Synthesis of Lipophilic Guanine N-9 Derivatives: Membrane Anchoring of Nucleobases Tailored to Fatty Acid Vesicles

Abstract

Covalent or noncovalent surface functionalization of soft-matter structures is an important tool for tailoring their function and stability. Functionalized surfaces and nanoparticles have found numerous applications in drug delivery and diagnostics, and new functionalization chemistry is continuously being developed in the discipline of bottom-up systems chemistry. The association of polar functional molecules, e.g., molecular recognition agents, with soft-matter structures can be achieved by derivatization with alkyl chains, allowing noncovalent anchoring into amphiphilic membranes. We report the synthesis of five new guanine-N9 derivatives bearing alkyl chains with different attachment chemistries, exploiting a synthesis pathway that allows a flexible choice of hydrophobic anchor moiety. In this study, these guanine derivatives were functionalized with C chains for insertion into decanoic acid bilayer structures, in which both alkyl chain length and attachment chemistry determined their interaction with the membrane. Incubation of these guanine conjugates, as solids, with a decanoic acid vesicle suspension, showed that ether- and triazole-linked C anchors yielded an increased partitioning of the guanine derivative into the membranous phase compared to directly N-9-linked saturated alkyl anchors. Decanoic acid vesicle membranes could be loaded with up to 5.5 mol % guanine derivative, a 6-fold increase over previous limits. Thus, anchor chemistries exhibiting favorable interactions with a bilayer's hydrophilic surface can significantly increase the degree of structure functionalization.

Nucleobase coupling by Mitsunobu reaction towards nucleoside analogs

“…Similar procedures have also been successfully used by other authors. 26,34 The influence of alcohol structure on reaction yield is clearly demonstrated by Šála et al 35 during coupling of 6-chloropurine with bicyclic alcohols 4, 5, 6 and 7 (Scheme 3) via MR protocol. While the yield was higher with a primary alcohol, resulting from less steric hindrance, those for the secondary alcohol substrates were considerably different, with the highest yield obtained for alcohol 5.…”

“…In carbocyclic nucleoside and isonucleoside synthesis the limiting reagent is the alcohol, while for acyclic nucleosides it is common to use an excess of alcohol in relation to the nucleobase. 26,28,[31][32][33][34] This excess may have to be handled in different ways, as demonstrated by Lu et al. 31 Aiming to overcome low yields caused by alcohol degradation, two successive additions of the non-limiting reagents (alcohol, DIAD and PPh3), separated by 6 hours, were made, resulting in a considerable yield increase.…”

“…The authors succeeded to couple this protected nucleobase with primary, secondary and aromatic alcohols by MR in yields ranging from 70% to 80%. 31 This base was also linked through MR to alkyl chains by Wamberg et al, 34 aiming to generate new molecules for noncovalent anchoring to amphiphilic membranes. While these two examples do not describe nucleoside analog synthesis, they illustrate N 9 -guanine alkylation through MR and may therefore be potentially useful for the synthesis of isonucleoside, carbocyclic nucleosides and acyclic nucleosides.…”