Phenolic Drugs Research Articles

Challenges in PBPK modeling of phenolic drugs extensively metabolized by intestinal phase II enzyme

Challenges in PBPK modeling of phenolic drugs extensively metabolized by intestinal phase II enzyme

C–H acylation as an enabling tool to tag phenolic drugs

A Pd-catalyzed directed C–H acylation of a collection of intricate phenol-containing compounds with ethanol and other alcohols and aldehydes is reported.

Synthesis of Phosphoramidate Prodrugs of Phenolic Natural Products and Drugs by Ester Exchange

AbstractDrug development based on phenolic natural products as drug candidates against various diseases has gained much attention in recent years. However, most of those molecules lack therapeutic efficacy in clinical trials, usually due to poor bioavailability. Therefore, a prodrug approach was adopted to address the bioavailability problem of phenolic drugs. This paper describes a mild and convenient method for late-stage ProTide-type prodrug synthesis of phenolic pharmaceuticals, which gives various phosphoramidate prodrugs from unprotected phenolic natural products and drugs in high yield. More importantly, this reaction is amenable for the selective phosphorylation of the phenolic hydroxyl group in the presence of otherwise problematic nucleophilic functional groups like amines and alcohols. We also observed that the chemical release rate of the phenol can be substantially tuned by changing the amino acid residue on the phosphoramidate moiety.

Hepatoenteric recycling is a new disposition mechanism for orally administered phenolic drugs and phytochemicals in rats.

Many orally administered phenolic drugs undergo enterohepatic recycling (EHR), presumably mediated by the hepatic phase II enzymes. However, the disposition of extrahepatically generated phase II metabolites is unclear. This paper aims to determine the new roles of liver and intestine in the disposition of oral phenolics. Sixteen representative phenolics were tested using direct portal vein infusion and/or intestinal perfusion. The results showed that certain glucuronides were efficiently recycled by liver. OATP1B1/1B3/2B1 were the responsible uptake transporters. Hepatic uptake is the rate-limiting step in hepatic recycling. Our findings showed that the disposition of many oral phenolics is mediated by intestinal glucuronidation and hepatic recycling. A new disposition mechanism 'Hepatoenteric Recycling (HER)", where intestine is the metabolic organ and liver is the recycling organ, was revealed. Further investigations focusing on HER should help interpret how intestinal aliments or co-administered drugs that alter gut enzymes (e.g. UGTs) expression/activities will impact the disposition of phenolics.

Synthesis, oral bioavailability evaluation and antiplatelet aggregation activity of three derivatives of 3,4‑dihydroxyacetophenone

3,4‑Dihydroxyacetophenone (DHAP) exerts therapeutic effects on cardiovascular disease and pulmonary heart disease. However, it is not utilized as a clinical drug due to its rapid metabolism, short‑acting effect and low oral bioavailability. In the present study, three derivatives of DHAP, including 4‑acetyl‑1,2‑phenylene dipropionate (APDP), 1‑(3‑hydroxy‑4‑phenoxy‑phenyl)‑ethanone (HPPE) and a polymer derivative, PEG‑DHAP, were synthesized via the esterification or etherification of hydroxyls at C3 and C4, which are the prime metabolism sites of DHAP. The physicochemical properties, pharmacokinetic and antiplatelet aggregation activities of these derivatives were measured to determine whether they can improve the defects of DHAP. The results revealed that APDP and HPPE exhibited markedly lower water solubility and higher oil‑water partition coefficients compared to DHAP. APDP rapidly transformed into DHAP invivo and invitro, indicating that there were no significant differences in the values of mean residence time invivo [MRT (0‑t)], half‑life [t1/2], oral bioavailability and antiplatelet aggregation activity invivo and invitro between the two agents. HPPE partially released DHAP for a period of time following oral administration. PEG‑DHAP contained 12.47% DHAP dispersed into nanoparticles with a mean particle size of 260.90nm. This was administered in aqueous solution and was demonstrated to release DHAP slowly following oral administration. These two derivatives significantly prolonged the invivo acting time and increased the oral bioavailability of DHAP: Following intragastric administration, their MRT (0‑t) and t1/2 values were 3.55‑11.47‑ and 6.63‑11.25‑fold higher compared with those of DHAP, respectively. Additionally, their relative bioavailability was 394.79 and 331.88%, respectively, and they exhibited longer acting times of significant antiplatelet aggregation activity. The results of the present study may thus provide a reference for the development of DHAP as an oral drug. Furthermore, the results if this study may prove to be useful to researchers addressing the issue of the poor bioavailability of phenolic drugs.

