Two new cerebrosides leptasteriacerebroside A (1) and B (2) were isolated from the starfish Leptasterias polaris acervata, together with two known ones (2S,3R,4E,9Z)-1-O-(β-D-glucopyranosyl)-2-[(2R)-2-hydroxyhexadecanoylamino]-4,9-docosadien-3-ol (3) and astrocerebroside B (4). The structures of the isolated compounds were characterized using spectroscopic techniques HRESIMS, ESIMS/MS, 1D and 2D NMR as well as by chemical modification and subsequent analysis of derivatives. The antimicrobial, urease inhibitory, cytotoxic, and cytoprotective activities of compounds 1–4 were investigated. Notably, compound 1 exhibited significant protection of H9c2 cardiomyocytes against CoCl2-induced toxicity, while compounds 2 and 4 demonstrated efficacy in mitigating TNF-α-mediated cytotoxicity, likely through inhibition of the NF-κB-dependent inflammatory pathway.

The glycosidic composition of Psolus phantapus was studied for the first time. Two new glycosides, phantapusosides A (1) and B (2), and the known psolusoside P (3) were isolated and their structures were established by analysis of 1H, 13C NMR, 1D TOCSY, and 2D NMR (1H,1H COSY, HMBC, HSQC, ROESY), and HR-ESI mass spectra. These compounds are structurally close to those isolated from other representatives of the genus Psolus: P. fabricii, P. peronii and P. chitonoides. These data confirm the chemotaxonomic significance of triterpene glycosides of sea cucumbers, demonstrating that closely related species biosynthesize structurally similar metabolites. The cytotoxic activity of compounds 1 and 2 was studied against four human breast cancer cell lines (MCF-7, T-47D, MDA-MB-231, MDA-MB-468), as well as the non-tumorigenic mammary epithelial cell line MCF-10A and the pancreatic epithelioid carcinoma cell line PANC-1. The glycosides were selectively active against the TNBC cell lines MDA-MB-231 and MDA-MB-468. Notably, both glycosides inhibited the clonogenic potential of TNBC cell lines more significantly than their metabolic activity (MTT assay) and demonstrated a more pronounced colony-inhibiting effect toward the basal-like cell line MDA-MB-468, making this cell line a promising model for future investigation of the antitumor effects of glycosides.

Unusual 1,2-cyclic acetal-type glycero-3-phosphoethanolamines, isolated from the EtOH extract of the Arctic starfish Asterias -microdiscus (Chukchi Sea), were analysed as constituents of a RP-HPLC fraction using extensive NMR, MS techniques, and chemical transformations. Four new ethanolamine glycerophospholipids were found to differ from each other in the positions of - CH = CH - CH(OOH/OH)- moieties in linear acetal-linked C20 chains. The mixture of these compounds showed cardioprotective activity against CoCl2-induced damage of H9c2 cardiomyocytes via partial restoration of mitochondrial membrane potential.

Thirteen new decaline polyketides, namely, zosteropenillines T-W (1-4), 8-hydroxypallidopenilline A (5), 13-epi-zosteropenilline P (6), 11-epi-zosteropenilline N (7), 15-hydroxyzosteropenilline M (8), 8-hydroxyzosteropenilline M (9), 11-epi-zosteropenilline M (10), and zosteropenillines X-Z (11-13), along with 17 known related compounds (14-30) were isolated from the ethyl acetate extract of the marine-derived fungus Penicillium yezoense KMM 4679 cultivated on MgCl2-containing nutrient medium. The structures of the isolated compounds were established based on spectroscopic methods. The absolute configurations of zosteropenillines T (1) and V (3) were determined using time-dependent density functional theory (TD-DFT) calculations of the ECD spectra. X-ray diffraction analysis data were obtained for the known zosteropenilline S (28). A biogenetic pathway for 1-13 was proposed. The effects of the compounds on Staphylococcus aureus and Candida albicans growth and biofilm formation were observed. Zosteropenillines U (2), Y (12) and Z (13) with higher activity against C. albicans biofilms were nontoxic for normal cardiomyocyte H9c2 cells, making them promising anti-candidal agents. Moreover, zosteropenillines U and Y demonstrated cardioprotective effects in acute ischemia/reperfusion and CoCl2-mimicking hypoxia in vitro models.

