of diisopropyl ether that was intensively stirred and the generated precipitate was collected by filtration the precipitate was recrystallized from 750 ml of acetonitrile and the crystal product was collected by filtration as a result of an nmr analysis the product included one molecule of acetonitrile when the crystal product was subjected to vacuum drying acetonitrile was lost the weight was 66 7 g when the obtained product was analyzed by high performance liquid chromatography ods octadecyl silica gel column acetonitrile water 8 2 using a uv detector 254 nm the purity was 99 5 the yield of n6 benzoyl 5 u2032 o 4 4 u2032 dimethoxytrityl 2 u2032 deoxyadenosine was 79 4 the largest impurity was n6 benzoyl 3 u2032 5 u2032 o bis 4 4 u2032 dimethoxytrityl 2 u2032 deoxyadenosine 0 15 by area after the filtrate obtained by the recrystallization in example 1 was concentrated the concentrate residue was purified by column chromatography ethyl acetate hexane the purified fraction was concentrated to obtained a yellow oily product the yellow oily product was then dropped into diisopropyl ether and the precipitate thus formed was recovered by filtration and dried whereby the titled compound was obtained as a light yellow powder 1 h nmr 400 mhz dmso d 6 u03b4 12 1 1h s 11 5 1h s 7 9 1h s 7 5 u2013 7 2 18h m 6 8 8h m.