothioesters

In S‐acylcysteines and homocysteines, the efficacy and rate of S→N‐acyl transfer (5 and 6 cyclic TSs) vary with the size of S‐acyl group. Conformational and quantum chemical calculations indicate that the spatial distance, b(N‐C), between the terminal amine and the thioester carbon is shortened by α‐C(O)X (X = OH, OMe, NH₂) substituents.     

Effect of inflammatory factor‐induced cyclo‐oxygenase expression on the development of reperfusion‐related no‐reflow phenomenon in acute myocardial infarction

No reflow after reperfusion therapy for myocardial infarction is a strong predictor of clinical outcome. Increased levels of inflammatory factors, including C‐reactive protein (CRP), in patients with acute myocardial infarction (AMI) undergoing primary percutaneous coronary intervention (PCI) may affect myocardial perfusion. However, why the no‐reflow phenomenon increases in inflammation stress after PCI is not clear. The aim of the present study was to determine the effects and molecular mechanisms underlying the effects of CRP on the expression of cyclo‐oxygenase (COX) on the development of the no‐reflow phenomenon. There was a significant increase in plasma levels of CRP and interleukin (IL)‐6 in no‐reflow patients, suggesting that inflammatory factors play an important role in the development of the no‐reflow phenomenon. The mechanisms involved were further evaluated after reperfusion in a rat model mimicking the no‐reflow phenomenon. Compared with normal reflow rats, there were significant increases in both COX‐1 and COX‐2 in cardiac tissue from no‐reflow rats. The COX inhibitor indomethacin (5 mg/kg, i.p.) significantly reduced the no‐reflow area. In another series of experiments, human coronary artery endothelial cells (HCAEC) were treated with CRP at clinically relevant concentrations (5–25 μg/mL). C‐Reactive protein significantly increased COX‐1 and COX‐2 levels in a time‐ and concentration‐dependent manner. In addition, extracellular signal‐regulated kinase (ERK) and Jun N‐terminal kinase (JNK) were activated in CRP (5, 10, 25 μg/mL)‐treated HCAEC cultures. Furthermore, the ERK inhibitor pd98059 (30 μmol/L) and the JNK inhibitor sp600125 (10 μmol/L) blocked CRP‐induced COX‐1 and COX‐2 expression for 12 h. Together, the findings of the present study suggest that CRP can promote the development of the no‐reflow phenomenon by increasing COX‐1 and COX‐2 expression, which is regulated, in part, via ERK and JNK activity.     

Insight into the Structural Features of Pyrazolopyrimidine‐ and Pyrazolopyridine‐based B‐RafV600E Kinase Inhibitors by Computational Explorations

Presently, both ligand‐based and receptor‐based 3D‐QSAR modelings were performed on 107 pyrazolopyrimidine‐ and pyrazolopyridine‐based inhibitors of B‐Raf^V600E kinase. The optimal model is successful to predict the inhibitors' activity with Q² of 0.504, R²_ncv of 0.960, and R²_pred of 0.872. Besides, the 3D contour maps explain well the structural requirements of the interaction between the ligand and the receptor. Furthermore, molecular docking and MD were also carried out to study the binding mode. Our findings are the following: (i) Bulky substituents at position 3, 10 and ring D improve the inhibitory activity, but impair the activity at position 5, 11, and 19. (ii) Electropositive groups at position 10, 13 and 20 and electronegative groups at position 2 increase the biological activity. (iii) Hydrophobic substituents at ring C are beneficial to improve the biological activity, while hydrophilic substituents at position 11 and ring D are good for the activity. (4) This scaffold of inhibitors may bind to the B‐Raf kinase with an ‘L’ conformation and belong to type III binding mode, which is fixed by hydrophobic interaction and hydrogen bonds with residues from hinge region and DFG motif. These results may be a guidance to develop new B‐Raf^V600E kinase inhibitors.     

Design,syntheses, and evaluation of novel 1,1‐dihalo‐2,3‐diphenylcyclopropanes as potential cyclooxygenase‐2 (COX‐2) inhibitors with analgesic‐antiinflammatory activity