As a result of investigation of glycosidic composition of the sea cucumber Ocnus glacialis (Cucumariidae, Dendrochirotida) two new glycosides, glacialisosides A (1) and B (2), were isolated. Their structures were established by in-depth analysis of 1H, 13C NMR, 1D TOCSY, and 2D NMR (1H,1H COSY, HMBC, HSQC, ROESY), in addition to HR-ESI mass spectra. The structures of the obtained desulfated derivatives 3, 4 were elucidated by HR-ESI-MS and ESI-MS/MS. The aglycone moieties of these glycosides are known from other glycosides of four species belonging to the order Dendrochirotida. However, despite sharing common sugar compositions and architectures, the carbohydrate chains of 1, 2 are novel due to the distinct positioning of sulfate groups. Glacialisosides A (1) and B (2) exhibit structural features shared with compounds from sea cucumbers of the orders Holothuriida, Elasipodida, and Dendrochirotida. The hemolytic and cytotoxic activities of compounds 1–4 were studied against human erythrocytes and four breast cancer cell lines (MCF-7, T-47D, MDA-MB-231, and MDA-MB-468), as well as the non-tumorigenic mammary epithelial cell line MCF-10A and the pancreatic epithelioid carcinoma cell line PANC-1. The sulfated native compounds 1 and 2 were significantly more potent than desulfated derivatives 3 and 4 across all tested cell lines, indicating a positive contribution of sulfate groups to bioactivity. Notably, the normal epithelial MCF-10A cells exhibited resistance to the membranolytic action of the glycosides, an important and favorable feature, particularly given the pronounced cytotoxicity observed against the triple-negative MDA-MB-231 cell line. Furthermore, glacialisoside A (1) demonstrated potent inhibitory activity against the formation and growth of MDA-MB-468 cell colonies, effectively blocking cell division even at concentrations below 0.2 μM and completely halting it at a dosage of 1 μM. Thus, the colony formation assay reveals a latent sensitivity of cancer cells—not only to the membranolytic action of triterpene glycosides, but also to the effects of these compounds relevant to other aspects of cell survival, division, and spread.

Reliable taxonomy of biological producers is essential for finding new natural substances. A recent study morphologically re-examined 21 accessed vouchers to confirm multiple reported misidentifications and suggested marine sponges from the genus Rhabdastrella as the only known source of the isomalabaricane triterpenoids. The present study aimed to find isomalabaricane-containing sponges among the samples collected during seven marine expeditions to the Vietnam waters of the South China Sea, accompanied with their identification confirmed using morphological and molecular (18S rRNA and 28S rRNA) analyses. As a result, nine sponges identified as Rhabdastrella globostellata were found to contain isomalabaricanes in their extracts. A chemical investigation of the R. globostellata (PIBOC O63-136) specimen led to the isolation of nine isomalabaricane triterpenoids including the new compound 1, of which the chemical structure was elucidated based on HRESIMS and NMR data. Subsequently, a combination of LC–MS/MS, multivariate statistical analysis, and feature-based molecular networking was applied to detect, annotate, and characterize the isomalabaricane chemical diversity across the nine R. globostellata specimens. As a result, two primary chemotypes containing individual sets of annotated compounds were discovered within the Vietnamese population of this sponge. Moreover, obtained data showed a series of new extremely rare isomalabaricanes in R. globostellata extracts including nitrogen-containing metabolites and glycosides of this structural class.

