Diazeniumdiolate ions as leaving groups in anomeric displacement reactions: a protection-deprotection strategy for ionic diazeniumdiolates

Use of carbonyldiimidazole as a derivatization agent for the detection of pinacolyl alcohol, a forensic marker for Soman, by EI-GC-MS and LC-HRMS in official OPCW proficiency test matrices

Pinacolyl alcohol (PA), a key forensic marker for the nerve agent Soman (GD), is a particularly difficult analyte to detect by various analytical methods. In this work, we have explored the reaction between PA and 1,1'-carbonyldiimidazole (CDI) to yield pinacolyl 1H-imidazole-1-carboxylate (PIC), a product that can be conveniently detected by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-high-resolution mass spectrometry (LC-HRMS). Regarding its GC-MS profile, this new carbamate derivative of PA possesses favorable chromatographic features such as a sharp peak and a longer retention time (RT = 16.62 min) relative to PA (broad peak and short retention time, RT = 4.1 min). The derivative can also be detected by LC-HRMS, providing an avenue for the analysis of this chemical using this technique where PA is virtually undetectable unless present in large concentrations. From a forensic science standpoint, detection of this low molecular weight alcohol signals the past or latent presence of the nerve agent Soman (GD) in a given matrix (i.e., environmental or biological). The efficiency of the protocol was tested separately in the analysis and detection of PA by EI-GC-MS and LC-HRMS when present at a 10 μg/mL in a soil matrix featured in the 44th PT and in a glycerol-rich liquid matrix featured in the 48th Official Organization for the Prohibition of Chemical Weapons (OPCW) Proficiency Test when present at a 5 μg/mL concentration. In both scenarios, PA was successfully transformed into PIC, establishing the protocol as an additional tool for the analysis of this unnatural and unique nerve agent marker by GC-MS and LC-HRMS.

Detection and confirmation of fentanyls in high clay-content soil by electron ionization gas chromatography-mass spectrometry

Detection of illicit drugs in the environment, particularly in soils, often suggests the present or past location of a clandestine production center for these substances. Thus, development of efficient methods for the analysis and detection of these chemicals is of paramount importance in the field of chemical forensics. In this work, a method involving the extraction and retrospective confirmation of fentanyl, acetylfentanyl, thiofentanyl, and acetylthiofentanyl using trichloroethoxycarbonylation chemistry in a high clay-content soil is presented. The soil was spiked separately with each fentanyl at two concentrations (1 and 10 μg/g) and their extraction accomplished using ethyl acetate and aqueous NH4 OH (pH ~ 11.4) with extraction recoveries ranging from ~56% to 82% for the high-concentration (10 μg/g) samples while ranging from ~68% to 83% for the low-concentration (1 μg/g) samples. After their extraction, residues containing each fentanyl were reacted with 2,2,2-trichloroethoxycarbonyl chloride (Troc-Cl) to generate two unique and predictable products from each opioid that can be used to retrospectively confirm their presence and identity using EI-GC-MS. The method's limit of detection (MDL/LOD) for Troc-norfentanyl and Troc-noracetylfentanyl were estimated to be 29.4 and 31.8 ng/mL in the organic extracts. In addition, the method's limit of quantitation for Troc-norfentanyl and Troc-noracetylfentanyl were determined to be 88.2 and 95.5 ng/mL, respectively. Collectively, the results presented herein strengthen the use of chloroformate chemistry as an additional chemical tool to confirm the presence of these highly toxic and lethal substances in the environment.

Practical benzylation of N,N-substituted ethanolamines related to chemical warfare agents for analysis and detection by electron ionization gas chromatography-mass spectrometry

The benzylation of three low molecular weight N,N-disubstituted ethanolamines related to chemical warfare agents (CWAs) to furnish derivatives with improved gas chromatography-mass spectrometry (GC-MS) profiles is described. Due to their low molecular weight and polar nature, N,N-disubstituted ethanolamines are notoriously difficult to detect by routine GC-MS analyses during Organisation for the Prohibition of Chemical Weapons (OPCW) proficiency tests (PTs), particularly in scenarios when they are present at low levels (~1-10 ppm) amidst more abundant interferences. Our studies revealed that the optimal derivatization conditions involved the treatment of the ethanolamine with benzyl bromide in the presence of an inorganic base (e.g., Na2 CO3 ) in dichloromethane at 55°C for 2 h. This optimized set of conditions was then successfully applied to the derivatization of N,N-dimethylethanolamine, N,N-diethylethanolamine and N,N-diisopropylethanolamine present separately at 1 and 10 μg/mL concentrations in a glycerol-rich matrix sample featured in the 48th OPCW PT. The benzylated derivatives of the three ethanolamines possessed retention times long enough to clear the massive glycerol-containing matrix interferences. The protocol herein is introduced as an alternative method for derivatization of these CWA and pharmaceutically important species and should find broad applicability in laboratories where routine forensic analysis is carried out.

