Acid 1b Research Articles

On the Allylic Oxidation of Ent-kaurenic Acid Methyl Ester with Lead Tetra-acetate

In this paper, results obtained upon treatment of the methyl ester of ent-kaur-16-en-19-oic acid (1b) with lead tetra-acetate under reflux in glacial acetic acid solution and an argon atmosphere are described. After 30 minutes reflux, GC-MS analysis of the product indicated the presence of three substances, the initial compound (1b, 7 %), the methyl ester of ent-kaur-16-en-15-O-acetyl-19-oic acid (2a, C₂₃H₃₀0₄, 45 %), and its isomer, the methyl ester of ent-kaur-15-en-17- 0-acetyl-19-oic acid (3a, 47 %). Flash chromatography over silica gel containing 20% AgNO₃ yielded 2b (456 mg), which was identified by direct comparison with an authentic sample, and 3a (472 mg), whose structure was established by uni- and bi-dimensional NMR analysis. Hydrolysis of 3a with dry ammonia in MeOH yielded the methyl ester of ent-kaur-15-en-17-hydroxy-19-oic acid (3b, C₂₁H₃₂ 0₃); treatment of this compound with chromic acid/pyridine complex rendered the aldehyde (4).

Asymmetric Reduction of Lactam-Based β-Aminoacrylates. Synthesis of Heterocyclic β(2)-Amino Acids.

The ability to affect asymmetric reduction of heterocyclic β-aminoacrylates 1 (n = 1-3) has been assessed with pyrrolidine and piperidone variants generating the corresponding N-heterocyclic β(2)-amino acids 3b and 5b with high enantioselectivity (≥97% ee) using a Rh/WALPHOS catalyst combination. The use of the carboxylic acid substrate was essential; the corresponding esters do undergo reduction but led to racemic products. The seven-ring azepanone variant (as the carboxylic acid 9b) underwent reduction, but only a minimal level of asymmetric induction was observed.

Biotransformations of Bile Acids with Bacteria from Cayambe Slaughterhouse (Ecuador): Synthesis of Bendigoles.

The biotransformations of cholic acid (1a), deoxycholic acid (1b), and hyodeoxycholic acid (1c) to bendigoles and other metabolites with bacteria isolated from the rural slaughterhouse of Cayambe (Pichincha Province, Ecuador) were reported. The more active strains were characterized, and belong to the genera Pseudomonas and Rhodococcus. Various biotransformation products were obtained depending on bacteria and substrates. Cholic acid (1a) afforded the 3-oxo and 3-oxo-4-ene derivatives 2a and 3a (45% and 45%, resp.) with P.mendocina ECS10, 3,12-dioxo-4-ene derivative 4a (60%) with Rh.erythropolis ECS25, and 9,10-secosteroid 6 (15%) with Rh.erythropolis ECS12. Bendigole F (5a) was obtained in 20% with P.fragi ECS22. Deoxycholic acid (1b) gave 3-oxo derivative 2b with P.prosekii ECS1 and Rh.erythropolis ECS25 (20% and 61%, resp.), while 3-oxo-4-ene derivative 3b was obtained with P.prosekii ECS1 and P.mendocina ECS10 (22% and 95%, resp.). Moreover, P.fragi ECS9 afforded bendigole A (8b; 80%). Finally, P.mendocina ECS10 biotransformed hyodeoxycholic acid (1c) to 3-oxo derivative 2c (50%) and Rh.erythropolis ECS12 to 6α-hydroxy-3-oxo-23,24-dinor-5β-cholan-22-oic acid (9c, 66%). Bendigole G (5c; 13%) with P.prosekii ECS1 and bendigole H(8c) with P.prosekii ECS1 and Rh.erythropolis ECS12 (20% and 16%, resp.) were obtained.

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.

Discovery of a New Class of Sortase A Transpeptidase Inhibitors to Tackle Gram-Positive Pathogens: 2-(2-Phenylhydrazinylidene)alkanoic Acids and Related Derivatives.

