The reversible attachment of a small-molecule drug to a carrier for targeted delivery can improve pharmacokinetics and the therapeutic index. Previous studies have reported the delivery of molecules that contain primary and secondary amines via an amide or carbamate bond; however, the ability to employ tertiary-amine-containing bioactive molecules has been elusive. Here we describe a bioreversible linkage based on a quaternary ammonium that can be used to connect a broad array of tertiary and heteroaryl amines to a carrier protein. Using a concise, protecting-group-free synthesis we demonstrate the chemoselective modification of 12 complex molecules that contain a range of reactive functional groups. We also show the utility of this connection with both protease-cleavable and reductively cleavable antibody-drug conjugates that were effective and stable in vitro and in vivo. Studies with a tertiary-amine-containing antibiotic show that the resulting antibody-antibiotic conjugate provided appropriate stability and release characteristics and led to an unexpected improvement in activity over the conjugates previously connected via a carbamate.

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Objective: Mangiferin (MGF) is a natural xanthone, with regulation effect on lipid metabolism. However, the molecular mechanism remains unclear. We purposed after oral administration, MGF is converted to its active metabolite(s), which contributes to the effects on lipid metabolism.Methods: KK-Ay mice were used to validate the effects of MGF on lipid metabolic disorders. Liver biochemical indices and gene expressions were determined. MGF metabolites were isolated from MGF administrated rat urine. Mechanism studies were carried out using HepG2 cells treated by MGF and its metabolite with or without inhibitors or small interfering RNA (siRNA). Western blot and immunoprecipitation methods were used to determine the lipid metabolism related gene expression. AMP/ATP ratios were measured by HPLC. AMP-activated protein kinase (AMPK) activation were identified by homogeneous time resolved fluorescence (HTRF) assays.Results: MGF significantly decreased liver triglyceride and free fatty acid levels, increased sirtuin-1 (SIRT-1) and AMPK phosphorylation in KK-Ay mice. HTRF studies indicated that MGF and its metabolites were not direct AMPK activators. Norathyriol, one of MGF’s metabolite, possess stronger regulating effect on hepatic lipid metabolism than MGF. The mechanism was mediated by activation of SIRT-1, liver kinase B1, and increasing the intracellular AMP level and AMP/ATP ratio, followed by AMPK phosphorylation, lead to increased phosphorylation level of sterol regulatory element-binding protein-1c.Conclusion: These results provided new insight into the molecular mechanisms of MGF in protecting against hepatic lipid metabolic disorders via regulating SIRT-1/AMPK pathway. Norathyriol showed potential therapeutic in treatment of non-alcoholic fatty liver disease.