Semisynthesis and Cytotoxic Evaluation of an Ether Analogue Library Based on a Polyhalogenated Diphenyl Ether Scaffold Isolated from a Lamellodysidea Sponge

The known oxygenated polyhalogenated diphenyl ether, 2-(2',4'-dibromophenoxy)-3,5-dibromophenol (1), with previously reported activity in multiple cytotoxicity assays was isolated from the sponge Lamellodysidea sp. and proved to be an amenable scaffold for semisynthetic library generation. The phenol group of 1 was targeted to generate 12 ether analogues in low-to-excellent yields, and the new library was fully characterized by NMR, UV, and MS analyses. The chemical structures for 2, 8, and 9 were additionally determined via single-crystal X-ray diffraction analysis. All natural and semisynthetic compounds were evaluated for their ability to inhibit the growth of DU145, LNCaP, MCF-7, and MDA-MB-231 cancer cell lines. Compound 3 was shown to have near-equivalent activity compared to scaffold 1 in two in vitro assays, and the activity of the compounds with an additional benzyl ring appeared to be reliant on the presence and position of additional halogens.

Cyclotheonellazoles D-I, Potent Elastase Inhibitory Thiazole-Containing Cyclic Peptides from Theonella sp. (2131)

Six new thiazole-containing cyclic peptides, the cyclotheonellazoles D-I (1-6), were isolated from the Australian marine sponge Theonella sp. (2131) with their structures assigned by comprehensive 1D and 2D NMR spectroscopic and MS spectrometric analyses, Marfey's derivatization studies, and comparison with time-dependent density functional theory (TDDFT) calculated ECD data. The Type 2 azole-homologated peptides herein comprise up to five nonproteinogenic amino acids, including the protease transition state mimic α-keto-β-amino acid residue 3-amino-4-methyl-2-oxohexanoic acid (Amoha), while 1-3 also contain a terminal hydantoin residue not previously found in cyclotheonellazoles. The keramamides A (7) and L (8) were reisolated affording expanded exploration of their biological activities. The peptides were examined for protease inhibitory activities against two mammalian serine proteases (elastase and chymotrypsin) and SARS-CoV-2 3-chymotrypsin-like protease (3CLpro), a validated antiviral therapeutic target for COVID-19. Peptides 1-6 and keramamide A (7) displayed potent nanomolar inhibition of elastase (IC50 16.0 to 61.8 nM), while 7 also contained modest inhibition of chymotrypsin and SARS-CoV-2 3CLpro (IC50 0.73 and 1.1 μM, respectively). The cyclotheonellazoles D-E (1-3) do not affect the viability of human breast, ovarian, and colon cancer cells (>100 μM), with the cytotoxicity previously reported for keramamide L (8) not replicated (inactive >20 μM).

Amphiphilic Polyamine α-Synuclein Aggregation Inhibitors from the Sponge Aaptos lobata

Bioassay-guided investigation of the sponge Aaptos lobata resulted in the isolation and identification of two new amphiphilic polyamines, aaptolobamines A (1) and B (2). Their structures were determined through analysis of NMR and MS data. MS analysis also indicated that A. lobata contained a complex mixture of aaptolobamine homologues. Both aaptolobamines A (1) and B (2) show broad bioactivity, including cytotoxicity against cancer cell lines, moderate antimicrobial activity against a methicillin-resistant strain of Staphylococcus aureus, and weak activity against a Pseudomonas aeruginosa strain. The mixtures of aaptolobamine homologues were shown to contain compounds that bind to the Parkinson's disease associated amyloid protein α-synuclein and inhibit its aggregation.

Using UHPLC-MS profiling for the discovery of new sponge-derived metabolites and anthelmintic screening of the NatureBank bromotyrosine library

In order to further expand the NatureBank open access compound library, chemical investigations of the Australian marine sponge, Ianthella basta, were undertaken since UHPLC-MS analysis of the extract from this sponge indicated the presence of a new alkaloid. Large-scale extraction and mass-directed isolation studies on the CH2Cl2/MeOH I. basta extract resulted in the purification of a new bromotyrosine-derived alkaloid, 5-debromopurealidin H (1), along with the known marine natural product, ianthesine E (2). The chemical structure of the new compound was determined following detailed spectroscopic and spectrometric data analysis. These two compounds (1 and 2) along with seven previously reported marine bromotyrosine alkaloids from the NatureBank open access library, which included psammaplysins F (3) and H (4), bastadins 4 (5), 8 (6) and 13 (7), aerothionin (8) and hexadellin A (9), were evaluated for their nematocidal activity against exsheathed third-stage larvae of Haemonchus contortus, a highly pathogenic parasite of ruminants. Of the nine compounds, bastadin 8 (6), hexadellin A (9) and bastadin 4 (5) showed inhibition towards larval motility after 72 h of exposure with IC50 values of 1.6 µM, 10.0 µM and 33.3 µM, respectively.

