Triphenylphosphine → 6-(2,2-Diphenyl-ethylamino)-9-((1R,4S)-4-hydroxy-cyclopent-2-enyl)-9H-purine-2-carboxylic acid methyl ester

6-(2,2-Diphenyl-ethylamino)-9H-purine-2-carboxylic acid methyl ester (Intermediate DA) (10.8 g 28.9 mmol) is placed in an oven-dried flask under an atmosphere of argon. Dry deoxygenated tetrahydrofuran (200 mL) and dry dimethyl sulfoxide (5 mL) are added and the suspension is cooled on an ice-bath. Sodium hydride 95% (0.69 g, 28.9 mmol) is then slowly added and the solution is stirred at room temperature for 30 minutes. (1S,4R)-cis 4-Acetoxy-2-cyclopenten-1-ol (3.9 g, 27.5 mmol), triphenylphosphine (1.08 g, 4.13 mmol) and tetrakis(triphenyl-phosphine)palladium(0) (1.27 g, 1.38 mmol) are placed in an oven-dried flask under an atmosphere of argon. Dry deoxygenated tetrahydrofuran (20 mL) is added and stirred at room temperature for 30 minutes. This solution is added to the anion solution via syringe and is then stirred at 50° C. for 6 hours. The reaction mixture is allowed to cool and the solvent is removed in vacuo. The title compound is obtained after purification by flash column chromatography (silica, 0% to 10% MeOH in DCM). 1H NMR (MeOD, 400 MHz); 8.15 (s, 1H), 7.40-7.15 (m, 10H), 6.30 (m, 1H), 5.95 (m, 1H), 5.60 (m, 1H), 5.50 (m, 1H), 4.85 (m, 1H), 4.55 (m, 1H), 4.30 (m 2H), 4.00 (s, 2H), 2.65 (s, 3H).