An improved synthesis of (±)-N#-nitrosonornicotine 5#-acetate

Full text of DOI:10.1021/jo9000417

SCHEME 1. Metabolic Activation of NNN to NNN-5′-OH
and the Proposed Route to NNN-5′-OAc, a Precursor for
NNN-5′-OH, from Isomyosmine
An Improved Synthesis of
(()-N′-Nitrosonornicotine 5′-Acetate
Gwendolyn A. Marriner and Sean M. Kerwin*
College of Pharmacy and Department of Chemistry and
Biochemistry, The UniVersity of Texas at Austin,
Austin, Texas 78712
skerwin@mail.utexas.edu
ReceiVed January 8, 2009
SCHEME 2. Synthesis of (()-NNN-5′-OAc
A concise and efficient route to (()-N′-nitrosonornicotine
5′-acetate (NNN-5′-OAc), a stable precursor of the active
metabolite 5′-hydroxy(()-N′-nitrosonornicotine NNN-5′-OH
is reported. The synthesis utilizes sulfinimine chemistry to
give (()-NNN-5′-OAc in 26% yield over 4 steps.
N′-Nitrosonornicotine (NNN) is a tobacco-specific N-nitro-
samine that is known to cause esophageal cancer in animals.1
Metabolic activation of NNN occurs by P450 R-oxidation to form
NNN-5′-OH (Scheme 1) and other metabolites.1,2 Unlike the
other metabolites of NNN, there have been very few studies of
the interaction of metabolically activated NNN-5′-OH with
biological macromolecules,3,4 which can at least partly be
attributed to a lack of ready synthetic access to a suitable stable
precursor of NNN-5′-OH. Although previous work by Hecht
and co-workers has demonstrated that N′-nitrosonornicotine 5′-
acetate (NNN-5′-OAc) can be deprotected by using pig liver
esterase under physiological conditions to afford the NNN-5′-
OH metabolite3 (Scheme 1), no efficient synthesis of NNN-5′-
OAc has been published. The only previously reported synthesis
affords an NNN-5′-OAc in less than 1% overall yield.3 Here
we report a much improved synthesis of NNN-5′-OAc that
employs sulfinimide chemistry.
reported.6 Nakane and Hutchinson obtained isomyosmine
through the reduction and subsequent, relatively inefficient
deprotection/cyclization of a 4-imino-4-(pyridin-3-yl)butanal
thioacetal.7 More recently, Campos and co-workers reported the
preparation of isomyosmine by photolysis of N-cyclopropyl-3-
pyridinecarboxaldhyde imine,8 but this did not appear amenable
to scale-up. Recently, Brinner and Ellman reported a route to
5-substituted-1-pyrrolines employing sulfinimide precursors,9
and we employed this approach to access isomyosmine.
Starting with commercially available 3-nicotinaldehyde and
racemic tert-butyl sulfinamide, chromatographically stable
sulfinimine 1 was formed in quantitative yield (Scheme 2).
Addition of the Grignard reagent derived from 2-(2′-bromo-
ethyl)-1,3-dioxane as a masked propanal homoenolate afforded
the desired sulfinamide 2. The level of relative stereochemical
control in this addition is high; the sulfinamine 2 was isolated
as a single diasteromer, which was found to have the (R*,R*)
configuration by X-ray crystallography (see the Supporting
Information). Deprotection of 2 with aqueous trifluoroacetic acid
followed by nitrosoacylation generates (()-NNN-5′-OAc as a
mixture of diastereomers in 26% overall yield over three steps.
We reasoned that NNN-5′-OAc could be prepared through
nitrosation of isomyosmine in the presence of acetic acid
(Scheme 1).5 Few previous routes to isomyosmine have been
(1) For reviews see: (a) Hoffmann, D.; Brunnemann, K. D.; Prokopczyk,
B.; Djordjevic, M. V. J. Toxicol. EnViron. Health 1994, 41, 1–52.