Four new minor monosulfated triterpene penta- and hexaosides, cladolosides S (1), S1 (2), T (3), and T1 (4), were isolated from the Vietnamese sea cucumber Cladolabes schmeltzii (Sclerodactylidae, Dendrochirotida). The structures of the compounds were established based on extensive analysis of 1D and 2D NMR spectra as well as HR-ESI-MS data. Cladodosides S (1), S1 (2) and T (3), T1 (4) are two pairs of dehydrogenated/hydrogenated compounds that share identical carbohydrate chains. The oligosaccharide chain of cladolosides of the group S is new for the sea cucumber glycosides due to the presence of xylose residue attached to C-4 Xyl1 in combination with a sulfate group at C-6 MeGlc4. The oligosaccharide moiety of cladolosides of the group T is unique because of the position of the sulfate group at C-3 of the terminal sugar residue instead of the 3-O-Me group. This suggests that the enzymatic processes of sulfation and O-methylation that occur during the biosynthesis of glycosides can compete with each other. This can presumably occur due to the high level of expression or activity of the enzymes that biosynthesize glycosides. The mosaicism of glycoside biosynthesis (time shifting or dropping out of some biosynthetic stages) may indicate a lack of compartmentalization inside the cells of organism producers, leading to a certain degree of randomness in enzymatic reactions; however, this also offers the advantage of providing chemical diversity of the glycosides. Analysis of the hemolytic activity of a series of 26 glycosides from C. schmeltzii revealed some patterns of structure–activity relationships: the presence or absence of 3-O-methyl groups has no significant impact, hexaosides, which are the final products of biosynthesis and predominant compounds of the glycosidic fraction of C. schmeltzii, are more active than their precursors, pentaosides, and the minor tetraosides, cladolosides of the group A, are weak membranolytics and therefore are not synthesized in large quantities. Two glycosides from C. schmeltzii, cladolosides D (18) and H1 (26), display selectivity of cytotoxic action toward triple-negative breast cancer cells MDA-MB-231, while remaining non-toxic in relation to normal mammary cells MCF-10A. Quantitative structure–activity relationships (QSAR) were calculated based on the correlational analysis of the physicochemical properties and structural features of the glycosides and their hemolytic and cytotoxic activities against healthy MCF-10A cells and cancer MCF-7 and MDA-MB-231 cell lines. QSAR highlighted the complexity of the relationships as the cumulative effect of many minor contributions from individual descriptors can have a significant impact. Furthermore, many structural elements were found to have different effects on the activity of the glycosides against different cell lines. The opposing effects were especially pronounced in relation to hormone-dependent breast cancer cells MCF-7 and triple-negative MDA-MB-231 cells.

β-D-Glucopyranosides of 3β, 12α,20S-trihydroxydammar-24-ene (1) and 3α,12α,20S-trihydroxydammar-24-ene (2), close structural analogs of ginsenoside-Rh2 and a metabolite of Panax ginseng glycosides (compound K), were synthesized. Glycosylation of 20S-hydroxydammar-24-ene-3,12-dione (5) and 3α-acetoxy-20S-hydroxydammar-24-en-12-one (6) by 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide (8) under classical Koenig-Knorr reaction conditions followed by deacetylation by NaOMe in MeOH gave free 20-O-β-D-glucopyranosides 10 and 13, treatment of which with NaBH4 in i-PrOH formed 20-O-β-D- glucopyranosides of the 12α-epimers of 20S-protopanaxadiol 11 and betulafolientriol 14. Condensation of 3β,12α,20S-trihydroxydammar-24-ene (1) and glycosyl donor 8 in the presence of Ag2O in CH2Cl2 followed by removal of the protecting groups gave 3-O-β-D-glucopyranoside 16; of 3α,12α,20S-trihydroxydammar-24-ene (2) under the same conditions, a mixture of 3- and 12-O-β-D-glucopyranosides 19 and 20.

New nor-isomalabaricanic acids 1 and 2 were isolated from polar fractions of the EtOH extract of the Vietnamese sponge Rhabdastrella globostellata using a combination of column chromatography and reversed-phase HPLC. The chemical structures of the new compounds, which were called stellettins W (1) and X (2), were elucidated by analyzing data from NMR experiments and HR-ESI-MS spectra and by comparison with the structures of associated isolated metabolites. Stellettin W was the first isomalabaricane derivative with a 13,14-epoxide group in its structure.

Four extracts of the marine-derived fungus Penicillium velutinum J.F.H. Beyma were obtained via metal ions stress conditions based on the OSMAC (One Strain Many Compounds) strategy. Using a combination of modern approaches such as LC/UV, LC/MS and bioactivity data analysis, as well as in silico calculations, influence metal stress factors to change metabolite profiles Penicillium velutinum were analyzed. From the ethyl acetate extract of the P. velutinum were isolated two new piperazine derivatives helvamides B (1) and C (2) together with known saroclazin A (3) (4S,5R,7S)-4,11-dihydroxy-guaia-1(2),9(10)-dien (4). Their structures were established based on spectroscopic methods. The absolute configuration of helvamide B (1) as 2R,5R was determined by a combination of the X-ray analysis and by time-dependent density functional theory (TD-DFT) calculations of electronic circular dichroism (ECD) spectra. The cytotoxic activity of the isolated compounds against human prostate cancer PC-3 and human embryonic kidney HEK-293 cells and growth inhibition activity against yeast-like fungi Candida albicans were assayed.