A FRET-based random screening assay was used to generate hit compounds as sortase A inhibitors that allowed us to identify ethyl 3-oxo-2-(2-phenylhydrazinylidene)butanoate as an example of a new class of sortase A inhibitors. Other analogues were generated by changing the ethoxycarbonyl function for a carboxy, cyano or amide group, or introducing substituents in the phenyl ring of the ester and acid derivatives. The most active derivative found was 3-oxo-2-(2-(3,4dichlorophenyl)hydrazinylidene)butanoic acid (2b), showing an IC50 value of 50 µM. For a preliminary assessment of their antivirulence properties the new derivatives were tested for their antibiofilm activity. The most active compound resulted 2a, which showed inhibition of about 60% against S. aureus ATCC 29213, S. aureus ATCC 25923, S. aureus ATCC 6538 and S. epidermidis RP62A at a screening concentration of 100 µM.

Synthesis of Hydroxy-Androstane-1,4-Diene-3, 17-Dione Derivatives by Biotransformations of Bile Acids with Pseudomonas alcaliphila

The synthesis of hydroxy-androstane-1,4-diene-3,17-dione derivatives (2a-d) by biotransformations with Pseudomonas alcaliphila of bile acids (1a-d) was reported. The scale-up of addition of deoxycholic acid (1a), cholic acid (1b), and chenodeoxycholic acid (1c) (1 g/L until 10 g/L) to the culture broth of P. alcaliphila switches the degradation process to the synthesis of 12β-hydroxy-androstane-1,4-diene-3,17-dione (2a, 95%), 7α,12β-dihydroxy-androstane- 1,4-diene-3,17-dione (2b, 52%), and 7α-hydroxy-androstane-1,4-diene-3,17-dione (2c, 23%) Also hyodeoxycholic acid (1d) was transformed by P. alcaliphila to 6α-hydroxy-androstane-1,4-diene-3,17-dione (2d) with as much good yields (83%) but with lower concentration (1 g/L) in the culture broth.

Development of an Efficient Synthesis of (2-Aminopyrimidin-5-yl) Boronic Acid

A practical and cost-effective synthesis of (2-aminopyrimidin-5-yl) boronic acid 1b has been developed. Key features of the synthesis include the inexpensive in situ protection of the amine via bis-silylation using TMSCl followed by metal–halogen exchange using n-BuLi and trapping with B(Oi-Pr)3. The water-soluble boronic acid is isolated by a well-designed acid–base sequence providing the target in 80% yield and high purity for the two-step process. The large-scale (15 kg) implementation of a Suzuki–Miyaura borylation to form the pinacol boronic ester is also described.

Novel Very Long-Chain α-Methoxylated Δ5,9 Fatty Acids from the Sponge Asteropus niger Are Effective Inhibitors of Topoisomerases IB.

The novel fatty acids (2R,5Z,9Z)-2-methoxy-25-methyl-5,9-hexacosadienoic acid (1a) and (2R,5Z,9Z)-2-methoxy-24-methyl-5,9-hexacosadienoic acid (1b) were isolated in 80 % purity from the Caribbean sponge Asteropus niger by chloroform/methanol extraction followed by solvent partitioning and silica gel column chromatography. The compounds were characterized by utilizing a combination of gas chromatography-mass spectrometry, nuclear magnetic resonance, and circular dichroism. Acids 1a and 1b were not detected in the phospholipids (PtdCho and PtdIns) of the sponge, but rather as free FA and possibly in glycosylceramides. The mixtures of 1a and 1b displayed cytotoxicity towards THP-1 and HepG2 cells with EC50's between 41 and 35 μg/mL. Apoptosis was not the preferred mode of cell death induced by 1a-1b in the THP-1 cells. This implies other types of cytotoxicity mechanisms, such as membrane disruption and/or the inhibition (EC50 = 1.8 μg/mL) of the human topoisomerase IB enzyme (hTopIB), with a mechanism of inhibition different from the one displayed by camptothecin (CPT). In a separate experiment, the mixture of 1a and 1b also displayed cytotoxicity towards ex vivo mouse splenocytes infected with Leishmania infantum amastigotes (IC(50) = 0.17 mg/mL) and free living promastigotes (IC(50) = 0.34 mg/mL). It was also found that the FA were inhibitory of the Leishmania topoisomerase IB (LTopIB) with an EC(50) = 5.1 μg/mL. Taken together, 1a and 1b represent a new class of FA with potential as TopIB inhibitors that preferentially inhibit hTopIB over LTopIB.

