In sequencing applications, the design of primers can be complicated by the degeneracy of the genetic code (there are 64 possible 3-base codon configurations and only 21 amino acids, and therefore the third base in a sequence codon is often unknown). The problem of degeneracy can also be tackled by the use of universal bases.⁽¹⁾ Deoxyinosine is often used as a degenerate base in an oligonucleotide to alleviate this problem.⁽²⁾ This is possible since its structure allows it to base pair with all four bases in various ‘wobble’ structures. However, the base-pairing is not equivalent with each of the 4 naturally occurring bases. The overall preferential order of base-pairing is: dI-dC > dI-dA > dI-dG = dI-dT. We provide both dI phosphoramidite and CPGs. 2'-Deoxynebularine⁽³⁾ is another example. In a true universal nucleoside, the base analogue does not hybridize significantly to the other four bases and makes up some of the duplex destabilization by acting as an intercalating agent. 3-nitropyrrole 2'-deoxynucleosides were the first example of a set of universal bases. Subsequently, 5-nitroindole was determined to be an effective universal base and to be superior to 3-nitropyrrole, based on duplex melting experiments. 

Ref:

1. The applications of universal DNA base analogues, D. Loakes, Nucleic Acids Research, 29, 2437-2447, 2001.
2. (a) Base pairing involving deoxyinosine: implications for probe design, F.H. Martin, M.M. Castro, F. Aboul- ela and I. Tinoco, Jr, Nucleic Acids Research, 13, 8927-8938, 1985; (b) Studies on the base pairing properties of deoxyinosine by solid phase hybridisation to oligonucleotides, S.C. Case-Green, E.M. Southern, Nucleic Acids Research, 22, 131-136, 1994.
3. (a) Synthesis and properties of oligonucleotides containing 2'-deoxynebularine and 2'-deoxyxanthosine, R. Eritja, D.M. Horowitz, P.A. Walker, J.P. Ziehler-Martin, M.S. Boosalis, M.F. Goodman, K. Itakura and B.E. Kaplan, Nucleic Acids Research, 14, 8135-8153, 1986; (b) As a custom item we have prepared the phosphoramidite, see: A convenient synthesis of deoxynebularine phosphoramidite, D. Picken and V. Gault, Nucleosides, Nucleotides and Nucleic Acids, 16, 937-939, 1997. Please enquire regarding availability.