Cytotoxic triterpenoids from the leaves of Microtropis fokienensis

Digital Database of Absorption Spectra of Diverse Flavonoids Enables Structural Comparisons and Quantitative Evaluations

Flavonoids play diverse roles in plants, comprise a non-negligible fraction of net primary photosynthetic production, and impart beneficial effects in human health from a plant-based diet. Absorption spectroscopy is an essential tool for quantitation of flavonoids isolated from complex plant extracts. The absorption spectra of flavonoids typically consist of two major bands, band I (300-380 nm) and band II (240-295 nm), where the former engenders a yellow color; in some flavonoids the absorption tails to 400-450 nm. The absorption spectra of 177 flavonoids and analogues of natural or synthetic origin have been assembled, including molar absorption coefficients (109 from the literature, 68 measured here). The spectral data are in digital form and can be viewed and accessed at http://www.photochemcad.com. The database enables comparison of the absorption spectral features of 12 distinct types of flavonoids including flavan-3-ols (e.g., catechin, epigallocatechin), flavanones (e.g., hesperidin, naringin), 3-hydroxyflavanones (e.g., taxifolin, silybin), isoflavones (e.g., daidzein, genistein), flavones (e.g., diosmin, luteolin), and flavonols (e.g., fisetin, myricetin). The structural features that give rise to shifts in wavelength and intensity are delineated. The availability of digital absorption spectra for diverse flavonoids facilitates analysis and quantitation of these valuable plant secondary metabolites. Four examples are provided of calculations─multicomponent analysis, solar ultraviolet photoprotection, sun protection factor (SPF), and Förster resonance energy transfer (FRET)─for which the spectra and accompanying molar absorption coefficients are sine qua non.

Pentacyclic Triterpenoids Isolated from Celastraceae: A Focus in the 13C-NMR Data

The Celastraceae family comprises about 96 genera and more than 1.350 species, occurring mainly in tropical and subtropical regions of the world. The species of this family stand out as important plant sources of triterpenes, both in terms of abundance and structural diversity. Triterpenoids found in Celastraceae species display mainly lupane, ursane, oleanane, and friedelane skeletons, exhibiting a wide range of biological activities such as antiviral, antimicrobial, analgesic, anti-inflammatory, and cytotoxic against various tumor cell lines. This review aimed to document all triterpenes isolated from different botanical parts of species of the Celastraceae family covering 2001 to 2021. Furthermore, a compilation of their ¹³C-NMR data was carried out to help characterize compounds in future investigations. A total of 504 pentacyclic triterpenes were compiled and distinguished as 29 aromatic, 50 dimers, 103 friedelanes, 89 lupanes, 102 oleananes, 22 quinonemethides, 88 ursanes and 21 classified as others.

Structural characterization and biological evaluation of chemical constituents from Ilex cornuta

One new ursane-type triterpenoid (1), one new ursane-type triterpenoid glycoside (2), and one new oleanane-type triterpenoid glycoside (3), along with 20 known compounds, were isolated from the leaves of Ilex cornuta. The structures of these natural products were elucidated on the basis of detailed spectroscopic analyses and chemical derivation. Our biological evaluation established that selective compounds showed moderate to significant antioxidant activities in the 1,1-diphenyl-2-picrylhydrazyl and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) methods.

Cytotoxic Triterpenoids from the Stalks of Microtropis triflora

Bioassay-guided phytochemical investigation of the stalks of Microtropis triflora Merr. & F.L. Freeman led to the isolation of ten triterpenes 1 - 10, including one novel compound 3,24-epoxy-2α,24-dihydroxyfriedelan-29-oic acid (1). Their chemical structures were identified on the basis of spectroscopic analysis, including HR-ESI mass spectrometry, 1D- and 2D-NMR (¹ H, ¹³ C, ¹ H,¹ H-COSY, HSQC, HMBC, and NOESY), and by comparison with the data reported. The cytotoxicities of compounds 1 - 10 against a panel of cultured human tumor cell lines (Bcap37, SMMC7721, HeLa, CNE) were evaluated. The new compound 1 showed moderate anti-tumor activities with IC₅₀ values of 39.22, 29.24, 23.28, and 68.81 μm/ml, respectively. These results might be helpful for explaining the use of M. triflora in traditional medicine. Triterpenes are characteristic of Microtropis genus and could be useful as potential chemotaxonomic markers.

Anti-hepatocellular carcinoma activity and mechanism of chemopreventive compounds: ursolic acid derivatives

CONTEXT

Hepatocellular carcinoma (HCC) is a common cancer around the world, with high mortality rate. Currently, there is no effective drug for the therapy of HCC. Ursolic acid (UA) is a natural product which exists in various medicinal herbs and fruits, exhibiting multiple biological effects such as its outstanding anticancer and hepatoprotective activity, which has drawn many pharmacists' attention.