Ten new decalin polyketides, zosteropenilline M (1), 11-epi-8-hydroxyzosteropenilline M (2), zosteropenilline N (3), 8-hydroxyzosteropenilline G (4), zosteropenilline O (5), zosteropenilline P (6), zosteropenilline Q (7), 13-dehydroxypallidopenilline A (8), zosteropenilline R (9) and zosteropenilline S (10), together with known zosteropenillines G (11) and J (12), pallidopenilline A (13) and 1-acetylpallidopenilline A (14), were isolated from the ethyl acetate extract of the fungus Penicillium yezoense KMM 4679 associated with the seagrass Zostera marina. The structures of isolated compounds were established based on spectroscopic methods. The absolute configurations of zosteropenilline Q (7) and zosteropenilline S (10) were determined using a combination of the modified Mosher’s method and ROESY data. The absolute configurations of zosteropenilline M (1) and zosteropenilline N (3) were determined using time-dependent density functional theory (TD-DFT) calculations of the ECD spectra. A biogenetic pathway for compounds 1–14 is proposed. The antimicrobial, cytotoxic and cytoprotective activities of the isolated compounds were also studied. The significant cytoprotective effects of the new zosteropenilline M and zosteropenillines O and R were found in a cobalt chloride (II) mimic in in vitro hypoxia in HEK-293 cells. 1-Acetylpallidopenilline A (14) exhibited high inhibition of human breast cancer MCF-7 cell colony formation with IC50 of 0.66 µM and its anticancer effect was reduced when MCF-7 cells were pretreated with 4-hydroxitamoxifen. Thus, we propose 1-acetylpallidopenilline A as a new xenoestrogen with significant activity against breast cancer.

Five new non-holostane di- and trisulfated triterpene pentaosides, conicospermiumosides A3-1 (1), A3-2 (2), A3-3 (3), A7-1 (4), and A7-2 (5) were isolated from the Far Eastern sea cucumber Cucumaria conicospermium Levin et Stepanov (Cucumariidae, Dendrochirotida). Twelve known glycosides found earlier in other Cucumaria species were also obtained and identified. The structures of new compounds were established on the basis of extensive analysis of the 1D and 2D NMR spectra, as well as by the HR-ESI-MS data. The aglycones of 1–5 differed by side chains structures. Additionally, conicospermiumoside A7-1 (4) had a 9(11)-double bond in the aglycone, while the remaining glycosides contained a 7(8)-intranuclear double bond. Eight types of carbohydrate chains known earlier from the glycosides of the sea cucumbers of the Cucumaria genus were found as part of the glycosides of C. conicospermium. The set of sugar chains of the glycosides from C. conicospermium was similar to that from C. okhotensis. The raw biogenetic series of aglycones, leading to the formation of hexa-nor-lanostane derivatives in the process of biosynthesis and a sort of functionally-structural division that was realized due to separation of biosynthetic pathways of holostane and lanostane derivatives, can be traced when the structures of the glycosides isolated from C. conicospermium are compared. The cytotoxic action against three human breast cancer cell lines (MCF-7, T-47D, MDA-MB-231), and non-tumor MCF-10A and hemolytic activity of compounds 1–5, as well as seven known glycosides were tested. Conicospermiumosides A3-3 (3) and A7-1 (4), having a 22-oxo-23(24)-en fragment, were strongly hemolytic despite lacking a lactone in their aglycones. Moreover, both compounds demonstrated a promising suppressing action against triple negative breast cancer cells. The cells of the MDA-MB-231 line were most sensitive to the cytotoxic action of the glycosides, while the MCF-7 cell line was most sustainable. Six glycosides were selected for further study of some aspects of anticancer action against MDA-MB-231. The selective action of the compounds 4 and 8 on the MDA-MB-231 cells without significant toxicity against the MCF-10A cells was noticeable. More importantly, the selectivity of the compounds was changed over time and maximal selectivity to cancer cells was demonstrated by glycoside 1 at 48 h of exposition. The glycosides 1, 3 and the desulfated derivative 7a strongly inhibited colony formation and growth of the TNBC cells until the process stops completely. Okhotoside B1 (8), DS-okhotoside A1-1 (7a), and conicospermiumoside A3-3 (3) showed a potent cell migration-inhibiting capacity. Quantitative structure–activity relationships (QSARs) calculated on the basis of a correlational analysis of the physicochemical properties and structural features of the glycosides and their cytotoxic activity against different cell lines showed some structural features influenced differently, sometimes even in opposite ways, on the activity of glycosides toward diverse cells (erythrocytes, MCF-10A, and TNBC MDA-MB-231 cells). This observation indicated that glycosides obviously target different membrane components, such as lipids of erythrocytes and some receptors on the surface of mammary normal or tumor cells.