A group of (Z)‐ and (E)‐1,1‐dihalo‐2‐(4‐substituted‐phenyl)‐3‐phenylcyclopropane [ (Z)‐10 , (E)‐11 ] stereoisomers having a variety of substituents (H, Br, Cl, F, NO₂, SO₂Me) at the para‐position of the C‐2 phenyl ring in conjunction with either two chloro or bromo substituents at C‐1 were synthesized for in vivo evaluation as analgesic and antiinflammatory (AI) agents, and as potential selective cyclooxygenase‐2 (COX‐2) inhibitors. This group of compounds ( 10‐11 ) exhibited significant analgesic activity since 4% NaCl‐induced abdominal constriction was reduced by 44–73% at 30 min, and 48–77% at 60 min, post‐drug administration relative to the reference drugs aspirin and celecoxib (58 and 32% inhibition at 30 min post‐drug administration) for a 50 mg/kg intraperitoneal dose. In the 1,1‐dichloro group of compounds, a Cl or MeSO₂ substituent at the para‐position of the C‐2 phenyl ring generally provided superior analgesic activity. The most active analgesic compound, (E)‐1,1‐dichloro‐2‐(4‐methanesufonylphenyl)‐3‐phenylcyclopropane ( 11h ) inhibited abdominal constriction by 72 and 77% at 30 and 60 min post‐drug administration, respectively. AI activities, determined using the carrageenan‐induced rat paw edema assay, showed that this class of ( Z)‐10 and ( E)‐11 compounds exhibited AI activities in the inactive‐to‐moderate activity range (1.5–45% inhibition) for a 50 mg/kg oral dose. The AI potency order, with respect to the para‐substitutent on the C‐2 phenyl ring, for the ( Z)‐10 compounds was NO₂ > MeSO₂ ≈ H ≥ Cl, and for the ( E)‐11 compounds was H ≥ MeSO₂ > Cl ≈ Br. (E)‐1,1‐dibromo‐2‐(4‐methanesufonylphenyl)‐3‐phenylcyclopropane ( 11l ), which was the most active AI compound, reduced inflammation by 45 and 37% at 3 and 5 h post‐drug administration, respectively. The ( E)‐11 stereoisomer was generally a more potent AI agent than the corresponding ( Z)‐10 stereoisomer. In vitro COX‐1 and COX‐2 inhibition studies showed that (E)‐1,1‐dichloro‐2‐(4‐nitrophenyl)‐3‐phenylcyclopropane ( 11c ) inhibited COX‐1 (IC₅₀ = 278.8 μM) and COX‐2 (IC₅₀ = 80.5 μM) for a COX‐2 selectivity index of 3.5, whereas (E)‐1,1‐dichloro‐2‐(4‐methanesulfonylphenyl)‐3‐phenylcyclopropane ( 11h ) was a more potent inhibitor of COX‐1 and COX‐2, but it was more selective for COX‐1 (COX‐1 IC₅₀ = 0.59 μM, COX‐2 IC₅₀ = 3.04 μM). A molecular modeling (docking) study for (E)‐1,1‐dichloro‐2‐(4‐methanesulfonylphenyl)‐3‐phenylcyclopropane ( 11h ) on the active site of the human COX‐2 isozyme shows it binds in the center of the active site with the 1,1‐dichloro substituents oriented in the direction of the mouth of the channel towards Arg¹²⁰, and the C‐2 MeSO₂ moiety oriented towards the apex of the active site with the S‐atom of the MeSO₂ substituent positioned about 6.56 Å inside the entrance to the secondary pocket (Val⁵²³) of COX‐2. In contrast, the corresponding (Z)‐10h stereoisomer assumes a different position in the COX‐2 binding site where the S‐atom of the MeSO₂ moiety is near (4.02 Å) the Ser⁵³⁰ OH, but a much greater distance from the COX‐2 secondary pocket (Val⁵²³). The results from these docking studies are consistent with the observation that (E)‐11h is an inhibitor of both COX isozymes, whereas the (Z)‐10h stereoisomer is an inactive COX inhibitor (COX‐1 IC₅₀ > 100 μM, COX‐2 IC₅₀ > 200 μM). Drug Dev. Res. 55:79–90, 2002. © 2002 Wiley‐Liss, Inc.     

Syntheses and analytical characterizations of the research chemical 1‐[1‐(2‐fluorophenyl)‐2‐phenylethyl]pyrrolidine (fluorolintane) and five of its isomers

