Provided are compounds represented by: X is O, S or NR6, R1 is H or (CH2)mR5, R2, R2', R3 and R3' are independently NO2, N3 or (CH2)mR5, OH R4 is H, OR6, SR6, NR6R6a, CN, C(O)OR6, C(O)NR6R6a, R6, OR7 or (CH2)nR7, R5 is H, halo, OR6, SR6, NR6R6a, CN, C(O)OR6, C(O)NR6R6a, R6, OR7 or (CH2)mR7, R6 and R6a are individually H,
alkyl, substituted
alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl,
aryl or substituted
aryl, R7 is: R8 is H, F, SR9 or OR9, R9 is H,
alkyl, alkenyl, alkynyl,
aryl or hydroxyprotecting group, Y is H, CH3 or (CH2)mR5, Z is O or S W is CH2, CF2, CHF or O, m is 0-4, B is adenine,
guanine,
cytosine,
uracil,
thymine, modified purines and pyrimidines substituted pyridines, five membered heterocycles substituted by at least one of amines, substituted amines, amides, substituted amides, esters, halogens, alkyls, ethers; and pharmaceutically acceptable salts thereof and prodrugs thereof. These ring systems may be substituted.