Antibacterial and Antifungal Sesquiterpenoids: Chemistry, Resource, and Activity.

Infectious diseases caused by bacteria and fungi are threatening human health all over the world. It is an increasingly serious problem that the efficacies of some antibacterial and antifungal agents have been weakened by the drug resistance of some bacteria and fungi, which makes a great need for new antibiotics. Sesquiterpenoids, with abundant structural skeleton types and a wide range of bioactivities, are considered as good candidates to be antibacterial and antifungal agents. In the past decades, many sesquiterpenoids were isolated from plants and fungi that exhibited good antibacterial and antifungal activities. In this review, the names, source, structures, antibacterial and antifungal degrees, and mechanisms of sesquiterpenoids with antibacterial and antifungal activity from 2012 to 2022 are summarized, and the structure-activity relationship of these sesquiterpenoids against bacteria and fungi is also discussed.

Cytochalasins from Xylaria sp. CFL5, an Endophytic Fungus of Cephalotaxus fortunei.

Three previously undescribed cytochalasins, named xylariasins A‒C (1‒3), together with six known ones (4‒9) were isolated from Xylaria sp. CFL5, an endophytic fungus of Cephalotaxus fortunei. The chemical structures of all new compounds were elucidated on the basis of extensive spectroscopic data analyses and electronic circular dichroism calculation, as well as optical rotation calculation. Biological activities of compounds 1, 4‒9 were evaluated, including cytotoxic, LAG3/MHC II binding inhibition and LAG3/FGL1 binding inhibition activities. Compounds 6 and 9 possessed cytotoxicity against AGS cells at 5 µM, with inhibition rates of 94% and 64%, respectively. In addition, all tested isolates, except compound 6, exhibited obvious inhibitory activity against the interaction of both LAG3/MHC II and LAG3/FGL1. Compounds 1, 5, 7, and 8 inhibited LAG3/MHC II with IC50 values ranging from 2.37 to 4.74 µM. Meanwhile, the IC50 values of compounds 1, 7, and 8 against LAG3/FGL1 were 11.78, 4.39, and 7.45 µM, respectively.

Halimane and labdane diterpenoids from Leonurus japonicus and their anti-inflammatory activity.

Ten highly oxygenated diterpenoids (nine undescribed ones) were isolated from the aerial parts of Leonurus japonicus Houtt. 14,15-Dinor-labd-5,8-dien-3,13-dione was a 14,15-dinor-labdane diterpenoid possessing a C18 skeleton. 7ß,9α-Dihydroxy-6-oxo-labd-13-en-15,16-amide represented a rare example of labdane diterpenoid featuring an α,ß-unsaturated-γ-lactam moiety. The structures of all compounds were elucidated using spectroscopic data analyses and comparisons. The effects of these obtained compounds on nitric oxide (NO) production induced by lipopolysaccharide (LPS) in RAW 264.7 cells were evaluated.(10R*,13R*,15R*)-15,16-Epoxy-6,13-dihydroxy-15-methoxy-labda-5,8-dien-7-one inhibited NO production with an IC50 value of 40.1 µM.

Phytotoxic neo-clerodane diterpenoids from the aerial parts of Scutellaria barbata.

Bioactivity guided the isolation of extracts from the aerial parts Scutellaria barbata D. Don to discover neo-clerodane diterpenoids with potent phytotoxic activity. Of the 34 isolates, 13 neo-clerodane diterpenoids were described for the first time. The structures of these undescribed compounds were elucidated by extensive analysis of NMR spectroscopic data, and the absolute configurations of scutebarbolides A and L and scutebata W were determined by X-ray diffraction. The phytotoxic activity of all compounds against the growth of the roots and shoots of L. perenne and L. sativa seedlings were first reported, and some compounds showed considerable inhibitory effects, especially scutebarbolide K, whose inhibition rates were higher than those of the positive control at concentrations ranging from 25 to 200 µg/mL. When L. perenne and L. sativa seedlings were treated at a concentration of 200 µg/mL, scutebarbolide K caused wilting symptoms on and finally death of these two tested plant seedlings. In addition, the structure-activity relationships of these neo-clerodane diterpenoids were also discussed.

