In a groundbreaking advancement from China's leading research institutions, a team at Shanghai Jiao Tong University (SJTU) has unveiled a novel asymmetric bimetallic catalysis strategy that enables the precise synthesis of chiral cyclic imine esters, also known as N-unprotected cyclic imidates. Published in the prestigious CCS Chemistry on March 5, 2026, this work represents a significant leap in organic synthesis, particularly for constructing complex chiral molecules with potential applications in pharmaceuticals and ligand design. The innovation, detailed in the paper titled "Bimetallic Copper-Catalyzed Asymmetric Propargylic Substitution: Synthesis of Chiral N-Unprotected Imidates, Mechanistic Study, and Antiviral Activity," showcases the prowess of SJTU's School of Chemistry and Chemical Engineering in pushing the boundaries of asymmetric catalysis.

This achievement not only highlights the university's role in China's drive toward scientific self-reliance under the Double First-Class initiative but also underscores the growing global influence of Chinese higher education in chemical sciences. With SJTU consistently ranking among the top chemistry programs in China—sixth nationally per Scimago Institutions Rankings 2026—the research exemplifies how elite universities are fostering interdisciplinary excellence to address real-world challenges in drug discovery and materials science.

🔬 The Significance of Chiral Cyclic Imine Esters in Modern Chemistry

Chiral cyclic imine esters are a class of optically active molecules featuring a cyclic structure with an imine (C=N) group esterified, where the chirality arises from specific stereocenters. These compounds are highly valued because one enantiomer—the mirror-image form—of a chiral molecule can be biologically active while the other is inert or even harmful. In pharmaceuticals, this stereoselectivity is crucial; for instance, over half of modern drugs are chiral, and producing the correct enantiomer can dramatically improve efficacy and reduce side effects.

Beyond drugs, these scaffolds serve as chiral ligands in catalysis, enhancing reaction selectivity in industrial processes. Traditional synthesis methods for N-unprotected versions—those without protecting groups on the nitrogen—have been limited, often requiring multi-step sequences with low yields or poor stereocontrol. The SJTU team's method addresses this gap, offering a direct, efficient route that opens new chemical space for exploration.

In the context of China's higher education landscape, where chemistry research output has surged—China leading global publications in organic chemistry per Nature Index 2026—this breakthrough aligns with national priorities for innovation in fine chemicals and biotech.

Unraveling the Challenges in Asymmetric Propargyl Substitution

Copper-catalyzed asymmetric propargyl substitution (CuAPS) is a powerful tool for building chiral propargyl frameworks, but prior systems struggled with simultaneous activation of both electrophile (propargyl carbonate) and nucleophile (α-cyano ester). Existing catalysts often favored one pathway, leading to suboptimal stereoselectivity or narrow substrate scope. The Pinner reaction, which converts nitriles to imino esters, further complicated tandem processes due to compatibility issues.

SJTU researchers identified these bottlenecks through mechanistic studies, revealing the need for a synergistic dual-copper system. Their solution: a transient binuclear copper complex that mimics enzyme-like cooperativity, achieving unprecedented efficiency with substrate-to-catalyst ratios (S/C) up to 2000—the highest reported for CuAPS.

The SJTU Team Behind the Innovation

Leading the effort are Professors Wanbin Zhang, Guoqiang Yang, and Jianming Zhang from SJTU's School of Chemistry and Chemical Engineering. Wanbin Zhang, a chair professor and pioneer in asymmetric catalysis, has authored over 300 papers, including landmark reviews in Chemical Society Reviews on bimetallic systems. His lab, the Shanghai Key Laboratory for Molecular Engineering of Chiral Drugs, has garnered awards like the Thieme Chemistry Journal Award and national recognition for antiviral drug synthesis.

Guoqiang Yang, a lecturer specializing in organic synthesis, brings expertise in metal-organic catalysis. Jianming Zhang, from the Institute of Translational Medicine, bridges chemistry and biology, evaluating the products' antiviral potential. Co-first authors Shen Zhao and Zheng Ling executed the experimental work, supported by collaborators across SJTU's veterinary and translational units. This multidisciplinary collaboration exemplifies SJTU's integrated research ecosystem, bolstered by state key labs and Frontiers Science Centers.

