Dong Jae Baek

Synthesis of selective inhibitors of sphingosine kinase 1

Sphingosine kinase isoform 1 (SK1) inhibitors may serve as therapeutic agents for proliferative diseases, including hypertension. We synthesized a series of sphingosine-based SK1-selective inhibitors, the most potent of which is RB-005 (IC(50) = 3.6 μM), which also induced proteasomal degradation of SK1 in human pulmonary arterial smooth muscle cells.

Structure–Activity Relationships and Molecular Modeling of Sphingosine Kinase Inhibitors

The design, synthesis, and evaluation of the potency of new isoform-selective inhibitors of sphingosine kinases 1 and 2 (SK1 and SK2), the enzyme that catalyzes the phosphorylation of d-erythro-sphingosine to produce the key signaling lipid, sphingosine 1-phosphate, are described. Recently, we reported that 1-(4-octylphenethyl)piperidin-4-ol (RB-005) is a selective inhibitor of SK1. Here we report the synthesis of 43 new analogues of RB-005, in which the lipophilic tail, polar headgroup, and linker region were modified to extend the structure–activity relationship profile for this lead compound, which we explain using modeling studies with the recently published crystal structure of SK1. We provide a basis for the key residues targeted by our profiled series and provide further evidence for the ability to discriminate between the two isoforms using pharmacological intervention.

Sphingosine 1-Phosphate Activation of EGFR as a Novel Target for Meningitic Escherichia coli Penetration of the Blood-Brain Barrier

Central nervous system (CNS) infection continues to be an important cause of mortality and morbidity, necessitating new approaches for investigating its pathogenesis, prevention and therapy. Escherichia coli is the most common Gram-negative bacillary organism causing meningitis, which develops following penetration of the blood–brain barrier (BBB). By chemical library screening, we identified epidermal growth factor receptor (EGFR) as a contributor to E. coli invasion of the BBB in vitro. Here, we obtained the direct evidence that CNS-infecting E. coli exploited sphingosine 1-phosphate (S1P) for EGFR activation in penetration of the BBB in vitro and in vivo. We found that S1P was upstream of EGFR and participated in EGFR activation through S1P receptor as well as through S1P-mediated up-regulation of EGFR-related ligand HB-EGF, and blockade of S1P function through targeting sphingosine kinase and S1P receptor inhibited EGFR activation, and also E. coli invasion of the BBB. We further found that both S1P and EGFR activations occurred in response to the same E. coli proteins (OmpA, FimH, NlpI), and that S1P and EGFR promoted E. coli invasion of the BBB by activating the downstream c-Src. These findings indicate that S1P and EGFR represent the novel host targets for meningitic E. coli penetration of the BBB, and counteracting such targets provide a novel approach for controlling E. coli meningitis in the era of increasing resistance to conventional antibiotics.

The 3-Deoxy Analogue of α-GalCer: Disclosing the Role of the 4-Hydroxyl Group for CD1d-Mediated NKT Cell Activation

KRN7000, or α-GalCer, is a potent agonist for natural killer T (NKT) cells. The 3-hydroxyl group of its phytosphingosine moiety is important for activating NKT cells, whereas its 4-hydroxyl group is perceived to be less crucial. To experimentally determine the role of the 4-hydroxyl group, we synthesized the 3-deoxy analogue of α-GalCer. It was found that 3-deoxy-α-GalCer induced potent cytokine responses from NKT cells, comparable to those of both α-GalCer and 4-deoxy-α-GalCer. This result and our docking studies suggest that the effects of an absence of the 3-hydroxyl group are compensated by the presence of a hydroxyl group at the C-4 position. Thus, we conclude that the 4-hydroxyl group of α-GalCer is as important to the mechanism of action as the 3-hydroxyl group and that the two hydroxyl groups could play individual and cooperative roles in orienting the glycolipid into the proper position in CD1d to be recognized by the T cell receptor of NKT cells.

Synthesis of cholesterol analogs having varying length alkyl side chains including cholesterol-23, 23, 24, 24, 25, 26, 26, 26, 27, 27, 27-d(11) as probes of cholesterol's functions and properties.

Cholesterol-23, 23, 24, 24, 25, 26, 26, 26, 27, 27, 27-d11 and nondeuterated long-chain analogs of cholesterol were prepared by alkylation of cyano-containing sterols with isopentyl-d11 4-methylbenzenesulfonate (1.0equiv.) or with isoalkyl bromides, followed by reductive decyanation with excess potassium metal and a crown ether in toluene. The products are potentially useful probes of the role of the side-chain of cholesterol in the sterols interactions with membrane lipids and proteins.

Design and Evaluation of ω-Hydroxy Fatty Acids Containing α-GalCer Analogues for CD1d-Mediated NKT Cell Activation

CD1d molecules recognize glycolipid antigens with straight chain fatty acid moieties. Although most of the residues in the CD1d binding groove are hydrophobic, some of the amino acids can form hydrogen bonds. Consequently, we have designed ω-hydroxy fatty acid-containing glycolipid derivatives of the prototypical CD1d ligand α-GalCer. The potency of the ω-hydroxy analogues of the proper length is comparable to that of α-GalCer. We propose, based on the biological results and molecular modeling studies, that a hydrogen bonding interaction is involved between the ω-hydroxy group and a polar amino acid residue in the hydrophobic binding groove.