Saundersiosides C-H, rearranged cholestane glycosides from the bulbs of Ornithogalum saundersiae and their cytostatic activity on HL-60 cells

Recent advances in discovery and biosynthesis of natural products from myxobacteria: an overview from 2017 to 2023

Covering: 2017.01 to 2023.11Natural products biosynthesized by myxobacteria are appealing due to their sophisticated chemical skeletons, remarkable biological activities, and intriguing biosynthetic enzymology. This review aims to systematically summarize the advances in the discovery methods, new structures, and bioactivities of myxobacterial NPs reported in the period of 2017-2023. In addition, the peculiar biosynthetic pathways of several structural families are also highlighted.

Steroidal glycosides from Ornithogalum thyrsoides bulbs and their cytotoxicity toward HL-60 human promyelocytic leukemia cells and SBC-3 human small-cell lung cancer cells

Ornithogalum thyrsoides Jacq belongs to the Asparagaceae family and is cultivated for ornamental purposes. The authors have previously reported several cholestane- and spirostan-type steroidal glycosides from O. thyrsoides. Conventional TLC analysis of the methanolic bulb extract of O. thyrsoides suggested the presence of unprecedented compounds; therefore, a detailed phytochemical investigation of the extract was performed and 35 steroidal glycosides (1-35), including 21 previously undescribed ones (1-21) were collected. The structures of 1-21 were determined mainly by analyses of their 1H and 13C NMR spectra with the aid of two-dimensional NMR spectroscopy. The isolated compounds were classified into three distinct groups: furostan-type (1, 2, 8-12, and 22), spirostan-type (3-7 and 23-26), and cholestane-type (13-21 and 27-35). Although the C/D-ring junction of the steroidal skeleton is typically trans-oriented, except for some cardiotonic and pregnane-type steroidal derivatives, 7 possess a cis C/D-ring junction. This is the first reported instance of such a configuration in spirostan-type steroidal derivatives, marking it as a finding of significant interest. Compounds 1-35 were evaluated for cytotoxicity against HL-60 human promyelocytic leukemia cells and SBC-3 human small-cell lung cancer cells. Compounds 3-6, 9, 17-21, 23-25, and 30-35 demonstrated cytotoxicity in a dose-dependent manner with IC50 values ranging from 0.000086 to 18 μM and from 0.00014 to 37 μM toward HL-60 and SBC-3 cells, respectively. Compound 19, which is obtained in a good yield and shows relatively potent cytotoxicity among the undescribed compounds, induces apoptosis in HL-60 cells, accompanied by arresting the cell cycle of HL-60 cells at the G2/M phase. In contrast, 19 causes oxidative stress-associated necrosis in SBC-3 cells. The cytotoxic mechanism of 19 is different between HL-60 and SBC-3 cells.

Seven new 1-oxygenated cholestane glycosides from Ornithogalum saundersiae

As the continuous scientific research, seven new 1-oxygenated cholestane glycosides named osaundersiosides 1 A - 1 G were isolated from an EtOH extract of the bulbs of Ornithogalum saundersiae. Their structures were deduced by means of spectroscopic data, chemical evidence and the results of hydrolytic cleavage. The cytotoxicity and anti-inflammatory effects of osaundersiosides 1 A - 1 G were evaluated, but none of them displayed significant activities. [Formula: see text].

Structure and bioactivity of cholestane glycosides from the bulbs of Ornithogalum saundersiae Baker

Eight undescribed cholestane glycosides named osaundersioside A-H, along with three previously known compounds named osaundersioside I-K were isolated from Ornithogalum saundersiae Baker bulbs (Asparagaceae). Their structures were elucidated by extensive spectroscopic analysis and chemical methods. All isolates were evaluated for their cytotoxic activity and inhibitory effects on lipopolysaccharide (LPS)-induced nitric oxide (NO) production. Osaundersioside C was thus determined to exhibit specific cytotoxicity towards MCF-7 cell line with an IC₅₀ value of 0.20 μM, Osaundersioside H exhibited inhibitory effect on NO production in macrophages at the concentration of 10^-5 M, with inhibition rate of 56.81%.

