Efficient regioselective enzymatic acylation of troxerutin: difference characterization of in vitro cellular uptake and cytotoxicity

In this study, we developed a multi-site acylation strategy to improve the lipophilicity and cellular uptake of troxerutin, a natural flavonoid with many health-promoting bioactivities. By clarifying the acylation properties of troxerutin catalyzed by lipases from different sources, a series of troxerutin ester derivatives acylated at different sites was synthesized, including troxerutin dipropyl (TDP), tripropyl (TTP), tetrapropyl (TEP), dibutyl (TDB), monohexyl (TMH), monooctyl (TMO) and monodecyl (TMD) esters. Interestingly, the troxerutin esters acylated at multiple sites with shorter fatty chains (TDP, TTP and TEP) had similar lipophilicity to the mono-acylated esters bearing longer fatty chains (TMH, TMO and TMD, respectively) and meanwhile demonstrated surprisingly lower cytotoxicity than that of the long fatty-chain mono-esters. In particular, the multi-acylated esters with shorter fatty chains showed remarkably higher cellular uptake than the mono-esters with long fatty chains. In vitro gastrointestinal digestion suggested that the multi-acylated esters of troxerutin were more resistant to gastrointestinal degradation than the mono-esters. These results indicated that multi-site acylation with short fatty chains could be an effective alternative to introducing one-site mono-acylation for the modification of troxerutin and other flavonoid compounds.