Scheme 1. Synthesis of 2′-deoxy diazepine phosphoramidite. Reagents and conditions: (i) N,N’-disuccinimidyl carbonate, THF, r.t., 2 h; (ii) TMS chloride, Et3N, benzene, r.t., overnight; (iii) Hoffer's chlorosugar, SnCl4, 1,2-dichloroethane, −35 °C, 1 h; (iv) benzoyl chloride, pyridine, 0 °C → r.t., overnight; (v) GreenCat™, dry DCM, reflux, 2 h; (vi) 30% aq. NH3, MeOH (1 : 10, v/v), r.t., 3 days; (vii) 4,4′-dimethoxytrityl chloride (DMTCl), pyridine, 0 °C → r.t., overnight; (viii) N,N-diisopropylamino-2-cyanoethoxychlorophosphine (CEP-Cl), Et3N, dry DCM, 0 °C, 20 min; and (ix) 30% aq. NH3, r.t., 15 min.