Cyclic Dipeptide-Guided Aggregation-Induced Emission of Naphthalimide and Its Application for the Detection of Phenolic Drugs.

The development of novel aggregation-induced emission-based fluorophoric systems (AIEgens) has gained prominent importance in recent years, owing to their wide range of applications. Herein, we demonstrate the design, syntheses, and molecular architectonics of cyclic dipeptide tethered naphthalimides (CDP-NIs) to evaluate their AIEgenic properties and applications. CDPs are versatile molecular auxiliaries that form robust intermolecular hydrogen bonding and are tethered to naphthalic anhydride with the ACQ (aggregation-caused quenching) feature. The introduction of a CDP auxiliary was anticipated to promote the molecular assembly of the resulting naphthalimide product to form AIE-active aggregates through intermolecular hydrogen bonding in aqueous media. The systematic photophysical studies of CDP-naphthalimide (CDP-NI) conjugates led to the identification of two AIEgenic fluorophores. The AIEgenic property of the lead candidate 4a was employed for the detection of phenolic drugs in aqueous media. In particular, modulation of the AIEgenic property of 4a offered the sensitive detection of drugs such as doxorubicin and rifampicin (LOD = 18 nM/9.7 ppb and 202 nM/164 ppb, respectively).

Composite alkali polysaccharide supramolecular nanovesicles improve biocharacteristics and anti-lung cancer activity of natural phenolic drugs via oral administration.

Natural phenolic drugs have good safety and various biological activities. However, poor bioavailability and inadequate bioactivity severely limit their application. A novel composite alkali polysaccharide nanovesicle was formed with supramolecule- and nano- technologies to efficiently deliver natural phenolic antitumor drugs. Alkali polysaccharide nanovesicles (ASDLM) containing supramolecular diferuloylmethane (DLM) had the additional effects of alkali polysaccharide nanovesicles and supramolecules of drug and high-molecular-weight polymers. DLM was isolated from the external environment when double loaded by cyclodextrin and nanovesicles; The nanosize, negative/positive charges and supramolecular structure were beneficial attributes that helped to increase the bioavailability and antitumor activity; supramolecular DLM-loaded nanovesicles made of natural biodegradable excipients showed good safety. Compared to free DLM, ASDLM exhibited superior physicochemical characteristics, favorable changes in the in vitro/in vivo kinetic performance, a possible in vitro-in vivo correlation, enhanced in situ gastrointestinal absorption, increased bioavailability, and an elevated anti-lung cancer efficiency. Composite alkali polysaccharide nanovesicles conjugated with supramolecular-/nano- technology may provide a valuable platform for the oral delivery of botanical drugs to meet clinical requirements.

Spectrophotometric Determination Methyldopa and Salbutamol by Oxidative Coupling, Cloud Point and Flow Injection in Pharmaceutical Formulations

TThree methods study in this research simple, sensitive, an expensive and rapid Oxidative Coupling reaction, Cloud Point Extraction and Flow Injection spectrophotometric methods for determination Methyldopa and Salbutamol, the first method oxidative coupling reaction between the Methyldopa and thiosemicarbazide in presence of ferric nitrate anhydrous to yield dark green colored product that have absorbance at λ max 460 nm. Salbutamol coupling reaction with 4-nitrophenyl hydrazine in presence the potassium Iodide and sodium hydroxide to product the violet colored has absorbance at λ max 530 nm. Beer’s law is obeyed from (1-50) µg/ mL with sandall’s sensitivity (0.039,0.073), correlation coefficient (0.9998) and molar absorptivity (0.536×104,0.327×104) for Methyldopa and Salbutamol respectively. The secondly method to estimation the trace amount of phenolic drugs that product from the oxidative coupling reaction it is cloud point extraction, cloud point extraction enables the drugs to be precisely estimated under the optimal experimental conditions, the maximum absorption at λ max (470,535) nm respectively. The concentration was range (0.25-6) µg/mL, molar absorptivity 0.510×105 ,0.483×105 and enrichment factor (9.51,14.72) respectively for Methyldopa and Salbutamol.Flow injection analysis is simple method to determination the phenolic is based on the measurement of absorption signal for product resulting from oxidative coupling reaction , study all experimental parameters chemical and physical to development and stability the colored of product .Total flow injection of 1.5mL/min was pumped and active material was detect at λ max (460,530)nm respectively for Methyldopa and Salbutamol . In this the proposed methods were suxciffuly, applied to the determination Methyldopa and Salbutamol in pharmaceutical preparation.

