The ability of 2â²-α-C-carboxyalkyl nucleosides to undergo an unusual two-step stereocontrolled nucleobase exchange process has been investigated. Upon silylation a protected 2â²-deoxy-2â²-α-C-(carboxymethyl)uridine derivative can undergo intramolecular displacement of the uracil base, by the 2â²-carboxylic acid group, to form a pentofuranosyl γ-lactone. Under identical conditions the homologous 2â²-deoxy-2â²-α-C-(carboxyethyl)uridine derivative does not yield the corresponding δ-lactone, but undergoes elimination of uracil to give the corresponding glycal. The pentofuranosyl γ-lactone is a good substrate for nucleoside synthesis by the Vorbrüggen procedures and undergoes completely stereoselective ring opening with either pyrimidine or purine silylated nucleobases to give novel 2â²-C-carboxymethyl β-nucleosides in moderate to high yield.
对2′-α-C-羧基烷基核苷在异常的两步立体控制核苷碱基交换过程中的能力进行了研究。在
硅化后,保护的2′-脱氧-2′-α-C-(羧甲基)
尿苷衍
生物可以通过2′-
羧酸基团进行尿
嘧啶基团的分子内置换,形成五碳
呋喃糖γ-内酯。在相同条件下,同 homologous 2′-脱氧-2′-α-C-(羧乙基)
尿苷衍
生物并未产生相应的δ-内酯,而是通过尿
嘧啶的消除生成相应的糖醇。五碳
呋喃糖γ-内酯是通过Vorbrüggen方法进行核苷合成的良好底物,并且与任何
嘧啶或
嘌呤硅化核苷碱基进行完全选择性的开环反应,从而中等至高产量地生成新型的2′-C-羧甲基β-核苷。