nucleo amino acid 2 (348 mg, 73%, >95% e.e.) as a white solid
(HPLC for H-(R)-Phe-(S)-NvaA-OH: tR = 24.3, gradient 8–
(R)-N-tert-Butoxycarbonyl-d-(N4-benzyloxycarbonyl-1-cyto-
sinyl)norvaline ent-3. The synthesis followed the procedure
for enantiomer 3. The analytical data of ent-3 and 3 are
19% B in 30 min). Rf [MeOH–AcOEt 1 : 4] = 0.52; [a]20 +3.9
D
(c 0.9 in MeOH); dH (300 MHz; [D6]DMSO; Me4Si) 1.35 (9 H, s,
Boc), 1.59 (2 H, m, H-b, H-c), 1.84 (2 H, m, H-b, H-c), 3.90
(1 H, m, H-a), 4.13 (2 H, t, 3J(H,H) = 6.6 Hz, H-d), 6.96 (1 H,
d, 3J(H,H) = 7.8 Hz, NH-Boc), 7.11 (2 H, s, NH2), 8.09 (1 H, s,
H-2, H-8), 8.12 (1 H, s, H-2, H-8); dC (75.5 MHz; [D6]DMSO;
identical except for [a]20 −8.7 (c 1.0 in MeOH) and HPLC for
D
H-(R)-Phe-(R)-NvaC-OH: tR = 13.4 min, gradient 25–40% B in
20 min.
(S)-N-tert-Butoxycarbonyl-d-(2-amino-6-chloro-9-purinyl)-
norvaline benzyl ester. To a solution of (S)-N-Boc-d-bromo-
norvaline benzyl ester (5) (1.50 g, 3.88 mmol) in anh. DMF
(150 mL) dry K2CO3 (805 mg, 5.82 mmol), 2-amino-6-
chloropurine (988 mg, 5.82 mmol) and tetrabutylammonium
iodide (144 mg, 390 lmol) were added. After 2 d AcOH
(334 lL, 5.82 mmol) was added and evaporated. Purification by
column chromatography on silica (hexane–AcOEt 1 : 2) gave
Me4Si) 26.3, 28.1 (C(CH3)3), 42.5, 53.1 (C-a), 77.9 (C-d, Cprim
–
Boc), 81.9 (C-d, Cqu–Boc), 118.7 (C-5), 140.7 (C-8), 149.5 (C-4),
152.2 (C-2), 155.4, 155.9, 173.7 (COOH); kmax(MeOH)/nm 260
(e/dm3 mol−1 cm−1 16 407); ESI-MS m/z: 351.4 [M + H]+, 373.3
[M + Na]+; HRMS calcd for C15H22N6O4 [M + H]+ 351.1772,
found 351.1775.
(S)-N-Boc-d-(2-amino-6-chloro-9-purinyl)-norvaline
benzyl
(R)-N-tert-Butoxycarbonyl-d-(9-adeninyl)norvaline ent-2. The
synthesis followed the procedure for enantiomer 2. The ana-
ester (1.60 g, 87%) as a white solid. Rf [hexane–AcOEt 1 : 2] =
0.29; [a]20 −14.9 (c 1.4 in MeOH); dH (300 MHz; CDCl3;
lytical data of ent-2 and 2 are identical except for [a]20 −11.5
D
D
Me4Si) 1.44 (9 H, s, Boc), 1.52–1.94 (4 H, m, H-b, H-c), 4.09
(2 H, m, H-d), 4.47 (1 H, m, H-a), 5.08–5.23 (4 H, m, CH2Ph,
(c 0.8 in MeOH) and HPLC for H-(R)-Phe-(R)-NvaA-OH: tR =
24.5 min, gradient 8–19% B in 30 min.
3
NH2), 5.38 (1 H, d, J(H,H) = 12.0 Hz, NH), 7.32 (m, 5 H;
(S)-N-tert-Butoxycarbonyl-d-(N4-benzyloxycarbonyl-1-cyto-
sinyl)norvaline benzyl ester. To a solution of (S)-N-Boc-
d-bromo-norvaline benzyl ester (5) (1.00 g, 2.59 mmol) in
anhydrous DMF (150 mL) dry K2CO3 (537 mg, 3.88 mmol),
N4-benzyloxycarbonyl cytosine (952 mg, 3.88 mmol) and
tetrabutylammonium iodide (96.2 mg, 260 lmol) were added.
After 3 d AcOH (222 lL, 3.88 mmol) was added and evaporated.
