The fully-protected pAUG (15) and pAUGACC (21) were synthesized by the phosphotriester approach where the phenylthio group was employed as the internal and 5′-terminal phosphate-protecting groups. The partially unblocked oligomers (32) and (33), obtained by alkaline treatment of (15) and (21), were condensed with a capping reagent (1a) in the presence of imidazole by activation with silver nitrate to afford the capped trimer and hexamer protected with the acid-labile protecting groups, i.e., 4,4,′4″-trimethoxytrityl (TMTr), 4-monomethoxytrityl (MMTr), tetrahydropyran-2-yl (THP), and methoxymethylene (mM) groups. The protected capped oligomers were unblocked by a dilute HCl solution to afford m7G5′ pppAUG and m7G5′ pppAUGACC, which were purified by HPLC and characterized by enzyme assays.
采用
磷酯化方法合成了完全保护的pAUG (15)和pAUGACC (21),其中苯
硫基用作内部和5′-末端
磷酸保护基团。通过(15)和(21)的碱性处理获得了部分未封闭的寡聚物(32)和(33),在
咪唑存在下,用
硝酸银活化,与封端试剂(1a)缩合,得到用酸不稳定保护基团保护的封端三聚体和六聚体,即4,4,′4″-
三甲氧基三苯甲基(
TMTr)、4-单甲氧基三苯甲基(MMTr)、
四氢吡喃-2-基(THP)和甲氧基甲烯基(MM)基团。用稀
盐酸溶液解除保护封端的寡聚物,得到m7G5′ pppAUG和m7G5′ pppAUGACC,通过HPLC纯化,并通过酶测定进行表征。