Browsing by Author "Kuhakarn C."

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    A Consecutive Two-Step Radical-Mediated Cyclization of gem-Difluorinated Diynes to Access gem-Difluorinated Cedrenes
    (2025-01-01) Thaharn W.; Soorukram D.; Kuhakarn C.; Thaharn W.; Mahidol University
    A consecutive two-step radical-mediated cyclization of gem-difluoromethylenated bis(3-arylpropagyl)-indane-1,3-diones to access structurally unique gem-difluoromethylenated cedrenes is described. Substituents located on the aryl rings of the two propagyl units play an important role in governing the consecutive cyclization pattern. Upon treatment of gem-difluoromethylenated 1,3-diane with Bu3SnH/AIBN, a tributylstannyl radical-mediated radical cyclization between the two diyne units chemoselectively took place, leading to the corresponding gem-difluoromethylenated acoradienes in good yields, after removal of tributylstannyl group by TFA. Subsequently, Bu3SnH/AIBN promoted reductive cleavage of the phenylsulfanyl group leading to difluoroalkyl radicals which spontaneously underwent radical cyclization to give a series of gem-difluoromethylenated cedrenes.
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    A dual-purpose NIR fluorescent probe for imaging cysteine/homocysteine in living cells and detecting cysteine in food samples
    (2026-10-01) Khaikate O.; Phudphong P.; Saiyasombat W.; Ouengwanarat B.; Wonglakhon T.; Kamkaew A.; Kuhakarn C.; Khaikate O.; Mahidol University
    Cysteine (Cys) and homocysteine (Hcy) are important biothiols that contribute to the maintenance of physiological homeostasis and are closely associated with various diseases. However, their concentrations in living systems are significantly lower than that of glutathione (GSH), which poses a considerable challenge for the selective detection of Cys/Hcy in the presence of abundant GSH. In this work, a 2-mercaptopyridine moiety that serves as both a quencher and a recognition unit was incorporated into an asymmetric heptamethine cyanine scaffold (Cy7-TCF) to create the near-infrared (NIR) fluorescent probe (Cy7-TCF-Spy). The Cy7-TCF-Spy probe enabled selective detection and fluorescence bioimaging of Cys/Hcy. Although the Cy7-TCF-Spy probe displayed negligible fluorescence in its initial state, upon interaction with Cys or Hcy, it exhibited a strong fluorescence emission at 774 nm even in the presence of GSH. The probe also demonstrated high sensitivity toward Cys/Hcy, with respective detection limit of 95 nM and 67 nM, low cytotoxicity, large Stokes shift (104 nm), and fast responsive time (within 1 min). In addition, high resolution mass spectrometry (HRMS) and time-dependent density functional theory (TD-DFT) calculations were performed to elucidate the fluorescence response mechanism of the probe. Importantly, Cy7-TCF-SPy successfully visualized exogenous Cys/Hcy in A549 cells. Furthermore, the probe was capable of detecting Cys in various food samples, including apple, cabbage, celery, carrot, potato, onion, red onion, and Thai whisky, highlighting its practical applicability in food analysis.
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    AgSCN/(NH4)2S2O8-Promoted Cascade Cyclization of 1-(2-Ethynylphenyl)-1H-indoles and Derivatives
    (2025-10-10) Hassa N.; Punnita S.; Uppalabat T.; La-ongthong K.; Sawektreeratana N.; Janthakit P.; Nalaoh P.; Promarak V.; Leowanawat P.; Soorukram D.; Reutrakul V.; Katrun P.; Bunchuay T.; Kuhakarn C.; Hassa N.; Mahidol University
    Described herein is an efficient and novel method for the synthesis of 6-arylindolo[1,2-a]quinoline-5,7-diones from 1-(2-ethynylphenyl)-1H-indoles. The reaction readily proceeded via a tandem process, leading to the desired products in moderate yields. The reaction can accommodate a broad range of functional groups and is efficient on a gram-scale synthesis. Under standard reaction conditions, 4-phenylpyrrolo[1,2-a]quinoline-3,5-dione can be readily accessed by using 1-(2-(phenylethynyl)phenyl)-1H-pyrrole as a substrate. The single-crystal X-ray diffraction data confirm the chemical structure of the product. Photophysical properties of some selected 6-arylindolo[1,2-a]quinoline-5,7-diones were studied by UV–visible and fluorescence spectroscopy.
