An important feature of this product is the t-butyldimethylsilyl(TBS) group, which protects the hydroxyethyl branching point. Unlike the TBS-protected secondary alcohols that are common in RNA synthesis, the TBS-protected primary alcohol of BA 0378 is labile to the solution of 3% trichloroacetic acid (TCA) in dichloromethane that is normally used for DMT deprotection in oligo synthesis. Another use for BA 0378 is asa “hydroxyl modifier.” The liberated hydroxyl group serves as a convenient attachment point for phosphoramidite coupling, which may be accomplished on the solid support. This allows the incorporation of a variety of reagents that are typically used to install 5’-labels with concomitant chain termination.For example, thiol modifiers such as BA 0332 and BA 0037 may be connected in the last automated synthesis cycle yet the disulfideresides at an internal sequence position of the oligo (3 → 5).