82 Wang et al.
temperature. After 5 min, benzyl N-(2-bromoethyl)
carbamate (774 mg, 3.0 mmol) was added. The re-
sulting mixture was stirred for 1 h, at which time
TLC analysis (25% EtOAc/hexane) indicated that the
desired product formed. The solution was extracted
with EtOAc (2 10 ml). The organic layers were com-
bined, dried (Na2SO4), and concentrated. The result-
ing oil was purified by silica gel chromatography
eluting with 25% EtOAc in hexanes to give 410 mg
(28%) of the desired thioether product as a clear oil.
1H NMR (CDCl3) 1.45 (s, 18H), 1.80 (s, 1H), 1.90
(m, 1H), 2.60–2.78 (m, 2H), 3.21 (m, 1H), 3.40 (m,
2H), 4.01 (s, 1H), 4.20 (dt, 1H), 7.38 (s, 5H). LCMS:
m/z = 503.2 [M + Na]+.
Preparation of (4S)-4-[[2-[(1-Iminoethyl)
amino]ethyl]thio]-L-proline (6)
A solution of 18 (890 mg, 2.3 mmol) was stirred in 4 N
HCl (6 ml, 1.5 mmol) in dioxane at room temperature
for 18 h. The solvent was removed in vacuo followed
by ether and methanol co-evaporations to afford
190 mg (30%) of the desired fully deprotected prod-
1
uct as a hygroscopic foamy-yellow solid. H NMR
(CDCL3) 2.20 (m, 1H), 2.23 (s, 3H), 2.81 (t, 1H),
3.57–3.83 (m, 8H), 4.56 (t, 1H). HRMS calcd. for
C9H17N3O2S: m/z = 232.1120 [M + H]+, found: 232.
1093. Anal. calcd. for C9H17N3O2S 3.6 HCl 0.3 H2
O 0.6 C4H8O2: C, 32.37; H, 6.22; N, 9.69. Found: C,
32.54; H, 6.23; N, 9.98.
Preparation of tert-Butyl (2S,4S)-4-(2-Amino-
ethylthio)-1-[(tert-Butyl)oxycarbonyl]pyrroli-
dine-2-carboxylate (17)
ACKNOWLEDGMENTS
The authors thank Mr. James P. Doom and Mr. David
F. Master-Moore for their assistance in obtaining
both low and high resolution mass spectral data.
Intermediate 16 (410 mg, 850 mmol) was dissolved
in EtOH (5 ml) at room temperature under nitrogen.
Then 10% Pd/C (50 mg, 0.05 mmol) was added, the
mixture was placed under a hydrogenation appara-
tus, and then hydrogenated at 45 psi for 26 h. The
Pd/C catalyst was removed by filtration through a
celite plug, and the filtrate was concentrated to an
oil. Subsequent LCMS analysis showed that some
unreacted starting material remained. The oil was
redissolved in 20% HOAc/EtOH (5 ml) and resub-
jected to hydrogenation at 45 psi for 3 h in the pres-
ence of 10% Pd/C (200 mg, 0.2 mmol). After filtration
through a celite plug, the filtrate was concentrated to
give 204 mg (69%) of the desired free amine product
as a clear oil. 1H NMR (CDCL3) 1.45 (s, 18H), 1.80
(bs, 2H), 2.60 (m, 1H), 2.81 (m, 1H), 3.21 (m, 2H),
4.01 (m, 1H), 4.20 (m, 1H). HRMS calcd. for C16H30N2
O4S: m/z = 347.2005 [M + H]+, found: 347.2010.
REFERENCES
[1] Bredt, D. S. Free Radic Res 1999, 31, 577.
[2] Pfeiffer, S.; Mayer, B.; Hemmens, B. Angew Chem Int
Ed 1999, 38, 1714.
[3] Marletta, M. A.; Hurshman, A. R.; Rusche, K. M. Curr
Opin Chem Biol 1998, 2, 656.
[4] Mocada, S.; Palmer, R. M. J.; Higgs, E. A. Pharmacol
Rev 1991, 43, 109.
[5] Bredt, D. S.; Hwang, P. M.; Snyder, S. H. Nature 1990,
347, 768.
[6] Garthwaite, J. Trends Neurosci 1991, 14, 60.
[7] Pollock, J. S.; Forstermann, U.; Mitchell, J. A.; Warner,
T. D.; Schmidt, H. H. H. W.; Nakane, M.; Murad, F.
Proc Natl Acad Sci USA 1991, 88, 10480.
[8] Stuehr, D. J.; Marletta, M. A. Proc Natl Acad Sci USA
1985, 82, 7738.
[9] Kroncke, K. D.; Fehsel, K.; Kolb-Bachofen, V. Clin
Exp Immunol 1998, 113, 147.
[10] Shah, A. M. Cardiovasc Res 2000, 45, 148.
[11] Marletta, M. A. J Med Chem 1994, 37, 1899.
[12] Rimoldi, J. M.; Chimote, S. S. Curr Opin Drug Dis-
covery Dev 1998, 1, 183.
[13] Hobbs, A. J.; Higgs, A.; Mocada, S. Annu Rev Phar-
macol Toxicol 1999, 39, 191.
[14] Lee, Y.; Marletta, M. A.; Martasek, P.; Roman, L. J.;
Masters, B. S. S.; Silverman, R. B. Bioorg Med Chem
1999, 7, 1097.
[15] Moore, W. M.; Webber, R. K.; Jerome, G. M.; Tjoeng,
F. S.; Misko, T. P.; Currie, M. G. J Med Chem 1994, 37,
3886.
[16] Moore, W. M.; Webber, R. K.; Fok, K. F.; Jerome,
G. M.; Kornmeier, C. M.; Tjoeng, F. S.; Currie, M. G.
Bioorg Med Chem Lett 1996, 4, 1559.
[17] Young, R. J.; Beams, R. M.; Carter, K.; Clark, H.
A. R.; Coe, D. M.; Chambers, C. L.; Davies, P. I.;
Dawson, J.; Drysdale, M. J.; Franzman, K. W.; French,
C.; Hodgson, S. T.; Hodson, H. F.; Kleanthous, S.;
Rider, P.; Sanders, D.; Sawyer, D. A.; Scott, K. J.;
Preparation of tert-Butyl (2S,4S)-1-[(tert-Butyl)
{
oxycarbonyl]-4- 2-[(iminoethyl)amino]
}
ethylthio pyrrolidine-2-carboxylate (18)
To a cold (0–5 C) solution of 17 (240 mg, 415 mmol)
in EtOH (6 ml) was added 1-(2-naphthylthio)etha-
nimine hydrobromide (120 mg, 415 mmol). After
25 min, the solvent was removed in vacuo, and the
product was partitioned between ether (3 ml) and
water (3 ml). The aqueous layer was removed and
concentrated to afford 102 mg (64%) of the desi-
red acetamidine hydrobromide salt as a hygroscopic
1
white solid. H NMR (CDCl3) 1.45 (s, 18H), 1.70–
1.81 (m, 1H), 2.15 (s, 3H), 2.66 (m, 1H), 2.77 (m,
2H), 3.11 (m, 1H), 3.32–3.39 (m, 3H), 3.82 (m, 1H),
4.13 (m, 1H). HRMS calcd. for C18H33N3O4S: m/z =
388.2270 [M + H]+, found: 388.2310.