Etheno-dA is a fluorescent nucleoside which is especially useful in observing the transition between DNA structural types. It is quite base labile and should be deprotected with ammonium hydroxide at room temperature for 24 hours. Alternatively, UltraMild chemistry can be used. 2-Aminopurine and AP-dC (G-Clamp) are also useful fluorescent
Coupling: No changes needed from standard method recommended by synthesizer manufacturer. The use of UltraMILD monomers are preferred. (Catalog Numbers: dA: 10-1601-xx, dC: 10-1015-xx, dG: 10-1621-xx, dT: 10-1030-xx). To avoid any exchange of the iPr-Pac group on the dG with acetyl, use the UltraMild Cap Mix A (40-4210-xx/ 40-4212-xx).
Deprotection: If UltraMILD reagents were used, deprotect in 0.05M Potassium Carbonate in Methanol for 4 hours at Room Temperature OR for 2 hours at hours in 30% Ammonium Hydroxide. If standard bases were used, deprotection in Ammonium Hydroxide at Room Temperature for 24-36 hours will give acceptable yields.
Due to the structure of the 1, N6 etheno structure etheno dA will not base-pair with T or dU. For this reason oligonucleotides with etheno-dA in the middle or 3'-end will not act as PCR or sequencing primers. However if located at or near the 5''-end etheno-dA can be incorporated one or more times and still act as an effective sequencing or PCR primer (1). Etheno-dA is somewhat labile to NH4OH so it is best to use base labile protecting groups such as Pac dA, isopropyl-Pac-dG and Ac-dC and either deprotect with K2CO3:MeOH, 4 hr. at RT. or NH4OH 4 hr. at RT.. If using standard protecting groups use mild deprotection conditions (0.4 M Methanolic NaOH; MeOH:H2O, 4:1) 17 hr. at room temperature.