Synthesis and Antiviral Activities of 8-Alkynyl-, 8-Alkenyl-, and 8-Alkyl-2'-deoxyadenosine Analogs

Palladium-catalyzed cross-coupling of 8-bromo-2'-deoxyadenosine with terminal alkynes in the presence of copper(I) iodide in dimethylformamide resulted in a series of 8-(1-alkyn-1-yl)-2'-deoxyadenosines. Hydrogenation of alkynyl derivatives over 10% Pd/C under atmospheric pressure gave 8-n-alkyl analogues in nearly quantitative yields. On partial saturation of heptynyl, pentynyl, and propynyl derivatives over Lindlar catalyst, the corresponding cis-olefins were obtained along with minor amounts of trans isomers. Of the analogues tested, the following showed some activity, i.e. they were found to be active at concentrations that were at least 3-fold lower than the cytotoxic concentrations: the 8-heptynyl derivative against vaccinia virus (VV), vesicular stomatitis virus (VSV), cytomegalovirus (CMV), and respiratory syncytial virus (RSV); the 8-propyl derivative against varicella-zoster virus (VZV) and CMV; the 8-pentyl derivative against CMV; the 8-heptyl derivative against VV, CMV, RSV, and influenza A; and the 8-heptenyl derivative against VV, RSV, and influenza A. The unsubstituted 2'-deoxyadenosine did not show any antiviral effect, except against RSV. Except for 8-propyl-dA, the antivirally active dA analogues were rather inhibitory to the growth of human embryonic lung cells. The most cytotoxic was the 8-ethynyl derivative.