Discovery of procyanidin condensed tannins of (-)-epicatechin from Kratom, Mitragyna speciosa, as virucidal agents against SARS-CoV-2.

Kratom, Mitragyna speciosa, is one of the most popular herbs in the West and Southeast Asia. A number of previous works have focused on bioactive alkaloids in this plant; however, non-alkaloids have never been investigated for their biological activities. Antiviral and virucidal assays of a methanol leaf extract of Kratom, M. speciosa, revealed that a crude extract displayed virucidal activity against the SARS-CoV-2. Activity-guided isolation of a methanol leaf extract of Kratom led to the identification of B-type procyanidin condensed tannins of (-)-epicatechin as virucidal compounds against SARS-CoV-2. The fraction containing condensed tannins exhibited virucidal activity with an EC50 value of 8.38 µg/mL and a selectivity index (SI) value >23.86. LC-MS/MS analysis and MALDI-TOF MS identified the structure of the virucidal compounds in Kratom as B-type procyanidin condensed tannins, while gel permeation chromatograph (GPC) revealed weight average molecular weight of 238,946 Da for high molecular-weight condensed tannins. In addition to alkaloids, (-)-epicatechin was found as a major component in the leaves of M. speciosa, but it did not have virucidal activity. Macromolecules of (-)-epicatechin, i.e., procyanidin condensed tannins, showed potent virucidal activity against SARS-CoV-2, suggesting that the high molecular weights of these polyphenols are important for virucidal activity.

Chemical constituents from Microstachys chamaelea (Euphorbiaceae) with cytotoxic and antioxidant properties.

Phytochemical investigation of Microstachys chamaelea led to the isolation and identification of fourteen known compounds after analysis of spectroscopic data. They consist of eight flavonoids (1-8), two benzoic acid derivatives (9-10), one brevifolin carboxylic acid derivative (11), one geraniinic acid derivative (12), shikimic acid (13), and ß-daucosterol (14). Remarkably, it is the second isolation of compound 12 from a natural source. Several isolates were evaluated against ten cancer cell lines and on a set of targets involved in oxidative stress, as no such assays were undertaken in previous works. Compound 7 showed moderate to strong cytotoxicity against eight cell lines (IC50 values of 6.0-39.0 µM), while compounds 2, 8, and 11 showed weak to moderate cytotoxicity. Compounds 1-3, 5, and 11-12 showed moderate to strong DPPH and XXO inhibitory activities (IC50 values of 13.1-16.5 and 6.0-69.0 µM, respectively).

A new secoiridoid glycoside and other constituents from the roots and flowers of Fagraea fragrans Roxb. (Gentianaceae).

A new secoiridoid glycoside, 3'-O-p-trans-coumaroylsweroside (1), together with twenty-nine compounds (2-30), were isolated from the roots and flowers of Fagraea fragrans Roxb. (Gentianaceae). Their structures were identified by analysis of mass spectrometric and NMR spectroscopic data. Compounds 2, 4, 6, 11 and 13-15 showed weak to moderate cytotoxicity against cholangiocarcinoma cancer cells lines (KKU-213, KKU-055 and KKU-214). We report the first phytochemical investigation of the roots and flowers of F. fragrans, as only the essential oil of the latter has been investigated.

New p-terphenyl and benzoquinone metabolites from the bioluminescent mushroom Neonothopanus nambi.

Two new p-terphenyls, neonambiterphenyls A and B (1-2), a new benzoquinone, neonambiquinone A (3), together with six known sesquiterpenes (4-9), were isolated from the bioluminescent mushroom Neonothopanus nambi PW3. The isolated compounds were identified by mass, IR and spectroscopic analyses (1D and 2D NMR). Compounds 1-3 and 5-7 showed cytotoxicity against cancer cell lines such as KB, NCI-H187 and MCF-7 with IC50 values ranging from 1.45 to 49.31 µg/mL. In addition, compounds 1 and 5 showed cytotoxicity against Vero cells with IC50 values of 38.72 and 32.90 µg/mL, respectively.

