The biological effects and thermal degradation of NPB-22, a synthetic cannabinoid.

PURPOSE: NPB-22 (quinolin-8-yl 1-pentyl-1H-indazole-3-carboxylate), Adamantyl-THPINACA (N-(1-adamantantyl)-1-[(tetrahydro-2H-pyran-4-yl)methyl]-1H-indazole-3-carboxamide), and CUMYL-4CN-B7AICA (1-(4-cyanobutyl)-N-(2-phenylpropan-2-yl)-1H- pyrrolo[2,3-b]pyridine-3-carboxamide), synthetic cannabinoids were evaluated in terms of CB1 (cannabinoid receptor type 1) and CB2 (cannabinoid receptor type 2) activities, and their biological effects when inhaled similar to cigarettes were examined. METHODS: The half maximal effective concentration values of the aforementioned synthetic cannabinoids at the CB1 and CB2 were investigated using [35S]guanosine-5'-O-(3-thio)-triphosphate binding assays. In addition, their biological effects were evaluated using the inhalation exposure test with mice. The smoke generated was recovered by organic solvents in the midget impingers, and the thermal degradation compounds of the smoke components were identified and quantified using a liquid chromatography-photo diode array detector. RESULTS: NPB-22 and Adamantyl-THPINACA had equivalent CB1 activity in in vitro assays. Meanwhile, NPB-22 had a weaker biological effect on some items on the inhalation exposure test than Adamantyl-THPINACA. When analyzing organic solvents in the midget impingers, it was revealed that NPB-22 was degraded to 8-quinolinol and pentyl indazole 3-carboxylic acid by combustion. In addition, these degradation compounds did not have CB1 activity. CONCLUSION: It was estimated that the biological effects of NPB-22 on the inhalation exposure test weakened because it underwent thermal degradation by combustion, and the resultant degradation compounds did not have any CB1 activity in vitro.

Design and characterization of mesoscopic dielectric cuboid antenna for operation in WR-3.4 waveguide bandwidth (220-330 GHz).

We designed a mesoscopic dielectric cuboid antenna connected to a flangeless WR-3.4 open-ended waveguide, and the antenna characteristics at 300 GHz were examined through simulations and experiments. Simulations confirmed that the flangeless design eliminated the flange-induced ripples in the radiation pattern, whose shape varied with frequency, and that the antenna operated in the full bandwidth of the WR-3.4 waveguide (220-330 GHz). Prototypes were then fabricated based on the simulation findings. A prototype with an antenna aperture area of 1.5 mm [Formula: see text] 1.5 mm and an antenna length of 2.35 mm exhibited an antenna gain of 17.2 dBi at 300 GHz and a voltage standing wave ratio of less than 1.5 throughout the WR-3.4 waveguide bandwidth. The level of the side lobes at about [Formula: see text] degrees in the E-plane pattern was approximately [Formula: see text] dB that of the main lobe. Therefore, the proposed antenna, connected to a flangeless waveguide, is a promising antenna for use in future short-range high-speed terahertz wireless applications such as kiosk downloads and board-to-board communication.

Analytical characterization and differentiation between threo- and erythro-4-fluoroethylphenidate.

PURPOSE: Methylphenidate analogs appeared on the drug market during the last years. Its analogs contain two chiral centers and, thus, have potential varying configurations (i.e., threo and erythro forms). This study presents the analytical characterization of 4-fluoroethylphenidate (4-FEP) and its differentiation between threo- and erythro-4-FEP. METHODS: Analysis of the samples included high-performance liquid chromatography (HPLC), gas chromatography-electron ionization-mass spectrometry (GC-EI-MS), high-resolution mass spectrometry (HRMS) analyses, nuclear magnetic resonance (NMR) spectroscopy and X-ray crystal structure analysis. RESULTS: NMR spectroscopic investigations confirmed the differences between threo- and erythro-4-FEP, and demonstrated that both isomers could be separated using HPLC and GC methods. Two samples obtained from one vendor in 2019 consisted of threo-4-FEP, whereas the other two samples obtained from a different vendor in 2020 consisted of a mixture of threo- and erythro-4-FEP. CONCLUSIONS: Several analytical approaches including HPLC, GC-EI-MS, HRMS analyses, NMR spectroscopy and X-ray crystal structure analysis enabled the unambiguous identification of threo- and erythro-4-FEP. The analytical data presented in this article will be useful for identifying threo- and erythro-4-FEP included in illicit products.

