3 2 02 s 3h sch 3 general chlorination procedure to a suspension of the appropriate 2 u2032 3 u2032 di o acetyl 5 u2032 alkylthio 5 u2032 deoxyguanosine 19 3 mmol predried and tetraethylammonium chloride 6 48 g 39 1 mmol predried in vacuo at 80 u00b0 c in acetonitrile 40 ml were added n n dimethylaniline 2 52 ml 20 0 mmol dried and distilled from koh and phosphoryl chloride pocl 3 10 95 ml 0 12 mol freshly distilled at room temperature the flask was placed in an oil bath preheated at 100 u00b0 c and the solution was refluxed for 10 15 minutes volatile materials were evaporated immediately in vacuo the resulting yellow foam was dissolved in ch 2 cl 2 100 ml and stirred vigorously for 15 minutes with crushed ice the layers were separated and the aqueous phase was extracted with ch 2 cl 2 again 75 ml the combined organic layers were kept cold by addition of crushed ice and washed with cold water 3 u00d7 75 ml 5 nahco 3 h 2 o to ph 7 dried over mgso 4 and filtered the residue was purified by column chromatography 2 amino 6 chloro 9 2 3 di o acetyl 5 deoxy 5 methylthio u03b2 d ribofuranosyl purine the reaction was carried out with 2 u2032 3 u2032 di o acetyl 5 u2032 deoxy 5 u2032 methylthioguanosine 5 96 g 15 0 mmol the mixture was purified by column chromatography eluens etoac pe40 60 1 1 to 2 1 yield 3 83 g 9 21 mmol 62 r f 0 28 etoac pe40 60 2 1 1 h nmr dmso d 6 u03b4 8 40 s 1h h 8 7 08 bs 2h nh 2.