Phenylpropanoid conjugated iridoids with anti-malarial activity from the leaves of Morinda morindoides

Two New α-Glucosidase Inhibitors from Haplophyllum tuberculatum: Inhibition Kinetics and Mechanistic Insights Through in Vitro and in Silico Approaches

Diabetes is a multifactorial global health disorder marked by unusually high plasma glucose levels, which can lead to serious consequences including diabetic neuropathy, kidney damage, retinopathy, and cardiovascular disease. One effective therapy approach for reducing hyperglycemia associated with type 2 diabetes is to target α-glucosidase, enzymes that catalyze starch breakdown in the intestine. In the current study, two new (1, 2) and nine known (3-11) compounds were isolated from the rutaceous plant Haplophyllum tuberculatum and characterized by extensive nuclear magnetic resonance spectroscopic techniques and high-resolution electrospray ionization mass spectrometry. After structural elucidation, nine compounds were evaluated for their ability to inhibit α-glucosidase, a target for the treatment of type-2 diabetes. Among them, three compounds (7, 5, and 2) exhibited notable inhibition with half-maximal inhibitory concentration (IC50) values of 3.42 ± 0.12, 5.79 ± 0.28, and 6.75 ± 1.18 µM, respectively, while the remaining six compounds (1, 3, 4, 6, 8, and 9) had a moderate activity with IC50 values ranging from 12.14 ± 0.35 to 24.60 ± 0.57 µM, compared to the standard drug acarbose (IC50 = 875.75 ± 1.24 µM). A kinetic study of compounds 5 and 7 exhibited the competitive type of inhibition with Ki values of 4.82 ± 0.0036 and 3.92 ± 0.0062 µM, respectively. Furthermore, a structure-based prediction of the compounds' binding mode suggested that these inhibitors fitted exceptionally well within the active site of the target enzyme, α-glucosidase, forming multiple hydrogen and hydrophobic interactions with its active site residues. In conclusion, compounds with potent α-glucosidase inhibitory activity are abundant in nature and can be explored and further developed for treating diabetes mellitus.

Discovery of antimalarial drugs from secondary metabolites in actinomycetes culture library

BACKGROUND

Natural products play a key role as potential sources of biologically active substances for the discovery of new drugs. This study aimed to identify secondary metabolites from actinomycete library extracts that are potent against the asexual stages of Plasmodium falciparum (P. falciparum).

METHODS

Secondary metabolites from actinomycete library extracts were isolated from culture supernatants by ethyl acetate extraction. Comprehensive screening was performed to identify novel antimalarial compounds from the actinomycete library extracts (n = 28). The antimalarial activity was initially evaluated in vitro against chloroquine/mefloquine-sensitive (3D7) and-resistant (Dd2) lines of P. falciparum. The cytotoxicity was then evaluated in primary adult mouse brain (AMB) cells.

RESULTS

Out of the 28 actinomycete extracts, 17 showed parasite growth inhibition > 50% at a concentration of 50 µg/mL, nine were identified with an IC50 value < 10 µg/mL, and seven suppressed the parasite significantly with an IC50 value < 5 µg/mL. The extracts from Streptomyces aureus strains HUT6003 (Extract ID number: 2), S. antibioticus HUT6035 (8), and Streptomyces sp. strains GK3 (26) and GK7 (27), were found to have the most potent antimalarial activity with IC50 values of 0.39, 0.09, 0.97, and 0.36 µg/mL (against 3D7), and 0.26, 0.22, 0.72, and 0.21 µg/mL (against Dd2), respectively. Among them, Streptomyces antibioticus strain HUT6035 (8) showed the highest antimalarial activity with an IC50 value of 0.09 µg/mL against 3D7 and 0.22 µg/mL against Dd2, and a selective index (SI) of 188 and 73.7, respectively.

CONCLUSION

Secondary metabolites obtained from the actinomycete extracts showed promising antimalarial activity in vitro against 3D7 and Dd2 cell lines of P. falciparum with minimal toxicity. Therefore, secondary metabolites obtained from actinomycete extracts represent an excellent starting point for the development of antimalarial drug leads.

Phukettosides A-E, mono- and bis-iridoid glycosides, from the leaves of Morinda umbellata L

Four undescribed bis-iridoid glycosides, named phukettosides A-D, and one iridoid glycoside, referred to as phukettoside E, were isolated and fully characterized from the leaves of Morinda umbellata L. Phytochemical analysis also revealed the presence of eight known compounds. The structures were determined through extensive analysis of 1D and 2D-NMR spectroscopic and HRMS spectral data, and the absolute configurations of the isolates were deduced through ECD calculations. Biogenetic pathways for the bis-iridoid glycosides, phukettosides A-C, through intermolecular Diels-Alder type reactions, were proposed. The isolated compounds, with the exception of phukettosides B and D, were evaluated against a panel of cancer cell lines (MOLT-3, HuCCA-1, A549, HeLa, HepG2, and MDA-MB-231) and a non-cancerous cell line (MRC-5) for their cytotoxicity. None of the isolates had significant cytotoxic effects on the tested cell lines.

Phenylpropanoid-conjugated iridoid glucosides from leaves of Morinda morindoides

Three phenylpropanoid-conjugated iridoid glucosides, acetylgaertneric acid (1), acetyldehydrogaertneroside (2), and dehydrogaertneric acid (10), together with nine known related iridoid glucosides (3-9, 11, and 12), two coumaroyl alkaloids, one benzenoid, and three flavonoid glucosides were isolated from leaves of Morinda morindoides (Rubiaceae). Structures of these isolated compounds were determined using spectroscopic analysis. Compounds 1-18 and previously isolated compounds (19-29) were evaluated for anti-trypanosomal activity against Trypanosoma cruzi Tulahuen strain (trypomastigote and amastigote) together with cytotoxicity against host cells, new-born mouse heart cells. Among them, molucidin (21) and prismatomerin (22) exhibited good anti-trypanosomal activity (IC₅₀ of 4.67 and 5.70 µM, respectively), together with cytotoxicity (CC₅₀ of 2.76 and 3.22 μM, respectively). Compounds 1-18 did not show anti-malarial activity against a chloroquine/mefloquine-sensitive strain of Plasmodium falciparum.