Chi-Yuan Chu

Fluorous oxime palladacycle: a precatalyst for carbon-carbon coupling reactions in aqueous and organic medium.

To facilitate precatalyst recovery and reuse, we have developed a fluorous, oxime-based palladacycle 1 and demonstrated that it is a very efficient and versatile precatalyst for a wide range of carbon-carbon bond formation reactions (Suzuki-Miyaura, Sonogashira, Stille, Heck, Glaser-type, and Kumada) in either aqueous or organic medium under microwave irradiation. Palladacycle 1 could be recovered through F-SPE in various coupling reactions with recovery ranging from 84 to 95% for the first cycle. Inductively coupled plasma optical emission spectrometry (ICP-OES) analyses of the Pd content in the crude product from each class of transformation indicated extremely low levels of leaching and the palladacycle could be reused four to five times without significant loss of activity.

Development of a fluorous, oxime-based palladacycle for microwave-promoted carbon–carbon coupling reactions in aqueous media

A thermally stable, fluorous oxime-based palladacycle has been developed and was shown to efficiently promote various carbon–carbon bond formation reactions (Suzuki–Miyaura, Sonogashira and Stille) in aqueous media under microwave irradiation. The palladacycle gave extremely low levels of Pd leaching and could be reused five times with no significant loss of activity.

Development of an Activity-Based Probe for Steroid Sulfatases

the enzyme family responsiblefor the removal of the sulfate moieties from various sulfatedbiomolecules has gained considerable attention. For example,human steroid sulfatase (STS, EC 3.1.6.2) has become a targetofdrug development over the last decade due to its involve-ment in estrogen-dependent tumors.

Selective activation of SHP2 activity by cisplatin revealed by a novel chemical probe-based assay.

Src homology-2 (SH2) domain-containing phosphatase 2 (SHP2) is known to participate in several different signaling pathways to mediate cell growth, survival, migration, and differentiation. However, due to the lack of proper analytical tools, it is unclear whether the phosphatase activity of SHP2 is activated in most studies. We have previously developed an activity-based probe LCL2 that formed covalent linkage with catalytically active protein tyrosine phosphatases (PTPs). Here, by combining LCL2 with a SHP2 specific antibody, we established an assay system that enables the direct monitoring of SHP2 activity upon cisplatin treatment of cancer cells. The protocol is advantageous over conventional colorimetric or in-gel PTP assays as it is specific and does not require the use of radioisotope reagents. Using this assay, we found SHP2 activity was selectively activated by cisplatin. Moreover, the activation of SHP2 appeared to be specific for cisplatin as other DNA damage agents failed to activate the activity. Although the role of SHP2 activation by cisplatin treatments is still unclear to us, our results provide the first direct evidence for the activation of SHP2 during cisplatin treatments. More importantly, the concept of using activity-based probe in conjunction with target-specific antibodies could be extended to other enzyme classes.

Development of Activity-Based Probes for Imaging Human α-l-Fucosidases in Cells

We have established a concise synthetic route relying on a key base-promoted epimerization step to synthesize two series of activity-based probes carrying a BODIPY fluorophore for α-l-fucosidase. The resulting probes were evaluated for labeling performance. The one utilizing an o-fluoromethylphenol derivative as the latent trapping unit was successfully applied for the first time to visualize and locate lysosomal α-l-fucosidase activity in human cells.

Development and Evaluation of Novel Phosphotyrosine Mimetic Inhibitors Targeting the Src Homology 2 Domain of Signaling Lymphocytic Activation Molecule (SLAM) Associated Protein

Specific interactions between Src homology 2 (SH2) domain-containing proteins and the phosphotyrosine-containing counterparts play significant role in cellular protein tyrosine kinase (PTK) signaling pathways. The SH2 domain inhibitors could potentially serve as drug candidates in treating human diseases. Here we have incorporated a novel phosphotyrosine mimetic, which is an unusual amino acid carrying a cyclosaligenyl (cycloSal) phosphodiester moiety, into dipeptides to investigate the inhibitory effect on SH2 domain-containing proteins. A plate-based assay was also established to screen for inhibitors that disrupt the interaction between a phosphopeptide of SLAM (signaling lymphocytic activation molecule) and its interacting protein SAP (SLAM-associated protein). We identified a number of inhibitors with IC50 values in the range of 17-35 μM, implying that the cycloSal phosphodiester-carrying amino acid could mimic the phosphotyrosyl residue. Our results also raise the possibility of integrating the newly developed phosphotyrosine mimetic moiety into inhibitors designed for other SH2 domain-containing proteins.

Application of a recyclable fluorous oxime in the convenient synthesis of 3-amino-1,2-benzisoxazoles and 4-amino-1H-2,3-benzoxazines

A microwave-assisted, fluorous synthetic route to 3-amino-1,2-benzisoxazoles and 4-amino-1H-2,3-benzoxazines has been developed. The strategy comprises linking the respective 2-fluorobenzonitrile or 2-(bromomethyl)benzonitrile to a fluorous oxime tag to give an aryloxime intermediate which then undergoes cyclization with concomitant cleavage of the substrate-tag in acidic conditions to provide the desired product in good to moderate yields. In addition, the aryloxime intermediate could be subjected to further reactions to expand the compound library. The product could be easily separated using fluorous solid-phase extraction (F-SPE) and the fluorous ketone recovered could be converted back to the fluorous oxime and reused in the next run of the synthesis.