Determination of Methyldopa and Paracetamol in Pharmaceutical Samples by a Low Cost Genipa americana L. Polyphenol Oxidase Based Biosensor.

Purpose: Jenipapo fruit (Genipa americana L) is a natural source of polyphenol oxidases (PPOs) whose potential in pharmaceutical analysis is noteworthy. Henceforth, this work reports the electrochemical study of a low-cost PPO-based biosensor produced from the crude extract of Jenipapo fruits and accounts a practical approach to employ this biosensor in the determination of methyldopa and paracetamol in pharmaceutical samples. Methods: In order to investigate the electrochemical properties of the biosensor, theoretical and practical approaches were employed, and both samples and the biosensor were analyzed through electrochemical impedance spectroscopy (EIS) and voltammetric techniques, namely: differential pulse voltammetry (DPV) and cyclic voltammetry (CV). Results: showcased that the biosensor presented good analytical features, as well as low detection limits (8 μmol L-1 for methyldopa and 5 μmol L-1 for paracetamol). The relative standard deviation was less than 5% mid-assay. Conclusion: The use of this biosensor is a reliable, low cost and useful alternative in the pharmaceutic determination of phenolic drugs (e.g. methyldopa and paracetamol).

Screening and greenness profiling of oxidative-coupling and electrophilic aromatic substitution reactions for determination of three phenolic drugs

In this study, we screened oxidative-coupling and electrophilic aromatic substitution reactions for developing simple, economic, and environment-friendly spectrophotometric methods for three widely prescribed phenolic drugs; salbutamol sulfate (SLB), terbutaline sulfate (TBT), and thymol (THY). Methods IA and IB rely on the oxidative-coupling reaction of SLB and TBT with p-phenylenediamine in the presence of an oxidizing agent in carbonate buffer while Method II depends on electrophilic aromatic substitution reaction of THY with sodium nitroprusside/hydroxylamine hydrochloride in phosphate buffer (pH 12.0). Different experimental conditions controlling the derivatization reactions were optimized and the reaction products were quantified at 552, 400, and 700 nm, for SLB, TBT, and THY, respectively. Beer's-Lambert law was obeyed over wide linearity ranges with limits of detection from 6 to 126 ppb for the target analytes. Furthermore, the developed methods were validated as per ICH guidance. In addition, profiling of the methods greenness was conducted by adopting the National Environmental Methods Index and the analytical eco-scale score approaches. The two approaches elucidated the excellent greenness of the developed methods which emphasized their applicability for quality control analysis. Thus, the developed methods were efficaciously used for the determination of the three drugs in different dosage forms with excellent accuracy, where % found ranged from 98.86%–102.77%, and no interference from additives in the formulations.

Base and Catalyst-Free Preparation of Silyl Ethers in the Choline Chloride/Urea Deep Eutectic Solvent (DES)

An efficient, fast, green, and mild procedure is reported for preparation of silyl ethers from aliphatic, benzylic, allylic, propargylic alcohols, phenols, naphthols, and some phenolic drugs. In this method, choline chloride/urea (ChCl/urea) deep eutectic solvent (DES) is used as an environmentally benign reaction medium. Silylation was accomplished by employing trimethylsilylchloride (TMSCl), triethylsilylchloride (TESCl), and t-butyldimethylsilylchloride (TDSCl) as the silylating agents. The significant advantages offered by this green protocol are high yields, operational simplicity, short reaction time, and also avoiding the use of any environmentally hazardous solvents, bases, and catalysts. This procedure can also be utilized in large scale silylation for industrial applications.

The Use of a Polyphenoloxidase Biosensor Obtained from the Fruit of Jurubeba (Solanum paniculatum L.) in the Determination of Paracetamol and Other Phenolic Drugs.

