Freshwater clam (C. fluminea, FC) was obtained from LiChuan Agriculture Farm (Changhua, Taiwan). The extraction method underwent modification based on a previous study [17 (link)]. First, to prepare the ethanol extract of freshwater clam (FCE), freshwater clam tissue was cut into small pieces, homogenized in a blender, and extracted three times with ethanol. The resulting supernatant was filtered and concentrated using a rotary evaporator under vacuum and then subjected to freeze-drying. Second, to prepare the ethyl acetate-extracted FCE (EA-FCE), the freeze-dried powder was extracted with ethyl acetate (FCE: water: ethyl acetate weight ratio = 1:2:3) and then subjected to freeze-drying. Third, TNHD was isolated from the EA-FCE by silica gel column chromatography (8 × 70 cm and 3.5 × 40 cm, Merck 40–63 μm) and further purified using HPLC with a Phenomenex Luna C-18 column (5 mm, 250 mm × 10 mm). The sample extraction process is shown in Fig. S1. The fractions were screened for bioactivity using a cell model, with those that showed high inhibition ability on HepG2 cells chosen and purified to obtain trans-2-nonadecyl-4-(hydroxymethyl)-1,3-dioxolane (TNHD) (Fig. S2A; Fig. S2B). The structure of TNHD was identified with NMR (Fig. S3).