A number of substances based on the 1,2‐diarylethylamine template have been investigated for various potential clinical applications whereas others have been encountered as research chemicals sold for non‐medical use. Some of these substances have transpired to function as NMDA receptor antagonists that elicit dissociative effects in people who use these substances recreationally. 1‐[1‐(2‐Fluorophenyl)‐2‐phenylethyl]pyrrolidine (fluorolintane, 2‐F‐DPPy) has recently appeared as a research chemical, which users report has dissociative effects. One common difficulty encountered by stakeholders confronting the appearance of new psychoactive substances is the presence of positional isomers. In the case of fluorolintane, the presence of the fluorine substituent on either the phenyl and benzyl moieties of the 1,2‐diarylethylamine structure results in a total number of six possible racemic isomers, namely 2‐F‐, 3‐F‐, and 4‐F‐DPPy (phenyl ring substituents) and 2”‐F‐, 3”‐F‐, and 4”‐F‐DPPy (benzyl ring substituents). The present study reports the chemical syntheses and comprehensive analytical characterizations of the two sets of three positional isomers. These studies included various low‐ and high‐resolution mass spectrometry platforms, gas‐ and liquid chromatography (GC and LC), nuclear magnetic resonance (NMR) spectroscopy and GC‐condensed phase and attenuated total reflection infrared spectroscopy analyses. The differentiation between each set of three isomers was possible under a variety of experimental conditions including GC chemical ionization triple quadrupole tandem mass spectrometric analysis of the [M + H – HF]⁺ species. The latter MS method was particularly helpful as it revealed distinct formations of product ions for each of the six investigated substances.     

Radiosynthesis and preliminary biodistribution in mice of 6‐deoxy‐6‐[131I]iodo‐L‐ascorbic acid

An ascorbate analog labeled with iodine‐131, 6‐deoxy‐ 6‐[¹³¹I]iodo‐L ‐ascorbic acid was prepared for evaluation as an in vivo tracer of L ‐ascorbic acid. The no‐carrier‐added radiosynthesis was conducted by nucleophilic bromine–iodine exchange between the brominated precursor and sodium [¹³¹I]iodide in 2‐pentanone at 130–140°C. HPLC purification using a reverse‐phase column gave 6‐deoxy‐6‐[¹³¹I]iodo‐L ‐ascorbic acid in radiochemical yield of 36–60% with high radiochemical purity and satisfactory‐specific radioactivity in a total preparation time of 90 min. Biodistribution studies in fibrosarcoma‐bearing mice showed a high uptake in the adrenal glands, accompanied by low activity of tumor accumulation, accumulation properties similar to previous results obtained with ¹⁴C‐labeled ascorbic acid and 6‐deoxy‐6‐[¹⁸F]fluoro‐L ‐ascorbic acid, in spite of high level of deiodination. Copyright © 2009 John Wiley & Sons, Ltd.     

2,3,7,8‐tetrachlorodibenzo‐p‐dioxin exposure influence the expression of glutamate transporter GLT‐1 in C6 glioma cells via the Ca2+/protein kinase C pathway

The widespread environmental contaminant, 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD), is considered one of the most toxic dioxin‐like compounds. Although epidemiological studies have shown that TCDD exposure is linked to some neurological and neurophysiological disorders, the underlying mechanism of TCDD‐mediated neurotoxicity has remained unclear. Astrocytes are the most abundant cells in the nervous systems, and are recognized as the important mediators of normal brain functions as well as neurological, neurodevelopmental and neurodegenerative brain diseases. In this study, we investigated the role of TCDD in regulating the expression of glutamate transporter GLT‐1 in astrocytes. TCDD, at concentrations of 0.1–100 nm , had no significantly harmful effect on the viability of C6 glioma cells. However, the expression of GLT‐1 in C6 glioma cells was downregulated in a dose‐ and time‐dependent manner. TCDD also caused activation of protein kinase C (PKC), as TCDD induced translocation of the PKC from the cytoplasm or perinuclear to the membrane. The translocation of PKC was inhibited by one Ca²⁺ blocker, nifedipine, suggesting that the effects are triggered by the initial elevated intracellular concentration of free Ca²⁺. Finally, we showed that inhibition of the PKC activity reverses the TCDD‐triggered reduction of GLT‐1. In summary, our results suggested that TCDD exposure could downregulate the expression of GLT‐1 in C6 via Ca²⁺/PKC pathway. The downregulation of GLT‐1 might participate in TCDD‐mediated neurotoxicity. Copyright © 2016 John Wiley & Sons, Ltd.     

