On the Necessity of Nucleobase Protection for 2-Thiouracil for Fmoc-Based Pseudo-Complementary Peptide Nucleic Acid Oligomer Synthesis

A selection of benzyl-based protecting groups for thiouracil (U-s) for the synthesis of pseudo-complementary peptide nucleic acid (PNA) has been evaluated. The 4-methoxybenzyl-protecting group that has found use for s U during Boc-based oligomerization is also suitable for Fmoc-based oligomerization. Furthermore, it is demonstrated that U-s protection is unnecessary for the successful synthesis of thiouracil-containing PNA. The new 2-thiothymine (T-s) PNA monomer has also been prepared and incorporated into an oligomer and its binding to complementary PNA evaluated.