中文摘要：

目的为寻找具有较好反义活性的药物，设计并合成脱氧胞苷5-甲基-N^4-烷基修饰的寡核苷酸。方法以胸苷为起始原料，合成了一系列N^4-烷基取代的5-甲基-5’-O-（4，4＇-二甲氧三苯甲基）-2’-脱氧胞苷-3’-O-（2-氰乙基-N，N-二异丙基）氨基亚磷酸酯，并把它们掺入到寡核苷酸中。结果与结论共合成了4条5-甲基-N^4-烷基修饰的寡核苷酸，考察了它们的杂交性质，测定了它们与互补DNA的解链温度Tm值。脱氧胞苷的5-位甲基取代物能够增加寡核苷酸双链的稳定性，而N^4-位的修饰则使双链稳定性下降。

英文摘要：

Aim To design and synthesize a series of new oligodeoxynucleotides（ODNs） modified at deoxycy- tidine by 5-methyl-N^4-alkyl ring and to screen more efficient antisense drugs. Methods A series of N^4-alkyl modified 5-methyl-5＇-O-（4, 4＇-dimethoxytrityl）-2＇-deoxycytidine-3＇-O-（2-cyanoethyl N, N-diisopropyl） phosphoramidite compounds was synthesized and incorporated into oligonucleotides. Results and conclusion Four new oligonucleotides containing 5-methyl-Ng-alkyl-deoxycytidines were synthesized. Also, the melting temperatures（Tin） of these ODNs with their DNA complements were determined. The hybridizing affinity of the ODNs with their DNA complements disclosed a different effect of 5-methyl-N^4-alkyl of deoxycytidines on the double helix stability. 5-Methyl substitution increased the stability of the ODN duplexes while N^4-alkylation caused a profound destabilization of the double helix.