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    Antibacterial activity evaluation of vinyl sulfones against global predominant methicillin-resistant Staphylococcus aureus USA300
    (2022-05-01) Vorasin O.; Momphanao K.; Katrun P.; Kuhakarn C.; Jiarpinitnun C.; Mahidol University
    The electrophilic potential of vinyl sulfone permits the rapid capture of cysteine-containing proteins under physiological conditions. These cysteine proteinases play vital roles in bacterial survival and pathogenesis of Staphylococcus aureus (S. aureus) and the global health threat methicillin resistant S. aureus (MRSA). Here in, total of 28 vinyl sulfones were synthesized and subjected to susceptibility testing of pathogenic bacteria, including global epidemic MRSA PFGE strain type USA300 (SF8300). Number of antibacterial vinyl sulfone derivatives were discovered. Among these, nitrile-substituted vinyl phenyl sulfones showed potent antibacterial activity. (E)-3-((4-methoxyphenyl)sulfonyl)acrylonitrile exhibited the strongest potency with MIC of 1.875 µg/mL against methicillin susceptible S. aureus and 3.75 µg/mL against MRSA USA300. Based on the structure–activity relationship analysis, the antibacterial activity of these compounds may involve sulfhydryl conjugation. In addition, the nitrile-substituted vinyl phenyl sulfone could also impair host cell adhesion. With their promising antibacterial activities, these vinyl sulfones have potential for S. aureus and MRSA therapeutics.
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    Asymmetric synthesis of ent-anorisol A and its stereoisomers and confirmation of the absolute configuration of anorisol A isolated from Anogeissus rivularis
    (2022-01-01) Chatpreecha R.; Kuhakarn C.; Leowanawat P.; Reutrakul V.; Soorukram D.; Mahidol University
    Asymmetric synthesis of (2 S,3 S,4 R,5 S)-2-(2,4-dihydroxyphenyl)-5-(4-methoxyphenyl)-3,4-dimethyltetrahydrofuran named as ent-anorisol A was accomplished. The uncommon relative 2,3-anti-3,4-syn-4,5-syn stereochemistry across tetrahydrofuran (THF) ring of ent-anorisol A was constructed with high yield and good stereoselectivity via an acid-catalyzed direct cyclization of unprotected chiral 1,4-diarylbutane-1,4-diol with non-symmetrical aromatic rings. Except for the sign of the specific rotation value, the spectroscopic data of the synthetic ent-anorisol A are in good agreement with those reported for natural anorisol A isolated from Anogeissus rivularis. In addition, (2 R,3 S,4 R,5 R) and (2 S,3 S,4 R,5 R) isomers of anorisol A were also synthesized. Comparison of the specific rotation value and the experimental electronic circular dichroism (ECD) data of natural anorisol A with those of the synthesized ent-anorisol A, (2 R,3 S,4 R,5 R), and (2 S,3 S,4 R,5 R) derivatives confirms the 2 R,3 R,4 S,5 R configurations assigned for natural anorisol A.
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    Asymmetric Total Synthesis of Ventilanones A and B, Two Naturally Occurring Pyranonaphthoquinones from Ventilago harmandiana
    (2022-07-01) Deelertpaiboon P.; Kongsriprapan S.; Krajangsri S.; Betterley N.M.; Kuhakarn C.; Reutrakul V.; Mahidol University
    The asymmetric synthesis of the novel pyranonaphthoquinones ventilanone A and ventilanone B, isolated from the Thai endemic plant Ventilago harmandiana, is accomplished by employing L-rhamnose and gallic acid as the starting materials. The key reactions are the utilization of a newly introduced reagent, PhSCF2H/SnCl4, for the formylation of sterically hindered aromatics containing an electron-withdrawing methyl ester, and the efficient Hauser annulation of phenylthiophthalides with optically active C-1 glycals derived from L-rhamnose. The developed synthetic methodologies solve the long-standing problem of the formylation of sterically hindered aromatics containing electron-withdrawing groups, and are applicable for the synthesis of other analogues with substituents on the aromatic and pyran rings.
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    Base-catalyzed diastereodivergent thia-Michael addition to chiral β-trifluoromethyl-α,β-unsaturated N-acylated oxazolidin-2-ones
    (2023-01-01) Racochote S.; Naweephattana P.; Surawatanawong P.; Kuhakarn C.; Leowanawat P.; Reutrakul V.; Soorukram D.; Mahidol University
    Base-catalyzed diastereodivergent thia-Michael addition of thiols to chiral β-trifluoromethyl-α,β-unsaturated N-acylated oxazolidin-2-ones is reported. By tuning the base-catalyst (i-Pr2NEt, DABCO, or P2-t-Bu), a range of chiral thia-Michael adducts was synthesized in good yields with high diastereoselectivities. A plausible mechanism was proposed on the basis of the experimental results. This work is complementary to the existing methods offering advantages, e.g., switchable diastereoselectivity using a readily synthesized chiral starting material, a cheap and readily available base catalyst, and a simple and practical operation, enabling synthetic application in organic synthesis.