Three new monosulfated polyhydroxysteroid glycosides, spiculiferosides A (1), B (2), and C (3), along with new related unsulfated monoglycoside, spiculiferoside D (4), were isolated from an ethanolic extract of the starfish Henricia leviuscula spiculifera collected in the Sea of Okhotsk. Compounds 1–3 contain two carbohydrate moieties, one of which is attached to C-3 of the steroid tetracyclic core, whereas another is located at C-24 of the side chain of aglycon. Two glycosides (2, 3) are biosides, and one glycoside (1), unlike them, includes three monosaccharide residues. Such type triosides are a rare group of polar steroids of sea stars. In addition, the 5-substituted 3-OSO3-α-L-Araf unit was found in steroid glycosides from starfish for the first time. Cell viability analysis showed that 1–3 (at concentrations up to 100 μM) had negligible cytotoxicity against human embryonic kidney HEK293, melanoma SK-MEL-28, breast cancer MDA-MB-231, and colorectal carcinoma HCT 116 cells. These compounds significantly inhibited proliferation and colony formation in HCT 116 cells at non-toxic concentrations, with compound 3 having the greatest effect. Compound 3 exerted anti-proliferative effects on HCT 116 cells through the induction of dose-dependent cell cycle arrest at the G2/M phase, regulation of expression of cell cycle proteins CDK2, CDK4, cyclin D1, p21, and inhibition of phosphorylation of protein kinases c-Raf, MEK1/2, ERK1/2 of the MAPK/ERK1/2 pathway.

Two new steroid 3β,21-disulfates (1, 2) and two new steroid 3β,22- and 3α,22-disulfates (3, 4), along with the previously known monoamine alkaloid tryptamine (5) were found in the ethanolic extract of the Far Eastern slime sea star Pteraster marsippus. Their structures were determined on the basis of detailed analysis of one-dimensional and two-dimensional NMR, HRESIMS, and HRESIMS/MS data. Compounds 1 and 2 have a Δ22-21-sulfoxy-24-norcholestane side chain. Compounds 3 and 4 contain a Δ24(28)-22-sulfoxy-24-methylcholestane side chain, which was first discovered in the polar steroids of starfish and brittle stars. The influence of substances 1–4 on cell viability, colony formation, and growth of human breast cancer T-47D, MCF-7, and MDA-MB-231 cells was investigated. It was shown that compounds 1 and 2 possess significant colony-inhibiting activity against T-47D cells, while compounds 3 and 4 were more effective against MDA-MB-231 cells.

Four new glycosides of polyhydroxysteroids, ceramasterosides A, B, D, and E (1–4), and two previously known compounds, ceramasteroside C1 (5) and attenuatoside B-I (6), were isolated from an extract of a deep-sea sea star species, the orange cookie star Ceramaster patagonicus. The structures of 1–4 were elucidated by the extensive NMR and ESIMS methods. Steroid monoglycosides 1 and 2 had a common 3β,6α,8,15β,16β-pentahydroxysteroid nucleus and a C–29 oxidized stigmastane side chain and differed from each other only in monosaccharide residues. Ceramasteroside A (1) contained 3-O-methyl-4-O-sulfated β-D-xylopyranose, while ceramasteroside B (2) had 3-O-methyl-4-O-sulfated β-D-glucopyranose, recorded from starfish-derived steroid glycosides for the first time. Their biological activity was studied using a model of lipopolysaccharide-induced (LPS) inflammation in a SIM-A9 murine microglial cell line. During the LPS-induced activation of microglial cells, 1, 3, and 5, at a non-toxic concentration of 1 µM, showed the highest efficiency in reducing the production of intracellular NO, while 4 proved to be most efficient in reducing the extracellular nitrite production. All the test compounds reduced the LPS-induced malondialdehyde (MDA) production. The in vitro experiments have demonstrated, for the first time, the antioxidant activity of the compounds under study.