Step-by-Step Breakdown of the Catalytic Process

The reaction commences with propargyl carbonates (1) and α-cyano esters (2) under mild conditions: chiral Cu(I)-BOX ligand, DIPEA base, in toluene at room temperature.

• Step 1: Activation of Propargyl Electrophile - One Cu center coordinates the alkyne, forming a Cu-allenylidene intermediate (I) via oxidative addition.
• Step 2: Nucleophile Deprotonation - The second Cu stabilizes the α-cyano ester enolate (II).
• Step 3: Transient Binuclear Assembly - I and II form a pseudo-C₂-symmetric dinuclear complex (III), locked by H···π stacking between ligands.
• Step 4: Stereoselective C-C Bond Formation - Nucleophilic attack yields the propargyl product (IV), with ΔG‡ favoring the (2R,3S)-TS.
• Step 5: Pinner Cyclization - Intramolecular addition forms the chiral cyclic imine ester (3).

DFT calculations confirmed the binuclear pathway lowers barriers by 13.8 kcal/mol over mono-Cu alternatives. The full mechanistic details are available in the open-access paper.

Impressive Performance Metrics and Substrate Scope

The protocol delivers yields up to 97%, enantiomeric ratios (er) up to 97:3 (94% ee), and diastereomeric ratios (dr) >20:1. It tolerates electron-rich/poor aryls on both partners, heterocycles (thiophene, indole, pyridine), and sterically hindered ortho-substituents. Aliphatic nucleophiles proved challenging, but aryl variants excelled.

Scalability shines with 0.05 mol% catalyst (S/C 2000) yielding 62% at 93:7 er.

Versatile Derivatizations Expanding Utility

The products' N-H and alkyne moieties enable orthogonal modifications:

• N-Alkylation with Ar-Br, BnBr (yields 80-95%).
• Sonogashira coupling with phenylacetylene.
• Click chemistry with zidovudine for antiviral conjugates.
• Hydrosilylation and phosphoryl protection.

These transformations yield diverse libraries, ideal for SAR studies in pharma.

Promising Antiviral Activity Against Feline Calicivirus

Biological assays in CRFK cells infected with FCV revealed IC₅₀ values for select imidates outperforming nitazoxanide (positive control). Compounds 3af, 3p, 3u, 3ab showed selectivity indices >3, with low cytotoxicity (CC₅₀ >30 μM). FCV, modeling norovirus, highlights potential for human antiviral leads. Details from the press release emphasize this translational impact.

In China, where veterinary biotech is rising—supported by SJTU's agriculture school—this bridges chemistry and animal health.

SJTU's Leadership in China's Asymmetric Catalysis Landscape

SJTU's chemistry program ranks top-10 in China (US News 2026), with strengths in catalysis amid national trends: China produced 40% of global asymmetric catalysis papers in 2025 (per Web of Science). Initiatives like the National Key R&D Program fund such work, positioning universities like SJTU, Tsinghua, and Peking as hubs. Zhang's group alone has 20+ JACS papers on bimetallics.

This aligns with China's 14th Five-Year Plan emphasizing chiral drugs, where domestic production rose 25% yearly.

Future Prospects and Broader Implications

The transient binuclear model inspires new Cu catalysts for other transformations. Scaling for pharma pilots is feasible given low loadings. Antiviral hits warrant in vivo studies, potentially yielding FCV therapeutics amid rising pet health demands in China (market >¥100B by 2026).

For aspiring researchers, SJTU exemplifies career paths in elite Chinese unis: PhD programs, state labs, international collaborations. Explore opportunities via research positions or China higher ed jobs.

Photo by Terry Vlisidis on Unsplash

This SJTU milestone reinforces China's ascent in chemistry, blending academic rigor with practical innovation. As asymmetric catalysis evolves—trends toward earth-abundant metals like Cu—the university's contributions will shape global drug discovery.