Steroidal glycosides from Ornithogalum dubium Houtt

The phytochemical study of Ornithogalum dubium Houtt. (Asparagaceae) led to the isolation of five undescribed steroidal glycosides together with two known ones. Their structures were established by using NMR analysis and mass spectrometry as (25R)-3β-hydroxyspirost-5-en-1β-yl O-α-L-arabinopyranosyl-(1 → 2)-α-L-rhamnopyranoside, (25S)-3β-hydroxyspirost-5-en-1β-yl O-β-D-glucopyranosyl-(1 → 6)-β-D-glucopyranoside, (22S)-16β-[(α-L-rhamnopyranosyl)oxy]-22-hydroxycholest-5-en-3β-yl O-β-D-glucopyranosyl-(1 → 4)-β-D-glucopyranoside, (22S,23S)-1β,3β,11α,16β,23-pentahydroxy-5α-cholest-24-en-22β-yl β-D-glucopyranoside, (22S,23S)-3β-[(β-D-glucopyranosyl)oxy]-22,23-dihydroxy-5α-cholest-24-en-16β-yl O-α-L-rhamnopyranosyl)-(1 → 4)-β-D-glucopyranoside. Their cytotoxic activities against two human cells, a lung carcinoma A-549 and a promyelocytic leukemia HL-60 cell lines, were evaluated by using the XTT method. The results showed no significant cytotoxicity on the tested cells. The influence of the potentiation of cisplatin cytotoxicity in A-549 cells was also investigated and a slight effect was observed only for the (25R) spirostane-type derivative.

Structures and Biological Activities of Plant Glycosides: Cholestane Glycosides from Ornithogalum Saundersiae, O. Thyrsoides and Galtonia Candicans, and Their Cytotoxic and Antitumor Activities

Systematic phytochemical screening of higher pants using a cytotoxicity-guided fractionation procedure resulted in the isolation from the bulbs of Ornithogalum saundersiae (Liliaceae) an acylated cholestane diglycoside, 17α-hydroxy-16β-[(O-(2-O-p-methoxybenzoyl-β-D-xylopyranosyl)-(1→3)-2-O-acetyl-α-L-arabinopyranosyl)oxy]cholest-5-en-22-one, tentatively named OSW-1. In vitro cytotoxic and in vivo antitumor screening of OSW-1 revealed that it is a possible candidate as a novel anticancer agent. Furthermore, more than 20 OSW-1-related compounds were isolated, not only from the bulbs of O. saundersiae, but also from those of O. thyrsoides and Galtonia candicans, which are taxonomically related to O. saundersiae. In vitro cytotoxic evaluation of all the isolated compounds and their semi-synthetic analogues allowed the structure-activity relationships of the OSW-1 derivatives to be established. In addition, these three plants were found to produce a series of novel cholestane glycosides with a new rearranged side-chain moiety, 24(23→22)abeo-cholestane, some of which showed potent cytotoxic activity against HL-60 leukemia cells.

Structural Characterization of Cholestane Rhamnosides from Ornithogalum saundersiae Bulbs and Their Cytotoxic Activity against Cultured Tumor Cells

Previous phytochemical studies of the bulbs of Ornithogalum saundersiae, an ornamental perennial plant native to South Africa, resulted in the isolation of 29 new cholestane glycosides, some of which were structurally unique and showed potent cytotoxic activity against cultured tumor cell lines. Therefore, we aimed to perform further phytochemical examinations of methanolic extracts obtained from Ornithogalum saundersiae bulbs, isolating 12 new cholestane rhamnosides (1-12) and seven known compounds (13-19). The structures of the new compounds (1-12) were identified via NMR-based structural characterization methods, and through a sequence of chemical transformations followed by spectroscopic and chromatographic analysis. The cytotoxic activity of the isolated compounds (1-19) and the derivatives (1a and 6a) against HL-60 human promyelocytic leukemia cells and A549 human lung adenocarcinoma cells was evaluated. Compounds 10-12, 16, and 17 showed cytotoxicity against both HL-60 and A549 cells. Compound 11 showed potent cytotoxicity with an IC₅₀ value of 0.16 µM against HL-60 cells and induced apoptotic cell death via a mitochondrion-independent pathway.

