Patent ID: 8809520

Claim:
A process for preparing a compound represented by the general formula (II): wherein: X 1 , X 2 , X 3 , X 4 and X 5 are each —O—, B is selected from the group consisting of adeninyl, thyminyl, uracilyl, cytosinyl and guaninyl, R 1 and R 2 are each independently selected from the group consisting of hydrogen, alkyl and P(O)(OH)—O—PO 3 H 2 , provided that when one of R 1 and R 2 is P(O)(OH)—O—PO 3 H 2 , the other one is hydrogen; R 4 and R 5 are each independently selected from the group consisting of hydrogen and OR 14 ; R 3 , R 6 , R 7 and R 8 are each hydrogen; R 14 is hydrogen or arylalkyl; and n is an integer representing the number of methylene groups between X 2 and P, and is selected from 1, 2, 3, 4, 5 and 6; or a pharmaceutically acceptable salt thereof, the process comprising the step of coupling a nucleobase B selected from the group consisting of adenine, thymine, uracil, cytosine and guanine, in the presence of a Lewis acid catalyst, with a precursor represented by the general formula wherein X 1 , X 2 , X 3 , X 4 , X 5 , R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 14 , and n are as defined in formula (II) and wherein R 9 is an O-acyl group.