Homosecoiridoids from the Flower Buds of Lonicera japonica

Homosecoiridoids (1–15) were isolated from the flower buds of Lonicera japonica. Compounds 1–4, designated as loniphenyruviridosides A–D, possess unprecedented skeletons featuring phenylpyruvic acid derived moieties coupled with an iridoid or a secoiridoid nucleus. Compounds 5–15 (lonijaposides D–N) are additional examples of the unusual pyridinium alkaloid-coupled secoiridoids (lonijaposides A–C). The validity of the CD data to determine the configuration of the secoiridoid derivatives is discussed on the basis of detailed CD data analysis and semisynthesis of 2 and 3 with the co-occurring secologanic acid. The configuration of secologanic acid was determined by a single-crystal X-ray crystallographic analysis using anomalous scattering of Cu Kα radiation. Biosynthetic pathways of the homosecoiridoids were postulated. Compounds 1–4 inhibited STAT-3 activity of HELF cells, and lonijaposides F (7), H (9), I (10), and K (12) showed activity against the release of glucuronidase in rat polymorphonuclear leukocytes induced by platelet-activating factor.