We synthesized a panel of unnatural base pairs whose pairing depends on hydrophobic and packing forces and identify d TPT3-d NaM, which is PCR amplified with a natural base pair-like efficiency and fidelity. In addition, the d TPT3 scaffold is uniquely tolerant of attaching a propargyl amine linker, resulting in the d TPT3 PA-d NaM pair, which is amplified only slightly less well. The identification of d TPT3 represents significant progress toward ...