Treatment of 2,6-diamino-9-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)purine (1c) with tert-butyl nitrite (TBN) in 60% anhydrous hydrogen fluoride/pyridine at −20 °C gave 2-fluoroadenosine triacetate (2) in 48% yield. Analogous treatment of the acetylated 2-amino-6-fluoropurine nucleoside (1a) gave the 2,6-difluoro compound (3a) in 63% yield. Anhydrous ammonia in 1,2-dimethoxy-ethane converted 3a → 2 without ammonolysis of the acetate groups. The overall conversion of 1a → 3a → 2 without isolation of 3a proceeded in 80% yield. Similar diazotization of the 2-amino-6-chloro nucleoside (1b) in HF/pyridine gave the 2-fluoro-6-chloro analogue (3b) in 89% yield. Treatment of 1b with TBN and pyridine hydrochloride in dichloromethane (77%) or TBN and antimony trichloride in 1,2-dichloroethane (84%) gave the 2,6-dichloropurine nucleoside (4b). The latter conditions converted 1a to the 2-chloro-6-fluoro product (4a) in 77% yield. Conversions of 1a and 1b to the 2-bromo-6-fluoro (5a, 67%) and 2-bromo-6-chloro (5b, 78%) analogues were effected using TBN and antimony tribromide in dibromomethane.
在60%无水氢氟酸/吡啶中,将2,6-二氨基-9-(2,3,5-三-O-乙酰-β-D-核糖呋喃基)嘌呤(1c)与叔丁基亚硝酸酯(TBN)处理,在-20℃下反应,得到2-氟腺苷三乙酸酯(2),收率为48%。对乙酰化的2-氨基-6-氟嘌呤核苷(1a)进行类似处理,得到2,6-二氟化合物(3a),收率为63%。在1,2-二甲氧基乙烷中使用无水氨转化3a → 2,但乙酸酯基不发生氨解。1a → 3a → 2的总转化率为80%,不分离3a。在HF/吡啶中类似地重氮化2-氨基-6-氯嘌呤核苷(1b),得到2-氟-6-氯类似物(3b),收率为89%。在二氯甲烷中使用TBN和吡啶盐酸盐(77%)或TBN和三氯化锑(84%)处理1b,得到2,6-二氯嘌呤核苷(4b)。后一种条件将1a转化为2-氯-6-氟产物(4a),收率为77%。使用TBN和三溴化锑在二溴甲烷中将1a和1b转化为2-溴-6-氟(5a,67%)和2-溴-6-氯(5b,78%)类似物。