Synthesis of (±)-6,6-[2H6ldimethyl-11-nor- Δ9-tetrahydrocannabivarin-9-carboxylic acid

Article abstract of DOI:10.1002/jlcr.586

Starting from divarinol (4) using previously published procedures, (±)-6, 6-[²H₆]Dimethyl-11-nor-Δ⁹THCV-9- carboxylic acid (3) was synthesized for use as an internal standard in GC/MS analysis of 11-nor-Δ⁹THCV-9

Full text of DOI:10.1002/jlcr.586

JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS
J Label Compd Radiopharm 2002; 45: 577–581.
Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jlcr.586
Research Article
Synthesis of ( Æ )-6,6-[2H6]dimethyl-11-nor-
D9-tetrahydrocannabivarin-9-carboxylic acid
Shixia Feng* and Mahmoud A. ElSohly
ElSohly Laboratories, Incorporated, 5 Industrial Park Drive, Oxford,
MS 38655, USA
Summary
Starting from divarinol (4) using previously published procedures, ( Æ )-6,
6-[2H6]Dimethyl-11-nor-D9THCV-9-carboxylic acid (3) was synthesized for use
as an internal standard in GC/MS analysis of 11-nor-D9THCV-9-carboxylic
acid (2). The detection of 2 distinguishes the use of marijuana from the
ingestion of Marinol1. Copyright # 2002 John Wiley & Sons, Ltd.
Key Words: ( Æ )-6,6-[2H6]dimethyl-11-nor-(D9-THCV-9-carboxylic acid; 11-
nor-D9-THCV-9-carboxylic acid; D9-THCV; marijuana; Marinol1
In the past several years, forensic toxicologists have been searching for a
scientifically acceptable way to distinguish the ingestion of Marinol1, a
prescription drug that contains synthetic D9-tetrahydrocannabinol (D9-
THC), from the use of marijuana, an illegal drug. We have previously
proposed1 that D9-tetrahydrocannabivarin (D9-THCV, 1), a C3 homo-
log of D9-THC and a natural component of cannabis plant, could be
used as a marker for the ingestion of marijuana (or a related product)
versus Marinol1 because 1 does not exist in Marinol1. Recently, we
reported that 11-nor-D9-tetrahydrocannabivarin-9-carboxylic acid (2) is
the major urinary metabolite of 1 through both in vitro metabolism and
clinical studies.2,3 It was concluded from these studies that the presence
*Correspondence to: S. Feng, ElSohly Laboratories, Inc 5 Industrial Park Drive, Oxford, MS
38655, USA. E-mail: shixiafeng@hotmail.com
Copyright # 2002 John Wiley & Sons, Ltd.
Received 12 December 2001
Accepted 27 February 2002

