NUCLEOSIDES AND NUCLEOTIDES .131. SYNTHESIS AND PROPERTIES OF OLIGONUCLEOTIDES CONTAINING 5-FORMYL-2'-DEOXYURIDINE

Thymidine was converted into 5-formyl-2'-deoxyuridine (1), which was i ncorporated into oligonucleotides, 5'd(GGAGA1CTCC)3' (I-1) and 5'd(GCT GC1GCGAAAGCTG)3' (II-1). To avoid side-reactions and degradation, prot ection of the formyl group of 1 using a newly developed protecting gro up, N,N-di-(3,5-dichloro phenyl)ethylenediamine, was necessary. Compou nd 1 was unstable under the conditions employed for enzymatic complete digestion of oligonucleotides, so that a peak corresponding to I was not detected clearly by HPLC analysis of a nucleoside mixture obtained by complete hydrolysis of I-1. Therefore, the oligonucleotide I-1 was treated with cyanomethylenetriphenylphosphorane to give an oligonucle otide containing (E) and (Z)-5-(2-cyanovinyl)-2'-deoxyuridine, which w as then hydrolyzed, and the newly generated nucleosides were detected by HPLC analysis. The T-m of the self-complementary oligonucleotide I- 1 (40 degrees C) was higher than that of the parent oligonucleotide, 5 'd(GGAGATCTCC)S', (31 degrees C) in a buffer containing 0.01 M sodium phosphate (pH 7.0) and 0.1 M NaCl. DNA replication study on a template -primer system [primer, 5'd(P-32-CAGCTTTCGC)3'; template, 3'd(GTCGAAAG CGXCGTCG)5' (X = 1 or T)] showed that dATP was incorporated into the D NA strand at a site opposite to 1 by Klenow DNA polymerase, but with a reduced rate. The formyl group of 1 in the oligonucleotides reacted w ith amines to give Schiff base derivatives.