R. Kleinmaier and R. M. Gschwind
was added in one portion via syringe. The mixture was stirred at
551C under reflux for 3 h. After cooling to r.t., the reaction
mixture was poured into 50 ml of ice-cold diethylether and kept
in the ice bath to allow complete precipitation of the product 1,
which was then sucked off on a glass frit, rinsed with cold
diethylether and dried under vacuum (540 mg, 77%). M.P. 1141C;
1H NMR (600 MHz, (CD3)2CO) d 2.77 (s, 3H, –SCH3), 8.5–9.5 (bs,
4H, NH2), 15N NMR (60 MHz, (CD3)2CO) d 106.37.
[
15NZ2]-Bz-Arg(NZ-propionyl)-OEt*TFA 9
0
Bz-Arg(NZ-boc,NZ -propionyl)-OEt
8 (160 mg, 0.34mmol) was
dissolved under stirring in dry dichloromethane/TFA (5 ml, 1:1)
under argon and cooling in an ice bath. The mixture was allowed
to warm up to r.t. and stirred for 3 h. After evaporation the residue
was purified by column chromatography over silica gel in CHCl3/
acetonitrile (5:1) to afford the title compound 9 as colourless solid
1
(80mg, 49%). H NMR (600 MHz, CD2Cl2/10% (CD3)2SO) d 1.08 (t,
3H, 3J= 7.52 Hz, –CH2CH3), 1.22 (t, 3H, 3J = 7.17Hz, OCH2CH3), 1.74
(m, 2H, g-CH2), 1.90 (dm, 2H, b-CH2) 2.45 (q, 2H, 3J = 7.52 Hz,
–CH2CH3), 3.29 (dm, 2H, d-CH2), 4.14 (q, 2H, 3J = 7.17Hz -
OCH2CH3), 4.60 (m, 1H, a-CH), 7.39 (m, 2H, m-Bz), 7.47 (m, 1H,
p-Bz), 7.84 (m, 2H, o-Bz), 7.96 (d, 1H, a-NH), 8.42 (d, 1H,
[
15N2]-mono(boc)-S-methylisothiourea 2
[15N2]-S-methylisothiourea 1 (540 mg, 2.45 mmol) was dissolved
in THF/water (1:1, 5 ml) and 1 M NaOH aq. (2.45 ml, 2.45 mmol)
was added under cooling in an ice bath. Boc-anhydride (545 mg,
2.45 mmol) was dissolved in 2.5 ml THF and dropped in. The
mixture was stirred overnight at r.t. EtOAc (20 ml) was added
and the organic phase was washed once with sat. aq. NaHCO3-
solution and brine, respectively. The organic phase was dried
over Na2SO4 and the solvents evaporated under reduced
pressure. The product 2 (440 mg, 94%) was used in the next
step immediately without further purification. 1H NMR (600 MHz,
CDCl3) d 1.50 (s, 9H, boc-CH3), 2.45 (s, 3H, –SCH3), 15N NMR
(60 MHz, CDCl3) d 44.21, 263.47.
1
1JNH = 92.13Hz, Z-NH2), 9.49 (d, 1H, JNH = 92.13Hz, Z-NH2), 10.14
(s, 1H, e-NH), 13.05 (s, 1H, Z-CONH); 13C NMR (150 MHz, CD2Cl2/
10% (CD3)2SO) d 8.3, 14.2, 24.7, 28.9, 30.3 (d), 41.0, 52.5, 61.4, 127.7,
128.5, 131.7, 154.6 (dd), 162.9 (q), 167.8, 172.3, 177.9 (d); 15N NMR
1
(60 MHz, CD2Cl2/10% (CD3)2SO) d 81.37 (t, NH2, JNH = 92.13 Hz),
132.22 (d, CONH, JNH = 89.6Hz); MS (ESI) 365 ([M12]).
1
Propionic acid NHS ester (propionyl-OSu) 4
Propionylchloride (1.87 ml, 21.6 mmol) and TEA (3.27 ml, 23.8 mmol)
were dissolved in THF (50 ml). N-hydroxysuccinimide (2.7 g,
23.8 mmol) was added and the reaction mixture stirred at room
temperature overnight. After evaporating the THF a low viscous
yellow oil remained, which was extracted with brine. The oil
crystallized upon removal of THF traces under the oilpump vacuum
[
15N2]-N(boc)-N0(propionyl)-S-methylisothiourea 3
[15N2]-mono-boc-S-methylisothiourea 2 (440 mg, 2.3 mmol) was
dissolved in dichloromethane (10 ml) in presence of TEA
(0.66 ml, 4.8 mmol). DMAP (88 mg, 0.72 mmol) and propionyl-
OSu 4 (821 mg, 4.8 mmol) were added under stirring. The
reaction was run overnight at r.t. After dilution with additional
dichloromethane (20 ml), the mixture was washed once with sat.
aq. NaHCO3-solution, water and brine, respectively. The organic
phase was dried over Na2SO4 and the solvents evaporated
under reduced pressure. The impure product was purified by
column chromatography over silica gel to yield N(boc)-
N0(propionyl)-[15N2]-S-methylisothiourea 3 as a white powder
(450 mg, 76%). 1H NMR (600 MHz, CDCl3) d 1.19 (m, 3H), 1.50
(s, 9H, boc-CH3), 2.39 (s, 3H, –SCH3), 2.46 (m, 2H), 15N NMR
(60 MHz, CDCl3) d 44.21; MS (ESI) 249 ([M12]11).