The vegetable kingdom is a wide source of a diverse variety of enzymes with broad biotechnological applications. Among the main classes of plant enzymes, the polyphenol oxidases, which convert phenolic compounds to the related quinones, have been successfully used for biosensor development. The oxidation products from such enzymes can be electrochemically reduced, and the sensing is easily achieved by amperometric transducers. In this work, the polyphenoloxidases were extracted from jurubeba (Solanum paniculatum L.) fruits, and the extract was used to construct a carbon paste-based biosensor for pharmaceutical analysis and applications. The assay optimization was performed using a 0.1 mM catechol probe, taking into account the amount of enzymatic extract (50 or 200 μL) and the optimum pH (3.0 to 9.0) as well as some electrochemical differential pulse voltammetric (DPV) parameters (e.g., pulse amplitude, pulse range, pulse width, scan rate). Under optimized conditions, the biosensor was evaluated for the quantitative determination of acetaminophen, acetylsalicylic acid, methyldopa, and ascorbic acid. The best performance was obtained for acetaminophen, which responded linearly in the range between 5 and 245 μM (R = 0.9994), presenting a limit of detection of 3 μM and suitable repeatability ranging between 1.52% and 1.74% relative standard deviation (RSD).

Characterization of catalytic and non-catalytic activities of EgGST2-3, a heterodimeric glutathione transferase from Echinococcus granulosus

Glutathione transferases (GSTs) perform several catalytic and non-catalytic roles in the defense against toxicities of electrophile compounds and oxidative stress, and therefore are involved in stress-response and cell detoxification. Previously, we have provided evidence indicating that EgGST2 and EgGST3, two phylogenetically distant Echinococcus granulosus GSTs, can naturally form a heterodimeric structure (EgGST2-3). In the present work, the recombinant heterodimer GST (rEgGST2-3) is characterized. Hence, rEgGST2-3 was able to conjugate GSH to three substrates: 1-chloro-2,4-dinitrobenzene (CDNB, general substrate for GSTs), 1,2-dichloro-4-nitrobenzene (specific substrate for mammalian Mu class) and trans,trans-deca-2,4-dienal (reactive carbonyl). The canonical activity was considerably reduced by all the conventional inhibitors (cybacron blue, triphenylthin chloride and bromosulfophthalein) and by other inhibitors (ellagic acid, alizarin and chenodeoxycholic acid). Besides this, rEgGST2-3 activity was inhibited by a number of anthelmintic drugs, where the halogenated phenolic drugs (mainly bithionol and hexachlorophene) acted as stronger inhibitors, suggesting they may bind to the EgGST2-3. Moreover, rEgGST2-3 exhibited glutathione-peroxidase activity, and its specific constant (kcat/KM) was calculated. Finally, rEgGST2-3 displayed the ability to bind non-substrate molecules, particularly anthelmintic drugs, suggesting that ligandin activity may have potential to act as a passive protection parasite mechanism. Overall, the rEgGST2-3 behavior was shown to be both complementary and redundant to that reported for rEgGST1, another characterized GST from E. granulosus. It would be appropriate that different enzymes in the same organism do not have exactly the same functional properties to develop a better adaptation to life in the host.

Novel kinetic spectrophotometric method for estimation of certain biologically active phenolic sympathomimetic drugs in their bulk powders and different pharmaceutical formulations

A simple, selective and sensitive kinetic spectrophotometric method was described for estimation of four phenolic sympathomimetic drugs namely; terbutaline sulfate, fenoterol hydrobromide, isoxsuprine hydrochloride and etilefrine hydrochloride. This method is depended on the oxidation of the phenolic drugs with Folin-Ciocalteu reagent in presence of sodium carbonate. The rate of color development at 747–760nm was measured spectrophotometrically. The experimental parameters controlling the color development were fully studied and optimized. The reaction mechanism for color development was proposed. The calibration graphs for both the initial rate and fixed time methods were constructed, where linear correlations were found in the general concentration ranges of 3.65×10−6–2.19×10−5molL−1 and 2–24.0μgmL−1 with correlation coefficients in the following range 0.9992–0.9999, 0.9991–0.9998 respectively. The limits of detection and quantitation for the initial rate and fixed time methods were found to be in general concentration range 0.109–0.273, 0.363–0.910 and 0.210–0.483, 0.700–1.611μgmL−1 respectively. The developed method was validated according to ICH and USP 30 –NF 25 guidelines. The suggested method was successfully implemented to the estimation of these drugs in their commercial pharmaceutical formulations and the recovery percentages obtained were ranged from 97.63%±1.37 to 100.17%±0.95 and 97.29%±0.74 to 100.14±0.81 for initial rate and fixed time methods respectively. The data obtained from the analysis of dosage forms were compared with those obtained by reported methods. Statistical analysis of these results indicated no significant variation in the accuracy and precision of both the proposed and reported methods.

