Analytical characterization and pharmacological evaluation of the new psychoactive substance 4-fluoromethylphenidate (4F-MPH) and differentiation between the (±)-threo and (±)-erythro diastereomers

Abstract

Misuse of (±)-threo-methylphenidate (methyl-2-phenyl-2-(piperidin-2-yl)acetate; Ritalin®; MPH) has long been acknowledged, but the appearance of MPH analogs in the form of 'research chemicals' has only emerged in more recent years. 4-Fluoromethylphenidate (4F-MPH) is one of these recent examples. This study presents the identification and analytical characterization of two powdered 4F-MPH products that were obtained from an online vendor in 2015. Interestingly, the products appeared to have originated from two distinct batches given that one product consisted of (±)-threo-4F-MPH isomers whereas the second sample consisted of a mixture of (±)-threo and (±)-erythro 4F-MPH. Monoamine transporter studies using rat brain synaptosomes revealed that the biological activity of the 4F-MPH mixture resided with the (±)-threo and not the (±)-erythro isomers based on higher potencies determined for blockage of dopamine uptake (IC₅₀ 4F-MPH_mixture = 66 nM vs. IC₅₀ (±)-threo = 61 nM vs. IC₅₀ (±)-erythro = 8,528 nM) and norepinephrine uptake (IC₅₀ 4F-MPH_mixture = 45 nM vs. (±)-threo = 31 nM vs. IC₅₀ (±)-erythro = 3,779 nM). In comparison, MPH was three times less potent than (±)-threo-4F-MPH at the dopamine transporter (IC₅₀ = 131 nM) and around 2.5 times less potent at the norepinephrine transporter (IC₅₀ = 83 nM). Both substances were catecholamine selective with IC₅₀ values of 8,805 nM and >10,000 nM for (±)-threo-4F-MPH and MPH at the serotonin transporter. These findings suggest that the psychostimulant properties of (±)-threo-4F-MPH might be more potent in humans than MPH. Copyright © 2017 John Wiley & Sons, Ltd.

Keywords: 4-fluoromethylphenidate; in vitro; monoamine transporters; new psychoactive substances; psychostimulants; methylphenidate.

Figure 1

Chemical structures of methy1phenidate, (±)-threo-racemate and (±)-erythro-racemate of 4-fluoromethylphenidate

Figure 2

A–E: Gas chromatographic (GC) separation obtained for the isolated (±)-threo-racemate, isolated (±)-erythro-racemate of 4F-MPH and vendor samples. F–G: Electron ionization mass spectra obtained for the isolated (±)-threo- and (±)-erythro- racemates of 4F-MPH. H: Proposed fragmentation pattern for both racemates.

Figure 3

A–E: HPLC separation achieved for the isolated (±)-threo-racemate, isolated (±)-erythro-racemate and vendor samples of 4F-MPH. F–G: Product ion spectra obtained for isolated (±)-threo- and (±)-erythro- racemates of 4F-MPH obtained from in-source collision induced dissociation at increased fraqmentor voltaqe (110 V). H: Proposed fragments for both racemates.

Figure 4

¹H NMF spectra obtained for the mixed 4F-MPH product the isolated (±)-threo-racemate and isolated (±)-erythro-racemates of 4F-MPH.

Figure 5

A: Structure of (±)-erythro and B: (±)-threo salts of 4F-MPH. Atomic displacement parameters shown at 50% probability and hydrogen atoms drawn as spheres of arbitrary radius. In B, only the major disordered fluorophenyl moiety is shown.

Figure 6

Effects of 4-fluoromethylphenidate isomers (4F-MPH) and comparison with methylphenidate (MPH) on inhibition of uptake at DAT, NET, and SERT in rat brain synaptosomes. Synaptosomes were incubated with different concentrations of test drugs in the presence of 5 nM [³H]dopamine (A, for DAT), 10 nM [³H]norepinephrine (B, for NET), or 5 nM [³H]serotonin (C, for SERT). Data are percentage of [³H] transmitter uptake expressed as mean ± s.e.m, for n = 3 experiments.