In vitro activity and in vivo efficacy of the saponin diosgenyl 2-amino-2-deoxy-β-D-glucopyranoside hydrochloride (HSM1) alone and in combination with daptomycin and vancomycin against Gram-positive cocci

Phytochemical evaluation, embryotoxic, and teratogenic effects of Buwakan (Decalobanthus peltatus (L.) A.R.Simões & Staples) leaf extracts on duck embryo

Decalobanthus peltatus is a woody vine that is commonly utilized in traditional Southeast Asian medicinal preparations. Despite the documented therapeutic uses of D. peltatus, there is hardly any information regarding its toxic effects on its consumers. In this study, crude leaf extracts (aqueous, methanol, ethyl acetate, and hexane) from D. peltatus were prepared and evaluated for their embryotoxicity and teratogenic effects. Phytochemical screening of bioactive compounds from the plants showed the presence of alkaloids, flavonoids, saponins, steroids, and tannins. In addition, investigations on the toxicity of the crude leaf extracts were determined using brine shrimp lethality assay, in which the LC50 was calculated. Results showed that the ethyl acetate leaf extract was the most toxic among the crude leaf extracts, with an LC50 of 14.54 ppm. Based on this result, ethyl acetate leaf extract was treated on duck embryos, and the alteration of vascular branching patterns in the chorioallantoic membrane was quantified. Gross morphological and histological analysis of the skin tissues from the treated duck embryos were also examined. We found significant reduction of primary and tertiary vessel diameters in the duck embryos treated with ethyl acetate leaf extracts in both concentrations compared to the control group. Treated duck embryos exhibited gross malformations, growth retardation, and hemorrhages on the external body surfaces at 1000 ppm. Histopathological analysis of the skin tissues from the 14-day-old treated duck embryos showed a reduced number of feather follicles compared to the control group. These results suggest that D. peltatus crude leaf extracts present risks when taken in significant dosages and comprehensive toxicity testing on therapeutic herbs should be performed to ensure their safety on the consumers.

Synthesis, Modification and Biological Activity of Diosgenyl β-d-Glycosaminosides: An Overview

Saponins are a structurally diverse class of natural glycosides that possess a broad spectrum of biological activities. They are composed of hydrophilic carbohydrate moiety and hydrophobic triterpenoid or steroid aglycon. Naturally occurring diosgenyl glycosides are the most abundant steroid saponins, and many of them exhibit various pharmacological properties. Herein, we present an overview of semisynthetic saponins syntheses-diosgenyl β-d-glycosaminosides (d-gluco and d-galacto). These glycosides possess a 2-amino group, which creates great possibilities for further modifications. A wide group of glycosyl donors, different N-protecting groups and various reaction conditions used for their synthesis are presented. In addition, this paper demonstrates the possibilities of chemical modifications of diosgenyl β-d-glycosaminosides, associated with functionalisation of the amino group. These provide N-acyl, N-alkyl, N,N-dialkyl, N-cinnamoyl, 2-ureido and 2-thiosemicarbazonyl derivatives of diosgenyl β-d-glycosaminosides, for which the results of biological activity tests (antifungal, antibacterial, anti-cancer and hemolytic) are presented.

N-Aminoacyl and N-hydroxyacyl derivatives of diosgenyl 2-amino-2-deoxy-β-d-glucopyranoside: Synthesis, antimicrobial and hemolytic activities

Diosgenyl 2-amino-2-deoxy-β-d-glucopyranoside is a semisynthetic saponin with antimicrobial and antitumor activities. To search for more effective analogues, N-aminoacyl and N-hydroxyacyl derivatives of this saponin were synthesized conventionally and with microwave assistance, and tested against the human pathogenic fungi and Gram-positive and Gram-negative bacteria. None of the tested compounds exhibit activity against Gram-negative bacteria. Almost all of the synthesized N-aminoacyl saponins exhibit antifungal activity and act effectively against Gram-positive bacteria, some better than the parent compound. The best acting saponins are the same size and possess sarcosine or l- or d-alanine attached to the parent glucosaminoside. Shorter and longer aminoacyl residues are less advantageous. d-Alanine derivative is the most effective against Gram positive bacteria. Structure-activity relationship (SAR) analysis indicates that the free α-amino group in aminoacyl residue is necessary for antimicrobial activities of the tested saponins. (N-Acetyl)aminoacyl and N-hydroxyacyl analogs are inactive. Measurements of the hemolytic activities demonstrate that the best acting saponins are not toxic towards human red blood cells.

