Post on 01-Oct-2020
transcript
Analytical Challenges in Identifying Structural Isomers of Drugs
JOHN GOODPASTER
DONNA ROSKOWSKI
ZACK ROBERSON
Forensic Chemistry ReduxIdentification
◦ Qualitative: Given an unknown, determine the presence or absence of a particular chemical species in the sample
◦ Quantitative: Given an unknown, determine the amount of a particular chemical species in the sample
◦ Keys to success are sensitivity, selectivity and specificity
Comparison◦ Compare the physical and chemical
characteristics of a questioned sample (Q) to the of a known sample (K)
◦ Provides circumstantial links between a suspect, victim and crime scene
◦ Keys to success are a large and diverse population of items, highly discerning analytical methods, and statistical analysis of the results
“cat and mouse synthetic drugs” (185,000 results on Google)
Analytical ChallengesThe analysis of synthetic drugs (cannabinoids, cathinones, etc.) is inherently more challenging because:
◦ The analysis is more complex and time consuming
◦ Complex mixtures are routine
◦ Closely related substances can appear very similar during analysis
◦ Reference materials may not be available
Drug OriginsNatural
◦ Marijuana
◦ Cocaine
Semi-synthetic◦ Heroin (from morphine)
◦ LSD (from lysergic acid)
Synthetic◦ Methamphetamine
◦ MDMA (“Ecstasy”)
Synthetic Drugs of Concern:◦ Cannabinoids (“Synthetic Marijuana”)
◦ Examples: “Spice”, “K2”
◦ A wide variety of compounds that target the cannabinoid recepters in the brain (CB! And CB2)
◦ Cathinones (“Bath Salts”)◦ Methcathinone
◦ 4-MET
◦ Opiates◦ fentanyl
◦ carfentanyl
◦ acetylfentanyl
◦ Psychedelic Hallucinogens◦ 25I-NOBMe
◦ 2C-I
◦ 25I-NBOH
IsomersChemically, one of two or more compounds having the same molecular formula (i.e., empirical formula), but different structures.
Structural Isomers (Constitutional Isomers)◦ Skeletal: Differ in 1o, 2o, or 3o configurations of the same functional group
◦ Positional (Regioisomers): Differ only in the location of a particular functional group
◦ Functional: Differ in functional groups (e.g., ethanol and dimethyl ether)
Stereoisomers (Spatial Isomers)◦ Diastereomers (non-superimposable, non-mirror images)
◦ Enantiomers (non-superimposable, mirror images)
Positional IsomersJWH-302
C22H25NO2
MW = 335.439 g/molNOT FEDERALLY SCHEDULED*
ANALGESIC (LESS POTENT)
JWH-250C22H25NO2
MW = 335.439 g/molDEA SCHEDULE I
ANALGESIC
* https://www.deadiversion.usdoj.gov/schedules/orangebook/c_cs_alpha.pdf
“meta”
“ortho”
Positional Isomers3,4-MDMAC11H15NO2
MW = 193.25 g/molDEA SCHEDULE I
PSYCHEDELIC / STIMULANT
2,3-MDMAC11H15NO2
MW = 193.25 g/molNOT SCHEDULED*
WEAKER EFFECTS ON SEROTONIN
* https://www.deadiversion.usdoj.gov/schedules/orangebook/c_cs_alpha.pdf
What Will It Take to “Catch the Mouse”?SCIENTIFIC INNOVATION
Increase the SPECIFICITY of analytical determinations
Develop instrumental methods that can separate and identify drugs, including as many isomers as possible.
STRUCTURE-BASED CONTROLS
Pass laws that control a “family” of compounds that is sufficiently specific to target the drugs of abuse yet avoid controlling everything
Requires direct participation of chemists in writing legislation
Scientific Innovation
Specificity / Discriminating PowerSpecificity is the ability of an analytical technique to unambiguously identify an analyte.
Highly specific methods can distinguish very subtle differences between analytes, including structural isomers.
