Molecular Networking-Guided Annotation of Flavonoid Glycosides from Quercus mongolica Bee Pollen

Bee pollen is a primary and secondary metabolite-rich natural product collected by pollinators such as honeybees. Polyphenols, particularly flavonoids, are well known for their potent antioxidant activities. Numerous phytochemical and biological studies have focused on Quercus mongolica, a member of the Fagaceae family. However, research focusing specifically on pollen is limited. Moreover, bee pollen chemical composition varies significantly depending on its geographical origin and cultivation conditions. In this study, the flavonoid glycosides of Q. mongolica pollen were profiled using LC-MS/MS-based molecular networking, which revealed that the largest molecular cluster corresponded to flavonoid glycosides. A total of 69 flavonoid glycosides, primarily comprising 2 kaempferol derivatives, 14 quercetin derivatives, and 46 isorhamnetin derivatives, were annotated based on MS/MS fragmentation patterns, spectral library matches in GNPS (Global Natural Products Social Molecular Networking), and comparison with previously reported data. Two primary compounds, isorhamnetin 3-O-β-_D-xylopyranosyl (1→6)-β-_D-glucopyranoside and isorhamnetin-3-O-neohesperidoside, were identified by comparison with reference standards. This study offers foundational insights into the flavonoid diversity of Q. mongolica pollen, contributing to a broad understanding of its secondary metabolite profile.