Evaluation of polyanionic cyclodextrins as high affinity binding scaffolds for fentanyl

Cyclodextrins (CDs) have been previously shown to display modest equilibrium binding affinities (K_a ~ 100-200 M^-1) for the synthetic opioid analgesic fentanyl. In this work, we describe the synthesis of new CDs possessing extended thioalkylcarboxyl or thioalkylhydroxyl moieties and assess their binding affinity towards fentanyl hydrochloride. The optimal CD studied displays a remarkable affinity for the opioid of K_a = 66,500 M^-1, the largest value reported for such an inclusion complex to date. One dimensional ¹H Nuclear Magnetic Resonance (NMR) as well as Rotational Frame Overhauser Spectroscopy (2D-ROESY) experiments supported by molecular dynamics (MD) simulations suggest an unexpected binding behavior, with fentanyl able to bind the CD interior in one of two distinct orientations. Binding energies derived from the MD simulations work correlate strongly with NMR-derived affinities highlighting its utility as a predictive tool for CD candidate optimization. The performance of these host molecules portends their utility as platforms for medical countermeasures for opioid exposure, as biosensors, and in other forensic science applications.

Benzyl trichloroacetimidates as derivatizing agents for phosphonic acids related to nerve agents by EI-GC-MS during OPCW proficiency test scenarios

The use of benzyl trichloroacetimidates for the benzylation of phosphonic acid nerve agent markers under neutral, basic, and slightly acidic conditions is presented. The benzyl-derived phosphonic acids were detected and analyzed by Electron Ionization Gas Chromatography-Mass Spectrometry (EI-GC-MS). The phosphonic acids used in this work included ethyl-, cyclohexyl- and pinacolyl methylphosphonic acid, first pass hydrolysis products from the nerve agents ethyl N-2-diisopropylaminoethyl methylphosphonothiolate (VX), cyclosarin (GF) and soman (GD) respectively. Optimization of reaction parameters for the benzylation included reaction time and solvent, temperature and the effect of the absence or presence of catalytic acid. The optimized conditions for the derivatization of the phosphonic acids specifically for their benzylation, included neutral as well as catalytic acid (< 5 mol%) and benzyl 2,2,2-trichloroacetimidate in excess coupled to heating the mixture to 60 °C in acetonitrile for 4 h. While the neutral conditions for the method proved to be efficient for the preparation of the p-methoxybenzyl esters of the phosphonic acids, the acid-catalyzed process appeared to provide much lower yields of the products relative to its benzyl counterpart. The method's efficiency was tested in the successful derivatization and identification of pinacolyl methylphosphonic acid (PMPA) as its benzyl ester when present at a concentration of ~ 5 μg/g in a soil matrix featured in the Organisation for the Prohibition of Chemical Weapons (OPCW) 44th proficiency test (PT). Additionally, the protocol was used in the detection and identification of PMPA when spiked at ~ 10 μg/mL concentration in a fatty acid-rich liquid matrix featured during the 38^th OPCW-PT. The benzyl derivative of PMPA was partially corroborated with the instrument's internal NIST spectral library and the OPCW central analytical database (OCAD v.21_2019) but unambiguously identified through comparison with a synthesized authentic standard. The method's MDL (LOD) values for the benzyl and the p-methoxybenzyl pinacolyl methylphosphonic acids were determined to be 35 and 63 ng/mL respectively, while the method's Limit of Quantitation (LOQ) was determined to be 104 and 189 ng/mL respectively in the OPCW-PT soil matrix evaluated.

