Synthesis of Protected 3'-amino Nucleoside Monomers

A method of preparing an adenosine, guanosine or cytidine monomer having a protected nucleoside base and a protected 3′-amino group, wherein said base and said 3′-amino group are orthogonally protected, the method comprising:

• (a) providing a 3′-amino-3′-deoxy adenosine, cytidine, or guanosine monomer in which the 5′-hydroxyl group, nucleoside base, and 3′-amino group are unprotected;
• (b) selectively reacting said 3′-amino group with a first protecting group;
• reacting said 5′-hydroxyl group with a second protecting group;
• and
• reacting said nucleoside base with a third protecting group;
• wherein said first protecting group can be removed from said 3′-amino group under conditions which do not deprotect said nucleoside base, and said second protecting group can be removed from said 5′-hydroxyl group under conditions which do not deprotect said nucleoside base or said 3′-amino group.