OBJECTIVE

This paper summarizes the current status of the hepatoprotective activity of UA analogues and explains the related mechanism, providing a clear direction for the development of novel anti-HCC drugs.

METHODS

All of the data resources were derived from PubMed. By comparing the IC50 values and analyzing the structure-activity relationships, we listed compounds with good pharmacological activity from the relevant literature, and summarized their anti-HCC mechanism.

RESULTS

From the database, 58 new UA derivatives possessing wonderful anticancer and hepatoprotective effects were listed, and the relevant anti-HCC mechanism were discussed.

CONCLUSION

UA's anti-HCC effect is the result of combined action of many mechanisms. These 58 new UA derivatives, particularly compounds 45 and 53, can be used as potential drugs for the treatment of liver cancer.

Polyoxygenated ursane and oleanane triterpenes from Siphonodon celastrineus

Twenty polyoxygenated triterpenes, including nineteen ursanes and one oleanane, were characterized from the stem material of Siphonodon celastrineus (Celastraceae) through the application of spectroscopic techniques and chemical transformation. Three of the ursane-type triterpenoids possessed the rare 13,27-cyclopropane ring skeleton.

Anti-inflammatory triterpenoids from the stems of Microtropis fokienensis

Three new ursane- and four new oleanane- type triterpenoids 1-7 were isolated, along with six known compounds 8-13, from the methanolic extract of Microtropis fokienensis. All structures were elucidated by mass and NMR spectroscopic methods. The isolates 4-10 and known compounds 14-17 that were previously isolated from this material were evaluated for anti-inflammatory activity based on effects against superoxide anion generation and elastase release by neutrophils in response to fMLP/CB. 11α,30-Dihydroxy-2,3-seco-olean-12-en-2,3-dioic anhydride (7) was the first triterpene anhydride from the genus of Microtropis to have the ring A expanded to a seven-membered ring; it showed significant anti-inflammatory activity against superoxide anion generation and elastase release. Unexpectedly, 30-hydroxy-2,3-seco-lup-20(29)-ene-2,3-dioic acid (17) showed the best effect against superoxide anion generation and elastase release with IC50 values of 0.06±0.01 and 1.03±0.35 µg/mL, respectively. Compound 17 had a dioic acid function, and compound 7 had an anhydride function modification in ring A; both showed promising activity in the target assays.

Lupane, friedelane, oleanane, and ursane triterpenes from the stem of Siphonodon celastrineus Griff

Twenty-one triterpenes consisting of a lupane derivative, two friedelanes, an oleanane derivative, and 17 ursane-type triterpenoids, together with three known triterpenes, three sterols, a fatty acid, a sesquiterpene alkaloid, and a glycerol derivative, were isolated from the stem of Siphonodon celastrineus. Their structures were characterized by various spectroscopic techniques, as well as comparison with literature data. Twenty-seven metabolites of these were evaluated for cytotoxic activity against six human cancer cell lines. The biosynthetic formation of a 1,4-dioxane bridge is also discussed.

Cytotoxic activity of ursolic acid derivatives obtained by isolation and oxidative derivatization

Structure-activity relationships of ursane-type pentacyclic triterpenes obtained from natural sources and by chemical derivatization are reviewed. Ursolic acid, corosolic acid, and a new ursane-type pentacyclic triterpene, 7,24-dihydroxyursolic acid, were isolated from the methanolic extract of the leaves of the Bangladeshi medicinal plant, Saurauja roxburghii. Derivatization of ursolic acid by oxidation with dioxoruthenium (VI) tetraphenylporphyrins was investigated. Oxidation selectivity on the terpene structure was modulated by the auxiliaries introduced on the tetraphenylporphyrin. The natural triterpenes and oxidized derivatives were tested for cytotoxicity against the C6 rat glioma and A431 human skin carcinoma cell lines. Although they have the same ursane-type pentacyclic triterpene cores, the position and numbers of hydroxyls on the terpene structures significantly affected the activity and the selectivity towards the tested cell lines.

Microtropiosides A-F: ent-Labdane diterpenoid glucosides from the leaves of Microtropis japonica (Celastraceae)

From a 1-BuOH-soluble fraction of a MeOH extract of the leaves of Microtropis japonica, collected in the Okinawa islands, six ent-labdane glucosides, named microtropiosides A-F, were isolated together with one known acyclic sesquiterpene glucoside. Their structures were elucidated by a combination of spectroscopic analyses, and their absolute configurations determined by application of the beta-D-glucopyranosylation-induced shift-trend rule in (13)C NMR spectroscopy and the modified Mosher's method.

