Ekaterina G. Lyakhova

Secondary metabolites of the Vietnamese nudibranch mollusk Phyllidiella pustulosa

The chemical composition of the EtOH extract of the nudibranch mollusk Phyllidiella pustulosa was studied. Six sesquiterpenoids including the novel secondary metabolite (+)-10(R)-isothiocyanoalloaromodendrane were isolated. The steroid composition of the extract was studied. The structures of three previously known ketosteroids and six sterols were identified.

Polyoxygenated steroids from the gorgonian Menella woodin with capabilities to modulate ROS levels in macrophages at response to LPS.

Four new polyoxygenated sterol derivatives (1-4) along with the compounds (5-7) previously known from other biological sources were isolated from the gorgonian Menella woodin, collected from the Vietnamese waters. Structures of 1-4 were elucidated by the detailed NMR spectroscopic and mass-spectrometric analyses as well as comparison with those reported in literature data. Compounds 1, 4, and 6 decrease the production of reactive oxygen species (ROS) by the murine macrophages of RAW 264.7 line at induction by endotoxic lipopolysaccharide (LPS) from Escherichia coli.

Structure and absolute configuration of a new rearranged chamigrane-type sesquiterpenoid from the sea hare Aplysia sp.

Abstract (6 S ,10 S )-3,10-Dimethyl-7,11-dimethylidenespiro[5,5]undec-2-en-4-one ( 1 ), a new rearranged chamigrane-type sesquiterpenoid with two sp 2 -hybridized carbons in α-positions to the spiro-atom, was isolated from the alcoholic extract of the sea hare Aplysia sp. and its structure and absolute configuration were established by chemical transformations, NMR, EIMS, IR, UV and CD spectroscopy.

Diterpenoid hydroperoxides from the Far-Eastern brown alga Dictyota dichotoma.

Two new compounds, dictyohydroperoxide 1 and hydroperoxyacetoxycrenulide 2, containing hydroperoxyl groups rarely found in algal terpenoids were isolated from the Russian population of brown alga Dictyota dichotoma. The known compounds acetoxycrenulide 4 and squalene were also found in this algal species for the first time. Some of the isolated compounds showed moderate cytoxicity against human cancer cell lines.

Isolation, structures, and biological activities of triterpenoids from a Penares sp. marine sponge.

Six new triterpenoids (1-6) and the previously known penasterone, acetylpenasterol, and ergosta-4,24(28)-dien-3-one were isolated from a Penares sp. sponge collected from Vietnamese waters. Structures of the obtained compounds were established by extensive 1D and 2D NMR spectroscopy and mass spectrometry. Configurations of the triterpene epoxy lactones (1-4) were determined on the basis of NOESY and CD data and calculation of spin coupling constants and confirmed by X-ray crystallographic analysis of compound 2. The isolated triterpenoid 6 was cytotoxic against human leukemia HL-60 cells (IC₅₀ = 9.7 μM).

Chemical properties of marine terpenoids. 1. Some reactions of (6S,10R)-10-bromo-3,11,11-trimethyl-7-methylidenespiro[5,5]undec-2-en-4-one, a sesquiterpenoid from the sea hare Aplysia dactylomela

The structures of products obtained by reductive debromination and CF3COOH- and KOH-induced transformations of natural chamigrane-type sesquiterpenoid (6S,10R)-10-bromo-3,11,11-trimethyl-7-methylidenespiro[5,5]undec-2-en-4-one (dactylone) isolated from the sea hare Aplysia dactylomela were analyzed. The absolute configurations of the reaction products were established by CD spectra taking into account the configuration of the starting dactylone.

Further study on Penares sp. from Vietnamese waters: Minor lanostane and nor-lanostane triterpenes

Eight new oxidized lanostane and nor-lanostane derivatives (1-8) along with the previously known penasterol (9) and 24-ethylcholesta-4,24(28)-dien-3-one (10) were isolated from a sponge Penares sp. collected from the Vietnamese waters. Structures of these minor compounds were elucidated by the detailed NMR spectroscopic and mass-spectrometric analyses and by comparison with earlier reported spectroscopic data. A hypothetic scheme of metabolism of the lanostane derivatives in sponges belonging to Penares and Erylus genera was proposed and discussed.

New Steroidal Glycosides from the Starfish Acanthaster planci

Two new and three known polyhydroxysteroid glycosides were isolated from the MeOH extract of the starfish Acanthaster planci. The structures of the isolated compounds were elucidated using NMR and mass spectrometry. The new glycosides had the same aglycon, (24S)-24-methyl-5α-cholestane-3β,4β,6α,8,15β,16β,28-heptaol, and different carbohydrate fragments,2-O-methyl-β-D-xylopyranosyl-(1→2)-β-D-galactofuranose and 5-O-sulfo-α-L-arabinofuranose, bonded to the C-28 position of the 24-methylcholestane side chain.

Lissodendoric Acids A and B, Manzamine-Related Alkaloids from the Far Eastern Sponge Lissodendoryx florida

The first representatives of a new group of manzamine-related alkaloids with a previously unknown skeletal systems, namely, lissodendoric acids A (1) and B (2), were isolated from the sponge Lissodendoryx florida collected from the Sea of Okhotsk. The structures and absolute configurations have been elucidated by extensive spectroscopic analysis together with chemical transformations and quantum-chemical modeling. The lissodendoric acids show a potent capability to decrease the production of reactive oxygen species in neuroblastoma Neuro 2a and somewhat increase the survival of these cells upon treatment with 6-hydroxydopamine (an in vitro antiparkinson biotest).

Steroidal Metabolites from the Vietnamese Nudibranch Mollusk Doriprismatica atromarginata

Nudibranch mollusks lack mechanical protection from natural enemies, have evolved to be shell-less, and have long intrigued chemists and naturalists with their ability to accumulate food metabolites that repel predators. The mollusk Doriprismatica (=Glossodoris) atromarginata inhabits the tropical Indo-Pacific and is well known as a species that accumulates such metabolites from marine sponges. Several studies of various collections of these mollusks showed that they contained either sponge secondary metabolites or their biotransformation products, which can be traced by comparing the isolated products and the starting sponge compounds [1, 2]. In continuation of research on secondary metabolites from marine invertebrates inhabiting Vietnamese waters, we recently isolated new sesquiterpenoids and polar steroids from the gorgonian Menella woodin [3–5]. Several specimens of D. atromarginata (15.8 g, moist weight) were found on the gorgonian during its collection. We decided to characterize the secondary metabolites from the mollusk in this unusual habitat and to compare them with published data on natural compounds from other collections. It was reported earlier that D. atromarginata from littoral waters of Sri Lanka, Australia, and India contained different sets of secondary metabolites. The differences were probably due to different sponge species in the mollusk diet or individual differences in the enzymatic mechanisms by which these marine animals detoxify sponge metabolites, which are often highly toxic. All currently known natural compounds from D. atromarginata are spongian-type furano-, di-, and sesquiterpenoids or scalarane-type sesquiterpenoids (nor-sesquiterpenoids) [1, 6]. Cholesterol (14.2 mg) and (22E)-chloest-5,22-dien-3 -ol (7.0 mg) were isolated from the secondary metabolites of the Vietnamese mollusk as the major constituents of the extract in addition to four minor trihydroxysterols 1a–d. However, traces of spongianor scalarane-type derivatives were completely absent in this collection of D. atromarginata.