Fast & fluorinated – Development and validation of a rapid benchtop NMR approach and other routine screening methods for the detection and quantification of synthesized fluorofentanyl derivatives

Assessment of the antinociceptive, respiratory-depressant, and reinforcing effects of the low pKa fluorinated fentanyl analogs, FF3 and NFEPP

RATIONALE

Recent studies report that fentanyl analogs with relatively low pKa values produce antinociception in rodents without other mu opioid-typical side effects due to the restriction of their activity to injured tissue with relatively low pH values. However, it is unclear if and to what degree these compounds may produce mu opioid-typical side effects (respiratory depression, reinforcing effects) at doses higher than those required to produce antinociception.

OBJECTIVES

The present study compared the inflammatory antinociceptive, respiratory-depressant, and reinforcing effects of fentanyl and two analogs of intermediate (FF3) and low (NFEPP) pKa values in terms of potency and efficacy in male and female Sprague-Dawley rats.

METHODS

Nociception was produced by administration of Complete Freund's Adjuvant into the hind paw of subjects, and antinociception was measured using an electronic Von Frey test. Respiratory depression was measured using whole-body plethysmography. Reinforcing effects were measured in self-administration using a progressive-ratio schedule of reinforcement. The dose ranges tested for each drug encompassed no effect to maximal effects.

RESULTS

All compounds produced full effects in all measures but varied in potency. FF3 and fentanyl were equipotent in antinociception and self-administration, but FF3 was less potent than fentanyl in respiratory depression. NFEPP was less potent than fentanyl in every measure. The magnitude of potency difference between antinociception and other effects was greater for FF3 than for NFEPP or fentanyl, indicating that FF3 had the widest margin of safety when relating antinociception to respiratory-depressant and reinforcing effects.

CONCLUSIONS

Low pKa fentanyl analogs possess potential as safer analgesics, but determining the optimal degree of difference for pKa relative to fentanyl will require further study due to some differences between the current results and findings from prior work with these analogs.

Enhancing 19F Benchtop NMR Spectroscopy by Combining para-Hydrogen Hyperpolarization and Multiplet Refocusing

Benchtop NMR spectrometers provide a promising alternative to high-field NMR for applications that are limited by instrument size and/or cost. ¹⁹F benchtop NMR is attractive due to the larger chemical shift range of ¹⁹F relative to ¹H and the lack of background signal in most applications. However, practical applications of benchtop ¹⁹F NMR are limited by its low sensitivity due to the relatively weak field strengths of benchtop NMR spectrometers. Here we present a sensitivity-enhancement strategy that combines SABRE (Signal Amplification By Reversible Exchange) hyperpolarization with the multiplet refocusing method SHARPER (Sensitive, Homogeneous, And Resolved PEaks in Real time). When applied to a range of fluoropyridines, SABRE-SHARPER achieves overall signal enhancements of up to 5700-fold through the combined effects of hyperpolarization and line-narrowing. This approach can be generalized to the analysis of mixtures through the use of a selective variant of the SHARPER sequence, selSHARPER. The ability of SABRE-selSHARPER to simultaneously boost sensitivity and discriminate between two components of a mixture is demonstrated, where selectivity is achieved through a combination of selective excitation and the choice of polarization transfer field during the SABRE step.

The application of 19F NMR spectroscopy for the analysis of fluorinated new psychoactive substances (NPS)