Anti-inflammatory evaluation and structure-activity relationships of diterpenoids isolated from Euphorbia hylonoma.

A phytochemical investigation to obtain chemical components with potential anti-inflammatory activity from E. hylonoma led to the isolation of nine new ent-isopimarane diterpenoids (1 and 3-10), a new ent-rosane diterpenoid (11), along with eight known ones (2 and 12-18) using various chromatographic techniques. Compounds 3, 4, 5, and 10 were rare examples of the epoxy-ent-isopimarane. The structures of these new compounds were confirmed by extensive spectroscopic data, crystal X-ray diffraction analysis, and electronic circular dichroism. And the isolates were evaluated for their inhibitory effects on nitric oxide production induced by lipopolysaccharide in RAW 264.7 cells. The results showed that compounds 2 and 12 exhibited noteworthy inhibitory effects against NO production with IC50 values of 7.12 and 12.73 µM, respectively, which were better than positive control (IC50 = 41.41 µM). The possible mechanism that compounds 2 and 12 could inhibit NO production was investigated by the Western blotting experiments.

Highly Oxygenated Triterpenoids and Rare Tetraterpenoids from Abies chensiensis and Their Antibacterial Activity.

Nine new cycloartane triterpenoids (1, 2, 4, 7, 8, 12, 15, 17, and 18) and two new rare tetraterpenoids (24 and 25) formed via a [4 + 2] Diels-Alder cycloaddition between a lanostane triterpenoid and a monoterpenoid, along with 14 previously known triterpenoids, were isolated from the bark of the branches of Abies chensiensis. The structures and absolute configurations of new compounds were elucidated based on spectroscopic data, X-ray diffraction analysis, and electronic circular dichroism. Some of the isolates were evaluated for their antibacterial activity by determining their minimum inhibitory concentrations and growth inhibition curves and examining for morphological alterations. Among the compounds tested, the new cycloartane triterpenoid 8 was the most active against Bacillus subtilis. Thus, morphological alterations of B. subtilis on treatment with 8 were observed by scanning electron microscopy, showing that the cells were irregular, wrinkled, and disrupted.

Labdane-Type Diterpenoids from Leonurus japonicus and Their Plant-Growth Regulatory Activity.

Thirteen new labdane-type diterpenoids 1-6, 9-11, 13, 14, 18, and 19 and seven known ones were isolated from the aerial parts of Leonurus japonicus. Compounds 1-5 represent rare examples of labdane-type diterpenoids, of which compounds 1-4 carry an N-chain linked at C-7 in their B-ring and compound 5 featured an α,ß-unsaturated-γ-lactam moiety. The structures and absolute configurations of these new diterpenoids were characterized by a combination of spectroscopic techniques, X-ray crystallography, electronic circular dichroism, and calculated specific rotations. The plant-growth regulatory activity of these compounds on the growth of the roots and shoots of Lactuca sativa and Lolium perenne seedlings were evaluated. Compound 3 showed a broad-spectrum inhibitory activity with the inhibition rates ranging from 60 to 83.5% at a concentration of 200 µg/mL, which were as active as those of glyphosate. Compound 8 had a selective inhibitory activity against the growth of the roots of L. perenne seedlings with an inhibition rate of 81.7%. However, compounds 11 and 16 exhibited significant stimulation effects on the roots of L. sativa with stimulation rates of 59.8 and 65.3%, respectively. In addition, compounds 3 and 8 exhibited inhibitory effects on the germination of L. perenne seeds.

Heliaquanoids A-E, Five Sesquiterpenoid Dimers from Inula helianthus-aquatica.

Heliaquanoid A (1), the first exo-2,4-linked Diels-Alder adduct between a pseudoguaianolide dienophile and a guaianolide diene, and heliaquanoids B-E (2-5), four new 2,4-linked Diels-Alder adducts between a xanthanolide dienophile and a guaianolide diene, were isolated from stems and leaves of Inula helianthus-aquatica. Their structures were determined by NMR spectroscopy, a modified Mosher's method, electronic circular dichroism, and X-ray diffraction analysis. Compounds 2 and 3 exhibited moderate cytotoxic activities against HL-60 cells with IC50 values of 7.5 and 4.9 µM, respectively.