With these optimized conditions established, the performance of differentially protected nucleoside P(V) monomers in SPOS (Figure ) was evaluated. To do this, a set of PSI monomers were prepared using the (+) and (-)-PSI Br reagents. Starting with protected 5'-O-DMTr-Nucleosides (A, C, T and G). Products (4-10) were obtained in 39-78% yields with perfect diastereoselectivities, on scales ranging from 0.1 to 2 mmol.