Spectrophotometric and spectrofluorimetric methods for determination of certain biologically active phenolic drugs in their bulk powders and different pharmaceutical formulations

Two simple and sensitive spectrophotometric and spectrofluorimetric methods for the determination of terbutaline sulfate, fenoterol hydrobromide, etilefrine hydrochloride, isoxsuprine hydrochloride, ethamsylate, doxycycline hyclate have been developed. Both methods were based on the oxidation of the cited drugs with cerium (IV) in acid medium. The spectrophotometric method was based on measurement of the absorbance difference (ΔA), which represents the excess cerium (IV), at 317nm for each drug. On the other hand, the spectrofluorimetric method was based on measurement of the fluorescent of the produced cerium (III) at emission wavelength 354nm (λexcitation=255nm) for the concentrations studied for each drug. For both methods, the variables affecting the reactions were carefully investigated and the conditions were optimized. Linear relationships were found between either ΔA or the fluorescent of the produced cerium (III) values and the concentration of the studied drugs in a general concentration range of 2.0–24.0μgmL−1, 20.0–24.0ngmL−1 with good correlation coefficients in the following range 0.9990–0.9999, 0.9990–0.9993 for spectrophotometric and spectrofluorimetric methods respectively. The limits of detection and quantitation of spectrophotometric method were found in general concentration range 0.190–0.787 and 0.634–2.624μgmL−1respectively. For spectrofluorimetric method, the limits of detection and quantitation were found in general concentration range 4.77–9.52 and 15.91–31.74ngmL−1 respectively. The stoichiometry of the reaction was determined, and the reactions pathways were postulated. The analytical performance of the methods, in terms of accuracy and precision, were statistically validated and the results obtained were satisfactory. The methods have been successfully applied to the determination of the cited drugs in their commercial pharmaceutical formulations. Statistical comparison of the results with the reference methods showed excellent agreement and proved that no significant difference in the accuracy and precision.

Oral Delivery of Propofol with Methoxymethylphosphonic Acid as the Delivery Vehicle.

Phosphonamidate 3a of methoxymethylphosphonic acid (MMPA) with propofol (1) and l-alanine ethyl ester was found to be an efficient scaffold for the oral delivery of compound 1. The synthesis and evaluation of MMPA based phosphonamidates of compound 1, HSK3486 (2), and other phenolic drugs revealed the general application of MMPA as the effective delivery vehicle for phenolic drugs. On the basis of plasma concentrations of compound 1 and SN38 (14), the oral bioavailability of compound 3a and 15 in beagle dogs was found to be 97.6% and 34.1%, respectively.

Sodium Oleate-Based Nanoemulsion Enhances Oral Absorption of Chrysin through Inhibition of UGT-Mediated Metabolism.

Oral bioavailability of flavonoids (and many phenolic drugs) is severely limited by extensive first-pass glucuronidation. Here we aimed to determine the modulatory effects of commonly used pharmaceutical excipients (PEs) on UDP-glucuronosyltransferase (UGT) activities and to evaluate the potential of nanoemulsions containing a UGT-inhibitory PE for oral absorption enhancement of chrysin, a model flavonoid. The effects of PEs on glucuronidation were determined using tissue (liver and intestine) microsomes, expressed UGT1A1 enzyme, and UGT1A1-overexpressing HeLa cells. Nanoemulsions were prepared using a modified emulsification technique and subsequently characterized by particle size, zeta-potential, morphology, and in vitro drug release. Pharmacokinetic studies were performed with rats to assess the effects of nanoemulsions on the metabolism and pharmacokinetics of chrysin. Of 21 PEs, five (i.e., Brij 35, Brij 58, labrasol, sodium oleate, and Tween 20) significantly inhibited chrysin glucuronidation. Of note, sodium oleate was the most potent inhibitor of glucuronidation. Eight PEs including Tween 80 had no effects on glucuronidation of chrysin. The chrysin nanoemulsions prepared with sodium oleate (named SO-NE) were spherical or near-spherical (particle size, 83.2 nm; zeta-potential, -43.7 mV; entrapment efficiency, 89.5%). The reference nanoemulsions prepared with Tween 80 (T80-NE) were highly similar to SO-NE in terms of particle size, zeta-potential, and drug release. It was demonstrated in pharmacokinetic studies that SO-NE led to a 4.3-fold increase in systemic exposure of chrysin and a 3.5-fold increase in Cmax value, whereas T80-NE did not cause any changes in chrysin pharmacokinetics. In conclusion, sodium oleate-based nanoemulsions greatly enhanced oral absorption of chrysin. Oral absorption enhancement of chrysin was attained through targeted inhibition of first-pass glucuronidation by sodium oleate.

