Patent ID: 7022851

Claim:
A compound having formula I: wherein R1, R2, R3, R4, R5 is independently H, halogen, C 1 –C 4 alkyl, nitro, cyano, C 1 –C 4 alkoxy, halogenated C 1 –C 4 alkyl, or halogenated C 1 –C 4 alkoxy, wherein at least one of R1, R3, and R5 is nitro; R6 is H or protected or unprotected side chain of natural or unnatural α-amino acid; and B is nucleobase thymine (T), cytosine (C), adenine (A), or guanine (G), wherein when said nucleobase has an exocyclic amino function, said function is protected by protecting group which is labile to acids but stable to organic bases.