Analysis, identification and confirmation of synthetic opioids using chloroformate chemistry: Retrospective detection of fentanyl and acetylfentanyl in urine and plasma samples by EI-GC-MS and HR-LC-MS

Electron Impact Gas Chromatography-Mass Spectrometry (EI-GC-MS) and High Resolution Liquid Chromatography-Mass Spectrometry (HR-LC-MS) have been used in the analysis of products arising from the trichloroethoxycarbonylation of fentanyl and acetylfentanyl in urine and plasma matrices. The method involves the initial extraction of both synthetic opioids separately from the matrices followed by detection of the unique products that arise from their reaction with 2,2,2-trichloroethoxycarbonyl chloride (Troc-Cl), namely Troc-norfentanyl and Troc-noracetylfentanyl. The optimized protocol was successfully evaluated for its efficacy at detecting these species formed from fentanyl and acetylfentanyl when present at low and high levels in urine (fentanyl: 5 and 10 ng/mL and acetylfentanyl: 20 and 100 ng/mL) and plasma (fentanyl: 10 and 20 ng/mL and acetylfentanyl: 50 and 200 ng/mL), values that reflect levels reported in overdose victims. The HR-LC-MS method's LOQ (limit of quantitation) for the Troc-norfentanyl and Troc-noracetylfentanyl products was determined to be ~10 ng/mL for both species. Even though the superiority in the detection of these species by HR-LC-MS over EI-GC-MS, the latter method proved to be important in the detection of the second product from the reaction, namely 2-phenylethyl chloride that is crucial in the determination of the original opioid. This observation highlights the importance of using complimentary analytical techniques in the analysis of a sample, whether biological or environmental in nature. The method herein serves as a complementary, qualitative confirmation for the presence of a fentanyl in collected urine, plasma and by extension other biological samples amenable to the common extraction procedures described for opioid analysis. More importantly, the method's main strength comes from its ability to react with unknown fentanyls to yield products that can be not only detected by EI-GC-MS and HR-LC-MS but can then be used to retrospectively identify an unknown fentanyl.

Design, Synthesis, and Evaluation of Diazeniumdiolate-Based DNA Cross-Linking Agents Activatable by Glutathione S-Transferase

A novel class of O²-(2,4-dinitrophenyl)-1-[N,N-bis(2-substituted ethyl)amino]diazen-1-ium-1,2-diolates 4-6 were designed, synthesized, and biologically evaluated. The most active compound 6 caused significant DNA damage by releasing N,N-bis(2-TsO ethyl)amine and two molecules of nitric oxide (NO) after activation by GST/GSH in cancer cells, being more cytotoxic against three cancer cell lines than a well-known diazeniumdiolate-based anticancer agent JS-K, suggesting that the strategy has potential to extend to other O²-derived diazeniumdiolates to improve anticancer activity.

Novel quantum dots-carboxymethyl chitosan nanocomposite nitric oxide donors capable of detecting release of nitric oxide in situ

Nitric oxide (NO) donor compounds are primarily monofunctional in that they release NO under the requisite conditions. To detect the amount and duration of NO released, subsequent analysis methods are required. It would be advantageous if a NO donor compound could both release and detect NO at the same time. This would eliminate potential errors in the analysis. In this paper, novel cadmium telluride quantum dots (CdTe QD)-carboxymethyl chitosan (CMCS) nanocomposite NO donors, including both diazeniumdiolates and fluorescence probes, were fabricated by first synthesizing CdTe QD in CMCS aqueous solution and then reacting NO as well as ethyl bromide with the resultant CdTe QD-CMCS nanocomposites. Transmission electron microscopy, scanning electron microscopy and particle size analysis were used to examine the morphology and size distribution of the CdTe QD-CMCS nanocomposite NO donors. The donors are nanospheres with CdTe QD encapsulated and have dimensions of ~300 nm. Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and contact angle tests were employed to characterize the chemical structure of the donors, and the results also show that CdTe QD are well incorporated into CMCS, and many of them are close to the surface of the donors. The precursors of the donors exhibit a fluorescent effect, and the fluorescence can be quenched by NO. The donors can release NO spontaneously in a phosphate-buffered saline solution similar to a physiological environment, and can quantitatively detect the release of NO in situ based on fluorescence quenching of the donors by the NO.

Fifty years of diazeniumdiolate research. From laboratory curiosity to broad-spectrum biomedical advances

Here I show that a “pure” research project, seemingly totally lacking in practical application when it was first published, can years later spark a whole new scientific field with the potential to revolutionize clinical practice. A 1961 publication describing adducts of nitric oxide (NO) with certain nucleophiles attracted little notice at the time, but later work showing that the adducts could be hydrolyzed to regenerate the NO in bioactive form has provided the foundation for a host of biomedical applications. Crucial to the discovery of widely used tools for studying NO’s chemical biology as well as for the design of a variety of promising therapeutic advances has been the increasingly detailed understanding of the physicochemical properties of these “diazeniumdiolates” (also known as NONOates).

