Zink et al.
The crude 220 mg of N-acetyl-3-cyanomorpholine was dissolved
in 0.1 M NaOH and stirred for 3 h at room temperature in order to
effect nitrile hydrolysis. The base was subsequently neutralized with
HCl, and additional HCl was added to a final concentration of ∼3.5
M. Amide hydrolysis was effected over 16 h at 100 °C, after which
the product was purified by recrystallization in H2O, yielding 171
mg of crude morpholine carboxylic acid. This was then nitrosated22
without prior purification to give, after purification by silica gel
column using hexane/ethyl acetate (6/4), 181 mg of spectroscopi-
cally pure material. E form49 (56.8%). 1H NMR (CDCl3): 5.47 (1H,
d, J ) 4 Hz), H5 4.65 (1H, m), 4.42 (1H, d, J ) 12.35 Hz), 4.10
(1H, m), 4.11 (1H, m), 3.63 (1H, td), 3.50 (1H, dd, J ) 12.35, 4.1
Hz), 11.59 (1H, s). 13C NMR (CDCl3) δ: 171.6, 67.3, 67.0, 51.1,
neutral media is markedly stimulated by primary and secondary
amines, although not by the tertiary amine DABCO or by
carbonate buffers. The lack of concordance between the rate
constants of decay of the ethoxyacetaldehyde adduct and those
derived for formation of the hydroxyethyl adduct (Results)
require the formation of a non-steady-state intermediate, possibly
an imine or enamine.48 Although some effort was expended to
detect such species, this was unsuccessful. Regardless, the
present results clearly indicate the potential, under physiological
conditions, for an ethoxyacetaldyde adduct, initially deposited
from nitrosomorpholine that was metabolically activated by
hydroxylation R to the nitroso nitrogen, to decompose to a
chemically more stable hydroxyethyl adduct. Whether the
ethoxyacetaldehyde adduct deposited in DNA is chemically
stabilized by potential cross-link formation with exocyclic amino
groups of the bases, or destabilized as a result of the interme-
diacy of such structures in the formation of the hydroxyethyl
adducts, is not presently clear.
1
47.9. Z form (43.2%). H NMR (CDCl3): 5.41 (1H, d J ) 3.68
Hz), 4.65 (1H, m), 4.51 (1H, d, J ) 11.91 Hz), 3.98 (1H, dd, J )
11.91, 4.6 Hz), 3.81 (1H, dd, J ) 11.91, 3.68 Hz), 3.32 (1H, td),
3.02 (1H, td), 11.59 (1H, s). 13C NMR (CDCl3): δ 173.6, 68.3,
65.8, 60.7, 39.0.
Methanesulfonic Acid 2-Allyloxyethyl Ester (20).50 2-Allyl-
oxyethanol (50.0 g, 0.49 mol) was dissolved in pyridine (80 mL).
Methane sulfonyl chloride (84.12 g, 0.73 mol) was slowly added
to the stirring solution at 0 °C. The mixture was allowed to stir at
0 °C for 1 h and was then stirred at room temperature for 2 h. The
reaction mixture was diluted with deionized water (100 mL) and 1
N HCl (300 mL). The mixture was extracted with CH2Cl2 (3 ×
100 mL) and washed with water (100 mL), 10% NaHCO3 (100
mL), and brine (100 mL). The organic layer was dried (MgSO4)
Experimental Section
Warning! Many nitrosamines are powerful carcinogens. Precau-
tions taken in handling include use of frequently changed double
pairs of disposable gloves and a well-ventilated hood. Contaminated,
and potentially contaminated, materials were treated with 50%
aqueous sulfuric acid containing a commercially available oxidant.
Materials. Typically, organic solvents were dried and purified
by distillation with CaH2 before use. The chemicals for synthesis
and kinetics were ACS grade or better. Organic chemicals were
typically purified prior to use in synthesis or kinetic experiments.
Deionized water was used in all analytical procedures.
1
and concentrated in vacuo (71% yield). H NMR (CDCl3): 3.01
(3H, s), 3.66 (2H, t, J ) 4.6 Hz), 3.99 (2H, d, J ) 5.9 Hz), 4.33
(2H, t, J ) 5.3 Hz), 5.22 (2H, dd, J ) 1.4, 10.5 Hz), 5.83 (1H, m).
13C NMR (CDCl3): δ 134.1, 117.8, 72.3, 69.4, 67.8, 37.8. Anal.
Calcd for C12H14N2O‚0.2H2O: C, 70.01; H, 7.05; N, 13.61.
Found: C, 70.29; H, 7.14; N, 13.64.
Synthesis. R-Acetoxy-N-nitrosomorpholine was prepared as
previously reported by Pb(AcO)4-catalyzed oxidative decarboxy-
lation of N-nitrosomorpholine carboxylic acid.22,40 Aspects of the
synthesis of morpholine carboxylic acid, beginning with anodic
oxidation in methanol of acetyl morpholine, as in eq 1, have also
been previously published,39 but the additions and alterations
described below were essential for success in our hands.