A new tocotrienol from the roots and branches of Allophylus cobbe (L.) Raeusch (Sapindaceae).

A new tocotrienol, 5-hydroxy-8-methyltocotrienol (1) was isolated from the roots and branches of A. cobbe (L.) Raeusch, together with seventeen known compounds (2-18). Their structures were elucidated by analysis of spectroscopic data and by comparison of 1H and 13C NMR data with previous literature reports. This is the first phytochemical investigation of the roots and branches of Allophylus cobbe (L.) Raeusch.

Two new bioactive triterpenoids from the roots of Colubrina asiatica.

Two new ceanothane triterpenes, 3,7-O,O-dibenzoyl ceanothic acid methylester (1) and 3-O-acetyl-7-O-benzoyl ceanothic acid methylester (2), along with nine known compounds (3-11), were isolated from the roots of Colubrina asiatica. The isolated compounds were identified by spectroscopic evidence. Compounds 1 and 2 showed antimalarial activity against Plasmodium falciparum with IC50 values of 4.67 and 3.07 µg/mL, respectively. Compound 2 also showed antimycobacterial activity against Mycobacterium tuberculosis (MIC 6.25 µg/mL). In addition, compounds 1, 2, 10 and 11 showed cytotoxicity against three cancer cell lines (KB, NCI-H187 and MCF-7) with IC50 values ranging from 8.32 to 46.72 µg/mL.

Chemical constituents and biological activities from branches of Colubrina asiatica.

Sixteen compounds were isolated from a Thai medicinal plant, Colubrina asiatica. The isolated compounds were elucidated on the basis of spectroscopic methods (IR, 1D and 2D NMR) as six triterpene acids (1-6), five steroids (7-11), one benzoic acid derivative (12), two peptides (13 and 14), one sesquiterpenoid (15) and one jujubogenin (16). Compounds 3 and 10 showed antimalarial activity against Plasmodium falciparum. Compound 5 showed antimycobacterial activity. Moreover, compounds 3, 5, 6, 10 and 14 exhibited weak cytotoxicity against cancer cell lines. Compounds 1-15 have been isolated for the first time from this plant.

Secondary Metabolites and Their Biological Activity from Aspergillus aculeatus KKU-CT2.

The bioactive compounds of the fungus Aspergillus aculeatus strain KKU-CT2, have been studied. The crude extracts from this fungus showed good antimicrobial activity against human pathogens, including Gram-positive and Gram-negative bacteria and yeast-like fungi. Its chemical components were isolated and purified by chromatographic methods. The structures of the secondary metabolites were elucidated by spectroscopic methods (IR, 1H, and 13C NMR). They were identified as ergosterol peroxide (1), secalonic acid D (2), secalonic acid F (3), variecolin (4), variecolactone (5), and ergosterol (6). Compounds 1 and 4-6 are reported for the first time as fungal metabolites from this species. Compound 1 displayed inhibitory effects on HSV-1 with an IC50 of 11.01 µg/ml. Compounds 3, 4, and 6 exhibited antimalarial activity against Plasmodium falciparum with IC50 of 1.03, 1.47, and 5.31 µg/ml, respectively. Additionally, all compounds from A. aculeatus KKU-CT2 showed unprecedented anticancer activities against human epidermoid carcinoma in the mouth (KB) (compounds 1-6), human breast cancer (MCF-7) (compounds 2, 4, and 5), and human lung cancer cells (NCI-H187) (compounds 1-4 and 6). These results suggest that secondary metabolites from A. aculeatus KKU-CT2 might be interesting for further derivatization, targeting diseases such as cancer.

A new coumarin from the roots of Micromelum minutum.

A new coumarin, minutuminolate (1), together with eleven known coumarins (2-12), was isolated from the roots of Micromelum minutum. The structures of these compounds were established on the basis of their 1D and 2D NMR spectroscopic data. Compounds 2, 5, 10, 11 and 12 showed cytotoxicity against KB cell line. In addition, compounds 2, 3, 4, 7, 11 and 12 also showed weak cytotoxicity against NCI-H187 cell line.