Six previously unknown triterpene glycosides, pacificusosides L–Q (1–6), and two previously known triterpene glycosides, cucumariosides B1 (7) and A5 (8), were isolated from an alcoholic extract of Pacific sun star, Solaster pacificus. The structures of 1–6 were determined using 1D and 2D NMR, ESIMS, and chemical modifications. Compound 1 is a rare type of triterpene glycoside with non-holostane aglycon, having a linear trisaccharide carbohydrate chain. Pacificusosides M–P (2–5) have new structures containing a Δ8(9)-3,16,18-trihydroxy tetracyclic triterpene moiety. This tetracyclic fragment in sea star or sea cucumber triterpene glycosides was described for the first time. All the compounds under study exhibit low or moderate cytotoxic activity against colorectal carcinoma HCT 116 cells, and breast cancer MDA-MB-231 cells were assessed by MTS assay. Compound 2 effectively suppresses the colony formation of cancer cells at a non-toxic concentration, using the soft-agar assay. A scratch assay has shown a significant anti-invasive potential of compound 2 against HCT 116 cells, but not against MDA-MB-231 cells.

Two new cyclopiane diterpenes and a new cladosporin precursor, together with four known related compounds, were isolated from the marine sediment-derived fungus Penicillium antarcticum KMM 4670, which was re-identified based on phylogenetic inference from ITS, BenA, CaM, and RPB2 gene regions. The absolute stereostructures of the isolated cyclopianes were determined using modified Mosher’s method and quantum chemical calculations of the ECD spectra. The isolation from the natural source of two biosynthetic precursors of cladosporin from a natural source has been reported for the first time. The antimicrobial activities of the isolated compounds against Staphylococcus aureus, Escherichia coli, and Candida albicans as well as the inhibition of staphylococcal sortase A activity were investigated. Moreover, the cytotoxicity of the compounds to mammalian cardiomyocytes H9c2 was studied. As a result, new cyclopiane diterpene 13-epi-conidiogenone F was found to be a sortase A inhibitor and a promising anti-staphylococcal agent.

Investigation of the Vietnamese marine sponge Rhabdastrella globostellata led to the isolation of two new polar isomalabaricanes: rhabdastrellosides A (1) and B (2). Their structures and stereochemistry were elucidated with the application of 1D and 2D NMR, HRESIMS, and HRESIMS/MS methods, as well as chemical modifications and GC–MS analysis. Metabolites 1 and 2 are the first isomalabaricanes with non-oxidized cyclopentane ring in the tricyclic core system. Moreover, having a 3-O-disaccharide moiety in their structures, they increase a very rare group of isomalabaricane glycosides. We report here a weak cytotoxicity of 1 and 2 toward human neuroblastoma SH-SY5Y cells and normal rat H9c2 cardiomyocytes, as well as the cytoprotective activity of rhabdastrelloside B (2) at 1 µM evaluated using CoCl2-treated SH-SY5Y and H9c2 cells.

