4
70
V. A. Timoshchuk and R. I. Hogrefe
purification. Their 4% solutions in methanol were treated with two equiva-
lents of quinone 1 at room temperature overnight. After evaporation, crude
products were purified by flash chromatography in an appropriate solvent
systems.
ꢁ
5
-(E)-[2-(4,6-Di-tert-butylbenzoxazol-2-yl)ethenyl)-2 -deoxyuridine (16).
1
System A (78% yield). H NMR (DMSO-d ): 11.69 (s, 1H, NH), 8.46 (s,
6
1
7
5
1
H, H-6), 7.54 (d, 1H, J = 16.0 Hz, = CH), 7.46 (d, 1H, J = 16.0 Hz, = CH),
ꢁ
.50 (d,1H, J = 1.8 Hz, Ar) 7.25 (d, 1H, J = 1.8 Hz, Ar), 6.17 (dd, 1H, H-1 ),
ꢁ
ꢁ
ꢁ
.28 (d, 1H, J = 4.5 Hz, 3 -OH), 5.22 (t, 1H, J = 5.4 Hz, 5 -OH), 4.29 (m,
ꢁ
ꢁ
ꢁ
H, H-3 , 3.81 (m, 1H, H-4 ), 3.69 (m, 1H, H-5 a), 3.62 (m, 1H, H-5 b), 2.27
ꢁ
ꢁ
(m, 1H, H-2 a), 2.18 (m, 1H, H-2 b), 1.47 and 1.34 (2s, 18H, 2 t-Bu). LRMS:
−
+
m/z = 482.5 [M−H] , 506.5 [M+Na] . UV: λ
(MeOH) 282 nm, 338
max
nm, 350 nm (sh.), 370 nm (sh.). λ
(EtOH) 415 nm.
em
ꢁ
5
-(E)-[2-(4,6-Di-tert-butylbenzoxazol-2-yl)ethenyl)-2 -deoxycytidine (17).
1
System A (63% yield). H NMR (DMSO-d ): 8.57 (s, 1H, H-6), 7.64 (d, 1H,
6
J = 16.0 Hz, = CH), 7.60 (br.s, 2H, NH ), 7.49 (d, 1H, J = 1.8 Hz, Ar), 7.25
2
ꢁ
(
5
1
(
d,1H, J = 1.8 Hz, Ar), 6.89 (d, 1H, J = 16.0 Hz, = CH), 6.17 (dd, 1H, H-1 ),
ꢁ
ꢁ
.25 (t, 1H, J = 5.5 Hz, 5 -OH), 5.23 (d, 1H, J = 4.5 Hz, 3 -OH), 4.28 (m,
ꢁ
ꢁ
ꢁ
ꢁ
H, H-3 ), 3.82 (m, 1H, H-4 ), 3.70 (m, 1H, H-5 a), 3.62 (m, 1H, H-5 b), 2.19
ꢁ
ꢁ
m, 2H, H-2 a, H-2 b), 1.49 and 1.34 (2s, 18H, t-Bu). LRMS: m/z = 481.4
−
+
+
[
M−H] , 483.5 [M+H] , 505.5 [M+Na] . UV: λ
(MeOH) 292 nm, 345
max
nm. λ
(EtOH) 410 nm.
em
8
-Aza-7-deaza-7-[(4,6-di-tert-butylbenzoxazol-2-yl)ethynyl)adenosine
1
(
18). System A (42% yield). H NMR (DMSO-d ): 8.33 (s, 1H, H-2), 8.2
6
(
br.s, 1H, NH), 7.66 (d, 1H, J = 1.8 Hz, Ar), 7.43 (d, 1H, J = 1.8 Hz, Ar),
ꢁ
7
2
4
.2 (br.s, 1H, NH), 6.17 (d, 1H, J = 4.8 Hz, H-1 ), 5.48 (d, 1H, J = 5.9 Hz,
ꢁ
ꢁ
ꢁ
-OH), 5.21 (d, 1H, J = 5.5 Hz, 3 -OH), 4.86 (t, 1H, J = 5.8 Hz, 5 -OH),
ꢁ
ꢁ
ꢁ
.63 (m, 1H, H-2 ), 4.24 (m, 1H, H-3 ), 3.94 (m, 1H, H-4 ), 3.60 (m, 1H,
ꢁ
ꢁ
H-5 a), 3.47 (m, 1H, H5 b), 1.48 and 1.37 (2s, 18H, t-Bu). LRMS: m/z =
−
+
+
+
5
19.6 [M−H] , 521.5 [M+H] , 543.6 [M+Na] , 559.5 [M+K] . UV: λ
max
(MeOH) 274 nm, 326 nm. λ
(EtOH) 390 nm, 415 nm (sh).
em
1
2
-Vinyl-4,6-di-tert-butylbenzoxazole (20). System C (78% yield). H NMR
(
DMSO-d ): 7.54 (d, 1H, J = 1.8 Hz, Ar), 7.29 (d, 1H, J = 1.8 Hz, Ar), 6.83
6
(
dd, 1H, J = 11.0 Hz, 17.5 Hz, = CH), 6.41 (dd, 1H, J = 1.0 Hz, 17.5 Hz, =
−
CH), 5.94 (dd, 1H, J = 1.0 Hz, 11.0 Hz, = CH). LRMS: m/z = 256.4 [M-H] ,
+
2
80.4 [M+Na] . UV: λ
(MeOH) 280 nm.
max
ꢁ
ꢁ
ꢁ
3
,5 -Di-O-benzoyl-5-(E)-[2-(4,6-di-tert-butylbenzoxazol-2-yl)ethenyl]-2 -
ꢁ
ꢁ
ꢁ
deoxyuridine (22). 3 ,5 -Di-O-benzoyl-5-iodo-2 -deoxyuridine (21) (562 mg,
mmol) was dissolved in 1,4-dioxane (20 mL) and heated together with
1
triethylamine (0.5 mL), 2-vinyl-4,6-di tert-butylbenzoxazole 20 (520 mg, 2
◦
mmol) and 10% Pd/C (100 mg) at 100–110 C for 3 hours. The volatiles
were evaporated and the residue was purified by flash chromatography
1
(
system B) to give title compound in 75% yield. H NMR (CDCI ): 8.85 (s,
3
1H, NH), 8.08–8.03 (m, 4H, Ar), 7.92 (s. 1H, H-6), 7.65 (d, 1H, J = 16.0