Triterpenes of Commiphora holtziana oleo-gum resin

Chemical analysis of the acetone extract of Commiphora holtziana gum resin has led to the isolation of triterpenes characterized as methyl 3-oxo-1α,19α,28-trihydroxyurs-12-en-24-oate (1), methyl 3β-acetyl-2α,11α,19α,28-tetrahydroxyurs-12-en-24-oate (2), methyl 3β,11α-diacetyl-1α,2α,28-trihydroxyurs-12-ene-24-oate (3), and 3β,28-diacetyl-1α,2α,25-trihydroxydammar-23-ene (4). The known compounds isolated from the same extract included cabraleadiol monoacetate (5), mansumbinol (6), 3β-acetylamyrin (7), 3α-acetylboswellic acid (8), 2-methoxy-8,12-epoxygermacra-1(10),7,11-trien-6-one (9), 2-methoxy-5-acetylfuranogermacra-1(10),7,11-trien-6-one (10), furadienone (11), 2-methoxy-5-acetyl-4-furanogermacra-1(10)Z-en-6-one (12), α-amyrin (13), sistosterol (14) and stigmasterol 3-O-acetate (15). Structural elucidation was carried out using spectroscopic and physical methods as well as by comparison with the literature data.

Cytotoxic triterpenoids from the stems of Microtropis japonica

Bioassay-guided fractionation of a methanol extract obtained from stems of Microtropis japonica led to the isolation of six new ursane-type triterpenoids (1-6) and a new 2,3-seco-oleanane-type triterpenoid (7), together with seven known compounds. The structures of the new compounds were elucidated using spectroscopic data analysis. Among the known compounds isolated, the main component, 8 (ursolic acid), was active for HL60 cells, and its effects on histone hyperacetylation and the inhibition of histone deacetylase (HDAC) activity were investigated.

Lupane-type triterpenoids from Microtropis fokienensis and Perrottetia arisanensis and the apoptotic effect of 28-hydroxy-3-oxo-lup-20(29)-en-30-al

Seven new lupane triterpenoids were isolated from bioactive methanol extracts of Microtropis fokienensis (1- 4) and Perrottetia arisanensis (4-7), along with 18 known compounds. The structures of the new compounds were elucidated on the basis of spectroscopic data analysis. All triterpenoids were evaluated for their in vitro cytotoxicity toward seven human cancer cell lines. Compound 8 (28-hydroxy-3-oxo-lup-20(29)-en-30-al) was among the most cytotoxic substances obtained and was found to induce apoptosis of human leukemia HL60 cells and mediate cleavage of PARP and up-regulation of Bax proteins.

Triterpenoids

This review covers the isolation and structure determination of triterpenoids including squalene derivatives, protostanes, lanostanes, holostanes, cycloartanes, dammaranes, euphanes, tirucallanes, tetranortriterpenoids, quassinoids, lupanes, oleananes, friedelanes, ursanes, hopanes, isomalabaricanes and saponins. The literature from January 2005 to December 2006 is reviewed and 478 references are cited.

Dihydroagarofuranoid sesquiterpenes, a lignan derivative, a benzenoid, and antitubercular constituents from the stem of Microtropis japonica

Four new compounds, including two new dihydroagarofuranoid sesquiterpenes, 8-benzoyloxymutangin (1) and 15-acetoxyorbiculin G (2), a new lignan derivative, 9,9'- O-di-(Z)-feruloyl-(-)-secoisolariciresinol (3), and a new benzenoid, 5'-methoxyevofolin B (4), have been isolated from the stem of Microtropis japonica, together with 20 known compounds (5- 24). 3-Ethoxy-4-hydroxybenzaldehyde (5) was identified from a natural source for the first time. The structures of these new compounds were determined through analyses of physical data. 15-Acetoxyorbiculin G (2), celahin C (6), and salasol A (7) exhibit antituberculosis activities (MICs < or = 39.6 microM) against Mycobacterium tuberculosis H 37Rv in vitro.

Triterpene, antioxidant, and antimicrobial compounds from Melissa officinalis

Six new triterpenes (1- 6) and four known compounds have been isolated from dried stems and leaves of Melissa officinalis. The known compounds were identified as quadranoside III, salvianic acid A, rosmarinic acid, and luteolin. The structures of compounds 1- 6 were established by analysis of spectroscopic data. Free radical scavenging and antimicrobial activities of the extracts and of rosmarinic acid, the major component, were evaluated.