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S. FENG AND M. A. ELSOHLY
of 2 in a urine specimen would confirm that the subject must have used
marijuana or a related product. The deuterium labeled analog, 3, was
required for quantitative analysis by GC/MS. Because of this important
forensic application, in this communication, we wish to report the
synthesis of 3 starting from divarinol (4) using our previously published
procedure4 for the synthesis of d6-11-nor-9-carboxy-D9-THC, the C5
analog. Although the latter could also be used as an internal standard, 3
is superior in terms of analytical performance such as dynamic linearity
range of analysis (1–1000 ng/ml versus 2–50 ng/ml for urine specimens)
(see Figure 1).
As shown in Scheme 1, treatment of 4 with diethyl 2-acetylglutarate
and POCl3 gave the bicyclic coumarin 5 in 61% yield in several crops as
Figure 1.
Scheme 1.
Copyright # 2002 John Wiley & Sons, Ltd.
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SYNTHESIS OF CARBOXYLIC ACID
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a white solid: m.p. 161–1638C; EI-MS m/z: 318 (M+, 14%), 244
1
(100%); H-NMR (CDCl3, 300 MHz) d: 6.64 (d, J=1.1 Hz, 1 H), 6.46
(m, 2 H including one exchangeable), 4.15 (q, J=7.2 Hz, 2 H), 2.99
(t, J=7.5 Hz, 2 H), 2.66 (s, 3 H), 2.54 (m, 4 H), 1.61 (m, 2 H), 1.27
(t, J=7.1 Hz, 3 H), 0.93 (t, J=7.3 Hz, 3 H); 13C-NMR (CDCl3, 75 MHz)
d: 173.5, 162.1, 154.7, 153.5, 150.4, 146.7, 121.3, 111.9, 108.6, 107.8,
60.8, 37.6, 32.9, 23.7, 22.8, 19.2, 14.1, 13.7. Anal. Calculated for
C18H22O5: C, 67.92; H, 6.92. Found: C, 67.82; H, 7.33.
Cyclization of 5 by treatment with NaH in dry DMSO gave 6 in 52%
as a white crystalline solid: m.p. 238.5–2408C; EI-MS m/z (as TMS
derivative): 344 (M+,100%); 1H-NMR (CDCl3) d: 7.54 (s,1 H,
exchangeable), 6.74 (br s, 1 H), 6.57 (br s, 1 H), 4.20 (s, 2 H), 3.08
(t, J=7.1 Hz, 2 H), 2.70 (t, J=7.1 Hz, 2 H), 2.58 (t, J=7.7 Hz, 2 H), 1.65
(m, 2 H), 0.95 (t, J=7.4 Hz, 3 H); 13C-NMR (d6-DMSO, 75 MHz)
d: 207.7, 166.9, 160.1, 156.1, 155.9, 153.9, 146.6, 118.8, 106.0, 105.9,
43.3, 37.1, 36.9, 23.5, 23.0, 13.7. Anal. Calculated for C16H16O4: C,
70.59; H, 5.88. Found: C, 70.30; H, 5.97.
By treatment of 6 with ethylene glycol and p-toluenesulfonic acid in
benzene, the ketal 7 was obtained as a pale yellow solid (m.p.
157–1598C) in 90% yield and was identified by GC/MS: m/z (calculated
MW 316 for C18H20O5): 316 (M+,100%). Without further purification,
7 was treated with commercially available CD3MgI (Aldrich Chemical
Company, 99+ atom% D) followed by acidic hydrolysis to afford the
racemic a,b-unsaturated ketone 8 in 60% yield as a pale-yellow
crystalline solid: m.p. 220–2238C; EI-MS m/z: 292 (M+,65%), 274
(100%); 1H-NMR (CDCl3) d: 10.7 (s, 1 H, exchangeable), 8.04
(d, J=2.1 Hz, 1 H), 6.52 (d, J=1.5 Hz, 1 H), 6.24 (d, J=1.5 Hz, 1 H),
2.82 (m, 1 H), 2.66 (m, 1 H), 2.44–2.57 (m, 3 H), 2.19 (m, 1 H), 1.56–1.79
(m, 3 H), 0.93 (t, J=7.3 Hz, 3 H); 13C-NMR (CDCl3, 75 MHz) d: 204.0,
159.2, 156.4, 154.1, 149.3, 122.2, 109.4, 108.9, 105.9, 77.1, 44.7, 37.9,
36.4, 24.3, 23.8, 13.9. Anal. Calculated for C18H16D6O3: C, 73.89; H,
7.81. Found: C, 73.45; H, 7.62.
Birch reduction of 8 gave trans-ketone 9 as a white solid in 60% yield:
1
m.p. 171–1728C; EI-MS m/z: 294 (M+, 100%); H-NMR (CDCl3) d:
8.17 (s, 1 H, exchangeable), 6.32 (d, J=1.5 Hz, 1 H), 6.23 (d, J=1.5 Hz,
1 H), 4.20 (ddd, J=2.4, 3.0, and 15.1 Hz, 1 H), 2.89 (m, 1 H), 2.63 (m,
1 H), 2.51 (m, 1 H), 2.43 (t, J=7.2 Hz, 2 H), 2.14 (m, 2 H), 1.97 (ddd,
J=2.6, 12.1, and 14.2 Hz, 1 H), 1.52–1.63 (m, 3 H), 0.92 (t, J=7.3 Hz,
3 H); 13C-NMR (CDCl3, 75 MHz) d: 215.6, 155.5, 154.4, 143.3, 108.9,
107.8 (C-2 and C-4), 76.3, 47.2, 44.7, 40.8, 37.6, 34.7, 26.9, 24.1, 13.9.
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Anal. Calculated for C18H18D6O3: C, 73.45; H, 8.46. Found: C, 73.77;
H, 8.20.
Finally, 9 was converted to 3 by a Shapiro reaction as reported
previously4 in 54% yield as a crude product which contained ca. 84% of
the desired D9-isomer. Recrystallization twice from ether–hexane gave
pure 3 as a white solid (99% by HPLC, tr=4.48 min using a
Microsorb1 C18 column, 3.9 Â 100 mm, CH3CN–H2O–HOAc 60:40:
0.05 at 1.0 ml/min, UV detector at 228 nm). The 1H-NMR spectrum was
identical to the previously reported spectrum of 2,2 the unlabeled analog
of 3, except for the total absence of the signals for the gem-dimethyl
protons at the C-6 position. Specifically, the two singlets at d 1.44 (3 H)
Figure 2. Comparison of EI-MS spectra of 3 (top) and 2 (bottom) as TBDMS
derivatives
Copyright # 2002 John Wiley & Sons, Ltd.
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SYNTHESIS OF CARBOXYLIC ACID
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and 1.12 (3 H) disappeared, indicating full deuteration of these methyl
groups. The structure of 3 was further confirmed by comparing the EI-
MS spectra of TBDMS derivatives of 3 (M+=550) and 2 (M+=544)
obtained by heating with N-(tert-butyldimethylsilyl)-N-methyltrifluor-
oacetamide containing 1% TBDMSCI (Figure 2). Our published data
show3 that 3 is a superior internal standard to its C5 analog in GC-MS
analysis of 2.
References
1. ElSohly MA, Feng S, Murphy TP, et al. J Anal Toxicol 1999; 23: 222–224.
2. ElSohly MA, Feng S, Murphy TP, et al. J Anal Toxicol 2001; 25: 476–480.
3. ElSohly MA, deWit H, Wachtel SR, Feng S, Murphy TP. J Anal Toxicol
2001; 25: 565–571.
4. Feng S, ElSohly MA. J Label Compd Radiopharm 2000; 43: 655–662.
Copyright # 2002 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2002; 45: 577–581