Constructing 24(23→22)-abeo-Cholestane from Tigogenin in a 20(22→23)-abeo-Way via a PhI(OAc)2-mediated Favorskii Rearrangement

Transforming tigogenin, a steroidal sapogenin, to a 24(23→22)-abeo-cholestane, which is an unusual structural feature shared by the aglycons of saundersiosides and candicanoside A, is described. The spiroketal of tigogenin was unfolded and the resulting C22-ketone was subjected to Favorskii rearrangement mediated by PhI(OAc)₂/KOH/MeOH to squeeze out the C22 from the side chain, thus reaching the 24(23→22)-abeo-cholestane structure.

Methanolic Fractions of Ornithogalum cuspidatum Induce Apoptosis in PC-3 Prostate Cancer Cell Line and WEHI-164 Fibrosarcoma Cancer Cell Line

PURPOSE

The present study, was aimed to assess the cytotoxic effects of Ornithogalum cuspidatum methanolic fractions on PC-3, prostate cancer cells and WEHI-164, Fibrosarcoma cells.

METHODS

Methanolic fractions of O. cuspidatum were prepared using solid phase extraction and the cells were treated with different concentrations for 12 and 24 hours. Cytotoxicity and cell viability were measured by MTT assay. ELISA was also employed to assess the histone-associated DNA fragments and the involvement of apoptotic mechanisms.

RESULTS

10 and 20% fractions had not significant cytotoxic effects (p>0.05) but other fractions exerted growth inhibition on both cancer cell lines (p<0.05). After 24h of incubation with 40, 60, 80 and 100% fractions, the IC50 values were: 165, 85, 65 and 45μg/ml on PC-3 cells and 200, 96, 76 and 73μg/ml against WEHI-164 cell line, respectively. ELISA results also revealed that, both cell lines had undergone apoptosis.

CONCLUSION

It is deduced that, 80% and 100% methanolic fractions had significant anti-proliferative and apoptotic impacts on PC-3 and WEHI-164 cells in vitro and could be considered for developing chemo-preventive substances.

The chemistry and biological activity of the Hyacinthaceae

The Hyacinthaceae (sensu APGII), with approximately 900 species in about 70 genera, can be divided into three main subfamilies, the Hyacinthoideae, the Urgineoideae and the Ornithogaloideae, with a small fourth subfamily the Oziroëoideae, restricted to South America. The plants included in this family have long been used in traditional medicine for a wide range of medicinal applications. This, together with some significant toxicity to livestock has led to the chemical composition of many of the species being investigated. The compounds found are, for the most part, subfamily-restricted, with homoisoflavanones and spirocyclic nortriterpenoids characterising the Hyacinthoideae, bufadienolides characterising the Urgineoideae, and cardenolides and steroidal glycosides characterising the Ornithogaloideae. The phytochemical profiles of 38 genera of the Hyacinthaceae will be discussed as well as any biological activity associated with both crude extracts and compounds isolated. The Hyacinthaceae of southern Africa were last reviewed in 2000 (T. S. Pohl, N. R. Crouch and D. A. Mulholland, Curr. Org. Chem., 2000, 4, 1287-1324; ref. 1); the current contribution considers the family at a global level.

Cholestane glycosides from the bulbs of Galtonia candicans and their cytotoxicity

Further search for cytotoxic compounds contained in the bulbs of Galtonia candicans (Liliaceae) led to the isolation of four potent cytotoxic cholestane glycosides (1-4) based upon 3beta,16beta,17alpha-trihydroxycholest-5-en-22-one, three of which (2-4) have not been reported previously. A new cholestane bisdesmoside (5) and a new rearranged cholestane glycoside (6) were also isolated. The structural assignment of the new constituents was carried out by spectroscopic analysis and a few chemical transformations.