Purification by column chromatography on silica (AcOEt) gave
the (S)-N-Boc-d-(N4-benzyloxycarbonyl-1-cytosinyl)-norvaline
benzyl ester (959 mg, 69%) as a white solid. Rf [AcOEt] = 0.45;
[a]20D +30.4 (c 1.0 in MeOH); dH (300 MHz; CDCl3; Me4Si) 1.43
(9 H, s, Boc), 1.64–1.91 (4 H, m, H-b, H-c), 3.86 (2 H, m, H-d),
4.39 (1 H, m, H-a), 5.11–5.23 (6 H, m, CH2Ph, NH-Boc), 7.14
(1 H, d, 3J(H,H) = 10.8 Hz, H-5), 7.32–7.40 (10 H, m, H–Ph),
H–Ph), 7.69 (s, 1 H; H-8); dC (50.3 MHz; CDCl3; Me4Si) 25.9,
28.2 (Cprim–Boc), 29.6, 42.8 (C-d), 53.6 (C-a), 67.2 (CH2Ph),
80.2 (Cqu–Boc), 125.0 (C-5), 128.3 (Ctert–Ph), 128.6 (Ctert–Ph),
128.6 (Ctert–Ph), 135.0 (Cqu–Ph), 142.2 (C-8), 151.3, 153.7,
155.4, 159.1, 172.1 (COBn); kmax(MeOH)/nm 248, 311; ESI-MS
m/z: 497.3 [M + Na]+, 970.9 [2 M + Na]+; HRMS calcd for
C22H27ClN6O2 [M + H]+ 475.1855, found 475.1857.
(R)-N-tert-Butoxycarbonyl-d-(2-amino-6-chloro-9-purinyl)-
norvaline benzyl ester. The synthesis followed the procedure
for the enantiomer. The analytical data were identical except
for [a]20 +20.5 (c 1.0 in MeOH).
D
(S)-d-(9-Guaninyl)norvaline benzyl ester. (S)-N-Boc-d-(2-
Amino-6-chloro-9-purinyl)norvaline benzyl ester (900 mg,
1.89 mmol) was dissolved in TFA–H2O (8 mL, 3 : 1) and
stirred for 2 d at room temperature. The solvent mixture was
coevaporated with toluene. After drying in vacuo a white solid
was obtained in quantitative yield. Rf [CHCl3–MeOH–H2O–
3
7.51 (1 H, d, J(H,H) = 10.8 Hz, H-6); dC (50.3 MHz; CDCl3;
Me4Si) 24.7, 28.2 (Cprim–Boc), 29.8, 49.8 (C-d), 52.5 (C-a), 67.2,
67.8, 80.1 (Cqu–Boc), 94.8 (C-5), 128.3–128.6 (Ctert–Ph), 135.0
(Cqu–Ph), 135.1 (Cqu–Ph), 148.5 (C-6), 152.3, 155.5, 162.1, 172.1
(COBn); kmax(MeOH)/nm 245, 295; ESI-MS m/z: 573.4 [M +
Na]+, 1123.3 [2 M + Na]+; HRMS calcd for C29H34N4O7 [M +
H]+ 551.2500, found 551.2503.
AcOH 70 : 30 : 3 : 0.3] = 0.25; [a]20 −0.2 (c 0.9 in MeOH);
D
dH (300 MHz; CDCl3; Me4Si) 1.94–2.08 (4 H, m, H-b, H-c),
4.21–4.35 (3 H, m, H-d, H-a), 5.27 (2 H, q, 3J(H,H) = 12.0 Hz,
CH2Ph), 7.36 (5 H, m, H–Ph), 9.05 (1 H, s, H-8); dC (50.3 MHz;
CDCl3; Me4Si) 26.0, 28.3, 45.4 (C-d), 53.3 (C-a), 69.2 (CH2Ph),
108.7 (C-5), 128.3 (C-8), 129.7 (Ctert–Ph), 129.8 (Ctert–Ph), 129.8
(Ctert–Ph), 136.3 (Cqu–Ph), 151.6, 154.9, 157.3, 170.0 (COBn);
kmax(MeOH)/nm 257; ESI-MS m/z: 357.4 [M + H]+, 713.3
[2 M + H]+, 735.2 [2 M + Na]+; HRMS calcd for C17H20N6O3
[M + H]+ 357.1670, found 357.1674.
(R)-N-tert-Butoxycarbonyl-d-(N-4-benzyloxycarbonyl-1-cyto-
sinyl)norvaline benzyl ester. The synthesis followed the
procedure for the enantiomer. The analytical data were identical
except for [a]20 −27.3 (c 1.0 in MeOH).
