The Significance of Oligomer C-Terminus Design in Solid-Phase Synthesis of Peptide Nucleic Acid Tetramers With the Incorporation of γ-S-Monomer Units Based on L-Glu

Peptide nucleic acids (PNAs) containing γ-S-modified monomers show promise for antisense applications but face synthetic challenges due to their charged backbone. This study aimed to optimize the Boc solid-phase synthesis protocol for L-Glu-based γ-S-PNA oligomers. We systematically evaluated four tetramer designs incorporating glycine or β-alanine C-terminal linkers, monitoring resin loading (0.1–0.2 mmol/g), chain elongation (via a novel N = M × Q mass-corrected metric), and cleavage stability. While monomer sequence order in the C-terminal region showed no significant impact, spacer presence proved critical: β-alanine linkers enabled target oligomer isolation (≤ 10% yields), whereas linker-free tetramers degraded during acidic cleavage. These findings establish a foundation for synthesizing γ-S-PNAs while highlighting the need for further linker optimization to improve yields.