Synthesis of piscidinol A derivatives and their ability to inhibit HIV-1 protease

Four types of piscidinol A derivatives were synthesized and evaluated their ability to inhibit HIV-1 protease to understand their structure-activity relationships. Of these tirucallane-type triterpene derivatives, an A-seco derivative (1b) moderately inhibited human immunodeficiency virus (HIV) protease (IC50 38.2 μM). The 2,2-dimethyl succinic acid (DMS) acylated tirucallane derivatives (4b, 6a, and 7b, 50 < IC50 < 100 μM) were more inhibitory against HIV-1 PR than the others (PA, 2a, 4a, 4c–4d, 5a, 6b–6d, and 7a, IC50 > 100 μM). These findings indicated that the 2,3-seco-2,3-dioic acid (1b) and DMS-acylated tirucallane-type derivatives preferably inhibited HIV viral protease.

Grinding and Microwave‐assisted Synthesis of Heterocyclic Molecules in High Yields and Their Biological Evaluation

Cis‐cyclohexane1,2‐dicarboxylic acid (1a), phthalic acid (1b), and pyrazine 2,3‐ dicarboxylic acid (1c) on grinding with hydrazine hydrate (2a) gave 2‐aminohexahydro‐1H‐isoindole‐1,3(2H)‐dione (3a), 2‐amino‐1H‐isoindole‐1,3(2H)‐dione (3b), and 6‐amino‐5H‐pyrrolo[3,4‐b]pyrazine‐5,7(6H)‐dione (3c), respectively. Condensation of (3a, 3b, 3c) with aldehydes (4x, 4y, 4z) and 2‐cyanopyridine, 4‐cyanopyridine, 2‐cyanopyrazine (5x, 5y, 5z) under microwave irradiation gave corresponding azomethine (6ax, 6ay, 6az, 6bx, 6by, 6bz, 6cx, 6cy, 6cz) and amidine (7ax, 7ay, 7az, 7bx, 7by, 7bz, 7cx, 7cy, 7cz) derivatives, respectively. Fully characterized azomethine (6ax, 6ay, 6az, 6bx, 6by, 6bz, 6cx, 6cy, 6cz) and amidine (7ax, 7ay, 7az, 7bx, 7by, 7bz, 7cx, 7cy, 7cz) derivatives were screened for anti‐inflammatory and anticancer activity against five human cancer cell lines. Compound 7cx exhibited 35% anti‐inflammatory activity at a dose of 50 mg/kg p.o. whereas standard drug ibuprofen showed 39% activity at a dose of 50 mg/kg p.o. Compounds 6bz, 7cx, 7cz (breast T47D), 6bz, 6cy (lung NCI H‐522), 6bx, 7bz (colon HCT‐15), 6bz (ovary PA‐1) and 6bx, and 6cz (liver HepG‐2) exhibited good (35–41% inhibition at 10 μM c) anticancer activity. IC50 values of 6bx, 6bz, 6cy, 6cz, 7bz, 7cx, and 7cz against various cancer cell lines and normal cell (COS‐1) are also reported.

Synthesis, Characterization and Application of Some Axially Chiral Binaphthyl Phosphoric Acids in Asymmetric Mannich Reaction

AbstractTwo novel chiral Br?nsted acids 3b and 3c were prepared without involving the complexity of Suzuki coupling. Catalyst 3c bearing two additional hydroxyl groups at 3 and 3′ positions of axially chiral 1,1‐binaphthalene‐2,2′‐diol phosphoric acid was applied in a model Mannich reaction to afford β‐amino ester in high yield (92%) and enantiomeric excess (91%) at low reacting temperature of −40°C. In addition, those β‐amino ester derivatives with high yields and excellent enatioselectivities were obtained in the presence of catalyst 3c under the above condition.

New cytotoxic cyclic peroxide acids from Plakortis sp. marine sponge.

Bioassay-guided fractionation of the extract of Jamaican marine sponge Plakortis sp. followed by preparative TLC and HPLC yielded several known methyl ester cyclic peroxides (1a, 2a, 3a, 4, 5), known plakortides (6,7), known bicyclic lactone (8) and new cyclic peroxide acids (1b, 2b, 3b). The chemical structures were elucidated by extensive interpretation of their spectroscopic data. These natural products showed remarkable in vitro cytotoxicity against several cancer cell lines.

