Pyrazolo[3,4-d]pyrimidine ribonucleosides related to 2-aminoadenosine and isoguanosine: synthesis, deamination and tautomerism
作者:Frank Seela、Kuiying Xu
DOI:10.1039/b708736e
日期:——
than that of the related purines. The pK(a) values indicate that the 7-non-functionalized nucleosides 1a (pK(a) 5.8) and 15 (pK(a) 6.4) are possibly protonated in neutral conditions when incorporated into RNA. The nucleosides 3a-d exist predominantly in the keto (lactam) form with K(TAUT) (keto/enol) values of 400-1200 compared to 10(3)-10(4) for pyrrolo[2,3-d]pyrimidine isoguanosine derivatives 4a-c
描述了与2-氨基腺苷和异鸟苷相关的8-氮杂-7-脱氮嘌呤(吡唑并[3,4-d]嘧啶)核糖核苷的合成和性质。在BF(3)存在下,将1-氮-乙酰基2,3,5-三-O-苯甲酰基-β-D-呋喃呋喃糖与8-氮杂7-脱氮嘌呤-2,6-二胺5糖基化。 )x Et(2)O作为催化剂,得到N(8)异构体14(73%)和痕量的N(9)异构体13a(4.8%)。在相同的反应条件下,7-卤代8-氮杂-7-脱氮嘌呤-2,6-二胺6-8提供了热力学上更稳定的N(9)核苷13b-d作为唯一产物(53-70%)。因此,位置7的卤素将糖基化作用从N(8)转移到N(9)。通过2-氨基的重氮化将8-氮杂-7-脱氮嘌呤-4,6-二胺核糖核苷1a-d转化为异鸟苷衍生物3a-d。尽管化合物1a b。在7位(酶结合位点)不含氮,它们被腺苷脱氨酶脱氨;但是,它们的脱氨速度比相关嘌呤的速度要慢得多。pK(a)值表明,将7个非功能化核苷1a(pK(a)5