Hwayoung Yun

Design, Synthesis, and Biological Evaluation of Novel Deguelin-Based Heat Shock Protein 90 (HSP90) Inhibitors Targeting Proliferation and Angiogenesis

Deguelin exhibits potent apoptotic and antiangiogenic activities in a variety of transformed cells and cancer cells. Deguelin also exhibits potent tumor suppressive effects in xenograft tumor models for many human cancers. Our initial studies confirmed that deguelin disrupts ATP binding to HSP90 and consequently induces destabilization of its client proteins such as HIF-1α. Interestingly, a fluorescence probe assay revealed that deguelin and its analogues do not compete with ATP binding to the N-terminus of HSP90, unlike most HSP90 inhibitors. To determine the key parts of deguelin that contribute to its potent HSP90 inhibition, as well as its antiproliferative and antiangiogenic activities, we have established a structure-activity relationship (SAR) of deguelin. In the course of these studies, we identified a series of novel and potent HSP90 inhibitors. In particular, analogues 54 and 69, the B- and C-ring-truncated compounds, exhibited excellent antiproliferative activities with IC(50) of 140 and 490 nM in the H1299 cell line, respectively, and antiangiogenic activities in zebrafish embryos in a dose dependent manner (0.25-1.25 μM).

Biarylpyrazolyl Oxadiazole as Potent, Selective, Orally Bioavailable Cannabinoid-1 Receptor Antagonists for the Treatment of Obesity

Since the CB1 cannabinoid receptor antagonist 1 (SR141716, rimonabant) was previously reported to modulate food intake, CB1 antagonism has been considered as a new therapeutic target for the treatment of obesity. In the present study, biarylpyrazole analogues based on a pyrazole core coupled with 1,3,4-oxadiazole were synthesized and tested for CB1 receptor binding affinity. Thorough SAR studies to optimize pyrazole substituents as well as 1,3,4-oxadiazole ring led to several novel CB1 antagonists with IC(50) approximately 1 nM for the CB1 receptor binding. Among these analogues, we identified 2-(4-((1H-1,2,4-triazol-1-yl)methyl)-5-(4-bromophenyl)-1-(2,4-dichlorophenyl)-1H-pyrazol-3-yl)-5-(1-(trifluoromethyl)cyclopropyl)-1,3,4-oxadiazole 43c as a promising precandidate for the development as an antiobesity agent.

FORCE-FREENESS OF SOLAR MAGNETIC FIELDS IN THE PHOTOSPHERE

It is widely believed that solar magnetic fields are force-free in the solar corona but not in the solar photosphere at all. In order to examine the force-freeness of active region magnetic fields at the photospheric level, we have calculated the integrated magnetic forces for 12 vector magnetograms of three flare-productive active regions. The magnetic field vectors are derived from simultaneous Stokes profiles of the Fe I doublet λλ6301.5 and 6302.5 obtained by the Haleakala Stokes Polarimeter of Mees Solar Observatory, with a nonlinear least-squares method adopted for field calibration. The resulting vertical Lorentz force normalized to the total magnetic pressure force |Fz/Fp| ranges from 0.06 to 0.32 with a median value of 0.13, which is smaller than the values (~0.4) obtained by Metcalf et al., who applied a weak field derivative method to the Stokes profiles of Na I λ5896. Our results indicate that the photospheric magnetic fields are not so far from force-free as conventionally regarded. As a good example of a linear force-free field, NOAA Active Region 5747 is examined. By applying three different methods (a most probable value method, a least-squares fitting method, and comparison with linear force-free solutions), we have derived relatively consistent linear force-free coefficients for NOAA AR 5747. It is found that the scaled downward Lorentz force (|Fz/Fp|) in the solar photosphere decreases with increasing |α|. Our results also show that the force-freeness of photospheric magnetic fields depends not only on the character of the active region but also on its evolutionary status.

Bispecific small molecule–antibody conjugate targeting prostate cancer

Significance We have developed a semisynthetic method for the production of bispecific antibody-like therapeutics consisting of a small molecule targeting moiety conjugated to an antibody. A highly selective prostate-specific membrane antigen-binding ligand was site specifically conjugated to a mutant α cluster of differentiation 3 (αCD3) Fab containing an unnatural amino acid with orthogonal chemical reactivity. The optimized conjugate showed potent in vitro activity, good serum half-life, and potent in vivo activity in prostate cancer xenograft mouse models. This semisynthetic approach is likely to be applicable to the generation of additional bispecific agents using drug-like ligands selective for other cell-surface receptors. Bispecific antibodies, which simultaneously target CD3 on T cells and tumor-associated antigens to recruit cytotoxic T cells to cancer cells, are a promising new approach to the treatment of hormone-refractory prostate cancer. Here we report a site-specific, semisynthetic method for the production of bispecific antibody-like therapeutics in which a derivative of the prostate-specific membrane antigen-binding small molecule DUPA was selectively conjugated to a mutant αCD3 Fab containing the unnatural amino acid, p-acetylphenylalanine, at a defined site. Homogeneous conjugates were generated in excellent yields and had good solubility. The efficacy of the conjugate was optimized by modifying the linker structure, relative binding orientation, and stoichiometry of the ligand. The optimized conjugate showed potent and selective in vitro activity (EC50 ∼100 pM), good serum half-life, and potent in vivo activity in prophylactic and treatment xenograft mouse models. This semisynthetic approach is likely to be applicable to the generation of additional bispecific agents using drug-like ligands selective for other cell-surface receptors.