Seven new monosulfated triterpene glycosides, djakonoviosides A (1), A1 (2), A2 (3), and B1–B4 (4–7), along with three known glycosides found earlier in the other Cucumaria species, namely okhotoside A1-1, cucumarioside A0-1, and frondoside D, have been isolated from the far eastern sea cucumber Cucumaria djakonovi (Cucumariidae, Dendrochirotida). The structures were established on the basis of extensive analysis of 1D and 2D NMR spectra and confirmed by HR-ESI-MS data. The compounds of groups A and B differ from each other in their carbohydrate chains, namely monosulfated tetrasaccharide chains are inherent to group A and pentasaccharide chains with one sulfate group, branched by C-2 Qui2, are characteristic of group B. The aglycones of djakonoviosides A2 (3), B2 (5), and B4 (7) are characterized by a unique structural feature, a 23,16-hemiketal fragment found first in the sea cucumbers’ glycosides. The biosynthetic pathway of its formation is discussed. The set of aglycones of C. djakonovi glycosides was species specific because of the presence of new aglycones. At the same time, the finding in C. djakonovi of the known glycosides isolated earlier from the other species of Cucumaria, as well as the set of carbohydrate chains characteristic of the glycosides of all investigated representatives of the genus Cucumaria, demonstrated the significance of these glycosides as chemotaxonomic markers. The membranolytic actions of compounds 1–7 and known glycosides okhotoside A1-1, cucumarioside A0-1, and frondoside D, isolated from C. djakonovi against human cell lines, including erythrocytes and breast cancer cells (MCF-7, T-47D, and triple negative MDA-MB-231), as well as leukemia HL-60 and the embryonic kidney HEK-293 cell line, have been studied. Okhotoside A1-1 was the most active compound from the series because of the presence of a tetrasaccharide linear chain and holostane aglycone with a 7(8)-double bond and 16β-O-acetoxy group, cucumarioside A0-1, having the same aglycone, was slightly less active because of the presence of branching xylose residue at C-2 Qui2. Generally, the activity of the djakonoviosides of group A was higher than that of the djakonoviosides of group B containing the same aglycones, indicating the significance of a linear chain containing four monosaccharide residues for the demonstration of membranolytic action by the glycosides. All the compounds containing hemiketal fragments, djakonovioside A2 (3), B2 (5), and B4 (7), were almost inactive. The most aggressive triple-negative MDA-MB-231 breast cancer cell line was the most sensitive to the glycosides action when compared with the other cancer cells. Okhotoside A1-1 and cucumarioside A0-1 demonstrated promising effects against MDA-MB-231 cells, significantly inhibiting the migration, as well as the formation and growth, of colonies.

Four new mono- and trisulfated triterpene penta- and tetraosides, djakonoviosides C1 (1), D1 (2), E1 (3), and F1 (4) were isolated from the Far Eastern sea cucumber Cucumaria djakonovi (Cucumariidae, Dendrochirotida), along with six known glycosides found earlier in other Cucumaria species. The structures of unreported compounds were established on the basis of extensive analysis of 1D and 2D NMR spectra as well as by HR-ESI-MS data. The set of compounds contains six different types of carbohydrate chains including two new ones. Thus, djakonovioside C1 (1) is characterized by xylose as the second residue, that was a branchpoint in the pentasaccharide chain. Meanwhile, only quinovose and rarely glucose have been found earlier in pentasaccharide chains branched at C-2 of the second sugar unit. Djakonovioside E1 (3) is characterized by a tetrasaccharide trisulfated chain, with glucose as the second residue. So, in the series of isolated glycosides, three types of sugars in the second position were presented: the most common, quinovose—in six compounds; glucose—in three substances; and the rare xylose—in one glycoside. The set of aglycones was composed of holostane- and non-holostane-type polycyclic systems; the latter comprised normal and reduced side chains. Noticeably, isokoreoside A (9), isolated from C. djakonovi, was a single glycoside having a 9(11)-double bond, indicating two oxidosqualenecyclases are operating in the process of the biosynthesis of aglycones. Some of the glycosides from C. djakonovi, which were characterized by pentasaccharide branched chains containing one to three sulfate groups, are chemotaxonomic features of the representatives of the genus Cucumaria. The assortment of sugar parts of Cucumaria’s glycosides was broadened with previously undescribed penta- and tetrasaccharide moieties. The metabolic network of sugar parts and aglycones is constructed based on biogenetic relationships. The cytotoxic action of compounds 1–10, isolated from C. djakonovi, against human breast cancer cell lines was investigated along with the hemolytic activity. Erythrocytes were, as usual, more sensitive to the membranolytic action of the glycosides than cancer cells. The triple-negative breast cancer MDA-MB-231 cell line was more vulnerable to the action of glycosides in comparison with the other tested cancer cells, while the MCF-7 cell line was less susceptible to cytotoxic action. Djakonovioside E1 (3) demonstrated selective action against ER-positive MCF-7 and triple-negative MDA-MB-231 cell lines, while the toxic effect in relation to normal mammary epithelial cells (MCF-10A) was absent. Cucumarioside A2-5 (6) inhibited the formation and growth of colonies of cancer cells to 44% and tumor cell migration to 85% of the control. Quantitative structure–activity relationships (QSAR) were calculated on the basis of the correlational analysis of the physicochemical properties and structural features of the glycosidic molecules and their membranolytic activity. QSAR revealed the extremely complex nature of such relationships, but these calculations correlated well with the observed SAR.