Hepatic and renal toxicities and metabolism of fentanyl analogues in rats.

New synthetic opioids continue to emerge in the illicit market, and among them, fentanyl analogues pose a serious threat to the public health with their abuse and trafficking. We investigated the toxicity of fentanyl analogues on the liver and kidneys mediated by the µ-opioid receptor (MOR). Our study focused on 4-fluoro-isobutyrylfentanyl (4F-iBF), which is classified as a "narcotic" in Japan; structurally similar analogues 4-chloro-isobutyrylfentanyl (4Cl-iBF) and isobutyrylfentanyl (iBF) were also investigated. Rats that were intraperitoneally administered 4F-iBF (5 mg/kg (12.3 µmol/kg)) or iBF (12.3 µmol/kg) displayed hepatic and renal ischemic-like damage, but 4Cl-iBF (12.3 µmol/kg) did milder renal damage only. We found that the agonist activity of 4F-iBF, at MORs was approximately 7.2 times that of 4Cl-iBF, and that pretreatment with MOR antagonist naltrexone (0.8 mg/kg) alleviated liver and kidney injuries caused by 4F-iBF. These results suggested that 4F-iBF might cause ischemic damage to the liver and kidneys, induced by respiratory depression mediated by MORs. Furthermore, to elucidate the metabolism of fentanyl analogues, we investigated the change over time in the amount of 4F-iBF, 4Cl-iBF, iBF (6.15 µmol/kg, respectively), and their respective metabolites in serum after intraperitoneal administration to rats. The results showed that in 24-h post-dose serum, 4Cl-iBF and iBF were substantially eliminated while 4F-iBF remained at about 30% of the maximum level, and each of the N-dephenylethylated metabolites of 4F-iBF, 4Cl-iBF, and iBF was detected in 2-h post-dose serum. The results from this study revealed information on the hepatic and renal toxicities and metabolism related to fentanyl analogues.

[Attempt to Calculate the Efficiency of Methylation Using 1H-NMR for Analyzing Brominated Vegetable Oil].

We studied the efficiency of methylation for analyzing brominated vegetable oil (BVO). In this report, we investigated whether 1H-NMR is an applicable method for assessing the efficiency of methylation to analyze BVO. 1H-NMR sufficiently calculated the efficiency of methylation using each integral and the numbers of protons derived from the methyl group, which is characteristic in products, and the methine group, which is characteristic in unreacted substances. Additionally, the efficiency of methylation calculated via 1H-NMR was in good agreement with changes in the peak area of BVO fatty acid methyl esters (BVOFAMEs) after various heating times obtained from GC-FID analysis. Therefore, 1H-NMR is applicable for calculating the efficiency of methylation to analyze BVO.

Stagnant forearc mantle wedge inferred from mapping of shear-wave anisotropy using S-net seafloor seismometers.

Shear-wave anisotropy in Earth's mantle helps constrain the lattice-preferred orientation of anisotropic minerals due to viscous flow. Previous studies at the Japan Trench subduction zone using land-based seismic networks identified strong anisotropy in the mantle wedge, reflecting viscous flow induced by the subducting slab. Here we map anisotropy in the previously uninvestigated offshore region by analyzing shear waves from interplate earthquakes that are recorded by a new seafloor network (the S-net). The newly detected anisotropy is not in the mantle wedge but only in the overlying crust (∼0.1 s time delay and trench-parallel fast direction). The distinct lack of anisotropy indicates that the forearc mantle wedge offshore is decoupled from the slab and does not participate in the viscous flow, in sharp contrast with the rest of the mantle wedge. A stagnant forearc mantle wedge provides a stable and cold tectonic environment that is important for the petrological evolution and earthquake processes of subduction zones.

[Identification of Descarbonsildenafil in an Adulterated Dietary Supplement and Evaluation of Its Inhibitory Activity for Phosphodiesterase Type 5 (PDE5)].