Site‐Specific Labeling of Proteins and Peptides with Trans‐cyclooctene Containing Handles Capable of Tetrazine Ligation

There is a growing library of functionalized non‐natural substrates for the enzyme protein farnesyltransferase (PFTase). PFTase covalently attaches these functionalized non‐natural substrates to proteins ending in the sequence CAAX, where C is a cysteine that becomes alkylated, A represents an aliphatic amino acid, and X is Ser, Met, Ala, or Gln. Reported substrates include a variety of functionalities that allow modified proteins to undergo subsequent bioconjugation reactions. To date the most common strategy used in this approach has been copper catalyzed azide‐alkyne cycloaddition (CuAAC). While being fast and bioorthogonal CuAAC has limited use in live cell experiments due to copper's toxicity.¹ Here, we report the synthesis of trans‐cyclooctene geranyl diphosphate. This substrate can be synthesized from geraniol in six steps and be enzymatically transferred to peptides and proteins that end in a CAAX sequence. Proteins and peptides site‐specially modified with trans‐cyclooctene geranyl diphosphate were subsequently targeted for further modification via tetrazine ligation. As tetrazine ligation is bioorthogonal, fast, and is contingent on ring strain rather than the addition of a copper catalyst, this labeling strategy should prove useful for labeling proteins where the presence of copper may hinder solubility or biological reactivity.     

Large‐scale preparation of 13C‐labeled 2‐(phenylthio)acetic acid and the corresponding labeled sulfoxides and sulfones

We have developed large‐scale efficient procedures for the conversion of commercially available [¹³C]‐ or [²H₃,¹³C]methanol and ¹³CO₂ or ¹³C‐labeled bromoacetic acid to 2‐(phenylthio)[1,2‐¹³C₂]‐, [1‐¹³C]‐, and [2‐¹³C]acetic acid. The resulting derivatives are versatile, chemically stable, and nonvolatile two‐carbon labeling precursors. We have used the ¹³C‐isotopomers of 2‐(phenylthio)acetic acid in the synthesis of ¹³C‐labeled acrylic acid, methacrylic acid, and trans‐crotonic acid.     

Different profiles of hepatic alkoxyresorufin O‐dealkylase activities in small rodents

The aims of the present study were to determine cytochrome P450 enzyme activity in six strains of experimental rodents (n = 5/sex/species): ICR, C57BL/6 and DBA/2 mice; Sprague Dawley and Wistar rats; and Dunkin Hartley guinea pigs. After animals were treated with the typical inducers β‐naphthoflavone (BNF), dexamethasone (DEX) and phenobarbital (PB), the levels of O‐dealkylation of ethoxyresorufin (EROD), methoxyresorufin (MROD), pentoxyresorufin (PROD) and benzyloxyresorufin (BROD) activity were determined using responsive catalytic reactions to study CYP1A1, CYP1A2 and CYP2B, respectively. A maximal induction of EROD and MROD was found in BNF‐treated animals from all strains (2.4‐ to 15.1‐fold) except DBA/2 (0.9‐ to 1.8‐fold). C57BL/6 mice had the strongest BNF‐induced EROD (15.1‐fold) and MROD (8.3‐fold) activities. No differences in BNF‐induced EROD and MROD activities were observed between males and females. However, the EROD activity of Wistar rats and the MROD activity of Sprague Dawley rats were higher in males than females. DEX induced PROD activity only in mice (1.3‐ to 7.1‐fold), but not in rats and guinea pigs (0.2‐ to 1.1‐fold). However, induction of BROD activity was found in DEX‐treated mice and rats (1.5 to 12.5‐fold), but not in guinea pigs (0.3 to 0.4‐fold). PB caused a significant elevation of PROD (1.7‐ to 10.4‐fold) and BROD (31‐ to 13.2‐fold) activities in all the animals. PB‐induced BROD activity was higher in females than males in Sprague Dawley rats. These observations strongly suggest that the choice of experimental animal strain, species and inducer is of critical importance for studies of drug metabolism and interaction. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and in vitro evaluation of 2‐[11C]methoxyestradiol‐3,17β‐O,O‐bissulfamate for in vivo studies of angiogenesis

In the present study, 2‐methoxyestradiol‐3,17β‐O,O‐bissulfamate (1), a known angiogenesis inhibitor, was prepared in a radiolabeled form by ¹¹C‐methylation of 2‐hydroxyestradiol‐3,17β‐O,O‐bis(N‐trityl)sulfamate (6) followed by detritylation. Synthesis of precursor 6 required a rather long step because of the presence of two sulfamoyl groups. The decay‐corrected radiochemical yield of [¹¹C]1 was 19 ± 2% based on [¹¹C]CH₃I, and the specific activity was 34–39 GBq/µmol. Although 1 is known to significantly inhibit the proliferation of human umbilical vascular endothelial cells (HUVECs), its radiolabeled form, [¹¹C]1 was not avidly taken up by HUVECs, and the uptake increased slightly in a time‐dependent manner (156% at 60 min relative to a value of 100% at 5 min). These results suggest that further studies are warranted to determine the molecular target for [¹¹C]1. Copyright © 2011 John Wiley & Sons, Ltd.