Structurally diverse glycosides of secoiridoid, bisiridoid, and triterpene-bisiridoid conjugates from the flower buds of two Caprifoliaceae plants and their ATP-citrate lyase inhibitory activities.

The ethanolic extracts of the dried flower buds of two Caprifoliaceae plants, Lonicera japonica and Abelia × grandiflora, showed considerable inhibitory activities against adenosine triphosphate (ATP)-citrate lyase (ACL), a new promising drug target for the treatment of metabolic disorders. Bioassay-guided purification in conjunction with HPLC-PDA profiling led to the isolation and characterization of thirty-five (1-35) and fourteen (1'-14') structurally diverse compounds from the above two plant extracts, respectively. Compounds 1-9 and 1'-6' are previously undescribed glycosides. Their structures were elucidated on the basis of spectroscopic data, electronic circular dichroism (ECD), and single crystal X-ray diffraction analyses. In particular, lonicejaposide A (1) has an unprecedented skeleton generated through the coupling of C-7 in secologanin with C-2'' in phenylacetaldehyde via an aldol condensation. Abeliflorosides A (1') and B (2') are hitherto unknown glycosides of triterpene and bisiridoid conjugates constructed through the formation of a 1,3-dioxane moiety. All the isolates were evaluated for their inhibitory activities against ACL. Compounds 9, 25-28, 31, 1', 2', and 14' displayed significant inhibitory effects, with IC50 values ranging from 0.1 to 14.2 µM. The interactions of selected compounds possessing different structure features (e.g., 9, 25, 31, and 2') with ACL were thereafter performed by employing molecular docking studies. In addition, compound 2', the most complex triterpene-bisiridoid conjugate glycoside reported herein, also inhibited acetyl-CoA carboxylase 1 (ACC1), with an IC50 value of 7.9 µM. The dried material of the flower buds of L. japonica (honeysuckle) is a well-known traditional oriental medicine (i.e., Flos Lonicerae Japonicae, FLJ) and has long been used in large quantities. The above findings not only provide new insights for the development of multipurpose utilization of FLJ in healthcare community, but also provide profitable clues indicating that the flower buds of A. × grandiflora might be a potential alternative to FLJ in the traditional Chinese medicine market.