The present invention relates to a new compound of 2-amino-9-(2-substituted ethyl)purine and an effective method for preparing 9-[4-acetoxy-3-(acetoxymethyl)but-1-yl]-2-aminopurin (famciclovir) using the same. The 2-amino-9-(2-substituted ethyl)purine according to the invention is represented by the following formula (II'): (Formula II') wherein R is a hydroxy, halogen, mesyloxy or tosyloxy group. The inventive method for the preparation of famciclovir comprises the steps of halogenating 2-amino-9-(2-substituted ethyl)purine to give 2-amino-9-(2-halogenoethyl)purine, and reacting the halogenated compound with diethylmalonate. The inventive preparation method allows famciclovir, a purine derivative drug with effective antiviral activity, to be prepared in a high selectivity of 100% in a pure form by using the inventive new compound of 2-amino-9-(2-substituted ethyl)purine. In addition, the inventive method allows the utilization of relatively mild reaction conditions, and thus, has high industrial process efficiency.
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