Some illegal dietary supplements contain phosphodiesterase type 5 (PDE5) inhibitors, such as sildenafil, for exerting "therapeutic" effects in erectile dysfunction. This is apparently dangerous, and thus, should be appropriately regulated. Identification of descarbonsildenafil was first reported in Singapore in a coffee sample labeled to exert male sexual performance enhancement effects. However, it is unclear whether the compound possesses PDE5 inhibitory activity. We encountered during our survey of dietary supplements, a sexual enhancement product commercially available in Tokyo, in which a peak presumed to be of descarbonsildenafil was detected by LC-UV and electrospray ionization-tandem MS (ESI-MS/MS). The compound was isolated and identified as descarbonsildenafil with liquid chromatography-quadrupole time-of-flight-mass spectrometry (LC-QTOF-MS), NMR, and X-ray crystal structural analysis. In addition, descarbonsildenafil showed PDE5 inhibitory activity in PDE5 inhibition assay, and its IC50 value for PDE5A1 was found to be 30 nmol/L. The results of INADEQUATE NMR and X-ray crystal structural analysis in this study provide information for the identification of descarbonsildenafil. Since this study indicates that this compound is a PDE5 inhibitor having adequate activity, it is regulated as a drug component in Japan.

[LC/Tribrid Orbitrap Analysis of Phosphodiesterase-5 Inhibitors and Their Analogs as Adulterants in Dietary Supplements].

LC/Tribrid Orbitrap was developed to determine phosphodiesterase-5 (PDE-5) inhibitors and their analogs as adulterants in dietary supplements. High-resolution MS/MS and MS3 spectra of PDE-5 inhibitors and their analogs were obtained by LC/Tribrid Orbitrap using both higher-energy collisional dissociation and collision-induced dissociation. We investigated dietary supplements that claim to enhance men's sexual performance, and detected PDE-5 inhibitors and their analogs. We also estimated the structures of the PDE-5 inhibitor analogs and the impurities of PDE-5 inhibitors and their analogs in the dietary supplements.

Fatal intoxication by 5F-ADB and diphenidine: Detection, quantification, and investigation of their main metabolic pathways in humans by LC/MS/MS and LC/Q-TOFMS.

Despite the implementation of a new blanket scheduling system in 2013, new psychoactive substance (NPS) abuse remains a serious social concern in Japan. We present a fatal intoxication case involving 5F-ADB (methyl 2-[1-(5-fluoropentyl)-1H-indazole-3-carboxamido]-3,3-dimethylbutanoate) and diphenidine. Postmortem blood screening by liquid chromatography/quadrupole time-of-flight mass spectrometry (LC/Q-TOFMS) in the information-dependent acquisition mode only detected diphenidine. Further urinary screening using an in-house database containing NPS and metabolites detected not only diphenidine but also possible 5F-ADB metabolites; subsequent targeted screening by LC/tandem mass spectrometry (LC/MS/MS) allowed for the detection of a very low level of unchanged 5F-ADB in postmortem heart blood. Quantification by standard addition resulted in the postmortem blood concentrations being 0.19 ± 0.04 ng/mL for 5F-ADB and 12 ± 2.6 ng/mL for diphenidine. Investigation of the urinary metabolites revealed pathways involving ester hydrolysis (M1) and oxidative defluorination (M2), and further oxidation to the carboxylic acid (M3) for 5F-ADB. Mono- and di-hydroxylated diphenidine metabolites were also found. The present case demonstrates the importance of urinary metabolite screening for drugs with low blood concentration. Synthetic cannabinoids (SCs) fluorinated at the terminal N-alkyl position are known to show higher cannabinoid receptor affinity relative to their non-fluorinated analogues; 5F-ADB is no exception with high CB1 receptor activity and much greater potency than Δ9 -THC and other earlier SCs, thus we suspect its acute toxicity to be high compared to other structurally related SC analogues. The low blood concentration of 5F-ADB may be attributed to enzymatic and/or non-enzymatic degradation, and further investigation into these possibilities is underway.

Inhalation Exposure Method for Illegal Drugs.

We developed a new inhalation exposure method to evaluate effects of synthetic cannabimimetics that are being distributed as new, unregulated drugs in the Tokyo area. We selected the commercial product "SOUTOU" containing AB-CHMINACA and 5F-AMB as the test drug and dried marshmallow (Althaea officinalis) leaves as the negative control. A half cigarette packed with dried marshmallow leaves or SOUTOU was ignited, then mainstream smoke from each was delivered to five mice in an exposure box. After the cigarettes were fully consumed, neurobehavioral observations and a catalepsy test were performed at 15, 30 and 60 min after exposure. The effluent air from the exposure box was poured into impingers containing acetonitrile (first impinger) and dimethyl sulfoxide (second impinger). The resulting solutions were analyzed to assess decomposition of the synthetic cannabimimetics. Mice exposed to SOUTOU smoke showed many excitement behaviors and some suppressive behaviors at 15, 30 and 60 min. These clearly included cannabimimetic specific pharmacological actions. Negative control mice also showed some suppressive behaviors at 15 min but these were attenuated at later times, nearly disappearing at 60 min. In addition, the behavioral effects observed in controls were less pronounced than those in SOUTOU exposed mice. The inhalation exposure method developed in our study would be effective for determining cannabinoid specific pharmacological effects of illegal drugs, as well as for assessing the presence of active compound(s) by comparing the test substance with a negative control.