1
3
(2.4 g, 65%). H NMR (300 MHz, CDCl3) d 1.26 (t, 3H, J=7.49Hz,
CH3), 2.63 (q, 2H, J=7.49Hz, CH2), 2.82 (s, 4H, succinimide CH2).
3
Orn(cbz)-OH and Orn(cbz)-OEt 5
Ornithine-HCl (7.5g, 44.5mmol) was solvated in 0.5 M NaOH aq.
(89 ml, 44.5mmol), CuSO4Ã5 H2O (5.55 g, 22.25 mmol) was added
and stirring was maintained for 15min. To the clear blue solution
solid K2CO3 (6.15 g, 44.5mmol) was added followed by Cbz-Cl
(8.2ml, 57.9mmol). The reaction mixture was stirred overnight at
r.t., the precipitate sucked off and washed two times with ice-cold
MeOH (20 ml each). The precipitate was refluxed in aqueous EDTA
(9.94 g, 26.7mmol) solution for 2 h and stirred at r.t. over night to
achieve complete decomplexation. The precipitated crude
Orn(cbz)-OH was sucked off and washed carefully with small
amounts of ice cold water to yield a pale blue solid that was dried
to constant weight in vacuo (9.71 g, 82%).
0
[
15NZ2]-Bz-Arg(N’-boc,Ng -propionyl)-OEt 8
Bz-Orn-OEt 7 (273 mg, 1.03mmol) was dissolved in dichloro-
methane (5ml) in presence of TEA (0.19 ml, 2.06mmol)
and N(boc)-N0(propionyl)-[15N2]-S-methylisothiourea
3 (0.17 g,
0.7 mmol) was added under stirring. HgCl2 was added in one
batch and the precipitate kept in motion by vigorous stirring.
After 2.5 h TLC analysis showed completion. The precipitate was
separated by centrifugation and rinsed two times with dichlor-
omethane. The combined fractions were washed once with sat.
aq. NaHCO3 solution, water and brine, respectively. The organic
phase was dried over Na2SO4 and the solvents evaporated under
reduced pressure. The colourless oily residue was purified by
Orn(cbz)-OH (9.7g, 36.5mmol) was solvated in EtOH (5ml/
mmol). After dropwise addition of thionylchloride under cooling
in an ice bath, the mixture was refluxed for 1 h and allowed to
cool to r.t. The solvent was evaporated to yield 5 as a sticky yellow
1
residue (12.17g, 99%). H NMR (300MHz, CD3OD) d 1.29 (t, 3H,
3J = 7.11Hz, –OCH2CH3), 1.61 (m, 2H, g-CH2), 1.91 (m, 2H, b-CH2),
3.16 (t, 2H, d-CH2), 4.03 (m, 1H, a-CH), 4.27 (q, 2H, 3J = 7.11Hz,
–OCH2CH3), 5.06 (s, 2H, bn-CH2), 7.24–7.38 (m, 5H, bn-Ph).
column chromatography over silica gel to yield pure
0
Bz-Arg(NZ-boc,NZ -propionyl)-OEt
8
(302mg,
95%).
Bz-Orn(cbz)-OEt 6
1H NMR (600 MHz, CDCl3) d 1.19 (t, 3H, 3J = 7.54 Hz, –CH2CH3),
1.29 (t, 3H, 3J = 7.14Hz, –OCH2CH3), 1.42 (s, 9H, boc), 1.66 (m, 1H),
1.76 (m, 1H), 1.87 (m, 1H), 2.02 (m, 1H), 2.43 (q, 2H, 3J = 7.54,
–CH2CH3), 3.38 (m, 1H), 3.58 (m, 1H), 4.22 (q, 2H, 3J = 7.14,
–OCH2CH3), 4.82 (m, 1H), 7.43 (m, 3H), 7.49 (m, 1H), 7.87 (d, 2H),
9.03 (d, 1H), 12.41 (d, 1H, 1JNH = 90.14 Hz),15N NMR (60 MHz, CDCl3)
d 133.77 (1JNH = 90.14 Hz), 162.45; MS (ESI) 465 ([M12]11).
Orn(cbz)-OEt
5 (3 g, 9.1 mmol) was dissolved in CHCl3
(5 ml/mmol) and TEA (3.8 ml, 27.3 mmol) was added. After
addition of benzoylchloride (1.16 ml, 10 mmol) using a dropping
funnel, the mixture was stirred overnight at r.t. The reaction
solution was washed two times with sat. aq. NaHCO3 solution,
then with water and finally with brine. The organic phase was
J. Label Compd. Radiopharm 2009, 52 29–32
Copyright r 2008 John Wiley & Sons, Ltd.