LAUSR

In the present study, seven previously undescribed resin glycosides, designated cusponins I-VII (1–7), together with one known analog (8), were isolated from the seeds of Cuscuta japonica, a traditional medicine used in China. Structural elucidation revealed them to be glycosidic acid methyl esters, generated through on-column methyl esterification of naturally occurring resin glycosides catalyzed by NH2-functionalized silica gel. All isolates were characterized as either pentasaccharides or tetrasaccharides, incorporating D-glucose, L-rhamnose, or D-fucose units as the sugar residues. Notably, compounds 1 and 3–7 contained the uncommon aglycone, 11S-hydroxypentadecanoic acid. Bioactivity assessments demonstrated that compounds 1–4, 6 and 8 suppressed α-glucosidase activity, with IC50 values between 8.02 and 71.39 μM. In addition, compounds 3 and 5 exhibited inhibitory effects on protein tyrosine phosphatase 1B (PTP1B), with IC50 values of 14.19 ± 1.29 μM and 62.31 ± 8.61 μM, respectively, marking the first report of PTP1B inhibitory activity among resin glycosides. Enzyme kinetic analyses indicated that compound 2 acted as an uncompetitive α-glucosidase inhibitor (Kis = 3.02 μM), whereas compound 3 inhibited PTP1B via a mixed-type mechanism (Kᵢ = 24.82 μM; Kis = 64.24 μM). Molecular docking combined with molecular dynamics simulations suggested that compounds 2 and 3 interacted with α-glucosidase-pNPG and PTP1B, respectively, forming stable complexes with favorable binding free energies. Collectively, this study reported eight resin glycosides from C. japonica, seven of them newly identified, with compounds 2 and 3 highlighted as promising scaffolds for antidiabetic drug discovery.