(2) (b) Hecht, S. H. Chem. Res. Toxicol. 1998, 11, 559–603. (c) Pfeifer, G. P.;
Denissenko, M. F.; Olivier, M.; Tretyakova, N.; Hecht, S. S.; Hainut, P. Oncogene
2002, 21, 7435–7451. McIntee, E. J.; Hecht, S. S. Chem. Res. Toxicol. 2000,
13, 192–199, and references cited therein.
(3) Hecht, S. S.; Chen, C. B. J. Org. Chem. 1979, 44, 1563–1566.
(4) (a) Lao, Y.; Yu, N.; Kassie, F.; Villalta, P. W.; Hecht, S. S. Chem. Res.
Toxicol. 2007, 20, 246–256. (b) Upadhyaya, P.; Hecht, S. S. Chem. Res. Toxicol.
2008, 21, 2164–2171.
(6) There is some confusion in the older literature as some authors mistakenly
attributed the 3-(3,4-dihydro-2H-pyrrol-2-yl)pyridine structure to myosmine, see
for example: Jarboe, C. H.; Rosene, C. J. J. Chem. Soc. 1961, 2455–2458.
(7) (a) Nakane, M.; Hutchinson, C. R. J. Org. Chem. 1978, 43, 3922–3931.
(b) Jalas, J. R.; Hecht, S. S.; Murphy, S. E. Chem. Res. Toxicol. 2005, 18, 95–
110.
(8) Campos, P. J.; Soldevilla, A.; Sampedro, D.; Rodrigues, M. A. Tetra-
hedron Lett. 2002, 43, 8811–8813.
(9) Brinner, K. M.; Ellman, J. A. Org. Biomol. Chem. 2005, 3, 2109–2113.
(5) Mueller, E.; Kettler, R.; Wiessler, M. Liebigs Ann. Chem. 1984, 1468–
1493.
10.1021/jo9000417 CCC: $40.75
Published on Web 03/09/2009
2009 American Chemical Society
J. Org. Chem. 2009, 74, 2891–2892 2891

This solution was cooled to -48 °C, and the sulfinimine 1 (900
mg, 4.3 mmol, 1 equiv) was added as a solution in THF (4.3 mL)
at -48 °C. This mixture was stirred at this temperature overnight.
After 16 h, the reaction was warmed to room temperature and
quenched with satd NH4Cl (10 mL). The reaction mixture was
partitioned between satd NH4Cl (50 mL) and EtOAc (50 mL). The
aqueous layer was extracted (2 × 50 mL of EtOAc), and the
combined organic layers were washed with satd NaCl (50 mL) and
dried (Na2SO4). After evaporation of the solvent, the product was
purified by flash chromatography (SiO2, 10% MeOH in CH2Cl2) to
yield 2 as a yellow oil (930 mg, 3.6 mmol, 85%). Crystallization
from EtOAc/Hex yielded a white crystalline solid with mp
99.0-99.5 °C. 1H NMR (400 MHz, CDCl3) δ 8.55 (1H, br s), 8.51
(1H, d, J ) 4.5 Hz), 7.65 (1H, d, J ) 7.9 Hz), 7.26 (1H, dd, J )
7.7, 5.5 Hz), 4.48 (1H, t, J ) 5.0 Hz), 4.38 (1H, q, J ) 6.8 Hz),
4.04 (2H, dd, J ) 11.7, 4.8 Hz), 3.70 (2H, t, J ) 11.7 Hz), 3.57
(1H, d, J ) 4.8 Hz), 2.05-2.15 (1H, m), 1.95-2.05 (1H, m),
1.81-1.92 (1H, m), 1.53-1.63 (1H, m), 1.40-1.50 (1H, m), 1.31
(1H, d of m, J ) 13.3 Hz), 1.20 (9H, s). 13C NMR δ (75 MHz,
CDCl3) 149.1, 148.7, 137.8, 134.8, 123.6, 101.4, 66.8, 57.1, 56.0,
31.2, 30.9, 30.7, 25.6, 22.5. LRMS (CI+) 327 (M + 1), 231 (M -
pyr). HRMS (CI+) calcd for C16H27N2O3S 327.1742, found
327.1746. IR (thin film) 3414, 3225, 3051, 2964, 2858, 1710, 1644,
Although not separable by HPLC (see the Supporting Informa-
tion), the (()-NNN-5′-OAc appears to consist of a ca. 4:1
mixture of (E)- and (Z)-N-nitroso rotamers10 of a 1:1 mixture
of cis-/trans-2,5-pyrrolidine diasteromers by NMR. Isolation of
the intermediate isomyosmine is possible by chromatography
on Fluorisil or basic alumina; however, isolation does not
improve the overall yield of NNN-5′-OAc. Yields remain
consistent on scales ranging from milligram to multigram
quantitites.11
This route should enable studies on the biological effects of
NNN-5′-OH. The synthesis is technically simple, uses readily
available starting materials, and provides the desired product
in satisfactory overall yields. An additional advantage of this
route is that by using nonracemic tert-butyl sulfinamide, it
should be possible to selectively access precursors of NNN
metabolites derived from both enantiomers of nicotine.
