The C-nucleoside 2'-deoxypseudoisocytidine is an isostere of dC that offers an additional hydrogen-bond donor at N3. Interest in the incorporation of 2'-deoxypseudoisocytidine and related compounds into oligonucleotides has grown due to their success in improving triplex formation between oligonucleotides and duplex DNA.[Ref (a) Ono, A.; Ts'o, P. O. P.; Kan, L. J. Org. Chem. 1992, 57, 3225-3230. (b) Ono, A.; Ts'o, P. O. P.; Kan, L. J. Am. Chem. Soc. 1991, 113, 4032-4033. (c) Chin, T.-M.; Lin, S.-B.; Lee, S.-Y.; Chang, M.-L.; Cheng, A. Y.-Y.; Chang, F.-C.; Pasternack, L.; Huang, D.-H.; Kan, L.-S. Biochemistry 2000, 39, 12457-12464.] The C to GC pyrimidine-purine-pyrimidine binding motif requires acidic conditions in order to protonate N3 of cytosine in the Hoogsteen strand (i.e., C+ to GC). Unfortunately, this interaction is disrupted under the higher pH of physiological conditions. Improvements have been observed using 5-methyl-2'-deoxycytidine in place of dC, although protonation of N3 is still required.⁽¹⁾ Kan and co-workers¹ have examined the use of 2'-deoxypseudoisocytidine and 2'-O-methylpseudoisocytidine as neutral replacements for protonated cytidine. Indeed, oligonucleotides containing these cytidine replacements form improved triplexes under neutral conditions. We offer 2'-Deoxypseudoisocytidine-CE Phosphoramidite^1c for incorporation of 2'-deoxypseudoisocytidine into oligonucleotides, allowing researchers to explore the alternate hydrogen-bonding motif afforded by this interesting dC surrogate. For those interested in nucleosides, we also offer pseudoisocytidine hydrochloride (PYA11060) and 2'-deoxypseudoisocytidine (PYA11005).

Ref:

1. Singleton, D. F.; Dervan, P. B. Biochemistry 1992, 31, 10995-11003.