Aucubin: Potential Antidote For Alpha-Amanitin Poisoning

Aucubin, an iridoid glucoside isolated from Aucuba japonica (Cornaceae), exhibited significant protective activity against alpha-amanitin intoxication in mice. When a single dose of aucubin was administered intraperitoneally, a 50% survival rate was obtained even when the treatment was withheld for 12 hr after alpha-amanitin administration. A possible mechanism of protective activity is partly due to a competitive effect of aucubin on alpha-amanitin inhibition of liver RNA biosynthesis.

Identification and Validation of Cryptochrome Inhibitors That Modulate the Molecular Circadian Clock

Circadian rhythms, biological oscillations with a period of about 24 h, are maintained by a genetically determined innate time-keeping system called the molecular circadian clockwork. Despite the physiological and clinical importance of the circadian clock, the development of small molecule modulators that directly target the core clock machinery has only been recently initiated. In the present study, we aimed to identify novel small molecule modulators influencing the molecular feedback loop of the circadian clock by applying our two-step cell-based screening strategy based on E-box-mediated transcriptional activity to test more than 1000 drug-like compounds. A derivative of 2-ethoxypropanoic acid designated as compound 15 was selected as the most promising candidate in terms of both efficacy and potency. We then performed pull-down assays with the biotinylated compound and find out that both cryptochrome (CRY)1 and 2 (CRY1/2), key negative components of the mammalian circadian clock, as molecular targets of compound 15. In accordance with the binding property, compound 15 enhanced E-box-mediated transcription in a CRY1/2-dependent manner, and more importantly, it attenuated the circadian oscillation of Per2-Luc and Bmal1-dLuc activities in cultured fibroblasts, indicating that compound 15 can functionally inhibit the effects of CRY1/2 in the molecular circadian clockwork. In conclusion, the present study describes the first novel chemical inhibitor of CRY1/2 that inhibits the repressive function of CRY1/2, thereby activating CLOCK-BMAL1-evoked E-box-mediated transcription. Further optimizations and subsequent functional studies of this compound may lead to development of efficient therapeutic strategies for a variety of physiological and metabolic disorders with circadian natures.

Ligand-Based Design, Synthesis, and Biological Evaluation of 2-Aminopyrimidines, a Novel Series of Receptor for Advanced Glycation End Products (RAGE) Inhibitors

Using the approach of ligand-based drug design, we discovered a novel series of 4,6-disubstituted 2-aminopyrimidines as RAGE inhibitors. In transgenic mouse models of AD, one of the 4,6-bis(4-chlorophenyl)pyrimidine analogs, 59, significantly lowered the concentration of toxic soluble Aβ in the brain and improved cognitive function. SPR analysis confirmed the direct binding of 59 with RAGE, which should contribute to its biological activities via inhibition of the RAGE-Aβ interaction. We also predicted the binding mode of the 4,6-bis(4-chlorophenyl)pyrimidine analogs to the RAGE V-domain through flexible docking study.

Enantioselective total synthesis of a natural iridoid.

The first total synthesis of 6-hydroxy-7-(hydroxymethyl)-4-methylenehexahydrocyclopenta[c]pyran-1(3H)-one has been accomplished. A key feature of the synthesis includes facile construction of the bicyclic lactone intermediate via intramolecular Pd(0)-catalyzed allylic alkylation and the efficient transformation of this intermediate into the iridoid skeleton employing silicon tethered radical cyclization.

Asymmetric syntheses of 1-deoxy-6,8a-di-epi-castanospermine and 1-deoxy-6-epi-castanospermine.

Asymmetric syntheses of both 1-deoxy-6,8a-di-epi-castanospermine and 1-deoxy-6-epi-castanospermine, polyhydroxylated indolizidine alkaloids that act as selective glycosidase inhibitors, have been accomplished in seven steps. The key feature of our unique syntheses includes the stereoselective introduction of the C-3 and C-4 hydroxyl groups utilizing the aza-Claisen rearrangement-induced ring expansion of 1-acyl-2-alkoxyvinyl pyrrolidine and a substrate-controlled stereoselective transannulation of the resulting azoninone intermediate.

Concise and Enantioselective Total Synthesis of 15-Deoxy-Δ12,14-Prostaglandin J2

The concise and enantioselective synthesis of 15-deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ(2)) has been accomplished in 11 steps from a known alcohol. The key step of the synthesis involves an asymmetric Rh-catalyzed cycloisomerization of ene-ynone, followed by an olefin isomerization.