Experimental Section
Caution. Nitrosamines are potent carcinogens. Care should be
taken in handling NNN-5′-OAc to avoid exposure and possible
environmental contamination.
1592, 1578 cm-1
.
(()-tert-Butylsulfinamide.12,13 A variation on the published
route to the racemic sulfinamine was followed: oxidation of di-
tert-butyldisulfide by hydrogen peroxide in AcOH14 afforded the
tert-butylthiosulfinate, which was then transformed to the tert-butyl
sulfinyl chloride with SO2Cl2. Subsequent reaction with NH4OH
as reported12 gave the desired product.
(()-5-(3-Pyridyl)-1-pyrroline ((()-Isomyosmine).7,8 The sul-
finamide 2 (4.34 g, 13.3 mmol, 1 equiv) was dissolved in 95% aq
TFA (67 mL, 0.2 M) and stirred at room temperature for 1 h. The
reaction was then quenched by pouring over satd NaHCO3 (150
mL) then extracted (4 × 80 mL of CHCl3). The organic layers
were combined, dried over Na2SO4, and concentrated by rotary
evaporation. Chromatography on Fluorisil (5% MeOH/CHCl3)
N-(3-Pyridinemethylidene)-2-methylpropane-2-sulfinamide (1).15
(()-tert-Butylsulfinamide (400 mg, 3.3 mmol, 1 equiv) was
dissolved in dry CH2Cl2 (6.6 mL) in a 10 mL oven-dried, Ar-flushed
round-bottomed flask. MgSO4 (2.0 mg, 16.5 mmol, 5 equiv) was
added, followed by pyridinium p-toluenesulfonate (42 mg, 0.17
mmol, 0.05 equiv). Nicotinaldehyde (354 mg, 3.3 mmol, 1 equiv)
was added as a liquid. This cloudy colorless solution was stirred at
room temperature for 16 h. The reaction mixture was filtered
through Celite, washed with CH2Cl2, and concentrated to yield a
yellow oil that was purified by flash chromatography (SiO2,
10-50% EtOAc/Hex) to yield the sulfinimine 1 as a yellow oil
1
yielded a brown oil (1.87 g, 12.8 mmol, quant.) whose H NMR
spectral data were in accordance with literature values.7,8 13C NMR
(CDCl3) δ 168.3, 148.2, 139.3, 133.9, 123.4, 73.5, 61.5, 37.5, 30.1.
LRMS (CI+) 147 (M + 1). HRMS (CI+) calcd for C9H11N2
147.0922, found 147.0923. IR (thin film) 3019, 2968, 1215 cm-1
.
(()-N′-Nitrosonornicotine 5′-Acetate.3 Isomyosmine (87 mg,
0.60 mmol, 1 equiv), prepared as above, but used immediately
without any chromatographic purification, was dissolved in glacial
acetic acid (1 mL) and cooled to 5 °C. NaNO2 (53 mg, 0.77 mmol,
1.3 equiv) was added, and the reaction mixture was allowed to warm
to room temperature for 1 h (until complete as judged by TLC).
