A series of new pyrimido[4,5-b]indole ribonucleosides bearing phenyl or hetaryl group at position 4 has been prepared by selective Pd-catalyzed cross-coupling reactions of the corresponding protected 4,6-dichloropyrimido[4,5-b]indole ribonucleoside with (het)arylboronic acids or stannanes followed by deprotection. Some of these compounds displayed antiviral activity against Dengue virus.