Synthesis and Characterization of 3-Hydroxybupivacaine and Deuterated 3-Hydroxybupivacaine for Use in Equine Medication Regulation.
Abstract: Bupivacaine is a local anesthetic widely used in equine and human medicine. Use of bupivacaine in performance horses is regulated because its ability to block pain means that it can be misused for advantage in performance horses. In racing regulation, bupivacaine is classified by the Association of Racing Commissioners International (ARCI) as a Class 2 Penalty Class A Foreign substance, the detection of which can lead to significant penalties. In horses, bupivacaine is metabolized by Phase-I hydroxylation to yield 3-hydroxybupivacaine, which is then glucuronidated to yield the Phase-II metabolite bupivacaine-3-hydroxyglucuronide, which is excreted at relatively high concentrations in equine urine. Standard regulatory procedure during urinalysis is to perform an enzymatic hydrolysis, thereby enabling subsequent detection of 3-hydroxybupivacaine, the primary analyte used for bupivacaine regulation in urine samples from competition horses. We now report on the synthesis of 3-hydroxybupivacaine and deuterated 3-hydroxybupivacaine from piperidine-2-carboxylic acid in six successive steps with moderate yield. The compounds were characterized by H and C NMR and their purity ascertained by HPLC-MS. The deuterated bupivacaine and 3-hydroxybupivacaine were further confirmed by HRMS. The synthesis of these compounds provides certified reference standards and stable isotope-labeled internal standards for drug testing in competitive equine sports including horse racing.
© 2025 John Wiley & Sons Ltd.
Publication Date: 2025-03-04 PubMed ID: 40035476DOI: 10.1002/jlcr.4132Google Scholar: Lookup
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Summary
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Objective Overview
- This research paper presents the synthesis and characterization of 3-hydroxybupivacaine and its deuterated form, designed to aid in the regulation of bupivacaine use in competitive horses by providing accurate standards for drug testing.
Introduction and Background
- Bupivacaine Usage: Bupivacaine is a local anesthetic commonly used in both equine and human medicine for pain management.
- Regulations in Horse Racing: Because bupivacaine can mask pain, its use in racehorses is tightly regulated to prevent unfair advantage; it is classified by the Association of Racing Commissioners International (ARCI) as a Class 2 Penalty Class A Foreign substance.
- Metabolism in Horses: In horses, bupivacaine undergoes Phase-I metabolism resulting in 3-hydroxybupivacaine. In Phase-II, this metabolite is glucuronidated to form bupivacaine-3-hydroxyglucuronide, which is excreted in urine in substantial amounts.
- Drug Testing Challenges: Standard urinalysis includes enzymatic hydrolysis to break down glucuronides, enabling detection of 3-hydroxybupivacaine—the main target analyte for regulation checks.
Synthesis of 3-Hydroxybupivacaine and Deuterated Analog
- Starting Material: The synthesis began with piperidine-2-carboxylic acid, chosen as the precursor molecule.
- Synthetic Route: A six-step chemical synthesis was carried out to produce both 3-hydroxybupivacaine and its deuterated variant.
- Deuteration Purpose: The introduction of deuterium atoms allows creation of isotopically labeled versions used as internal standards in mass spectrometry-based drug testing, improving quantification accuracy.
- Yield: The synthesis provided moderate yields of both compounds, indicating an efficient and practical process for producing these standards.
Characterization and Verification
- NMR Analysis: Proton (¹H) and Carbon (¹³C) Nuclear Magnetic Resonance spectroscopy were utilized to confirm the chemical structures of the synthesized molecules.
- Purity Assessment: High-Performance Liquid Chromatography coupled with Mass Spectrometry (HPLC-MS) was employed to verify purity levels suitable for use as reference standards.
- High-Resolution Mass Spectrometry (HRMS): Further confirmation of the deuterated version and identity of the compounds was achieved through HRMS analysis, providing precise molecular weight and isotopic patterns.
Significance and Applications
- Regulatory Utility: These synthesized compounds serve as certified reference standards, enabling laboratories to accurately detect and measure bupivacaine metabolites in equine urine.
- Stable Isotope-Labeled Standards: The deuterated 3-hydroxybupivacaine is used as an internal standard during mass spectrometry, compensating for variability in sample preparation and instrument response, thus enhancing testing reliability.
- Impact on Equine Sports: This research supports fair competition in horse racing by improving the ability to monitor unauthorized use of pain-masking drugs effectively through precise biochemical testing.
Cite This Article
APA
Arojojoye AS, Holmes J, Buchart MP, Awuah SG, Eisenberg R, Fenger CK, Maylin GA, Tobin T.
(2025).
Synthesis and Characterization of 3-Hydroxybupivacaine and Deuterated 3-Hydroxybupivacaine for Use in Equine Medication Regulation.
J Labelled Comp Radiopharm, 68(3), e4132.
https://doi.org/10.1002/jlcr.4132 Publication
Researcher Affiliations
- Department of Chemistry, University of Kentucky, Lexington, Kentucky, USA.
- Department of Chemistry, University of Kentucky, Lexington, Kentucky, USA.
- The Department of Veterinary Science and the Maxwell H. Gluck Equine Research Center, Martin-Gatton College of Agriculture, Food and Environment and the Department of Toxicology and Cancer Biology, University of Kentucky, Lexington, Kentucky, USA.
- Department of Chemistry, University of Kentucky, Lexington, Kentucky, USA.
- Center for Pharmaceutical Research and Innovation, College of Pharmacy and Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington, Kentucky, USA.
- Frontier BioPharm, LLC, Richmond, Kentucky, USA.
- Equine Integrated Medicine, Georgetown, Kentucky, USA.
- New York Drug Testing and Research Program, Ithaca, New York, USA.
- The Department of Veterinary Science and the Maxwell H. Gluck Equine Research Center, Martin-Gatton College of Agriculture, Food and Environment and the Department of Toxicology and Cancer Biology, University of Kentucky, Lexington, Kentucky, USA.
MeSH Terms
- Horses
- Animals
- Bupivacaine / analogs & derivatives
- Bupivacaine / chemical synthesis
- Bupivacaine / chemistry
- Bupivacaine / urine
- Deuterium / chemistry
- Chemistry Techniques, Synthetic
- Doping in Sports
- Anesthetics, Local / chemical synthesis
- Anesthetics, Local / chemistry
Grant Funding
- KY014066 / National Institute of Food and Agriculture, U.S. Department of Agriculture, Hatch Program
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