Novel analogues of the naturally occurring purine nucleosides were synthesized in the thiazolo[4,5-d]pyrimidine ring system to determine the immunomodulatory effects of insertion of a sulfur atom in place of nitrogen at position 7 of the purine ring. In particular, 5-amino-3-beta-D-ribofuranosylthiazolo[4,5-d]pyrimidine-2,7(3H,6H) -dione (7, guanosine analogue), 3-beta-D-ribofuranosylthiazolo[4,5-d]pyrimidine-2,5,7(3H,4H,6H) trione (8, xanthosine analogue), 3-beta-D-ribofuranosylthiazolo[4,5-d]pyrimidine-2,7(3H,6H)-dione (10, inosine analogue), and 7-amino-3-beta-D-ribofuranosylthiazolo[4,5-d]pyrimidin-2(3H)-one (32, adenosine analogue) were prepared, as well as the 8-mercaptoguanosine (14) and 6-mercaptoguanosine (17) analogues. Single-crystal X-ray studies confirmed the structural assignment of 17 and 32 as having the beta-configuration with the site of glycosylation at N3. The nucleosides were evaluated for their ability to potentiate various murine immune functions in direct comparison to the known active agents 8-bromoguanosine (1), 8-mercaptoguanosine (2), and 7-methyl-8-oxoguanosine (3). Two of the guanosine analogues, 7 and 14, were found to exhibit significant immunoactivity relative to the positive control compounds (1-3), while the adenosine, inosine, xanthosine, and 6-mercaptoguanosine analogues were devoid of activity. Compound 7 exhibited greater immunoactivity than any of the other guanosine analogues and derivatives in all test systems. Specifically, 7 was shown to be about twice as potent as 3 in the murine spleen cell mitogenicity assay. In addition, treatment with 7 produced about a 4-fold increase in natural killer cell cytotoxicity, while treatment with 3 afforded a 3-fold increase over controls. Finally, 7 provided excellent protection (92% survivors compared to 0% for placebo controls) against Semliki Forest virus in mice. Induction of interferon may account for the major mode of action of these guanosine analogues.

中文翻译：

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噻唑并[4,5-d]嘧啶核苷。某些3-β-D-呋喃核糖基噻唑并[4,5-d]嘧啶的合成作为潜在的免疫治疗剂。

在噻唑并[4,5-d]嘧啶环系统中合成了天然存在的嘌呤核苷的新类似物，以确定在嘌呤环第7位插入硫原子代替氮的免疫调节作用。特别是5-氨基-3-β-D-呋喃核糖基噻唑并[4,5-d]嘧啶-2,7（3H，6H）-二酮（7，鸟苷类似物），3-β-D-呋喃核糖基噻唑并[4， 5-d]嘧啶-2,5,7（3H，4H，6H）三酮（8，黄嘌呤类似物），3-beta-D-呋喃呋喃糖基噻唑并[4,5-d]嘧啶-2,7（3H，6H） -dione（10，肌苷类似物）和7-amino-3-beta-D-rifurfuranosylthiazolo [4,5-d] pyrimidin-2（3H）-1（32，腺苷类似物）以及8 -巯基鸟苷（14）和6-巯基鸟苷（17）类似物。单晶X射线研究证实17和32的结构分配具有β构型，在N3处有糖基化位点。与已知的活性剂8-溴鸟苷（1），8-巯基鸟苷（2）和7-甲基-8-氧代鸟苷（3）直接比较，评估了核苷增强各种鼠类免疫功能的能力。发现两个鸟苷类似物7和14相对于阳性对照化合物（1-3）表现出显着的免疫活性，而腺苷，肌苷，黄嘌呤和6-巯基鸟苷类似物没有活性。在所有测试系统中，化合物7的免疫活性均高于其他鸟苷类似物和衍生物。具体地，在鼠脾细胞有丝分裂性测定中，显示7的效力是3的约两倍。此外，用7处理可以使自然杀伤细胞的细胞毒性提高约4倍，而用3处理可以使对照的杀伤细胞增加3倍。最终，有7种小鼠对小鼠的Semliki Forest病毒提供了出色的保护作用（92％的幸存者与安慰剂对照为0％）。干扰素的诱导可能解释了这些鸟苷类似物的主要作用方式。