D
(S)-N-tert-Butoxycarbonyl-d-(N4-benzyloxycarbonyl-1-cyto-
sinyl)norvaline 3. To a solution of (S)-N-Boc-d-(N4-benzyl-
oxycarbonyl-1-cytosinyl)norvaline benzyl ester (400 mg,
730 lmol) in dioxane–H2O (60 mL, 3 : 2) 1 N sodium
hydroxide (940 lL) was added. After stirring for 1 d at room
temperature 1 N HCl was added until pH 6 was obtained. After
coevaporation with toluene the residue was purified by column
chromatography on RP silica (H2O to H2O–MeOH 3 : 1)
yielding nucleo amino acid 3 (211 mg, 63%, >97% e.e.) as a
white solid (HPLC for H-(R)-Phe-(S)-NvaC-OH: tR = 14.9 min,
(R)-d-(9-Guaninyl)norvaline benzyl ester. The synthesis fol-
lowed the procedure for the enantiomer. The analytical data
were identical except for [a]20 + 1.3 (c 1.0 in MeOH).
D
(S)-N-tert-Butoxycarbonyl-d-(9-guaninyl)norvaline 4. (S)-d-
(9-Guaninyl)norvaline benzyl ester (874 mg, 3.28 mmol) was
dissolved in H2O–1 N Na◦OH–dioxane (25 mL, 1 : 1 : 2, pH 9)
and stirred for 4 h. At 0 C di-tert-butyldicarbonate (787 mg,
3.61 mmol) was added, stirred for 45 min at 0 ◦C and 3 d at room
temperature keeping the pH slightly higher than 9. Finally, the
reaction mixture was acidified to pH 6 and evaporated. The
residue was purified by column chromatography on RP silica
(AcOEt–MeOH 4 : 1, 1% AcOH) to provide (S)-N-Boc-d-(9-
guaninyl)norvaline 4 (633 mg, 55%, >98% e.e.) as a white solid
(HPLC for H-(R)-Phe-(S)-NvaG-OH: tR = 11.7 min, gradient
12–20% B in 20 min). Rf [CHCl3–MeOH–H2O–AcOH 70 : 30 :
gradient 25–40% B in 20 min). Rf [MeOH] = 0.53; [a]20 +39.2
D
(c 1.0 in MeOH); dH (300 MHz; [D6]DMSO; Me4Si) 1.34
(9 H, s, Boc), 1.42–1.67 (4 H, m, H-b, H-c), 3.57 (1 H, m,
H-a), 3.74 (2 H, m, H-d), 5.16 (2 H, s, CH2Ph), 5.95 (1 H, m,
NH-Boc), 6.92 (1 H, d, 3J(H,H) = 7.2 Hz, H-5), 7.37 (5 H, m,
H–Ph), 8.02 (1 H, d, 3J(H,H) = 7.2 Hz, H-6), 10.66 (1 H, br s,
NH–C); dC (50.3 MHz; CD3OH; Me4Si) 26.1, 28.8 (Cprim–Boc),
31.2, 51.4 (C-d), 56.5 (C-a), 68.5 (CH2Ph), 80.0 (Cqu–Boc),
96.8 (C-5), 129.3 (Ctert–Ph), 129.4 (Ctert–Ph), 129.6 (Ctert–Ph),
137.1 (Cqu–Ph), 150.7 (C-6), 154.4, 157.6, 158.4, 164.6, 179.1
(COOH); kmax(MeOH)/nm 241, 296 (e/dm3 mol−1 cm−1 14
179); ESI-MS m/z: 505.4 [M − H + 2 Na]+; HRMS calcd for
C22H28N4O7 [M + H]+ 461.2031, found 461.2033.
3 : 0.3] = 0.20; [a]20 +22.9 (c 1.0 in MeOH); dH (300 MHz;
D
[D6]DMSO; Me4Si) 1.34 (9 H, s, Boc), 1.94–1.72 (4 H, m, H-
b, H-c), 3.72 (1 H, br s, H-a), 3.88 (2 H, m, H-d), 6.11 (1 H,
m, NH-Boc), 6.64 (2 H, br s, NH2), 7.61 (1 H, s, H-8), 11.0
(1 H, br s, NH-guanine); dC (75.5 MHz; [D6]DMSO; Me4Si)
1 0 6 4
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 0 5 8 – 1 0 6 6