6-Chloropurine and 2,6-dichloropurine were regioselectively glycosylated at position 7 to give the corresponding peracetylated N7-nucleosides, which can be suitable for other purine transformations. In this work, we study the distribution of N7/N9-isomers produced via the Vorbrüggen method under different conditions, using an N-trimethylsilylated purine derivative and SnCl4 or TiCl4 as a catalyst. The main effort is devoted to reversing the disadvantageous predominant selectivity of most glycosylation reactions at the N9 position and thus to determining conditions that maximize the regioselectivity of glycosylation toward the desired N7-isomer.

Department of Organic Chemistry Faculty of Science Palacký University 17 listopadu 1192 12 771 46 Olomouc Czech Republic

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Study of Direct N7 Regioselective tert-Alkylation of 6-Substituted Purines and Their Modification at Position C6 through O, S, N, and C Substituents