Antimicrobial activities of saponins from Melanthera elliptica and their synergistic effects with antibiotics against pathogenic phenotypes

BACKGROUND

Resistance of bacteria and fungi to antibiotics is one of the biggest problems that faces public health. The present work was designated to evaluate the antimicrobial activities of saponins from Melanthera elliptica and their synergistic effects with standard antibiotics against pathogenic phenotypes. The plant extract was prepared by maceration in methanol. The methanol extract was partitioned into ethyl acetate and n-butanol extracts. Column chromatography of the n-butanol extract followed by purification of different fractions led to the isolation of four saponins. Their structures were elucidated on the basis of spectra analysis, and by comparison with those from the literature. The antimicrobial activities of the extracts/compounds alone and their combinations with tetracycline and fluconazole were evaluated using the broth microdilution method through the determination of minimum inhibitory concentration (MIC) and minimum microbicidal concentration.

RESULTS

Four compounds: 3-O-β-D-glucuronopyranosyl-oleanolic acid (1), 3-O-β-D-glucuronopyranosyloleanolic acid 28-O-β-D-glucopyranosyl ester (2), 3-O-β-D-glucopyranosyl(1 → 2)-β-D-glucuronopyranosyl oleanolic acid (3) and 3-O-β-D-glucopyranosyl(1 → 2)-β-D-glucuronopyranosyl oleanolic acid 28-O-β-D-glucopyranosyl ester (4) were isolated. Compounds 1, 2 and 3 showed the largest antibacterial activities (MIC = 8-128 μg/mL) whereas compound 4 displayed the highest antifungal activities (MIC = 8-16 μg/mL). The antibacterial activities of compounds 1 and 2 (MIC = 16-32 μg/mL) against multi-drug-resistant Escherichia coli S2 (1) and Shigella flexneri SDINT are equal to those of vancomycin (MIC = 16-32 μg/mL) used as reference antibiotic.

CONCLUSIONS

The present study showed significant antimicrobial activity of compounds 1, 2, 3 and 4 against the tested microorganisms. The saponins act in synergy with the tested standard antibiotics. This synergy could lead to new options for the treatment of infectious diseases and emerging drug resistance.

Diversified synthesis and α-selective glycosylation of 3-amino-2,3,6-trideoxy sugars

Quick access to various unnatural 3-amino-2,3,6-trideoxy sugars was achieved by sequential functionalization of a glycal intermediate. This strategy and the further glycosylation method allowed the efficient late-stage modification of bioactive natural products and drugs.

Diosgenyl 2-amino-2-deoxy-β-D-galactopyranoside: synthesis, derivatives and antimicrobial activity

The synthesis of diosgenyl 2-amino-2-deoxy-β-D-galactopyranoside is presented for the first time. This synthetic saponin was transformed into its hydrochloride as well as N-acyl, 2-ureido, N-alkyl, and N,N-dialkyl derivatives. Antifungal and antibacterial studies show that some of the obtained compounds are active against Gram-positive bacteria and Candida type fungi.

N-Alkyl derivatives of diosgenyl 2-amino-2-deoxy-β-D-glucopyranoside; synthesis and antimicrobial activity

Diosgenyl 2-amino-2-deoxy-β-D-glucopyranoside is a synthetic saponin exhibiting attractive pharmacological properties. Different pathways tested by us to obtain this glycoside are summarized here. Moreover, the synthesis of N-alkyl and N,N-dialkyl derivatives of the glucopyranoside is presented. Evaluation of antibacterial and antifungal activities of these derivatives indicates that they have no inhibitory activity against Gram-negative bacteria, whereas many of the tested N-alkyl saponins were found to inhibit the growth of Gram-positive bacteria and human pathogenic fungi.

Saponins increase susceptibility of vancomycin-resistant enterococci to antibiotic compounds

The resistance of commensal bacteria to first and second line antibiotics has reached an alarming level in many parts of the world and endangers the effective treatment of infectious diseases. In this study, the influence of the plant-derived natural saponins glycyrrhizic acid, β-aescin, α-hederin, hederacoside C, and primulic acid 1 on the susceptibility of vancomycin-resistant enterococci (VRE) against antibiotics of clinical relevance was investigated in 20 clinical isolates. Furthermore, the antibacterial properties of saponins under study against VRE were determined in vitro. Results reveal that the susceptibility of VRE against gentamicin, teicoplanin, and daptomycin was enhanced in the presence of the saponin glycyrrhizic acid. Most importantly, glycyrrhizic acid (1 mg/ml) diminished the minimal inhibitory concentration (MIC) of gentamicin in gentamicin low-level intrinsic resistant VRE from 2 - >8 mg/l to ≤ 0.125-1 mg/l. The adding of β-aescin, α-hederin, hederacoside C, and primulic acid 1 to the antibiotics under study showed, compared to glycyrrhizic acid, less influence on the antibiotic potency. Only glycyrrhizic acid (1 mg/ml) and α‑hederin (0.2 mg/ml) showed weak antibacterial properties against the clinical isolates. Our study points towards a therapeutic potential of saponins in the coapplication with antibiotics for bacterial infections.