Synthesis of 5-/8-Halogenated or Ethynylated Lipophilic Nucleobases as PoLtential Synthetic Intermediates for Supramolecular Chemistry

A series of lipophilic nucleobases that are substituted at the 5-(pyrimidines) or 8-(purines) position with either a halogen atom or a terminal triple bond have been synthesized. The sequences and reactions studied in this work, which mainly comprise halogenation, alkylation, Sonogashira coupling, and trimethylsilylacetylene deprotection, have been carefully optimized, to reach the final compounds in the most straightforward and convenient way, with the highest possible purity and yield. These compounds include cytosine, isocytosine, and uracil derivatives as pyrimidine heterocycles, and guanine, isoguanine, and 2-aminoadenine derivatives as complementary purine bases. Variability was introduced at the N-1/N-9 positions of these pyrimidine/purine nucleobases, which were functionalized with alkyl or benzyl groups, as well as with protected amine or carboxylic acid substituents. The molecules prepared constitute a useful collection of synthetic intermediates for the field of chemical self-assembly.