The reaction was neutralized by pouring over satd NaHCO3 (20
mL) then extracted (3 × 15 mL CHCl3), dried (Na2SO4), and
concentrated. The resulting brown oil was passed immediately
through a Fluorisil column with EtOAc as the eluent. The resulting
yellow oil was purified by flash chromatography (SiO2, 50-75%
EtOAc/Hex) to yield a light yellow oil (48.2 mg, 0.22 mmol, 37%)
whose 1H NMR, IR, and MS spectral data were in accordance with
the literature values.3 Subsequent chromatography (SiO2, 75%
EtOAc/Hex) yielded an inseparable mixture of (()-NNN-5′-OAc
diastereomers as a pale yellow solid, mp 57.4-64.1 °C. 13C NMR
(CDCl3) δ 169.5, 169.4, 148.8, 148.7, 147.8, 147.1, 135.0, 133.9,
133.5, 132.7, 123.5, 123.4, 85.0, 83.8, 59.3, 58.5, 31.1, 30.5, 29.6,
29.5, 21.1, 21.0. Analysis by LC-MS (see the Supporting Informa-
tion for details): 92.5% pure (diastereomers not resolved).
1
(680 mg, 3.2 mmol, 98%). H NMR (400 MHz, CDCl3) δ 8.96
(1H, br s), 8.69 (1H, d, J ) 4.8 Hz), 8.59 (1H, s), 8.11 (1H, d, J
) 8.2 Hz), 7.37 (1H, dd, J ) 7.9, 5.2 Hz), 1.19 (9H, s). 13C NMR
(75 MHz, CDCl3) δ 160.32, 152.79, 150.86, 135.60, 129.54, 123.83,
t
57.99, 22.48. LRMS (CI+) 211 (M + 1), 155 (M - Bu). HRMS
(CI+) calcd for C10H15N2OS 211.0905, found 211.0903; IR (thin
film) 3411, 2964, 2860, 1652, 1429, 1380 cm-1
.
(()-N-(3-[1,3]Dioxan-2-yl-1-pyridin-3-yl-propyl)-2-methyl-
propanesulfinamide (2). Freshly ground magnesium turnings (1.56
g, 64.2 mmol, 15 equiv) were placed in a 10 mL oven-dried, Ar-
flushed, round-bottomed flask. THF (7.1 mL, 3 M) was added. A
3 M solution of 2-(2′-bromoethyl)-1,3-dioxane (1.62 mL, 21.4
mmol, 5 equiv) in THF (21.4 mL) was added dropwise. With
intermittent heating and the addition of a catalytic amount of iodine
(1 small crystal) to initiate the reaction, the mixture was stirred at
room temperature for 1 h. The resulting solution of Grignard reagent
was separated from the excess Mg metal by removal via syringe
to a clean 10 mL oven-dried, Ar-flushed, round-bottomed flask.
Acknowledgment. This work was supported by the Phillip
Morris Foundation. Karin Keller is thanked for assistance with
LC-MS.
(10) Hitchcock, S. R.; Nora, G. P.; Hedberg, C.; Casper, D. M.; Buchanan,
L. S.; Squire, M. D.; West, D. X. Tetrahedron 2000, 56, 8799–8807.
(11) At the largest scale attempted (15.7 mmol), the yield from 2 is 18%.
See the Supporting Information for details.
(12) Backes, B. J.; Dragoli, D. R.; Ellman, J. A. J. Org. Chem. 1999, 64,
5472–5478.
(13) (()-tert-Butylsulfinamide [(()-2-methyl-2-propansulfinamine] is also
commercially available.
(14) Netscher, T.; Prinzbach, H. Synthesis 1987, 683–688.
(15) The (R-enantiomer of 1 has previously been reported: Tang, T. P.;
Ellman, J. A. J. Org. Chem. 1999, 64, 12–13.
Supporting Information Available: X-ray structural infor-
mation for 2, LC-MS chromatogram for (()-NNN-5′-OAc, and
NMR spectra for isomyosmine, NNN-5′-OAc, and compounds
1 and 2. This material is available free of charge via the Internet
at http://pubs.acs.org.
JO9000417
2892 J. Org. Chem. Vol. 74, No. 7, 2009