Hierarchy of Results:1. Chemical Structure
(confirmatory)
2. Compound Class
3. Functional Groups (presumptive)
Confirmatory data must be reviewable:
◦ Printed spectra
◦ Printed chromatograms
SWGDRUG Classifications
Goodpaster Group ResearchAutomated Derivatization and Identification of Controlled Substances via Total Vaporization Solid Phase Microextraction (TV-SPME) and Gas Chromatography/Mass Spectrometry (GC/MS) (NIJ Award 2015-DN-BX-K058)
Goal: Developing SPME-based GC/MS methods for thermally unstable drugs “as is” or by forming derivatives on-fiber
Coupling Gas Chromatography (GC) and Vacuum Ultraviolet (VUV) Spectroscopy for Forensic Applications (NIJ Award 2017-R2-CX-0018)
Goals: Assessing the sensitivity, selectivity and specificity of a GC/VUV system with a focus on differentiating structural isomers of controlled substances
GC/VUV analysis
0.0
0.2
0.4
0.6
0.8
1.0
0 2 4 6 8
AB
SOR
BA
NC
E
RETENTION TIME (min)
125 - 160 nm 140 - 160 nm 170 - 200 nm 125 - 240 nm
Methamphetamine (C-I)Phentermine (C-IV)
Methcathinone (C-I)
Pseudoephedrine (BTC)GC Column: Agilent HP-5 30m x 0.32mm x 0.25µmInjector Mode: Splitless - 0.5 min, 250°C, 1µLGC Oven: 50°C, hold 1 min, 15°C/min to 150°CTransfer Line and Flow Cell: 275°CColumn Flow Rate: 5 mL/min H2
Makeup Gas Pressure: 0.25 PSI N2
EI Mass Spectra (Category “A”)
58 58
9191
91
5858
91
(M-15)134
Formula: C10H15N
Molecular weight: 149.2328
(M-15)134
Formula: C10H15N
Molecular weight: 149.2328
These two compounds are structural (i.e., skeletal) isomers
VUV Spectra (130 – 240 nm)
0
0.2
0.4
0.6
0.8
1
130 150 170 190 210 230NO
RM
ALI
ZED
AB
SOR
BA
NC
E
WAVELENGTH (nm)
(±)-Methamphetamine Phentermine
These two compounds are structural (i.e., skeletal) isomers
EI Mass Spectra (Category “A”)
58
91
58
91
134
•Formula: C10H13NO
•Molecular weight: 163.2163
Formula: C10H15NO
Molecular weight: 165.2322
58 58
7777105 105, 106
587758
77
These two compounds are NOT isomers
105
VUV Spectra (130 – 240 nm)
0
0.2
0.4
0.6
0.8
1
130 155 180 205 230
NO
RM
ALI
ZED
AB
SOR
BA
NC
E
WAVELENGTH (nm)