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    Bioinspired Collective Synthesis of Gymnothelignans I, F, K, and L
    (2026-04-17) Chumsri N.; Chualong K.; Chairoungdua A.; Kuhakarn C.; Leowanawat P.; Reutrakul V.; Soorukram D.; Chumsri N.; Mahidol University
    We report a collective stereoselective synthesis of gymnothelignan members, i.e., gymnothelignans I, F, K, and L, based on their proposed biosynthetic pathways. A chiral eupomatilone skeleton was employed as a key common intermediate. Reduction of a carbonyl moiety of eupomatilone readily gave gymnothelignan I, which was smoothly converted to the corresponding oxocarbenium ion upon treatment with an acid. Subsequent intermolecular and intramolecular nucleophilic additions of respective nucleophiles to the oxocarbenium ion provided gymnothelignans F, K, and L. This work provides information to support the plausible biosynthetic pathway of these structurally unique lignans.
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    Cascade Oxidative Trifluoromethylthiolation and Cyclization of 3-Alkyl-1-(2-(alkynyl)phenyl)indoles
    (2023-05-05) Uppalabat T.; Hassa N.; Sawektreeratana N.; Leowanawat P.; Janthakit P.; Nalaoh P.; Promarak V.; Soorukram D.; Reutrakul V.; Kuhakarn C.; Mahidol University
    Persulfate-promoted radical cascade trifluoromethylthiolation and cyclization of 3-alkyl-1-(2-(alkynyl)phenyl)indoles with AgSCF3 were investigated. This protocol provides a novel route to CF3S-substituted indolo[1,2-a]quinoline-7-carbaldehydes and CF3S-substituted indolo[1,2-a]quinoline-7-methanone derivatives via the formation of the C-SCF3 bond and C-C bond and benzylic carbon oxidation in a single step. This reaction can accommodate a broad range of functional groups. The single-crystal X-ray diffraction data confirm the chemical structure of the product. A scale-up experiment and radical inhibition experiments were operated in the reaction system. Photophysical properties of some selected 5-((trifluoromethyl)thio)indolo[1,2-a]quinoline-7-carbaldehydes were studied by UV-visible and fluorescence spectroscopy.
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    Color-tunable emissive heptagon-embedded polycyclic aromatic dicarboximides
    (2022-07-20) Kantarod K.; Soorukram D.; Kuhakarn C.; Surawatanawong P.; Wattanathana W.; Reutrakul V.; Leowanawat P.; Mahidol University
    Heptagon-embedded polycyclic aromatic dicarboximides were developed as new push-pull fluorescent dyes through palladium-catalysed [4+3] annulation followed by nucleophilic substitution. The introduction of a seven-membered ring in these push-pull systems can efficiently modulate the optical properties leading to an enhancement of the fluorescence quantum yields up to 0.93 with color tunable emission covering the visible-NIR spectrum.
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    Corrigendum to “Pyranonaphthoquinone and anthraquinone derivatives from Ventilago harmandiana and their potent anti-inflammatory activity” [Phytochemistry (2020) 112182 169] (Phytochemistry (2020) 169, (S0031942219306594), (10.1016/j.phytochem.2019.112182))
    (2022-08-01) Panthong K.; Hongthong S.; Kuhakarn C.; Piyachaturawat P.; Suksen K.; Panthong A.; Chiranthanut N.; Kongsaeree P.; Prabpai S.; Nuntasaen N.; Reutrakul V.; Mahidol University
    The authors regret an error with the magnitude of specific rotation value for Ventilanone A. The corrected [α]D value is listed below. Ventilanone A (1) [α]D26 = +422.4 (c 0.46, CHCl3). The authors would like to apologise for any inconvenience caused.
