Table 1.

Physical properties of C5-modified 2′-deoxyuridines determined using ¹H NMR

Compound	Percentage of anti-conformation	Percentage of S-conformera (2′-endo)	Orientation of alkenyl group	pKa valueb
3a (alkane)	78	59	—	10.00 ± 0.04 (8.96)
4a (alkyne)	71	58	—	8.53 ± 0.09 (8.05)
5a (Z-alkene)	89	56	Slight cisoid preference	9.79 ± 0.15 (9.31)
6a (E-alkene)	76	58	Cisoid	9.69 ± 0.04 (9.34)
Thymidine	78c	62d	—	10.42 ± 0.04 (9.96)

^aCalculated from H1′, H2′ and H2″ coupling constants as described previously (32).

^bThe pK_a value shown in parentheses is the lower value obtained after fitting the data to two pK_as.

^cData taken from (31).

^dData taken from (42).