Exploiting Aryl Mesylates and Tosylates in Catalytic Mono-α-arylation of Aryl- and Heteroarylketones.

The first general palladium catalyst for the catalytic mono-α-arylation of aryl- and heteroarylketones with aryl mesylates and tosylates is described. The newly developed indolyl-derived phosphine ligand L7 has been identified to promote this reaction efficiently. The key to success is attributed to the enhanced steric congestion of the catalyst and effective oxidative addition of the C(Ar)-OMs bond. In the presence of Pd(OAc)2 (0.25-2.5 mol %) and L7, selective monoarylations are achieved with ample reaction scope and product yields up to 95%. Importantly, we demonstrated the applicability of this protocol with the modification of biological phenolic compounds, rendering it amenable for functionalization of phenolic (pro)drugs.

PP29 - Regulation of Myeloperoxidase NO Oxidase Activity by Pharmacological Agents: Novel Biochemical Basis for NO Preservation by Phenolics and Nitroxides (Tempol)

Introduction The leukocyte-derived heme enzyme myeloperoxidase (MPO) plays a key role in impairing NO bioavailability during inflammatory conditions. MPO can consume NO as a direct enzyme substrate as well as by generating NO-consuming free radicals. While our recent studies reveal that endogenous agents (thiocyanate, ascorbate) inhibit this NO oxidase activity, their protective action is incomplete (FRBM, 2014;72:91-103). Aims We sought to identify pharmacological agents that can afford additional protection against MPO NO oxidase activity in complex physiological fluids. We also sought to identify drugs that stimulate this activity, as these may have unforeseen side-effects. Methods Diverse pharmacological agents with established redox activities as MPO substrates and/or radical scavengers were screened for their effects on MPO NO oxidase activity in human plasma and physiological model systems containing endogenous MPO substrates and antioxidants. Results Unexpectedly, the hydrazide MPO inhibitors ABAH and isoniazid, and the peroxidase-activated NO donor hydroxyurea all greatly stimulated MPO NO oxidase activity under physiological conditions. Melatonin marginally increased NO consumption. The phenolic drugs acetaminophen and resveratrol, which are excellent peroxidase substrates, initially stimulated NO consumption but ultimately limited the extent of NO losses. Tempol and related nitroxides were uniquely able to inhibit the rate of MPO-catalyzed NO consumption in ascorbate-replete fluids. Discussion Kinetic analyses revealed the mechanistic basis of drug activities and identified criteria for developing drugs with improved activity. Overall, our data reveal that widely-used pharmacological agents strongly influence MPO NO oxidase activity in complex physiological fluids and identify novel mechanisms by which phenolic drugs and nitroxides may preserve NO bioavailability during inflammatory conditions.

Discussing endogenous NO(•)/HNO interconversion aided by phenolic drugs and vitamins.

The reduction of NO(•) to HNO/NO(-) under biologically compatible conditions has always been thought as unlikely, mostly because of the negative reduction potential: E°(NO(•),H(+)/HNO) = -0.55 V vs NHE at physiological pH. Nonetheless, during the past decade, several works hinted at the possible NO-to-HNO conversion mediated by moderate biological reductants. Very recently, we have shown that the reaction of NO(•) with ascorbate and aromatic alcohols occurs through a proton-coupled nucleophilic attack (PCNA) of the alcohol to NO(•), yielding an intermediate RO-N(H)O(•) species, which further decomposes to release HNO. For the present work, we decided to inspect whether other common biological aromatic alcohols obtained from foods, such as Vitamin E, or used as over-the-counter drugs, like aspirin, are able to undergo the reaction. The positive results suggest that the conversion of NO to HNO could occur far more commonly than previously expected. Taking these as the starting point, we set to review our and other groups' previous reports on the possible NO-to-HNO conversion mediated by biological compounds including phenolic drugs and vitamins, as well as several thiol-bearing compounds. Analysis of revised data prompted us to ask ourselves the following key questions: What are the most likely physio/pathological conditions for NO(•)-to-HNO conversion to take place? Which effects usually attributed to NO(•) are indeed mediated by HNO? These inquiries are discussed in the context of 2 decades of NO and HNO research.