In this study, fluorine-19 nuclear magnetic resonance spectroscopy (¹⁹F NMR) served as a highly specific tool for identification of fluorinated new psychoactive substances (NPS) as well as a suitable analytical method for the accurate quantification of fluorinated NPS in different seized samples. In the first part of the study, ¹⁹F NMR spectroscopy of a number of different fluorinated NPS, including 51 synthetic cannabinoids, 8 synthetic cathinones, 7 phenethylamines, 8 fentanyl analogues, and 9 other types of compounds was conducted. The chemical shifts and multiplet of the primary fluorides (RCH₂F), fluorobenzenes (ortho-ArF, meta-ArF, and para-ArF), and trifluoromethylbenzenes (ArCF₃) were discussed in detail to illustrate the role of ¹⁹F signals as special fingerprints in assisting the structure identification of fluorine-containing NPS. To the best of our knowledge, this study is the largest evaluation of fluorinated NPS compounds by ¹⁹F NMR. The second part of this study dealt with the problems encountered in the ¹⁹F quantification procedure and the criteria to be considered for successful quantification by ¹⁹F NMR. General high field (HF)- and low field (LF)- ¹⁹F qNMR methods for the quantification of fluorinated NPS were established after the thorough discussion of NMR spectrum acquisition and processing parameters such as: transmitter frequency offset (O1P), spin-lattice relaxation time (T₁), and different baseline correction methods. The limit of quantifications (LOQs) for HF-¹⁹F qNMR varied between 0.1 mg/mL and 0.2 mg/mL, and for LF-¹⁹F qNMR varied between 1.0 mg/mL and 2.0 mg/mL. The limit of detections (LODs) for HF-¹⁹F qNMR varied between 0.03 mg/mL and 0.06 mg/mL, and for LF-¹⁹F qNMR varied between 0.3 mg/mL and 0.6 mg/mL. Finally, the developed methods were applied for the quantification of fluorinated-NPS in seventeen herbal blends, e-liquid, tablet, and powder NPS seizures.

Toxicological Analysis of Fluorofentanyl Isomers in Postmortem Blood

The opioid epidemic continues to evolve in the United States (US) with fentanyl the most prevalent synthetic opioid in fatal drug overdoses. Following the scheduling of fentanyl’s core structure in 2018, there was a notable decline in the prevalence of fentanyl analogs in decedents; however, fluorofentanyl began being reported in casework in the winter of 2020. Fluorofentanyl has three positional isomers (para-fluorofentanyl, ortho-fluorofentanyl, and meta-fluorofentanyl) with the most predominant isomer that has recently emerged in the US being para-fluorofentanyl. The goal of this study was to identify para-fluorofentanyl in postmortem cases between October 2020 and April 2021. Urine and blood were extracted using UCT Clean Screen® extraction columns then screened using an Agilent 1290 Infinity liquid chromatograph (LC) coupled to an Agilent 6545 accurate mass time-of-flight mass spectrometer (TOF-MS) and quantified using an Agilent 6890N GC system coupled with an Agilent 5973 MS. The limit of quantitation (LOQ) for fentanyl, acetyl fentanyl, butyryl fentanyl, para-fluorofentanyl, ortho-fluorofentanyl, and meta-fluorofentanyl was 2.5 ng/mL. The screening method could not differentiate the three positional isomers of fluorofentanyl. Suspected overdose cases (n=270) received from October 2020 through March 2021 from four Medical Examiner Districts in the state of Florida were analyzed for the presence of fluorofentanyl. The LC–QTOF-MS screen yielded 27 decedents positive for fluorofentanyl with a majority being Caucasian (93%) and male (70%) with ages ranging from 27 to 63 years old. Analysis of the blood and urine by GC–MS yielded fourteen decedents positive for para-fluorofentanyl, nine of which were positive in the blood. The blood concentrations (n=9) for para-fluorofentanyl ranged from <LOQ to 30 ng/mL, with an average and median of 9.87 ng/mL and 5.5 ng/mL, respectively. Para-fluorofentanyl was identified in the blood of 33% of the cases, and the concentration of para-fluorofentanyl was generally higher than previously reported.

Quantitative and convenient real-time reaction monitoring using stopped-flow benchtop NMR

We present a stopped-flow benchtop NMR system (composed of commercially available hardware components) that allows for quantitative reaction monitoring to be completed with relative ease, even with experimentally complex reaction systems.

Recent Applications of Benchtop Nuclear Magnetic Resonance Spectroscopy

Benchtop nuclear magnetic resonance (NMR) spectroscopy uses small permanent magnets to generate magnetic fields and therefore offers the advantages of operational simplicity and reasonable cost, presenting a viable alternative to high-field NMR spectroscopy. In particular, the use of benchtop NMR spectroscopy for rapid in-field analysis, e.g., for quality control or forensic science purposes, has attracted considerable attention. As benchtop NMR spectrometers are sufficiently compact to be operated in a fume hood, they can be efficiently used for real-time reaction and process monitoring. This review introduces the recent applications of benchtop NMR spectroscopy in diverse fields, including food science, pharmaceuticals, process and reaction monitoring, metabolomics, and polymer materials.