13877-56-0

68703-67-3

13877-56-0

The general procedure for the synthesis of 1H-pyrazolo[4,3-d]pyrimidin-7-amine from 4-amino-1H-pyrazole-3-carbonitrile was as follows: 4-nitro-1H-5-pyrazolecarbonitrile (6.25 g, 45.3 mmol) was dissolved in ethanol (100 mL), and 10% palladium carbon (0.50 g) was added as a catalyst. The mixture was placed in a Parr shaker and hydrogenated at 50 psi hydrogen pressure for 18 hours. Upon completion of the reaction, it was filtered through a diatomaceous earth pad to remove the catalyst. Formamidine acetate (37.7 g, 0.363 mol) was added to the filtrate and the mixture was subsequently heated to reflux for 1 hour. The reaction solution was cooled and about 50 mL of solvent was removed by distillation under reduced pressure. The precipitate precipitated was separated by filtration and washed with ethyl acetate (3 x 25 mL) and the precipitate was discarded. The filtrate was concentrated under reduced pressure to about 40 mL. the mixture was heated until completely dissolved and separated by silica gel column chromatography using ethyl acetate/methanol (8:2) as eluent. The fraction containing the target product was collected and concentrated under reduced pressure to afford 1H-pyrazolo[4,3-d]pyrimidin-7-amine (3.85 g, 61% yield), which contained 18% by weight of formamidine acetate. The product was characterized by 1H NMR (DMSO-d6, 400 MHz) and RP-HPLC (Hypersil HSC18, 5 μm, 100?, 250 × 4.6 mm; 5%-100% acetonitrile-0.05 M ammonium acetate, 1 mL/min over 25 min), with a retention time (tr) of 4.95 min; the mass spectrum (MS) showed a 136.1 for MH+ and 134.1 for M-H+.