1-(2-(Allyloxy)ethyl)-1H-benzo[d]imidazole (21). Sodium hy-
dride (4.4 g, 0.11 mol, 60 wt %) was added in portions to a cold
(0 °C) solution of benzimidazole (13.1 g, 0.11 mol) in DMF (50
mL). After the mixture had been stirred at room temperature for 1
h, 20 (5.0 g, 0.028 mol) was added. The mixture was heated at 65
°C for 2 h. After being allowed to cool, the mixture was
concentrated in vacuo. The crude mixture was purified by silica
gel column chromatography (CHCl3/CH3CN, 7/3) followed by
1
distillation, bp 162 °C at 1.5 mmHg (89% yield). H NMR (CD2-
Cl2): 3.76 (2H, t, J ) 5.3 Hz), 3.93 (2H, d, J ) 5.3 Hz), 4.33 (2H,
t, J ) 5.3 Hz), 5.14 (2H, ddd, J ) 1.4, 10.6 Hz), 5.81 (1H, m),
7.27 (2H, m), 7.44 (1H, d, J ) 7.3 Hz), 7.75 (1H, d, J ) 7.3 Hz),
7.95 (1H, s). 13C NMR (CD2Cl2): δ 144.36, 144.25, 134.9, 134.6,
123.0, 122.2, 120.5, 117.2, 110.2, 72.5, 68.8, 45.5.
3-Methoxy-N-acetylmorpholine (10). To a solution of tetra-
ethylammonium perchlorate (510 mg, 2.2 mmol) in 100 mL of
methanol, contained in a water-jacketed titration vessel the inner
wall of which was lined with a reticulated carbon anode, was added
5 g of N-acetylmorpholine (38 mmol). The temperature was
maintained at 14 °C by means of a refrigerated recirculating bath,
and electrolysis was carried out by passing a constant current of
370 mA through the solution, the cathode being suspended in the
center of the vessel. After 7 h, electrolysis was stopped. The solvent
was stripped in vacuo, and to the residue was added 100 mL of
ethyl acetate. The solution was washed with 15 mL of water and
dried over Na2SO4. The product was purified by distillation, bp 97
°C at 0.25 mmHg. NMR (CDCl3): 2.10 and 2.15 (2s, 3H), 3.27
and 3.30 (2s, 3H), 3.45-4.2 (m, 6H), 4.74 and 5.53 (2s, 1H).
N-Nitrosomorpholine-3-carboxylic Acid (11). To a solution of
10 (2.02 g, 12.8 mmol) in 50 mL of CH2Cl2 were added 3.4 mL of
trimethylsilyl cyanide and a few drops of borontrifluoride etherate.
The reaction mixture was stirred for 15 h at room temperature under
Ar. Further purification was not effected prior to the next two
hydrolysis reactions.
2-(2-(1H-Benzo[d]imidazol-1-yl)ethoxy)acetaldehyde (12). 21
(520 mg, 2.6 mmol) was dissolved in CH2Cl2 (50 mL) and cooled
to -78 °C. Ozone was bubbled through the solution until a blue
color appeared. The solution was purged with oxygen, and (Ph)3P
(674 mg, 2.6 mmol) was added. The solution was allowed to warm
to room temperature and stirred for 24 h. The cloudy solution was
diluted with water (50 mL). The aqueous layer was collected,
washed with ether (2 × 100 mL), and concentrated in vacuo. The
resulting red oil (550 mg) was dissolved in 1.0 M TFA (2.5 mL).
The product, in the hydrate form, was purified as the TFA salt by
1
HPLC (25% yield). H NMR (D2O): 3.45 (2H, d, J ) 5.1 Hz),
4.03 (2H, t, J ) 4.6 Hz), 4.70 (2H, t, J ) 4.6 Hz), 5.03 (1H, t, J )
5.1 Hz), 7.64 (2H, m), 7.84 (2H, m), 9.23 (1H, s). 13C NMR
(D2O): δ 140.4, 130.9, 130.4, 126.9, 126.5, 114.5, 112.8, 88.0,
73.3, 68.1, 46.6. Anal. Calcd for C13H13F3N2O4: C, 49.06; H, 4.12;
N, 8.8. Found: C, 49.25; H, 4.22; N, 8.57.
tert-Butyl-(2-chloroethoxy)dimethylsilane (22).51 Imidazole
(5.07 g, 75 mmol) was added to a cold (0 °C) solution of
(49) Karabatsos, G. J.; Taller, R. A. J. Org. Chem. 1964, 29, 4373.
(50) Barton, J. E.; Clinch, K.; O’Hanlon, P.; Ormrod, J.; Rice, M.;
Turnbull, M. International Patent Application WO 9319599, 1993.
(51) Hill, S. T.; Mokotoff, M. J. Org. Chem. 1984, 49, 1441-1442.
(48) Sollenberger, P. Y.; Martin, R. B. J. Am. Chem. Soc. 1970, 92,
4261-4270.
208 J. Org. Chem., Vol. 71, No. 1, 2006