Fenghua Kang

Nuclear magnetic resonance (NMR) chemical shift calculation is a powerful tool for structural elucidation, and has been extensively employed in both synthetic and natural product chemistry. However, density functional theory (DFT) NMR chemical shift calculations are usually time-consuming, while fast data-driven methods often lack reliability, making it challenging to apply them to computationally intensive tasks. Herein, we have constructed a 54-layer deep graph convolutional network for 13C NMR chemical shift calculation, which achieved high accuracy with low time-cost, and performed competitively with DFT NMR chemical shift calculations on structure assignment benchmarks. Our model utilizes a semi-empirical method, GFN2-xTB, and is compatible with a broad variety of organic systems, including those composed of hundreds of atoms or elements ranging from H to Rn. We used this model to resolve the controversial J/K rings junction problem of maitotoxin, which is the largest whole molecule assigned by NMR calculation to date. This model has been developed into a user-friendly software, providing a useful tool for routinary rapid structure validation and assignation, as well as a new approach to elucidate the large structures that were previously unsuitable for NMR calculation.

Two new phthalide derivatives, rhytidhylides A (1) and B (2), together with ten known compounds (3–12) were isolated from cultures of Rhytidhysteron sp. BZM-9, an endophyte isolated from the leaves of Leptospermum brachyandrum. Their structures were identified by an extensive analysis of NMR, HRESIMS, ECD, and through comparison with data reported in the literature. In addition, the cytotoxic activities against two human hepatoma cell lines (HepG2 and SMMC7721) and antibacterial activities against MRSA and E. coli were evaluated.

Four new biflavonoids (1–4) were isolated from Selaginella doederleinii together with a known biflavonoid derivative (5). Their structures contained a rare linker of individual flavones to each other by direct C-3-O-C-4′′′ bonds, and were elucidated by extensive spectroscopic data, including HRESIMS, NMR and ECD data. All isolates significantly inhibited the proliferation of NSCLC cells (IC₅₀ = 2.3–8.4 μM) with low toxicity to non-cancer MRC-5 cells, superior to the clinically used drug DDP. Furthermore, the most active compound 3 suppressed XIAP and survivin expression, promoted upregulation of caspase-3/cleaved-caspase-3, as well as induced cell apoptosis and cycle arrest in A549 cells. Together, our findings suggest that 3 may be worth studying further for intervention of NSCLC.