合成路线1

In an alternative procedure, reaction of L-arabinose (X) with cyanamide in the presence of ammonium hydroxide produced the cyclic isourea (XI). Subsequent cycloaddition of methyl propiolate (XII) to (XI) generated the fused pyrimidone system (XIII). After protection of the free hydroxyl groups of (XIII) as the dibenzoate ester (XIV), treatment with HCl in DMF furnished uridine derivative (XV). Dechlorination of (XV) employing Bu3SnH and AIBN afforded intermediate (VIII), which was treated with Lawesson's reagent to give the thiocarbonyl analogue (IX). Finally, sulfur displacement with concomitant benzoate ester hydrolysis employing methanolic ammonia at 100 C in a pressure bomb furnished the title compound.