Lijing Fang

Synthesis of the C1-C12 fragment of iriomoteolide 1a by sequential catalytic asymmetric vinylogous aldol reactions.

An efficient synthesis of the C1-C12 fragment of iriomoteolide 1a has been accomplished via sequential application of two catalytic, asymmetric, vinylogous aldol reactions: a catalytic vinylogous aldol reaction was used to enantioselectively introduce the C5-C8 segment, and a second catalytic vinylogous aldol reaction was used to install the remaining two stereocenters and a stereodefined alkene in the form of an alpha,beta-unsaturated delta-lactone in one step.

Synthesis and structure–activity relationship studies of teixobactin analogues

A new series of teixobactin analogues were synthesized via an oxidative cyclative cleavage approach using aryl hydrazide resin as the solid support. Structure–activity relationship studies revealed that the guanidine or amine group at position 10, the hydroxyl group of Ser7 residue and the NH proton of the N-terminal Phe1 residue are critical to the antibacterial activities, while side chain size and functional group changes are tolerated at position 4. These findings will facilitate the development of new teixobactin analogues with enhanced pharmacological properties.

Enantioselective Synthesis of a Diastereomer of Iriomoteolide-1a. What Is the Correct Structure of the Natural Product?

An enantioselective approach to a diastereomer of iriomoteolide-1a is described. Highlighted is a SmI(2)-mediated intramolecular reductive cyclization approach to complex cyclic hemiketals. An acetylide-chloroformate coupling strategy is also featured. Our results show that the structures of iriomoteolide-1a-1c require careful reassessment.

Efficient Synthesis and Stereochemical Revision of Coibamide A

Coibamide A is a highly potent antiproliferative cyclodepsipeptide originally isolated from a Panamanian marine cyanobacterium. Herein we report an efficient solid-phase strategy for assembly of highly N-methylated cyclodepsipeptides, which is invaluable in generating coibamide A derivatives for structure-activity relationship studies. As a consequence of our synthetic studies, two stereochemical assignments of coibamide A were revised and the total synthesis of this natural compound was achieved for the first time.

NUMB negatively regulates the epithelial-mesenchymal transition of triple-negative breast cancer by antagonizing Notch signaling

Triple-negative breast cancer (TNBC), an aggressive subtype of breast cancer with higher rates of early relapse and metastasis, is frequently associated with aberrant activation of epithelial-mesenchymal transition (EMT). Nonetheless, how EMT is initiated and regulated during TNBC progression is not well understood. Here, we report that NUMB is a negative regulator of EMT in both human mammary epithelial cells and breast cancer cells. Reduced NUMB expression was significantly associated with elevated EMT in TNBC. Conversely, overexpression of NUMB strongly attenuated the EMT program and metastasis of TNBC cell lines. Interestingly, we showed that NUMB employs different molecular mechanisms to regulate EMT. In normal mammary epithelial cells and breast cancer cells expressing wild-type p53, NUMB suppressed EMT by stabilizing p53. However, in TNBC cells, loss of NUMB facilitated the EMT program by activating Notch signaling. Consistent with these findings, low NUMB expression and high Notch activity were significantly correlated with the TNBC subtype in patients. Collectively, these findings reveal novel molecular mechanisms of NUMB in the regulation of breast tumor EMT, especially in TNBC.

Fully automated synthesis of DNA-binding Py-Im polyamides using a triphosgene coupling strategy.

The fully automated solid-phase synthetic strategy of hairpin pyrrole-imidazole polyamides is described. A key advance is the development of methodology for the application of triphosgene as a coupling agent in the automated synthesis of hairpin polyamides without racemization. This automated methodology is compatible with all the typical building blocks, enabling the facile synthesis of polyamide libraries in good yield (9-15%) and crude purity.

Total Synthesis and Stereochemical Assignment of Gymnopeptides A and B

Gymnopeptides A and B are unprecedented highly N-methylated cyclic β-hairpin octadecapeptides with striking antiproliferative activities isolated from the mushroom Gymnopus fusipes. Using Fmoc-based solid-phase peptide synthesis, followed by macrolactamization of the resulting linear peptides, the first total synthesis of gymnopeptides A and B was successfully achieved in this study. The coupling methods used for the solid-phase synthesis and the cyclization were optimized, and the configuration of the Ser1/Thr1 residue in gymnopeptide A/B was determined to be l.

Pyrrole‐Imidazole Polyamides: Automated Solid‐Phase Synthesis

In this unit, the fully automated solid‐phase synthetic strategy of hairpin Py‐Im polyamides is described using triphosgene (BTC) as a coupling agent. This automated methodology is compatible with all the typical building blocks, enabling the facile synthesis of polyamide libraries in 9% to 20% yield in 3 days.

Targeting Polo-like Kinase 1 by a Novel Pyrrole-Imidazole Polyamide–Hoechst Conjugate Suppresses Tumor Growth In Vivo

The serine/threonine kinase Polo-like kinase 1 (Plk1) plays a pivotal role in cell proliferation and has been validated as a promising anticancer drug target. However, very limited success has been achieved in clinical applications using existing Plk1 inhibitors, due to lack of sufficient specificity toward Plk1. To develop a novel Plk1 inhibitor with high selectivity and efficacy, we designed and synthesized a pyrrole-imidazole polyamide–Hoechst conjugate, PIP3, targeted to specific DNA sequence in the PLK1 promoter. PIP3 could specifically inhibit the cell cycle–regulated Plk1 expression and consequently retard tumor cell growth. Cancer cells treated with PIP3 exhibited severe mitotic defects and increased apoptosis, whereas normal cells were not affected by PIP3 treatment. Furthermore, subcutaneous injection of PIP3 into mice bearing human cancer xenografts induced significant tumor growth suppression with low host toxicity. Therefore, PIP3 exhibits the potential as an effective agent for targeted cancer therapy. Mol Cancer Ther; 17(5); 988–1002. ©2018 AACR.

Improved Total Synthesis and Biological Evaluation of Coibamide A Analogues

To enable the large-scale synthesis of coibamide A, we developed an improved synthetic strategy for this class of cyclodepsipeptide. The versatility of the synthetic procedure was demonstrated by the preparation of a series of designed coibamide A analogues, which enabled the preliminary structure-activity relationship (SAR) studies for this compound. Although most modifications of coibamide A resulted in decrease or loss of the antiproliferativity, we found that versatile substitution at position 3 was well tolerated. Remarkably, a simplified analogue, [MeAla3-MeAla6]-coibamide (1f), not only showed nearly the same inhibition as coibamide A against the tested cancer cells but also significantly inhibited tumor growth in vivo. The improved synthetic strategy and the relevant trends of SAR disclosed in this study will be valuable for further optimization of the overall profile of coibamide A.