Synthesis and anti-fungal activity of seven oleanolic acid glycosides

Synthesis, Anti-Oomycete and Anti-Fungal Activities of Anhydride Derivatives of Oleanolic Acid

Oleanolic acid is a pentacyclic triterpenoid extracted and isolated from the fruit of plants in the Ligustrum lucidum Ait. in the family Oleaceae. To discover biorational natural product-based pesticides, a series of oleanolic acid derivatives containing anhydride active skeletons were prepared by ingeniously introducing an active acyloxy group at its C-28 carboxyl position, and their structures were well characterized by 1H-NMR, 13C NMR, HRMS, and m.p. The stereochemical configuration of compound 8 e was confirmed using single-crystal X-ray diffraction. Furthermore, bioactivities of these compounds as anti-oomycete and anti-fungal agents against two serious agricultural pests, Phytophthora capsici (P. capsici) and Fusarium graminearum (F. graminearum) we assessed. Amongst evaluated compounds, 1) Compounds 8 h and 8 j displayed significant anti-oomycete against P. capsici, with EC50 values of 54.73 and 65.15 mg/L, respectively. 2) The target compounds have obvious selectivity, and their anti-oomycete activity is significantly better than their anti-fungal activity. 3) Interestingly, there are significant differences in the structure-activity relationship of different substituents or the same substituent at different positions anti-oomycete and anti-fungal against P. capsici and F. graminearum, respectively. The study provides an idea for further exploring the bioactivities of 28-acyloxyoleanolic acid derivatives, and develops the application of 28-acyloxyoleanolic acid derivatives containing anhydride in agriculture.

Efficient synthesis of diverse C-3 monodesmosidic saponins by a continuous microfluidic glycosylation/batch deprotection method

Triterpene and steroid saponins have various pharmacological activities but the synthesis of C-3 monodesmosidic saponins remains challenging. Herein, a series of C-3 glycosyl monodesmosidic saponins was synthesized via the microfluidic glycosylation of triterpenoids or steroids at the C-3 position, without the formation of orthoester byproducts, and subsequent deprotection of the benzoyl (Bz) group. This microfluidic glycosylation/batch deprotection sequence enabled the efficient synthesis of C-3 saponins with fewer purification steps and a shorter reaction time than conventional batch synthesis and stepwise microfluidic glycosylation. Furthermore, this system minimized the consumption of the imidate donor. Using this reaction system, 18 different C-3 saponins and 13 different C-28-benzyl-C-3 saponins, including 8 new compounds, were synthesized from various sugars and triterpenes or steroids. Our synthetic approach is expected to be suitable for further expanding the C-3 saponin library for pharmacological studies.

Anti-Proliferative Effect of Triterpenoidal Glycosides from the Roots of Anemone vitifolia through a Pro-Apoptotic Way

A cytotoxicity-guided phytochemical investigation of Anemone vitifolia roots led to the isolation of six oleanane saponins (1-6), which were reported from the species for the first time. Their structures were determined by comparing its MS and NMR data with those in literature. Compounds 1-4 showed significant inhibitory effects on the proliferation of hepatocellular carcinoma HepG2 cells with IC₅₀ values ranging from 2.0 to 8.5 μM, compared to positive control methotrexate with IC₅₀ value of 15.8 μM. Flow cytometry analysis revealed that compounds 1-4 exerted anti-proliferative effects through a pro-apoptotic way of hepatocellular carcinoma cells.

Saponins of Trifolium spp. aerial parts as modulators of Candida albicans virulence attributes

The aim was to provide the insight into the biology of C. albicans influenced by undescribed yet properties of saponin-rich (80%–98%) fractions (SAPFs), isolated from extracts of Trifolium alexandrinum, T. incarnatum, T. resupinatum var. resupinatum aerial parts. Their concentrations below 0.5 mg/mL were arbitrarily considered as subMICs for C. albicans ATCC 10231 and were further used. SAPFs affected yeast enzymatic activity, lowered tolerance to the oxidative stress, to the osmotic stress and to the action of the cell wall disrupting agent. In their presence, germ tubes formation was significantly and irreversibly inhibited, as well as Candida invasive capacity. The evaluation of SAPFs interactions with anti-mycotics showed synergistic activity, mainly with azoles. Fluconazole MIC was lowered—susceptible C. albicans ATCC 10231 was more susceptible, and resistant C. glabrata (clinical strain) become more susceptible (eightfold). Moreover, the tested samples showed no hemolytic activity and at the concentrations up to 0.5 mg/mL did not reduce viability of fibroblasts L929. This study provided the original evidence that SAPFs of Trifolium spp. aerial part exhibit significant antimicrobial activity, by reduce the expression/quantity of important Candida virulence factors and have good potential for the development of novel antifungal products supporting classic drugs.

Efficient synthesis and anti-fungal activity of oleanolic acid oxime esters

In order to develop potential glucosamine-6-phosphate synthase inhibitors and anti-fungal agents, twenty five oleanolic acid oxime esters were synthesized in an efficient way. The structures of the new compounds were confirmed by MS, HRMS, ¹H-NMR and ¹³C-NMR. Preliminary studies based on means of the Elson-Morgan method indicated that many compounds exhibited some inhibitory activity of glucosamine-6-phosphate synthase (GlmS), and the original fungicidal activities results showed that some of the compounds exhibited good fungicidal activities towards Sclerotinia sclerotiorum (Lib.) de Bary, Rhizoctonia solani Kuhn and Botrytis cinerea Pers at the concentration of 50 µg/mL. These compounds would thus merit further study and development as antifungal agents.