Despropionyl p-Fluoro Fentanyl
[CAS# 122861-41-0]

Identification

• Classification: Organic raw materials >> Heterocyclic compound >> Piperidines
• Name: Despropionyl p-Fluoro Fentanyl
• Synonyms: N-(4-fluorophenyl)-1-(2-phenylethyl)piperidin-4-amine
• Molecular Formula: C₁₉H₂₃FN₂
• Molecular Weight: 298.40
• CAS Registry Number: 122861-41-0
• SMILES: C1CN(CCC1NC2=CC=C(C=C2)F)CCC3=CC=CC=C3

Properties

• Density: 1.1±0.1 g/cm³ Calc.^*
• Boiling point: 424.3±45.0 ºC 760 mmHg (Calc.)^*
• Flash point: 210.4±28.7 ºC (Calc.)^*
• Index of refraction: 1.592 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Discovory and Applicatios

Despropionyl p-fluoro fentanyl is a synthetic opioid and chemical intermediate structurally related to p-fluorofentanyl, a known analog of fentanyl. In this compound, the characteristic N-phenyl-N-\[1-(2-phenylethyl)piperidin-4-yl]propanamide core of fentanyl is modified by removal of the propionyl group, resulting in a primary amine at the nitrogen atom. This alteration significantly reduces the opioid receptor binding affinity of the molecule, rendering it pharmacologically inactive or minimally active compared to the fully acylated derivatives like fentanyl or p-fluorofentanyl.

The structure of despropionyl p-fluoro fentanyl retains the critical piperidine ring system and a fluorinated phenyl group at the para position, which is known to modulate receptor binding and metabolic behavior in fluorinated analogs. However, the absence of the acyl (propanoyl) group disrupts the compound’s ability to efficiently bind to the μ-opioid receptor, which requires a specific spatial orientation and lipophilic interaction provided by the full amide chain. This makes the despropionyl variant primarily relevant as a precursor in chemical synthesis rather than as a pharmacologically active compound.

Despropionyl p-fluoro fentanyl is often encountered in the context of illicit fentanyl manufacture, where it serves as a synthetic intermediate. In clandestine operations, this compound may be acylated through reaction with propionic anhydride or other acylating agents to produce the fully active fentanyl analog. This step is critical in the final stages of production, as it restores the pharmacophore necessary for high opioid activity.

The presence of despropionylated fentanyl derivatives in seized drug materials or synthetic laboratories has been used as forensic evidence of active or incomplete synthesis. In such cases, detection of intermediates like despropionyl p-fluoro fentanyl may indicate precursor diversion or unauthorized manufacturing. Analytical identification is typically achieved through techniques such as gas chromatography-mass spectrometry (GC-MS), liquid chromatography-tandem mass spectrometry (LC-MS/MS), or nuclear magnetic resonance (NMR) spectroscopy, which can accurately determine the structure and purity of the compound.

Despite its low or negligible pharmacological activity, despropionyl p-fluoro fentanyl is often subject to regulation under analog laws or precursor control statutes due to its clear role in the synthesis of controlled fentanyl analogs. This is especially relevant in jurisdictions that implement class-based or structure-based scheduling frameworks to prevent the synthesis and distribution of novel synthetic opioids.

Although it may appear in trace amounts in toxicological analyses, despropionyl p-fluoro fentanyl is not typically associated with overdose cases or clinical effects on its own. Its presence in biological samples is more often indicative of exposure to synthetic routes or contamination with synthetic intermediates. However, accidental administration through poorly purified street preparations cannot be ruled out entirely.

The continued emergence of fentanyl analogs and their precursors underscores the challenges in controlling synthetic opioid proliferation. Compounds such as despropionyl p-fluoro fentanyl, while not pharmacologically active, play a critical role in the synthesis pipeline and remain targets of chemical monitoring, regulatory enforcement, and forensic investigation.