Physicochemical and Biological Characterisation of a Crystalline Wood Exudate (“Wood Snow”) From the Endemic Conifer Cupressus tonkinensis

Objective Cupressus tonkinensis is a rare, endangered conifer confined to the limestone mountains of northern Vietnam and is prized for its fragrant, exceptionally durable timber. A thin, white, crystal-like layer, locally called “wood snow” (tuyết Hoàng đàn), often forms on the surface of wood, yet its nature has never been scientifically established. This gap has allowed misconceptions to spread - most damagingly, the belief that the layer is a fungal growth - undermining the reputation and sustainable use of the species. Methods This study aimed to determine the chemical identity, physicochemical behaviour, and antibacterial and antibiofilm activities of the exudate. The crystalline material was collected directly from the wood surface and characterised by GC–MS, one- and two-dimensional NMR, optical rotation, differential scanning calorimetry, and solubility testing. Results Its single constituent was identified as the sesquiterpene alcohol (–)- epi -cedrol, which melted sharply at 87.4 °C (ΔH = 65.64 J g -1 ). Contrary to the fungal misconception, (–)- epi -cedrol inhibited five multidrug-resistant Gram-positive and Gram-negative pathogens by 79.7–83.9% at the highest concentration tested (1000 µg/mL), although visible growth was not abolished at this level (MIC > 1000 µg/mL), and it suppressed biofilm formation, most strongly against Pseudomonas aeruginosa (70.5 ± 2.6% at 1000 µg/mL). Conclusion These findings provide the first chemical evidence that “wood snow” is a wood-derived terpenoid rather than a contaminant and offer new insights into the chemical ecology of C. tonkinensis . As the material originated from a single site and a single collection event, the data constitute a preliminary, single-source baseline.