Targeted Isolation of Antiviral Labdane Diterpenes from the Bark of Neo-uvaria foetida(Annonaceae) using LC-MS/MS-Based Molecular Networking

In the search of new inhibitors for human coronavirus (HCoV), we screened extracts of endemic Annonaceae plants on an assay using a cellular model of Huh-7 cells infected with the human alphacoronavirus HCoV-229E. The EtOAc bark extract of the rare Southeast Asian plant Neo-uvaria foetidaexhibited inhibition of HCoV-229E and SARS-CoV-2 viruses with IC50values of 3.8 and 7.8 μg/mL, respectively. Using LC-MS/MS and molecular networking analysis guided isolation, we discovered two new labdane-type diterpenoids, 8-epi-acuminolide (1) and foetidalabdane A (4), and three known labdane diterpenoids, acuminolide (2), 17-O-acetylacuminolide (3), and spiroacuminolide (5). A new norlabdane diterpene, 16-foetinorlabdoic acid (6), was also isolated and identified. Excluding compounds 5and 6, all other metabolites were active against the virus HCoV-229E. Terpenoids 1and 4presented antiviral activity against SARS-CoV-2 with IC50values of 63.3 and 93.5 μM, respectively, indicating lower potency. Additionally, virological assays demonstrated that compounds 1, 2, and 3exert antiviral effects against Zika virus by specifically interfering with the late stage of its infectious cycle with IC50values of 76.0, 31.9, and 14.9 μM, respectively.