Lipophilic Decyl Chain-Pterin Conjugates with Sensitizer Properties

A new series of decyl chain [-(CH₂)₉CH₃] pterin conjugates have been investigated by photochemical and photophysical methods, and with theoretical solubility calculations. To synthesize the pterins, a nucleophilic substitution (S_N2) reaction was used for the regioselective coupling of the alkyl chain to the O site over the N³ site. However, the O-alkylated pterin converts to N³-alkylated pterin under basic conditions, pointing to a kinetic product in the former and a thermodynamic product in the latter. Two additional adducts were also obtained from an N-amine condensation of DMF solvent molecule as byproducts. In comparison to the natural product pterin, the alkyl chain pterins possess reduced fluorescence quantum yields (Φ_F) and increased singlet oxygen quantum yields (Φ_Δ). It is shown that the DMF-condensed pterins were more photostable compared to the N³- and O-alkylated pterins bearing a free amine group. The alkyl chain pterins efficiently intercalate in large unilamellar vesicles, which is a good indicator of their potential use as photosensitizers in biomembranes. Our study serves as a starting point where the synthesis can be expanded to produce a wider series of lipophilic, photooxidatively active pterins.