Reese C B, Zard L
Nucleic Acids Res. 1981 Sep 25;9(18):4611-26. doi: 10.1093/nar/9.18.4611.
The action of the N1, N1, N3, N3-tetramethylguanidinium salts of a number of oximes on 5'-O-methoxytetrahydropyranylthymidylyl-(3' leads to 5')-3'-O-methoxytetrahydropyranylthmidine aryl esters (7a-c) in dioxan-water (1:1 v/v) has been investigated. The O-chlorophenyl ester (7a) was unblocked by 4-nitrobenzaldoximate ion ca. 2.5 times as rapidly as the p-chlorophenyl ester (7b) and ca. 25 times as rapidly as the phenyl ester (7c). syn-2-Nitrobenzaldoxime (15a) is the unblocking agent of choice; its conjugate base reacts with 7a and 7b ca. 4 and 2.5 times, respectively, as rapidly as does the conjugate base of its 4-isomer (1). Internucleotide cleavage cannot be detected in the reaction between 2-nitrobenzaldoximate ion and 7a; its extent has been estimated to be no greater than 0.1%. Experiments with the corresponding fully-protected tetranucleoside triphosphate (14a) confirm the greater reactivity of 2- and 4-nitrobenzaldoximate ion and suggest that, if the molecular concentrations both of protected oligonucleotide and oximate ions are maintained, rates of unblocking may not decrease significantly with increasing oligonucleotide chain lengths.
已对多种肟的N1,N1,N3,N3-四甲基胍盐在二氧六环-水（1:1 v/v）中对5'-O-甲氧基四氢吡喃基胸苷酰基-(3'→5')-3'-O-甲氧基四氢吡喃基胸苷芳基酯（7a - c）的作用进行了研究。邻氯苯基酯（7a）被4-硝基苯甲醛肟离子去保护的速度约为对氯苯基酯（7b）的2.5倍，约为苯基酯（7c）的25倍。顺式-2-硝基苯甲醛肟（15a）是首选的去保护剂；其共轭碱与7a和7b反应的速度分别约为其4-异构体（1）的共轭碱的4倍和2.5倍。在2-硝基苯甲醛肟离子与7a的反应中未检测到核苷酸间裂解；据估计其程度不超过0.1%。用相应的完全保护的四核苷三磷酸（14a）进行的实验证实了2-和4-硝基苯甲醛肟离子具有更高的反应活性，并表明，如果保持保护的寡核苷酸和肟离子的分子浓度，去保护速率可能不会随着寡核苷酸链长度的增加而显著降低。
