Flow and Microwave-Assisted Synthesis of N-(Triethylene glycol)glycine Oligomers and Their Remarkable Cellular Transporter Activities.

Peptidomimetics, such as oligo-N-alkylglycines (peptoids), are attractive alternatives to traditional cationic cell-penetrating peptides (such as R9) due to their robust proteolytic stability and reduced cellular toxicity. Here, monomeric N-alkylglycines, incorporating amino-functionalized hexyl or triethylene glycol (TEG) side chains, were synthesized via a three-step continuous-flow reaction sequence, giving the monomers N-Fmoc-(6-Boc-aminohexyl)glycine and N-Fmoc-((2-(2-Boc-aminoethoxy)ethoxy)ethyl)glycine in 49% and 41% overall yields, respectively. These were converted into oligomers (5, 7, and 9-mers) using an Fmoc-based solid-phase protocol and evaluated as cellular transporters. Hybrid oligomers, constructed of alternating units of the aminohexyl and amino-TEG monomers, were non-cytotoxic and exhibited remarkable cellular uptake activity compared to the analogous fully TEG or lysine-like compounds.

Flow-mediated synthesis of Boc, Fmoc, and Ddiv monoprotected diamines.

A series of monoprotected aliphatic diamines (21 examples) were synthesized via continuous flow methods. The carbamates and enamines were obtained in 45-91% yields using a 0.5 mm diameter PTFE tubular flow reactor. Using readily accessible protecting group precursors, the procedure serves as an attractive alternative to existing batch-mode synthetic routes by providing direct, multigram access to N-Boc-, N-Fmoc-, and N-Ddiv-protected compounds with productivity indexes of 1.2-3.6 g/h.