Tremor activity inhibited by well-drained conditions above a megathrust.

Tremor occurs on megathrusts under conditions of near-lithostatic pore-fluid pressures and extremely weakened shear strengths. Although metamorphic reactions in the slab liberate large amounts of fluids, the mechanism for enhancing pore-fluid pressures along the megathrust to near-lithostatic values remains poorly understood. Here we show anti-correlation between low-frequency earthquake (LFE) activity and properties that are markers of the degree of metamorphism above the megathrust, whereby LFEs occur beneath the unmetamorphosed overlying plate but are rare or limited below portions that are metamorphosed. The extent of metamorphism in the overlying plate is likely controlled by along-strike contrasts in permeability. Undrained conditions are required for pore-fluid pressures to be enhanced to near-lithostatic values and for shear strength to reduce sufficiently for LFE generation, whereas well-drained conditions reduce pore-fluid pressures at the megathrust and LFEs no longer occur at the somewhat strengthened megathrust. Our observations suggest that undrained conditions are a key factor for the genesis of LFEs.

Positional isomer differentiation of synthetic cannabinoid JWH-081 by GC-MS/MS.

Like many new designer drugs of abuse, synthetic cannabinoids (SC) have structural or positional isomers which may or may not all be regulated under law. Differences in acute toxicity may exist between isomers which impose further burden in the fields of forensic toxicology, medicine and legislation. Isomer differentiation therefore becomes crucial from these standpoints as new designer drugs continuously emerge with just minor positional modifications to their preexisting analogs. The aim of this study was to differentiate the positional isomers of JWH-081. Purchased standard compounds of JWH-081 and its positional isomers were analyzed by gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) first in scan mode to investigate those isomers who could be differentiated by EI scan spectra. Isomers with identical or near-identical EI spectra were further subjected to GC-tandem mass spectrometry (MS/MS) analysis with appropriate precursor ions. EI scan was able to distinguish 3 of the 7 isomers: 2-methoxy, 7-methoxy and 8-methoxy. The remaining isomers exhibited near-identical spectra; hence, MS/MS was performed by selecting m/z 185 and 157 as precursor ions. 3-Methoxy and 5-methoxy isomers produced characteristic product ions that enabled the differentiation between them. Product ion spectrum of 6-methoxy isomer resembled that of JWH-081; however, the relative ion intensities were clearly different from one another. The combination of EI scan and MS/MS allowed for the regioisomeric differentiation of the targeted compounds in this study.

Rapid identification of a narcotic plant Papaver bracteatum using flow cytometry.

In May 2011, numerous poppy plants closely resembling Papaver bracteatum Lindl., a type of narcotic plant that is illegal in Japan, were distributed directly from several large flower shops or through online shopping throughout Japan, including the Tokyo Metropolitan area. In order to better identify the narcotic plants, the relative nuclear DNA content at the vegetative stage was measured by flow cytometric (FCM) analysis in 3 closely-related species of the genus Papaver section Oxytona, namely P. orientale, P. pseudo-orientale, and P. bracteatum, based on the difference between the chromosome numbers of these species. The results showed that the nuclear DNA content differed between these 3 species, and that most of the commercially distributed plants examined in this study could be identified as P. bracteatum. The remaining plants were P. pseudo-orientale, a non-narcotic plant. In addition, the FCM results for the identification of P. bracteatum completely agreed with the results obtained by the morphological analysis, the inter-genic spacer sequence of rpl16-rpl14 (PS-ID sequence) of chloroplast DNA, and the presence of thebaine. These results clearly indicate the usefulness of FCM analysis for the identification of P. bracteatum plants, including when they are in their vegetative stage.

Structure-dependent inhibitory effects of synthetic cannabinoids against 12-O-tetradecanoylphorbol-13-acetate-induced inflammation and skin tumour promotion in mice.

