A new labdane diterpenoid, in vitro and in silico cytotoxicity, and protease inhibitory effects of phytochemicals from Juniperus polycarpos K. Koch leaves

Cytotoxicity-guided purification of Juniperus polycarpos K. Koch leaves (Cupressaceae) led to the isolation of a new labdane diterpenoid, 3-(acetyloxy)-acetylisocupressic acid (1), together with isocupressic acid (2), 3,4-dimethoxycinnamoyl alcohol (3) and deoxypodophyllotoxin (4). The chemical structures of 1-4 were established by detailed 1D and 2D NMR, HRFAB-MS and LRESI-MS, as well as by comparing the spectral data with those reported in the literature. Compound 1 was ineffective against HepG2 cells and protease enzyme, while 2 showed potent cytotoxicity against HepG2 cells (IC₅₀ of 3.73 μg/mL) compared to cisplatin (IC₅₀ of 12.65 μg/mL). Computational analyses with CDK1 protein (a prominent protein in the cell cycle of HepG2 cells) revealed the binding affinity of 2 (-31.86 kcal/mol) was better than 1 (-19.70 kcal/mol) because the acetoxy groups did not allow binding deeply to the ATP binding site. Compounds 2 and 4 moderately inhibited the protease activity (IC₅₀ = 52.7 and 63.0 μg/mL, respectively). Further in vitro and in vivo studies on the plant are strongly recommended.