Advances in plant-derived C-glycosides: Phytochemistry, bioactivities, and biotechnological production

C-glycosides represent a large group of natural products with a C-C bond between the aglycone and the sugar moiety. They exhibit great structural diversity, wide natural distribution, and significant biological activities. By the end of 2021, at least 754 C-glycosides and their derivatives have been isolated and characterized from plants. Thus far, 66 functional C-glycosyltransferases (CGTs) have been discovered from plants, and provide green and efficient approaches to synthesize C-glycosides. Herein, advances in plant-derived C-glycosides are comprehensively summarized from aspects of structural diversity and identification, bioactivities, and biotechnological production. New strategies to discover novel C-glycosides and CGTs, as well as the applications of biotechnological methods to produce C-glycosides in the future are also discussed.

Structurally diverse diterpenoids from Isodon pharicus

Twenty-one structurally diverse diterpenoids (1–21), wherein 1, 2, and 4 represented unprecedented architectures, were isolated from Isodon pharicus.

Diterpenoids from Isodon species: an update

Covering: December 2005 to June 2016. Previous review: Nat. Prod. Rep., 2006, 23, 673-698Over the last decade, great efforts have been made to conduct phytochemistry research on the genus Isodon, which have led to the isolation and identification of a number of diterpenoids. At the same time, these newly reported diterpenoids with diverse structures have led to new findings on their biological functions and chemical synthesis research. In this update, we review more than 600 new diterpenoids, including their structures, classifications, biogenetic pathways, bioactivities, and chemical synthesis.

Fimbriatols A-J, Highly Oxidized ent-Kaurane Diterpenoids from Traditional Chinese Plant Flickingeria fimbriata (B1.) Hawkes

Fimbriatols A–J (1–10), ten new ent-kaurane diterpenoids possessing differently highly oxidized sites, were isolated from Flickingeria fimbriata (B1.) Hawkes. The structures of these new compounds were determined by HRESI-MS, NMR, CD spectra and X-ray diffraction analysis. Compound 1 displayed moderately inhibitory ratio (48.5%) compared with the positive compound NSC-87877 (81.6%) at the concentration of 0.022 μg/mL. Compounds 7–10 possess 3, 4-seco-ent-kaurane skeleton containing a disaccharide moiety with an unusual linkage at C-2′ to C-1′′ instead of the common linkage at C-6′ to C-1′′, and this is the first report in 600 more ent-kauranes found in nature, which might be originated from ent-kaurane diterpenoids through post-modified reactions of Baeyer-Villiger oxygenation and glycosylation.

Cytotoxic ent-kaurane diterpenoids from Isodon wikstroemioides

Phytochemical investigation of EtOAc extracts of the aerial parts of Isodon wikstroemioides afforded 18 new ent-kaurane diterpenoids (wikstroemioidins E-V, 1-18), along with 17 known analogues (19-35). The absolute configurations of 1 and 16 were confirmed by single-crystal X-ray diffraction analysis. The isolates were screened against five human tumor cell lines; compounds 3, 4, 9, 11-13, 23, 25-28, and 33 exhibited significant cytotoxic activity against all five, with IC50 values ranging from 0.4 to 5.1 μM. In addition, 17 of the isolates strongly inhibited nitric oxide production in LPS-activated RAW264.7 macrophages.

Enmein-type 6,7-seco-ent-kauranoids from Isodon sculponeatus

Fourteen enmein-type 6,7-seco-ent-kaurane diterpenoids, seven new ones (sculponins M-S, 1-7) and seven known compounds (8-14), were isolated from the aerial parts of Isodon sculponeatus . Compound 1 is the first example of an ent-kauranoid, possessing a 11,12-epoxy group, and compounds 6 and 7 have a rare 3,6-epoxy group. The structures were established primarily by NMR and MS methods, and the absolute configurations of 1, 3, and 6 were determined by single-crystal X-ray diffraction. Compound 14 showed significant cytotoxic activity against five human tumor lines, with IC50 values ranging from 1.0 to 3.5 μM, and it also inhibited NO production in LPS-stimulated RAW264.7 cells, with an IC50 value of 2.2 μM.