On the afternoon of 20 March 2026, at VNUHCM–University of Science (HCMUS), researcher Đoàn Thiên Thanh (Biotechnology, class of 2017) successfully defended a doctoral thesis at the institutional level. The research is entitled: “Study on the activity and mechanism of action against Helicobacter pylori of extracts and compounds from hexane fractions of Cleistocalyx operculatus (Roxb.) Merr. et Perry (synonym Syzygium nervosum) leaves and flower buds”.

The thesis was conducted under the academic supervision of Senior Lecturer Dr Lương Thị Mỹ Ngân and Senior Lecturer Dr Trần Trung Hiếu. The study focuses on harnessing the medicinal potential of Cleistocalyx operculatus—a species familiar in daily life with significant value in traditional medicine, though the biological mechanisms of the species remain insufficiently researched.

The scope of the research involved the collection of total extracts and fractional extracts from the leaves and flower buds of C. operculatus, alongside the qualitative and quantitative analysis of natural compounds present within these extracts. On this basis, the thesis evaluated the anti-Helicobacter pylori activity and the in vitro urease enzyme inhibition capacity. The hexane fraction from flower buds was selected for further isolation and identification of primary bioactive compounds. Furthermore, the study analysed the mechanisms by which the extracts and compounds affect biofilm formation, cellular integrity, and morphology, as well as the expression levels of bacterial virulence genes.

The research findings yielded 14 total extracts and 6 fractional extracts from the leaves and flower buds. These fractional extracts demonstrated higher concentrations of natural compounds—specifically phenols and flavonoids—compared to the total extracts. Hexane fractions exhibited marked inhibitory activity against H. pylori, with Minimum Inhibitory Concentrations (MIC) ranging from 62.5 to 125 µg/mL, whilst effectively inhibiting the urease enzyme. From the hexane fraction of the flower buds, the study isolated and identified three representative compounds: DMC, kaempferol, and β-sitosterol, with DMC and kaempferol showing prominent anti-H. pylori activity.

These compounds not only inhibit bacterial growth but also influence several critical biological mechanisms. Such actions include the suppression of biofilm formation, increasing membrane permeability, and disrupting cell membrane structure. There was also a significant reduction in the expression of virulence genes, namely cagA, vacA, ureA, ureB, flaA, flaB, flgE, and dnaA. Toxicity assessments indicated a high level of safety on normal cells, suggesting significant potential for application within the biomedical field.

From the achieved results, the thesis provides further scientific evidence regarding the medicinal value of C. operculatus in the prevention and supportive treatment of gastric diseases related to Helicobacter pylori. This approach, utilising natural compounds, is regarded as a promising pathway to reduce reliance on antibiotics and contribute to mitigating the rise of drug resistance.

The Board commended the thesis for the systematic approach, clear data, and reliability. The findings hold scientific value and provide a significant reference for future research in medicinal plants and microbiology.