Derivatives of 3β-amino-5-cholestene (3β-cholesterylamine) are of substantial interest as cellular probes and have potential medicinal applications. However, existing syntheses of 3β-amino-5-cholestene are of limited preparative utility. We report here a practical method for the stereoselective preparation of 3β-amino-5-cholestene, 3β-chloro-5-cholestene, 3β-bromo-5-cholestene, and 3β-iodo-5-cholestene from inexpensive cholesterol. A sequential i-steroid/retro-i-steroid rearrangement promoted by boron trifluoride etherate and trimethylsilyl azide converted cholest-5-en-3β-ol methanesulfonate to 3β-azido-cholest-5-ene with retention of configuration in 93% yield.

The use of endocytic uptake pathways to deliver poorly permeable molecules into mammalian cells is often plagued by entrapment and degradation of material in late endosomes and lysosomes. As a strategy to prevent the exposure of cargo to these highly hydrolytic membrane-sealed compartments, we synthesized derivatives of the membrane anchor N-alkyl-3β-cholesterylamine that selectively target linked compounds to less hydrolytic early/recycling endosomes. By targeting a pH-dependent membrane-lytic dodecapeptide and a disulfide-linked fluorophore to these compartments in Chinese hamster ovary cells or Jurkat lymphocytes, membranes of early/recycling endosomes were selectively disrupted, resulting in cleavage of the disulfide and escape of the fluorophore into the cytosol and nucleus with low toxicity. The ability of appropriately designed N-alkyl-3β-cholesterylamines to deliver cargo into and release disulfide-linked cargo from relatively nonhydrolytic early/recycling endosomes may be useful for the delivery of a variety of sensitive molecules into living mammalian cells.Receptor-mediated endocytosis (RME) is a major mechanism of uptake of impermeant molecules by mammalian cells. 1 In this process, extracellular ligands bind cell surface receptors that cluster in dynamic regions of cellular plasma membranes. By actively pinching off to form intracellular vesicles, these membrane regions are internalized, encapsulating ligand-receptor complexes in the cytoplasm. These vesicles fuse and form early (primary/ sorting) endosomes that are acidified (pH ∼ 6) by the activation of proton pumps, conditions that generally promote the dissociation of receptors from bound ligands. Free receptors often cycle back to the cell surface, generally via subsequent trafficking through related recycling endosomes (also termed the endocytic recycling compartment). 2 In contrast, free ligands are typically directed to more acidic late endosomes and lysosomes (pH ∼ 5), where hydrolases and other enzymes promote their degradation. Some viruses and other intracellular pathogens exploit RME to enter cells, but these organisms avoid degradation in lysosomes by expressing pH-dependent fusogenic proteins that disrupt endosomal membranes. 3 To escape entrapment within these membranes and gain access to the cytosol, Semliki Forest virus disrupts early endosomes whereas influenza virus disrupts late endosomes during the course of infection. 3Correspondence to: Blake R. Peterson. We report here the synthesis of novel compounds designed to enable membrane-bound disulfide-linked cargo to selectively escape from early/recycling endosomes of living mammalian cells. Because these endosomes are less acidic and less hydrolytically active than late endosomes/lysosomes, this approach may be advantageous when compared to delivery methods that penetrate deeper into the endosomal system. To selectively deliver compounds into early/recycling endosomes, we synthesized four derivatives of the dynamic membrane anchor N-alkyl-3β-cholesterylamine 4,5 (1-4). Tw...

Reverse cholesterol transport is the process by which extrahepatic cells, including macrophage-derived foam cells in arterial atherosclerotic plaque, transport excessive cholesterol back to the liver for bile acid synthesis and excretion, thus lowering the peripheral lipid burden. Cholesterol efflux from peripheral cells is the first step in this process, and finding drugs and interventions that promote this event is an important endeavor. Radioisotope-labeled cholesterol traditionally has been employed in measuring efflux efficiency, but this reagent has limitations for high-throughput screening. We developed an alternative method to measure cholesterol efflux in macrophage-derived foam cells using a novel fluorescent cholesterol mimic comprising the Pennsylvania Green fluorophore, attached by a linker containing a glutamic acid residue, to a derivative of N-alkyl-3β-cholesterylamine. Compared with the traditional radioisotope-based assay, this fluorescence-based assay gave similar results in the presence of known modulators of cholesterol efflux, such as cyclic AMP, and different cholesterol acceptors. When the fluorescent probe was employed in a high-throughput screening format, a variety of chemicals and bioactive compounds with known and unknown effects on cholesterol efflux could be tested simultaneously by plate-reader in a short period of time. Treatment of THP-1-derived macrophages with inhibitors of the membrane transporter ATP-binding cassette A1, such as glyburide or a specific antibody, significantly reduced the export of this fluorescent compound, indicating that ATP-binding cassette A1 represents the primary mediator of its cellular efflux. This fluorescent mimic of cholesterol provides a safe, sensitive, and reproducible alternative to radioactive assays in efflux experiments and has great potential as a valuable tool when incorporated into a drug discovery program.

Inhibitors of the PI3-kinase/AKT (protein kinase B) pathway are under investigation as anticancer and antiviral agents. The benzimidazole derivative AKT inhibitor-IV (ChemBridge 5233705) affects this pathway and exhibits potent anticancer and antiviral activity. To probe its biological activity, we synthesized AKT inhibitor-IV and 21 analogues using a novel six-step route based on ZrCl4-catalyzed cyclization of 1,2-arylenediamines with α,β-unsaturated aldehydes. We examined effects on viability of HeLa carcinoma cells, viability of normal human cells (NHBE), replication of recombinant parainfluenza virus 5 (PIV5) in HeLa cells, and replication of the intracellular bacterium Mycobacterium fortuitum in HeLa cells. Replacement of the benzimidazole N-ethyl substitutent of AKT inhibitor-IV with N-hexyl and N-dodecyl groups enhanced antiviral activity and cytotoxicity against the cancer cell line, but these compounds showed substantially lower toxicity (from 6-fold to >20-fold) against NHBE cells, and no effect on M. fortuitum, suggesting inhibition of one or more host protein(s) required for proliferation of cancer cells and PIV5. The key structural elements identified here may facilitate identification of targets of this highly biologically active scaffold.