Novel neplanocin A analogues modified at the 6'-position, i.e. 6'-deoxy derivatives (2, 3, 5, 6, 14), 6'-O-methylneplanocin A (10) and 6'-C-methylneplanocin A (16a and 16b) were synthesized and evaluated for their antiviral activity in a wide variety of virus systems. Compound 16a (TJ-13025) surpassed neplanocin A both in antiviral potency and selectivity.