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    Cyclization of o -Alkynylisocyanobenzenes with 1,3-Dicarbonyl Compounds
    (2022-09-01) La-Ongthong K.; Sawekteeratana N.; Klaysuk J.; Soorukram D.; Leowanawat P.; Reutrakul V.; Krobthong S.; Wongtrakoongate P.; Kuhakarn C.; Mahidol University
    A facile and convenient reaction of o-alkynylisocyanobenzenes with various active-methylene compounds, including 1,3-diesters, 1,3-diketones, -keto esters, and -keto amides, under Br nsted basic conditions, has been developed. Diethyl malonate reacted smoothly with a collection of o-alkynylisocyanobenzenes to provide the corresponding 2-quinolin-2-yl malonates in excellent yields. Acetylacetone gave a mixture of quinolin-4-yl and quinolin-2-yl derivatives. Acetoacetate esters and acetoacetyl amide derivative initially gave 2-quinolin- 2-yl adducts that underwent partial deacetylation under the reaction conditions.
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    Cytotoxic compounds from Goniothalamus repevensis Pierre ex Finet & Gagnep
    (2022-01-01) Chanakul W.; Reutrakul V.; Kuhakarn C.; Bunteang S.; Piyachaturawat P.; Suksen K.; Hongthong S.; Thanasansurapong S.; Nuntasaen N.; Mahidol University
    Phytochemical investigation of the methanol extract of the leaves and twigs of Goniothalamus repevensis led to the isolation of five known compounds including two styryl lactones; (–)-goniodiol-7-monoacetate (1) and (–)-goniodiol diacetate (2) as well as three aristolactam alkaloids; piperolactam C (3), aristolactam A III (4), and aristolactam B III (5). The structure determination was established by various spectroscopic methods and by comparison with the literature data. Cytotoxic activity against a panel of mammalian cancerous cell lines of compounds 1–4 was investigated. Piperolactam C (3) was found to be active in all tested cell lines with IC50 values in the range of 3.30–64.6 µM. (–)-Goniodiol-7-monoacetate (1) exhibited cytotoxic activity only against ASK cells with IC50 value of 10.28 µM. Having been isolated as a major component, compound 1 can be considered chemotaxonomic significance for G. repevensis.
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    DBU-Mediated Dimerization: Facile Access to 9,9′-Bifluorenylidenes and Isoindigos
    (2023-01-01) Purahong N.; Hongthong S.; Chotsaeng N.; Kuhakarn C.; Meesin J.; Mahidol University
    The present work describes 1,8-diazabicyclo[5.4.0]-7-undecene (DBU)-promoted self-dimerization of 9-chlorofluorenes and 3-chlorooxindoles for the production of the respective 9,9′-bifluorenylidene and isoindigo derivatives in moderate to good yields (29-97% yield). The reaction readily proceeded under mild and metal-free conditions with short reaction time. A scale-up synthesis (5.0 mmol) of some selected 9,9′-bifluorenylidene derivatives in decent yields highlights the synthetic utility of the reported protocol.
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    DBU-Mediated Reaction of 3-Chlorooxindole and 9-Xanthyl Fluorene for Synthesis of 3-Arylidene Oxindole
    (2025-01-01) Purahong N.; Teerawatananond T.; Chotsaeng N.; Janthakit P.; Nalaoh P.; Promarak V.; Kuhakarn C.; Meesin J.; Purahong N.; Mahidol University
    This work reports a new route for the synthesis of 3-(9H-fluoren-9-ylidene)indolin-2-one derivatives via the reaction of 3-chlorooxindoles and O-ethyl S-(9H-fluoren-9-yl) carbonodithioates mediated by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The reactions readily proceeded at room temperature, enable a collection of 3-alkenyl oxindoles to be prepared within a short reaction time (15 minutes). The 3-alkenyl oxindoles can be easily converted to 3-fluorenyl oxindoles by NaBH4 reduction.
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    Decarboxylation of Paraconic Acids by a Silver(I) Nitrate/Persulfate Combination: An Entry to β-Nitro- and β-Hydroxy γ-Butyrolactones
    (2022-09-01) Phae-Nok S.; Kuhakarn C.; Leowanawat P.; Reutrakul V.; Soorukram D.; Mahidol University
    Decarboxylative transformations of paraconic acids, a class of γ-butyrolactones containing a carboxylic acid group at the β-position as their characteristic functionality, by using a combination of Ag- NO3/K2S2O8 were investigated. The dual function of AgNO3 as an initiator of the decarboxylation process and as a source of nitrogen dioxide radicals that react with aliphatic carboxylic substrates is reported for the first time. Starting from paraconic acids, β-nitro- and β-hydroxy γ-butyrolactones were obtained in good combined yields (41 85%) with moderate selectivity in a one-pot operation. The reactions were completed within an acceptable reaction time (two hours) under mild conditions that were tolerated by the γ-butyrolactone core. This study provides a direct and site-specific entry to β-nitro- and β-hydroxy γ-butyrolactones, which are important precursors in organic transformations.
