An unusual solvent effect on the regiochemical outcome (N-9 versus N-7) of guanine glycosylation using Robinsʹ reagent (2-N-acetyl-6-O-diphenylcarbamoylguanine)

An unexpectedly low N-9/N-7 regioselectivity was obtained when Robinsʹ reagent (2-N-acetyl-6-O-diphenylcarbamoylguanine) was coupled with a d-glucosamine derivative under trimethylsilyl trifluoromethanesulfonate activation. An unprecedented solvent effect (toluene versus dichloroethane) on the N-9/N-7 ratio was also observed in the same study. The use of 2-N-acetyl-6-O-benzylguanine to successfully overcome the above regioselectivity problem is described.