Antibacterial and Enzyme Inhibition Study of Hydrazone Derivatives Bearing 1, 3, 4-Oxadiazole

The antibacterial and lipoxygenase enzyme inhibition activities of two series of compounds have been investigated in the presented work. The 4-methyl/hydroxy benzoic acids (1a & 1b) were used as starting materials to prepare corresponding esters (2a & 2b), hydrazides (3a & 3b), 5-(4-methylphenyl/4-hydroxyphenyl)-1,3,4-oxadiazol-2-thiols (4a & 4b), S-substituted esters (5a & 5b) and acetohydrazides (6a & 6b). The acetohydrazones, 8a-i & 9a-i, were synthesized by stirring 6a & 6b with mono(di)substituted phenylcarboxaldehydes (7a-i) in methanol. The data of IR, 1 H-NMR and EIMS spectral techniques well confirmed the structural formulae of synthesized compounds. The molecules of 4-methyl series rendered the better results than those of 4-hydroxy series.

Rhodium/chiral diene complexes in the catalytic asymmetric arylation of β-pyrazol-1-yl acrylates.

The asymmetric conjugate addition of arylboronic acids to substituted and unsubstituted β-pyrazol-1-yl (E)-tert-butyl acrylates 4 catalyzed by 5 mol % of the Rh(I)/diene 2a catalyst provided the corresponding addition products in 44-98% yield and 91->99.5% ee. The method was applied to the formal synthesis of (3S)-3-aryl-3-(pyrazol-1-yl)propanoic acid 1b with agonistic activity toward the human GPR40 G-protein coupled receptor.

Fluorescent derivatization of aromatic carboxylic acids with horseradish peroxidase in the presence of excess hydrogen peroxide.

The fluorescent derivatization of aromatic carboxylic acids by the catalytic activity of horseradish peroxidase (HRP) in the presence of excess H2O2 was investigated. Four monocarboxylic acids, nine dicarboxylic acids, and two tricarboxylic acids, all of which are non- or weakly fluorescent, were effectively converted into fluorescent compounds using this new method. This technique was further developed for the fluorometric determination of trace amounts of terephthalic acid (3c) and lutidinic acid (2b), and linear calibration curves for concentrations between 2.5 and 20.0 nmol of terephthalic acid (3c) and 1.0 and 10.0 nmol of lutidinic acid (2b) were demonstrated. Compound III, an intermediate of HRP, played an essential role in this process. Additionally, lactoperoxidase and manganese peroxidase, peroxidases similar to HRP, showed successful fluorescent derivatization of nicotinic acid (1b), lutidinic acid (2b), and hemimellitic acid (4a) in the presence of excess H2O2.

Synthesis and Anti-HIV-1 Activity of Olean-9(11),12(13)-Dien-30-Oic Acid 3β-(2-O-β-D-Glucuronopyranosyl-β-D-Glucuronopyranoside).

The glycyrrhizic acid (GA) analog olean-9(11),12(13)-dien-30-oic acid 3β-(2-O-β-D-glucuronopyranosyl-β-D-glucuronopyranoside) (II) was synthesized via reduction of GA by NaBH4 in refluxing 2-PrOH:H2O with subsequent work up with HCl (5%). The cytotoxicity and antiviral activity of this glycoside against HIV-1 was studied in MT-4 cell culture. It was found that II was practically non-toxic for MT-4 cells while inhibiting accumulation of virus-specific protein p24 and RNA-dependent DNA-polymerase activity of HIV-1 reverse transcriptase (RT) (IC50 3.1 ±1.0 μg/mL).

