Nucleosides and nucleotides. 135. DNA duplex and triplex formation and resistance to nucleolytic degradation of oligodeoxynucleotides containing syn-norspermidine at the 5-position of 2'-deoxyuridine.

A novel 2'-deoxyuridine analogue with syn-norspermidine at the 5-position, 5-[4-[N,N-bis(3-amino-propyl)amino]butyl]-2'-deoxyuridine (1), has been synthesized from 5-iodo-2'-deoxyuridine. This nucleoside 1 was incorporated into heptadecadeoxynucleotides 5'-d[1(MT)8]-3' and 5'-[(TM)(4)1(MT)4]-3'(M = 5-methyl-2'-deoxycytidine). The triamine group stabilized duplex and triplex formation of the heptadecadeoxynucleotides with a complementary strand and a target duplex, respectively. The oligonucleotides containing 1 were more resistant to nuclease P1 and snake venom phosphodiesterase than an unmodified heptadecadeoxynucleotide, 5'-d[T(MT)8]-3'.