Patent ID: 8642756

Claim:
A process for preparing a compound represented by formula (4), or a phosphorous-based diastereomer thereof: wherein P* represents a chiral phosphorus atom, and wherein said phosphorous-based diastereomer is represented by formula (Rp-4) or (Sp-4): which comprises: a) reacting a mixture comprising an isopropyl-alanate (A), a di-X′-phenylphosphate (B), 2′-deoxy-2′-fluoro-2′-C-methyluridine (3), and a base to obtain a first mixture comprising (4), or the phosphorous-based diastereomer thereof: wherein X is a conjugate base of an acid, n is 0 or 1, and X′ is a halogen; b) reacting the first mixture with a protecting compound to obtain a second mixture comprising protected (4), or the phosphorous-based diastereomer thereof; and c) optionally subjecting the second mixture to crystallization, chromatography, or extraction in order to obtain (4), or the phosphorous-based diastereomer thereof.