2-Thiopyrimidinone ribofuranoside (2-thiozebularine, s2zeb) was synthesized by the adaptation of silyl method of N-glycosidic bond formation and using thionation of protected 2-oxonucleoside derivative (zebularine, zeb) with Lawesson reagent. The X-ray crystal structure of s2zeb and NMR determined conformations of s2zeb and zeb in solution were compared with structures of 2-thiouridine (s2U) and uridine (U). In the solid state s2zeb molecule adopts conformation typical for ribonucleosides: C3′-endo C2′-exo twist type of ribofuranose pucker, anti of N-glycosidic bond and trans around C4′–C5′ bond. In aqueous solution, however, almost 100% population of s2zeb exhibits C3′-endo ribofuranose pucker. The population of N-conformer of s2zeb is about 20% higher than for zeb (analogously to pair of s2U and U nucleosides) indicating similar influence of steric effect of bulky sulfur atom on stabilization of N-type ribose conformation. Interestingly, the absence of 4-carbonyl function in zeb and s2zeb raises the population of C3′-endo conformation by about 30% in comparison to U and s2U as a result of significant anomeric effect. Additive action of both effects makes the 2-thiozebularine almost fully constrained in C3′-endo conformation in aqueous solution. Cytotoxic properties of s2zeb are less pronounced in comparison to zebularine, with IC50 > 100 mM for HeLa and K562 cancer cells and for HUVEC non-cancerous cells.
2-硫代嘧啶核糖苷(2-thiozebularine,s2zeb)是通过采用硅基N-糖苷键形成的方法,并利用Lawesson试剂对保护的2-氧代核苷衍生物(zebularine,zeb)进行硫化而合成的。将s2zeb的X射线晶体结构和NMR测定的s2zeb和zeb在溶液中的构象与2-硫代尿苷(s2U)和尿苷(U)的结构进行了比较。在固态中,s2zeb分子采用核糖核苷酸的典型构象:C3'-内旋C2'-外旋的核糖环扭曲类型,N-糖苷键为反式,C4'-C5'之间为顺式。然而,在水溶液中,几乎100%的s2zeb呈现C3'-内旋的核糖环扭曲类型。s2zeb的N构象的种群比zeb高约20%(类似于s2U和U核苷的一对),表明巨大的硫原子对N型核糖构象的稳定具有类似的立体效应。有趣的是,zeb和s2zeb中缺少的4-羰基功能使C3'-内旋构象的种群比U和s2U高约30%,这是由于显著的异构效应。两种效应的加成使得2-硫代嘧啶核糖苷在水溶液中几乎完全限制在C3'-内旋构象中。s2zeb的细胞毒性性质比zebularine要稍弱,对HeLa和K562癌细胞以及HUVEC非癌细胞的IC50> 100 mM。