Biocatalytic desymmetrization of 3-substituted glutaronitriles by nitrilases. A convenient chemoenzymatic access to optically active (S)-Pregabalin and (R)-Baclofen

Desymmetrization of prochiral 3-substituted glutaronitriles offers a new approach to access (S)-Pregabalin and (R)-Baclofen. A number of nitrilases from diverse sources were screened with 3-isobutylglutaronitriles (1a) or 3-(4′-chlorophenyl)glutaronitriles (1b) as the substrate. Some nitrilases were found to catalyze the desymmetric hydrolysis of 1a and 1b to form optically active 3-(cyanomethyl)-5-methylhexanoic acid (2a) and 3-(4′-chlorophenyl)-4-cyanobutanoic acid (2b) with high enantiomeric excesse (ee), respectively. This cannot be achieved using traditional chemical hydrolysis. Among them, AtNIT3 generated (R)-2b, whereas BjNIT6402 and HsNIT produced the opposite (S)-enantiomer with high conversions and ee values. Not only the nitrilases showed different activities and stereoselectivities toward these 3-substituted glutaronitriles, the 3-substituent of the substrates also exerted great effect on the enzyme activity and stereoselectivity. (S)-2a and (S)-2b were prepared with high yields and ee values using BjNIT6402 and HsNIT as the biocatalysts, respectively. A straightforward Curtius rearrangement of (S)-2a and (S)-2b, followed by the acidic hydrolysis, afforded (S)-Pregabalin and (R)-Baclofen. This offers a new platform methodology for the synthesis of optically active β-substituted γ-amino acids of pharmaceutical importance.

Application of engineered cytochrome P450 mutants as biocatalysts for the synthesis of benzylic and aromatic metabolites of fenamic acid NSAIDs

Cytochrome P450 BM3 mutants are promising biocatalysts for the production of drug metabolites. In the present study, the ability of cytochrome P450 BM3 mutants to produce oxidative metabolites of structurally related NSAIDs meclofenamic acid, mefenamic acid and tolfenamic acid was investigated. A library of engineered P450 BM3 mutants was screened with meclofenamic acid (1) to identify catalytically active and selective mutants. Three mono-hydroxylated metabolites were identified for 1. The hydroxylated products were confirmed by NMR analysis to be 3′-OH-methyl-meclofenamic acid (1a), 5-OH-meclofenamic acid (1b) and 4′-OH-meclofenamic acid (1c) which are human relevant metabolites. P450 BM3 variants containing V87I and V87F mutation showed high selectivity for benzylic and aromatic hydroxylation of 1 respectively. The applicability of these mutants to selectively hydroxylate structurally similar drugs such as mefenamic acid (2) and tolfenamic acid (3) was also investigated. The tested variants showed high total turnover numbers in the order of 4000–6000 and can be used as biocatalysts for preparative scale synthesis. Both 1 and 2 could undergo benzylic and aromatic hydroxylation by the P450 BM3 mutants, whereas 3 was hydroxylated only on aromatic rings. The P450 BM3 variant M11 V87F hydroxylated the aromatic ring at 4′ position of all three drugs tested with high regioselectivity. Reference metabolites produced by P450 BM3 mutants allowed the characterisation of activity and regioselectivity of metabolism of all three NSAIDs by thirteen recombinant human P450s. In conclusion, engineered P450 BM3 mutants that are capable of benzylic or aromatic hydroxylation of fenamic acid containing NSAIDs, with high selectivity and turnover numbers have been identified. This shows their potential use as a greener alternative for the generation of drug metabolites.

Tumor-specific delivery of siRNA using supramolecular assembly of hyaluronic acid nanoparticles and 2b RNA-binding protein/siRNA complexes

Anticancer therapeutics delivering exogenous siRNA have been explored to suppress the tumor-associated genes, but several limitations of siRNA delivery such as tumor-targeted delivery, controlled siRNA release at the sites of interest, or instabilities of siRNA in physiological fluids should be preferentially addressed for its clinical applications. As an attempt to meet these criteria, we designed a supramolecular assembly, which was composed of cholesterol-bearing hyaluronic acid (HA-Chol) conjugates and 2b RNA-binding protein (2b)/siRNA complexes. In contrast to the traditional siRNA polyplexes using electrostatic interactions, HA-Chol nanoparticles, as a results of self-assembly of HA-Chol conjugates, provide the hydrophobic core that acts as the container for 2b protein/siRNA complexes, where a high affinity of 2b protein for siRNA could neutralize the negative-charged siRNA. Here, we investigated the potential of HA-Chol/2b/siRNA complexes as the siRNA carriers that provide encapsulation, protection, and targeted delivery of siRNA. The HA-Chol nanoparticles could selectively deliver 2b protein/siRNA complexes to the tumor cells with up-regulated CD44 receptors and suppress the expression of target gene. The pH-associated binding properties of siRNA for 2b proteins allowed the controlled release of siRNA in the endocytic compartments, and ultimately the released siRNA could obtain the RNAi acitivities in the cells, whereas the encapsulated 2b proteins still stayed within the HA-Chol nanoparticles. Our delivery systems demonstrate the promising potential of the efficient siRNA carriers in the anticancer therapeutic applications.