OBJECTIVES: Whether and how synthetic cannabinoids affect inflammation and carcinogenesis has not been well studied. The present study was thus conducted to assess effects of synthetic cannabinoids on inflammation and carcinogenesis in vivo in mice. METHODS: Twenty-three analogues of synthetic cannabinoids were isolated from, and identified as adulterants in, illegal drugs distributed in the Tokyo metropolitan area, and were examined for their inhibitory effects on the induction of oedema in mouse ears by 12-O-tetradecanoylphorbol-13-acetate (TPA). Furthermore, selected cannabinoids, JWH-018, -122 and -210, were studied for their effects on carcinogenesis induced in mouse skin initiated with 7,12-dimethylbenz[a]anthracene (DMBA) and promoted by TPA. KEY FINDINGS: Among cannabinoids, naphthoylindoles mostly exhibited superior inhibitory effects against TPA-induced ear oedema and, especially, JWH-018, -122 and -210 showed potent activity with 50% inhibitory dose (ID50) values of 168, 346 and 542 nm, respectively (an activity corresponding to that of indometacin (ID50 = 908 nm)). Furthermore these three compounds also markedly suppressed the tumour-promoting activity of TPA. CONCLUSIONS: This is the first report indicating the structure-activity relationships for the anti-inflammatory activity of synthetic cannabinoids on TPA-induced inflammation in mice. Naphthoylindoles, JWH-018, -122 and -210, had the most potent anti-inflammatory activity and also markedly inhibited tumour promotion by TPA in the two-stage mouse skin carcinogenesis model. The present results suggest that synthetic cannabinoids, such as JWH-018, -122 and -210, may be used as cancer chemopreventive agents in the future.

Direct imaging of hyperpolarized 129Xe alveolar gas uptake in a mouse model of emphysema.

MRI of hyperpolarized (129)Xe dissolved in pulmonary tissues, and blood has the potential to offer a new tool for regional evaluation of pulmonary gas exchange and perfusion; however, the extremely short T2* and low magnetization density make it difficult to acquire the image. In this study, an ultrashort echo-time sequence was introduced, and its feasibility to quantitatively assess emphysema-like pulmonary tissue destruction by a combination of dissolved- and gas-phase (129)Xe lung MRI was investigated. The ultrashort echo-time has made it possible to acquire dissolved (129)Xe images with reasonably high spatial resolution of 0.625 × 0.625 mm(2) and to obtain T2* of 0.67 ± 0.30 ms in a spontaneously breathing mouse at 9.4 T. The regional dynamic alveolar gas uptake as well as subsequent transport by pulmonary blood flow was also visualized. The ratio of (129)Xe magnetization that diffused into the septa relative to the gas-phase magnetization F was regionally evaluated. The mean F value of elastase-treated mice was 2.28 ± 0.46%, which was significantly reduced from that of control mice 3.41 ± 0.48% (P = 0.0052). This reflects the reduced uptake efficiency due to alveolar tissue destruction and is correlated with the histologically derived alveolar surface-to-volume ratio.

[Structural analyses of unknown red dyes detected in dried strawberry].

We examined two unknown red dyes (designated as red dyes "A" and "B") from a dried strawberry package with a label that indicated the presence of food red No. 40 (R40). Red dye "A" was identified as trisodium 3-hydroxy-4-[(2'-methoxy-5'-methyl-4'-sulfonatophenyl)azo]-2,7-naphthalenedisulfonate (CSA-R) by HPLC, UV-VIS spectra and MS spectra. This compound is one of the four reported subsidiary colors of R40. Detailed analyses of red dye "B" by MS and NMR demonstrated that its structure was disodium 3-hydroxy-4-[(2'-methoxy-5'-methyl-4'-sulfonatophenyl)azo]-2-naphthalenesulfonate. Red dye "B" is a structural isomer of R40, that has not been reported previously. Our results suggest that the two minor red dyes were subsidiary colors contained in R40, which had been added to the dried strawberries.

Peyote identification on the basis of differences in morphology, mescaline content, and trnL/trnF sequence between Lophophora williamsii and L. diffusa.

