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

Recent developments on the synthesis of biologically active glycohybrids

The exploration of hybridization emerges as a potent tool in advancing drug discovery research, with a significant emphasis on carbohydrate-containing hybrid scaffolds. Evidence indicates that linking carbohydrate molecules to privileged bioactive scaffolds enhances the bioactivity of drug molecules. This synergy results in a diverse range of activities, making carbohydrate scaffolds pivotal for synthesizing compound libraries with significant functional and structural diversity. Beyond their synthesis utility, these scaffolds offer applications in screening bioactive molecules, presenting alternative avenues for drug development. This comprehensive review spanning 2015 to 2023 focuses on synthesized glycohybrid molecules, revealing their bioactivity in areas such as anti-microbial, anti-cancer, anti-diabetic, anti-inflammatory activities, enzyme inhibition and pesticides. Numerous novel glycohybrids surpass positive control drugs in biological activity. This focused study not only highlights the diverse bioactivities of glycohybrids but also underscores their promising role in innovative drug development strategies.

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.

Biological and Pharmacological Effects of Synthetic Saponins

Saponins are amphiphilic molecules consisting of carbohydrate and either triterpenoid or steroid aglycone moieties and are noted for their multiple biological activities-Fungicidal, antimicrobial, antiviral, anti-inflammatory, anticancer, antioxidant and immunomodulatory effects have all been observed. Saponins from natural sources have long been used in herbal and traditional medicines; however, the isolation of complexed saponins from nature is difficult and laborious, due to the scarce amount and structure heterogeneity. Chemical synthesis is considered a powerful tool to expand the structural diversity of saponin, leading to the discovery of promising compounds. This review focuses on recent developments in the structure optimization and biological evaluation of synthetic triterpenoid and steroid saponin derivatives. By summarizing the structure-activity relationship (SAR) results, we hope to provide the direction for future development of saponin-based bioactive compounds.

Design, synthesis and biological evaluation of betulin-3-yl 2-amino-2-deoxy-β-d-glycopyranosides

Betulin is a natural pentacyclic triterpenoid, possessing a lupane-structure, with a wide range of pharmacological activities. Its weak hydrosolubility hinders the biological activity of the compound and its derivatives. To circumvent this problem, we synthesized and tested in vitro three d-glycosaminosides of betulin. The structure of betulin was modified by incorporation of 2-amino-2-deoxy-d-gluco- and -d-galactopyranosyl moieties to its C-3 position. So far betulinyl glycosides containing these amino-sugars have not been reported in the literature. The structure of the studied derivatives was confirmed by ¹H and ¹³C NMR spectroscopy as well as mass spectrometry. The 28-O-acetylbetulin-3-yl 2-amino-2-deoxy-β-d-glucopyranoside and betulin-3-yl 2-amino-2-deoxy-β-d-gluco- and β-d-galactopyranoside were tested against the human pathogenic fungi and Gram-positive and Gram-negative bacteria. Moreover, the MTT assay of their cytotoxicity was performed on the MCF-7 breast cancer cell line and on the HDFa, human dermal fibroblasts. The Ames test on mutagenic properties completed our biological assays.

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.

1,4-Naphthoquinone derivatives potently suppress Candida albicans growth, inhibit formation of hyphae and show no toxicity toward zebrafish embryos

PURPOSE

In this study, we applied various assays to find new activities of 1,4-naphthoquinone derivatives for potential anti-Candida albicans applications.

METHODOLOGY

These assays determined (a) the antimicrobial effect on growth/cell multiplication in fungal cultures, (b) the effect on formation of hyphae and biofilm, (c) the influence on cell membrane integrity, (d) the effect on cell morphology using atomic force microscopy, and (e) toxicity against zebrafish embryos. We have demonstrated the activity of these compounds against different Candida species and clinical isolates of C. albicans.

KEY FINDINGS

1,4-Naphthoquinones significantly affected fungal strains at 8-250 mg l^-1 of MIC. Interestingly, at concentrations below MICs, the chemicals showed effectiveness in inhibition of hyphal formation and cell aggregation in Candida. Of note, atomic force microscopy (AFM) analysis revealed an influence of the compounds on cell morphological properties. However, at low concentrations (0.8-31.2 mg l^-1), it did not exert any evident toxic effects on zebrafish embryos.

CONCLUSIONS

Our research has evidenced the effectiveness of 1,4-naphthoquinones as potential anti-Candida agents.

Synthesis of the repeating unit of O-specific polysaccharide isolated from the water-borne bacteria Aeromonas bestiarum 207

Aeromonas bestiarum 207 is a bacterial pathogen with severe impact on aquaculture. In a recent study, the structure of OPS antigens from Aeromonas bestiarum was identified as pentasaccharide repeating units. Synthesis of the pentasaccharide repeating unit and its derivative are reported. Stereo- and regio-specific synthesis was achieved under Schmidt glycosylation conditions employing appropriately protected L-rhamopyranosyl and D-glucopyranosylamine building blocks. The pentasaccharide synthesis was achieved using a [3 + 2] strategy with an overall yield of 5.2% through 11 linear steps from the monosaccharide building blocks 10 and 14.

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.

Highly Efficient Synthesis of Multiantennary Bisected N-glycans Based on Imidates

The occurrence of N-glycans with a bisecting GlcNAc modification on glycoproteins has many implications in developmental and immune biology. However, these particular N-glycans are difficult to obtain either from nature or through synthesis. We have developed a flexible and general method for synthesizing bisected N-glycans of the complex type by employing modular TFAc-protected donors for all antennae. The TFAc-protected N-glycans are suitable for the late introduction of a bisecting GlcNAc. This integrated strategy permits for the first time the use of a single approach for multiantennary N-glycans as well as their bisected derivatives via imidates, with unprecedented yields even in a one-pot double glycosylation. With this new method, rare N-glycans of the bisected type can be obtained readily, thereby providing defined tools to decipher the biological roles of bisecting GlcNAc modifications.