Novel β-galactosidase-specific O2-glycosylated diazeniumdiolate probes

Three β-galactosidase-specific nitric-oxide-releasing diazeniumdiolate conjugated probes were prepared as a prelude to studies of new potential molecular MRI imaging agents. A glycosylated derivative, 2e, designed to be trafficked across cell membranes, was also prepared. We report, in detail, the synthesis and characterization of these probes. In addition, the release of diazeniumdiolate from the probes by β-galactosidase-catalyzed hydrolysis was used to estimate their efficacy as serum-stable, specific NO donors.

Nitrogen-bound diazeniumdiolated amidines

In contrast to amidines bearing ionizable alpha-CH bonds, which react with nitric oxide (NO) to add diazeniumdiolate groups at their alpha-carbons, benzamidine forms an N-bound diazeniumdiolate that can be further derivatized at the other amidine nitrogen and/or the terminal oxygen to form caged NO compounds as potential NO prodrugs.

Nucleophilic reactivity of thiolate, hydroxide and phenolate ions towards a model O-arylated diazeniumdiolate prodrug in aqueous and cationic surfactant media

The kinetics of aromatic nucleophilic substitution of the nitric oxide generating diazeniumdiolate ion, DEA/NO, by thiols, (L-glutathione, L-cysteine, DL-homocysteine, 1-propanethiol, 2-mercaptoethanol and sodium thioglycolate) from the prodrug, DNP-DEA/NO, has been examined in aqueous solution and in solutions of cationic DOTAP vesicles. Second-order rate constants in buffered aqueous solutions (k(RS(-) ) = 3.48 - 30.9 M(-1)s(-1); 30 °C) gave a linear Brønsted plot (β(nuc) = 0.414 ± 0.068) consistent with rate-limiting S(N)Ar nucleophilic attack by thiolate ions. Cationic DOTAP vesicles catalyze the thiolysis reactions with rate enhancements between 11 and 486-fold in Tris-HCl buffered solutions at pH 7.4. The maximum rate increase was obtained with thioglycolate ion. Thiolysis data are compared to data for nucleophilic displacement by phenolate (k(PhO(-) ) = 0.114 M(-1)s(-1)) and hydroxide (k(OH(-) ) = 1.82 × 10(-2) M(-1)s(-1), 37 °C) ions. The base hydrolysis reaction is accelerated by CTAB micelles and DODAC vesicles with vesicles being ca 3-fold more effective as catalysts. Analysis of the data using pseudophase ion-exchange formalism implies that the rate enhancement of the thiolysis and base hydrolysis reactions is due primarily to reactant concentration in the surfactant pseudophase.

Tailored Synthesis of Nitric Oxide-Releasing Polyurethanes Using O-Protected Diazeniumdiolated Chain Extenders

Nitric oxide (NO) has been shown to exhibit significant anti-platelet activity and its release from polymer matrices has been already utilized to increase the biocompatibility of various blood-contacting devices. Herein, details of a new synthetic approach for preparing NO-releasing diazeniumdiolated polyurethanes (PU) are described. The method's utility is demonstrated by the incorporation of methoxymethyl- or sugar-protected pre-formed diazeniumdiolate moieties directly into chain extender diols which are then incorporated into the polyurethane backbone. This approach provides the ability to control the number of diazeniumdiolate groups incorporated into the polymer backbone, and hence the surface flux of NO that can ultimately be liberated from polymeric films prepared from the new PU materials. The method provides a means of covalently attaching diazeniumdiolate groups to polyurethanes in a form that resists dissociation of NO during processing but can be activated for spontaneous NO release via hydrolysis of the carbohydrate or methoxymethyl moieties under basic and acidic conditions, respectively.

Glycosylated PROLI/NO derivatives as nitric oxide prodrugs

GlcNAc-PROLI/NO prodrugs that are activated by N-acetylglucosaminidase to release nitric oxide (NO) are described. A classical acid-amine coupling is used to bifunctionalize these PROLI/NO prodrugs, which on activation generate up to 4 mol of NO, a peptide residue, and an N-acetylglucosamine residue. Many of the prodrugs synthesized are efficient sources of intracellular NO.