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    Development of D–π–A hemicyanine based NIR fluorescent probes for sensitive detection of intracellular viscosity variations
    (2026-03-15) Saiyasombat W.; Kesorn W.; Thukhammi S.; Naweephattana P.; Ouengwanarat B.; Rungrotmongkol T.; Kamkaew A.; Kuhakarn C.; Khaikate O.; Saiyasombat W.; Mahidol University
    Intracellular viscosity plays a crucial role in regulating cellular signaling and molecular transport. Abnormal variations in viscosity have been associated with various diseases, particularly cancer. Traditional viscometers are inadequate for measuring intracellular viscosity, prompting the development of alternative sensing methods. In this work, two small-molecule fluorescent probes were designed and compared in terms of their responses to viscosity variations. These probes possess a donor–π–acceptor (D–π–A) structure, where the 4-(dimethylamino)phenyl group serves as the electron donor, while two different electron-accepting groups are incorporated. Furthermore, two π-bonds were introduced to enhance fluorescence efficiency within the far-red to near-infrared (NIR) region (λ = 650–900 nm), enabling deeper tissue penetration. In this work, the fluorescent probes, NIR-IND and NIR-BZO, were successfully prepared via a few-step synthesis. They exhibited moderate polarity sensitivity, pronounced viscosity-responsive NIR fluorescence properties, large Stokes shift (up to 162 nm), a broad pH stability range (3–13), high specificity, and strong photostability. The fluorescence intensities of NIR-IND and NIR-BZO at 690 and 688 nm, respectively, increased by to 43-fold from pure water (0.75 cP) to pure glycerol (630.4 cP). In addition, computational studies strongly supported the designation of these probes as effective viscosity-responsive fluorophores, highlighting their potential for applications in viscosity sensing and intracellular imaging, rather than polarity detection.
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    Diastereoselective Addition of PhSCF2SiMe3to Chiral N- tert-Butanesulfinyl Ketimines Derived from Isatins: Synthesis of Enantioenriched gem-Difluoromethylenated Spiro-pyrrolidinyl and Spiro-piperidinyl Oxindoles
    (2022-12-02) Keereewan S.; Kuhakarn C.; Leowanawat P.; Saithong S.; Reutrakul V.; Soorukram D.; Mahidol University
    A convenient and efficient synthetic strategy to prepare enantioenriched gem-difluoromethylenated spiro-pyrrolidinyl and spiro-piperidinyl oxindoles is described. Fluoride-mediated diastereoselective nucleophilic addition of PhSCF2SiMe3to chiral N-tert-butanesulfinyl ketimines derived from isatins was a key step and provided diastereomeric adducts, which were readily separable. Removal of the chiral sulfinyl group followed by structural manipulation afforded chiral gem-difluoromethylenated spiro-pyrrolidinyl and spiro-piperidinyl oxindoles.
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    Dimerization of 3-Chlorooxindoles Mediated by Potassium Ethyl­xanthate: Synthesis of Isoindigos
    (2022-09-01) Meesin J.; Chotsaeng N.; Kuhakarn C.; Mahidol University
    A novel dimerization of 3-chlorooxindoles promoted by potassium ethylxanthate to access isoindigo derivatives is described. The reactions proceeded readily at room temperature in short reaction times. A mechanistic study revealed that the 3-chlorooxindole is initially converted into O-ethyl S-(2-oxo-2,3-dihydro-1H-indol-3-yl) dithiocarbonate, which subsequently undergoes dimerization with elimination of arbon disulfide. In almost all cases, analytically pure isoindigos were isolated in moderate to good yields without a requirement for chromatographic purification.
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    Electro-oxidative Methylation of 2-Isocyanobiaryls Using N,N-dimethylformamide (DMF) as Carbon Source: Synthesis of 6-Methylphenanthridines
    (2024-01-01) La-ongthong K.; Chantarojsiri T.; Soorukram D.; Leowanawat P.; Reutrakul V.; Kuhakarn C.; La-ongthong K.; Mahidol University
    A benign electrochemical method to access 6-methylphenanthridines from 2-isocyanobiaryls using N,N-dimethylformamide (DMF) as a methyl source is reported. The protocol operates at ambient temperature without the need for harmful methylating reagents. Mechanistic studies suggested that DMF delivered a methylene synthon, followed by reduction at the cathode and tautomerization. The method offers environmental benefits by avoiding metal-based reagents and harsh conditions.