Genus Lophophora (Cactaceae) has two species: Lophophora williamsii Coulter, which is called peyote, and L. diffusa Bravo. Although it was reported that L. williamsii contained mescaline and L. diffusa did not, we found L. williamsii specimens that did not contain mescaline. This finding indicated that the two species could not be differentiated in terms of mescaline content. Moreover, the relationship between mescaline content and morphology of the two species is also unknown. In this study, we attempted to clarify the difference in morphology, mescaline content, and DNA alignment of the chloroplast trnL/trnF region between L. williamsii and L. diffusa. As a result, L. williamsii specimens were classified into two groups. Group 1 had small protuberances on the epidermis, contained mescaline, and the analyzed region on the trnL/trnF sequence was 881 base pairs (bp) long in all except one (877 bp). Group 2 had large protuberances on the epidermis, did not contain mescaline, and the analyzed region was 893 bp long. On the other hand, L. diffusa had medium-sized protuberances on the epidermis, did not contain mescaline, and the analyzed region was 903 bp long. Also investigated was the potential application of the PCR-restriction fragment length polymorphism (RFLP) method as a means of identification based on the trnL/trnF sequence. By applying the PCR-RFLP method, the two species could be distinguished and L. williamsii specimens could be differentiated into group 1 and group 2.

Differentiation between sulfoaildenafil and its analogs.

An analog of aildenafil, which is a potent and highly selective inhibitor of phosphodiesterase 5, was found in a dietary supplement marketed for enhancement of sexual function. The compound was isolated by silica gel column chromatography, and its structure was identified by means of 13C-NMR spectrometry, 1H-NMR spectrometry, high-resolution MS, and X-ray structure determination. The compound was identified to be sulfoaildenafil (other names: thioaildenafil, dimethyl sildenafil thione, and thiomethisosildenafil). Sulfoaildenafil is very similar to the compound thiohomosildenafil. As it is difficult to distinguish between them by LC-photodiode array detector analysis, ultra-performance LC (UPLC)/MS, ion trap LC/MS/MS (LC/IT-MS/MS), and GC/MS were performed. The mass spectra of thiohomosildenafil by UPLC/MS and LC/IT-MS/MS showed mass fragments of m/z 58, 72, and 355, and the mass spectrum by GC/MS showed mass fragments of m/z 56, 72, and 420. Some of these fragments had low intensities, but they were useful for distinguishing between the two compounds. The relationship between aildenafil (other names: dimethylsildenafil and methisosildenafil) and homosildenafil is similar to that between sulfoaildenafil and thiohomosildenafil. Therefore, these compounds were also examined.

Determination of traces of palladium in stream sediment and auto catalyst by FI-ICP-OES using on-line separation and preconcentration with QuadraSil TA.

A flow injection analysis (FIA) method using on-line separation and preconcentration with a novel metal scavenger beads, QuadraSil TA, has been developed for the ICP-OES determination of traces of palladium. QuadraSil TA contains diethylenetriamine as a functional group on spherical silica beads and shows the highest selectivity for Pd(II) at pH 1 (0.1 mol l(-1) hydrochloric acid) solution. An aliquot of the sample solution prepared as 0.1 mol l(-1) in hydrochloric acid was passed through the QuadraSil TA column. After washing the column with the carrier solution, the Pd(II) retained on the column was eluted with 0.05 mol l(-1) thiourea solution and the eluate was directly introduced into an ICP-OES. The proposed method was successfully applied to the determination of traces of palladium in JSd-2 stream sediment certified reference material [0.019+/-0.001 microg g(-1) (n=3); provisional value: 0.0212 microg g(-1)] and SRM 2556 used auto catalyst certified reference material [315+/-4 microg g(-1) (n=4); certified value: 326 microg g(-1)]. The detection limit (3 sigma) of 0.28 ng ml(-1) was obtained for 5 ml of sample solution. The sample through puts for 5 ml and 100 microl of the sample solutions were 10 and 15 h(-1), respectively.

Reaction of tetramethylpiperidine N-oxides with persistent triplet diphenylcarbenes.

Persistent triplet diphenylcarbenes with considerable stability have been shown to be trapped by tetramethylpiperidine N-oxides (TEMPOs) to give the corresponding benzophenones as major products along with tetramethylpiperidine, which indicates that the reaction pattern is essentially identical with that observed for parent triplet diphenylcarbene. The absolute rate constants for the quenching reaction were measured by a laser flash photolysis technique and compared with those for quenching by other typical triplet carbene quenchers. The results showed that the reactivity of TEMPOs toward triplet carbenes was lower than that of oxygen but higher than that of 1,4-cyclohexadiene. The advantages of TEMPOs as a triplet carbene quencher as opposed to the other quenchers are discussed, and TEMPOs are shown to be very convenient reagents to estimate the reactivity of triplet carbenes.