S(-)-Methcathinone HCl R,R(-)-Pseudoephedrine
These two compounds are NOT isomers
Measured Characteristics of the VUV Detector
1. Wavelength Accuracy: Meets expected specifications of ±2 nm
2. Wavelength Repeatability: Exceeds expected specifications of ±1 nm, observed ±0.5 nm
3. Baseline Noise Level (Root Mean Square Noise): Exceeds expectations of 0.001 A.U., observed 0.0005 A.U.
4. Baseline Stability: Meets expected specification of < 0.003 A.U. h-1
5. Assessed sensitivity, detection limit and linear range using cinnamaldehyde as a model compound
Chemical formula C9H8O
Molar mass 132.16 g/mol
Sensitivity, Linearity, Detection Limit
Linear range: 3 – 750 ppm
y = 0.0116x - 0.0014R² = 0.9998
0.01
0.1
1
10
1 10 100 1000
SUM
MED
AB
SOR
BA
NC
E AT
MA
XIM
UM
W
AV
ELEN
GTH
CONCENTRATION (ppm)
y = 0.8931x + 2.1793R² = 0.9047
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
-2.0 -1.0 0.0 1.0 2.0
log(
S/N
)
log(S) (peak area)
Phenylethylamine VUV Reference Spectra Acquired Thus Far (120 – 430 nm)
1. N-benzeneethanamine (C8H11N, 121.2 g/mol)
2. Amphetamine (C9H13N, 135.2 g/mol)
3. Methamphetamine (C10H15N, 149.2 g/mol)
4. Ephedrine (C10H15NO, 165.2 g/mol)
5. Pseudoephedrine (C10H15NO, 165.2 g/mol)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
120 220 320 420
NO
RM
ALI
ZED
AB
SOR
BA
NC
E
WAVELENGTH (nm)
Amphetamine Methamphetamine
N-benzeneethanamine Ephedrine
Pseudoephedrine
drug RN Rα Rβ R2 R3 R4 R5 R6
Benzeneethanamine H H H H H H H H
Amphetamine* CH3 H H H H H H H
Methamphetamine CH3 CH3 H H H H H H
Ephedrine CH3 CH3 OH H H H H H
pseudoephedrine CH3 CH3 OH H H H H H
The Role of Multi-variate Statistics
Sauzier, G.; Reichard, E.; Lewis, S.; van Bronswiijk, W., Goodpaster, J.V. Improving the confidence of “questioned versus
known” fiber comparisons using microspectrophotometry and chemometrics. Forensic Chemistry 2016; 2:15-21
Structure-Based Controls
Structure-Based Control of Synthetic DrugsControls the base molecule with certain allowable substitutions
Controls a large number of substances◦ Including their isomers and analogs
◦ Getting more difficult and expensive to make things that are not included.
◦ New drugs emerging to get around the law
What About Skeletal + Positional + Functional Isomers?
4-Methylethcathinone (4-MET)C12H17NO
MW = 191.27DEA SCHEDULE I
STIMULANT
N,N-Diethyl-meta-toluamide (DEET)C12H17NO
MW = 191.27NOT SCHEDULED
INSECT REPELLANT
meta-, 3o amide para-, ketone + 2o amine
Synthetic Cannabinoids (Included Structures)Any compound structurally derived from 3-(1-naphthoyl)indole or 1H-indol-3-yl-(1-naphthyl)methane by substitution at the nitrogen atom of the indole ring by alkyl, haloalkyl, alkenyl, cycloalkylmethyl, cycloalkylethyl, 1-(N-methyl-2-piperidinyl)methyl or 2-(4-morpholinyl)ethyl group, whether or not further substituted in the indole ring to any extent and whether or not substituted in the naphthyl ring to any extent.
Synthetic Cannabinoids Base StructuresNaphthoylindoles
◦ [3-(1-naphthoyl)indole]
Napthoylpyrroles◦ [3-(1-naphthoyl) pyrrole]
Naphthylmethylindenes◦ [1-(1-naphthylmethyl)indene]
Phenylacetylindoles◦ [3-phenylacetylindole ]
HydroxyCyclohexylphenols◦ [2-(3-hydroxycyclohexyl)phenol ]
Benzoylindoles◦ [3-(benzoyl)indole ]
As of June 2018, the following JWH compounds are controlled (DEA Schedule I): JWH-018, JWH-019, JWH-073, JWH-081, JWH-122, JWH-200, JWH-203, JWH-250, JWH-398 (these compounds are either naphthoylindoles or phenylacetylindoles)
Naphthylindole (JWH-018)
napthyl ring
indole ring
alkyl substituent
CathinonesSubstituted 2-aminopropan-1-ones
Aka “Bath Salts”
Same type of wording in the law◦ Contains the base structure
◦ Included modifications, or additions to the base structure
CathinoneC9H11NO
MW = 149.1897DEA SCHEDULE I
STIMULANT
Substituted Cathinones
Methylenedioxypyrovalerone (MDPV)
SummaryThe “go to” analytical technique of GC/MS is sensitive, selective and specific, but not for ALL compounds
The issue of dominant fragmentation mechanisms means that several isomeric and/or closely related compounds cannot be distinguished by GC/MS
GC/VUV shows promise for discriminating drugs
Synthetic drug law controls a large number of substances, but not ALL of them.
Ultimately, the analysis and identification of a specific isomer may be difficult.