To a refluxing solution of (2S,3R)-diethyl 2-((5-(benzyloxymethyl)-4-methoxy-5H-pyrrolo[3,2-d]pyrimidin-7-yl)methylamino)-3-hydroxysuccinate (0.6 g, 1.233 mmol) in THF (10 ml) and methanol (0.499 ml, 12.33 mmol) was added lithium borohydride (0.134 g, 6.17 mmol) in portions over about 1 h. Tlc (CH2Cl2-MeOH-cNH3, 9:1:0.1) still showed (uv, ninhydrin or molybdate) sm. More MeOH (0.5 ml) was added and small portions of LiBH4 (total ˜134 mg) added over about 1 h until tlc showed reaction finished. The solvent was evaporated and the residue chromatographed (CH2Cl2-MeOH-cNH3, 95:5:0.5, then 85:15:0.5) to give a colourless gum which soon crystallized (214 mg, 41%). The gum was of sufficient purity to proceed to the next step, but a small quantity was recrystallised by dissolving a portion of the crude (2R,3R)-3-((5-(benzyloxymethyl)-4-methoxy-5H-pyrrolo[3,2-d]pyrimidin-7-yl)methylamino)butane-1,2,4-triol in MeOH and evaporating the solvent to leave a mobile gum. The gum was dissolved in hot ethyl acetate, cooled to rt and seeded. The colourless solid was filtered off and dried to give clusters of very tiny crystals under the microscope. Mpt 108-109° C. [α]D18 −6.1 (c 0.59, MeOH). 1H NMR (CD3OD, 300 MHz), δ ppm, 8.42 (s, 1H), 7.64 (s, 1H), 7.28-7.16 (m, 5H), 5.75 (s, 2H), 4.50 (s, 2H), 4.10 (s, 3H), 3.83-3.68 (m, 3H), 3.63 (d, 2H, J 5.5 Hz), 3.31 (pentet, 1H, J 1.6 Hz). 13C NMR (CD3OD, 75.5 MHz), δ ppm, 158.0 (C), 150.8 (CH), 150.7 (C), 138.8 (C), 134.2 (CH), 129.3 (CH), 128.8 (CH), 128.6 (CH), 117.0 (C), 116.1 (C), 78.5 (CH2), 72.1 (CH), 71.5 (CH2), 65.6 (CH2), 62.3 (CH), 61.0 (CH2), 54.3 (CH3), 41.6 (CH2). +ESMS Found 403.1980 (M+H)+ C20H27N4O5 requires 403.1981.