Synthesis of Polyfluorobenzoic Acids By Regioselective Electrochemical Carboxylation of Polyfluoroarenes

Since carbon dioxide (CO2) is an abundant, economical, nontoxic and environmentally benign C1 chemical reagent, fixation of carbon dioxide in organic molecules has recently become an attractive project in organic synthesis. An electrochemical method has contributed greatly to this area because it enables an efficient fixation of carbon dioxide in organic molecules even under atmospheric pressure of carbon dioxide when a reactive metal, such as magnesium or aluminum metal, is used as a sacrificial anode. There have been a number of reports on electrochemical fixation of carbon dioxide, and we have also reported synthesis of useful carboxylic acids by electrochemical carboxylation of various organic compounds. On the other hands, it is well known that fluorine-containing organic compounds have unique chemical and physical properties. The introduction of fluorine atoms into biologically-active compounds is also known to cause remarkable modification of their original activities. Therefore, considerable attention has been paid to efficient and selective preparation methods of organofluorine compounds. However, little attention has been paid to electrochemical carboxylation to afford fluorinated carboxylic acids.1-4 During the course of our continuous studies on the synthesis of useful carboxylic acids by electrochemical fixation of carbon dioxide,5 we recently found that electrochemical reduction of polyfluoroarenes in the presence of carbon dioxide resulted in a regioselective cleavage of a C-F bond of the phenyl ring followed by reaction with carbon dioxide to give the corresponding mono-carboxylated products, polyfluorobenzoic acids, in moderate to good yields.6 We report herein the results for synthesis of polyfluorobenzoic acids by regioselective electrochemical carboxylation of polyfluoroarenes.First, we screened reaction conditions for electrochemical carboxylation of hexafluorobenzene (1a) as a substrate. When constant current electrolysis of 1a was carried out in DMF using a one-compartment cell equipped with a Pt cathode and an Mg anode with 3 F/mol of electricity in the presence of carbon dioxide, reductive cleavage of a C-F bond on the phenyl ring followed by reaction with carbon dioxide took place to give pentafluorobenzoic acid (2a). After reaction conditions screening, 2a could be obtained in 73% 19F NMR yield by electrolysis of 1a at –40°C with 5 mA/cm2 of current density. After recrystallization with hexane and acetone, pentafluorobenzoic acid (2a) was obtained in 65% isolated yield as a pure product.We next investigated similar electrochemical carboxylations of several polyfluoroarenes, and the results are shown in Scheme. When pentafluorobenzene (1b) was subjected to the present electrochemical carboxylation under the same conditions for the reaction of 1a, C-F bond cleavage followed by carboxylation also took place efficiently to give 2,3,5,6-tetrafluorobenzoic acid (2b) in 78% 19F NMR yield and 66% isolated yield after recrystallization. It is noteworthy that C-F bond cleavage followed by carboxylation of 1b occurred at the C3 position of 1b predominantly to give 2b as a major product. Similar regioselective electrochemical carboxylation was also achieved when pentafluoroarenes 1c-f were used as substrates. Under the same conditions except for 1d, electrochemical carboxylation of 1c-f gave 4-substituted-2,3,5,6-tetrafluorobenzoic acids 2c-f in 61-84% 19F NMR yields and 49-76% isolated yields after recrystallization. It is also to note that C-F bond cleavage occurred at the para position of the substituents of Me-, AcO-, Me(RO)2C-, and MeS- in pentafluoroethylarenes 1c-f predominantly in all cases to give 4-substituted-2,3,5,6-tetrafluorobenzoic acids 2c-f as major products.<Scheme>Other results of electrochemical carboxylation of polyfluoroarenes and proposed reaction mechanism including regioselectivity of the carboxylation will be presented.