Synthesis, mechanistic studies, and anti-proliferative activity of glutathione/glutathione S-transferase-activated nitric oxide prodrugs

Nitric oxide (NO) prodrugs such as O(2)-(2,4-dinitrophenyl) 1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate (JS-K) are a growing class of promising NO-based therapeutics. Nitric oxide release from the anti-cancer lead compound, JS-K, is proposed to occur through a nucleophilic aromatic substitution by glutathione (GSH) catalyzed by glutathione S-transferase (GST) to form a diazeniumdiolate anion that spontaneously releases NO. In this study, a number of structural analogues of JS-K were synthesized and their chemical and biological properties were compared with those of JS-K. The homopiperazine analogue of JS-K showed anti-cancer activity that is comparable with that of JS-K but with a diminished reactivity towards both GSH and GSH/GST; both the aforementioned compounds displayed no cytotoxic activity towards normal renal epithelial cell line at concentrations where they significantly diminished the proliferation of a panel of renal cancer cell lines. These properties may prove advantageous in the further development of this class of nitric oxide prodrugs as cancer therapeutic agents.

Cell-permeable esters of diazeniumdiolate-based nitric oxide prodrugs

Although O(2)-(2,4-dinitrophenyl) derivatives of diazeniumdiolate-based nitric oxide (NO) prodrugs bearing a free carboxylic acid group were activated by glutathione to release NO, these compounds were poor sources of intracellular NO and showed diminished antiproliferative activity against human leukemia HL-60 cells. The carboxylic acid esters of these prodrugs, however, were found to be superior sources of intracellular NO and potent inhibitors of HL-60 cell proliferation.

Hydrolytic reactivity trends among potential prodrugs of the O2-glycosylated diazeniumdiolate family. Targeting nitric oxide to macrophages for antileishmanial activity

Glycosylated diazeniumdiolates of structure R 2NN(O)NO-R' (R' = a saccharide residue) are potential prodrugs of the nitric oxide (NO)-releasing but acid-sensitive R 2NN(O)NO (-) ion. Moreover, cleaving the acid-stable glycosides under alkaline conditions provides a convenient protecting group strategy for diazeniumdiolate ions. Here, we report comparative hydrolysis rate data for five representative glycosylated diazeniumdiolates at pH 14, 7.4, and 3.8-4.6 as background for further developing both the protecting group application and the ability to target NO pharmacologically to macrophages harboring intracellular pathogens. Confirming the potential in the latter application, adding R 2NN(O)NO-GlcNAc (where R 2N = diethylamino or pyrrolidin-l-yl and GlcNAc = N-acetylglucosamin-l-yl) to cultures of infected mouse macrophages that were deficient in inducible NO synthase caused rapid death of the intracellular protozoan parasite Leishmania major with no host cell toxicity.

Synthesis, nitric oxide release, and anti-leukemic activity of glutathione-activated nitric oxide prodrugs: Structural analogues of PABA/NO, an anti-cancer lead compound

Diazeniumdiolate anions and their prodrug forms are reliable sources of nitric oxide (NO) that have generated interest as promising therapeutic agents. A number of structural analogues of O(2)-(2,4-dinitro-5-(4-(N-methylamino)benzoyloxy)phenyl) 1-(N,N-dimethylamino)diazen-1-ium-1,2-diolate (PABA/NO), an anti-cancer lead compound that is designed to release NO upon activation by glutathione, were prepared. The nitric oxide release patterns of these O(2)-(2,4-dinitrophenyl) diazeniumdiolates in the presence of glutathione were tested and it was found that in the absence of competing pathways, these compounds release nearly quantitative amounts of NO. The ability of PABA/NO and its structural analogues to inhibit human leukemia cell proliferation was determined and it was found that compounds releasing elevated amounts of NO displayed superior cytotoxic effects.

V-PROLI/NO, a prodrug of the nitric oxide donor, PROLI/NO

The sensitivity to decomposition of the nitric oxide (NO) donor ion, 1-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (PROLI/NO), complicates direct electrophilic substitution to form useful prodrug derivatives. A modified general synthetic approach involving 1-[2-(hydroxymethyl)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate ion (structure A, above) was used to prepare several PROLI/NO prodrugs including the previously inaccessible O2-vinyl derivative, V-PROLI/NO. Metabolism of V-PROLI/NO by liver microsomes enriched in human cytochrome P450 isoforms was demonstrated.