Abstract
The objective of the present work is to demonstrate a rational way to prepare selective sorbents able to extract simultaneously several structural analogs. For this purpose the binding specificity of two hexapeptides computationally designed (VYWLVW and YYIGGF) versus four synthetic cannabinoids Naphthalen-1-yl-(1-pentylindol-3-yl)methanone (JWH 018), naphthalen-1-yl-(1-butylindol-3-yl)methanone (JWH 073), (R)-(1-((1-methylpiperidin-2-yl)methyl)-1H-indol-3-yl)(naphthalen-1-yl)methanone (AM 1220) and (R)-(+)-[2,3-Dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-napthalenylmethanone (WIN 55) was computationally studied and then experimentally tested by solid-phase extraction (SPE) clean-up and ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) analysis. The two peptides were chosen using a semi combinatorial virtual technique by generating 4 cycles of peptide libraries (around 2.3×104 elements). To select the two peptides, the simulated binding scores between synthetic cannabinoids and peptides was used by maximizing the recognition properties of amino acid motif between the two JWH and the other synthetic cannabinoids. In particular, the peptide YYIGGF, having also affinity for AM 120, was selected as control because it was the only one without tryptophan residues within the best peptides obtained from simulation. Experimentally, the two hexapeptides were tested as SPE sorbent using nanomolar solutions of the four drugs. After optimization of best retentions the binding constants were calculated by loading synthetic cannabinoids solutions at different concentrations. The results indicated a strong interaction between hexapeptide VYWLVW and JWH 018 (15.58±2.03×106M–1), 3-fold and 40-fold larger compared to the analog JWH 073 and both AM 1220 and the WIN 55. Similar trend was observed for the hexapeptide YYIGGF but the binding constants were at least three times lower highlighting the key role of the tryptophan. To demonstrate the hexapeptides specific interaction with only synthetic cannabinoids, a cross-reactivity study was carried out using other drugs (cocaine, morphine, phencyclidine and methamphetamine) in the same SPE condition. Finally the practical utility of these peptide modified sorbent materials was further demonstrated by detecting the synthetic cannabinoids in real samples using hair matrix.
Highlights
In the last years new synthetic cannabinoids were extensively studied in forensic science [1,2,3,4,5]
In this work we investigated the thermodynamic binding properties versus synthetic cannabinoids of hexapeptides used as stationary phase in solid-phase extraction (SPE)
Avoiding very large procedures like combinatorial work, we obtained a focused peptides with high affinity properties vs the two JWH synthetic cannabinoids
Summary
In the last years new synthetic cannabinoids were extensively studied in forensic science [1,2,3,4,5] The importance of this type of drugs is well described by different works reporting that these new substances with cannabis-like effects are more and more frequently observed in the drug scene [6,7,8,9]. New molecular recognition sorbents were proposed in SPE as aptamers, peptides and molecular imprinted polymers (MIPs) [18,19,20,21]. These new affinity media used in selective extraction, have similar performances of antibodies by overcoming several drawbacks as cost, variability in binding properties between lot-to-lot and chemical degradation [22,23]. The introduction of predictive computational models, instead of trial and error procedures, offers advantages in minimizing experimental problems like non-specific recognition, reagent stability and costs
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