Sophia A. Kolesnikova

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.

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).

Bionanocomposite from self-assembled building blocks of nacre-like crystalline polymorph of chitosan with clay nanoplatelets

Biopolymers are biocompatible and nontoxic but their other properties rank much below synthetic polymers. Their mechanical performance is improved significantly in bionanocomposites with a layered brick-and-mortar structure biomimicking the nacre of a crustaceous shell after integration with nanoparticles. Biopolymers are found in a disordered state, whereas crustaceans hold chitin in a crystalline form. Herein, it is biomimicked in a bionanocomposite of chitosan with clay nanoplatelets. Films were prepared using a new one-pot technique combining an initial formation in situ of building blocks of clay nanoplatelets and chitosan macromolecules charged progressively in their presence with evaporation-induced self-assembly, which results in highly ordered nanocrystalline narrow rectangle microparticles of thickness is ca. 15 nm that are made from interstratified layers of a new crystalline polymorph of chitosan with nanoplatelets. Its presence and structure is characterized by small/wide-angle X-ray scattering, scanning and transmission electron microscopy, microRaman spectroscopy. Crystalline polymorph can be separated easily. It is insoluble in water and organics that provide scope for its use in nanocomposites.

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.

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.