Identification of Anthelmintic Bishomoscalarane Sesterterpenes from the Australian Marine Sponge Phyllospongia bergquistae and Structure Revision of Phyllolactones A-D

High-throughput screening of the NatureBank marine extract library (7616 samples) identified an extract derived from the Australian marine sponge Phyllospongia bergquistae with activity against Hemonchus contortus (barber's pole worm), an economically important parasitic nematode. Bioassay-guided fractionation of the CH₂Cl₂/MeOH extract from P. bergquistae led to the purification of four known bishomoscalarane sesterterpenes, phyllolactones A-D (1-4). The absolute configurations of phyllolactones B (2) and C (3) were determined by single-crystal X-ray diffraction analysis; literature and data analyses revealed the need for these chemical structures to be revised. Compounds 2-4 induced a lethal, skinny (Ski) phenotype in larvae of H. contortus at concentrations between 5.3 and 10.1 μM. These data indicate that the bishomoscalarane sesterterpene structure class warrants further investigation for nematocidal or nematostatic activity.

α-Synuclein binding activity of the plant growth promoter asterubine

Preventing the aggregation of certain amyloid proteins has the potential to slow down the progression of diseases like Alzheimer's, Parkinson's, and type 2 diabetes mellitus. During a high-throughput screen of 300 Australian marine invertebrate extracts, the extract of the marine sponge Thorectandra sp. 4408 displayed binding activity to the Parkinson's disease-associated protein, α-synuclein. Isolation of the active component led to its identification as the known plant growth promoter asterubine (1). This molecule shares distinct structural similarities with potent amyloid beta aggregation inhibitors tramiprosate (homotaurine) and ALZ-801. Herein we report the isolation, NMR data acquired in DMSO and α-synuclein binding activity of asterubine (1).

Dysidenin from the Marine Sponge Citronia sp. Affects the Motility and Morphology of Haemonchus contortus Larvae In Vitro

High-throughput screening of the NatureBank marine extract library (n = 7616) using a phenotypic assay for the parasitic nematode Haemonchus contortus identified an active extract derived from the Australian marine sponge Citronia sp. Bioassay-guided fractionation of the CH₂Cl₂/MeOH extract from Citronia sp. resulted in the purification of two known hexachlorinated peptides, dysidenin (1) and dysideathiazole (2). Compound 1 inhibited the growth/development of H. contortus larvae and induced multiple phenotypic changes, including a lethal evisceration (Evi) phenotype and/or somatic cell and tissue destruction. This is the first report of anthelmintic activity for these rare and unique polychlorinated peptides.

High Throughput Screening of the NatureBank 'Marine Collection' in a Haemonchus Bioassay Identifies Anthelmintic Activity in Extracts from a Range of Sponges from Australian Waters

Widespread resistance in parasitic nematodes to most classes of anthelmintic drugs demands the discovery and development of novel compounds with distinct mechanisms of action to complement strategic or integrated parasite control programs. Products from nature-which assume a diverse 'chemical space'-have significant potential as a source of anthelmintic compounds. In the present study, we screened a collection of extracts (n = 7616) derived from marine invertebrates sampled from Australian waters in a high throughput bioassay for in vitro anti-parasitic activity against the barber's pole worm (Haemonchus contortus)-an economically important parasitic nematode of livestock animals. In this high throughput screen (HTS), we identified 58 active extracts that reduced larval motility by ≥70% (at 90 h), equating to an overall 'hit rate' of ~0.8%. Of these 58 extracts, 16 also inhibited larval development by ≥80% (at 168 h) and/or induced 'non-wild-type' (abnormal) larval phenotypes with reference to 'wild-type' (normal) larvae not exposed to extract (negative controls). Most active extracts (54 of 58) originated from sponges, three from chordates (tunicates) and one from a coral; these extracts represented 37 distinct species/taxa of 23 families. An analysis of samples by 1H NMR fingerprinting was utilised to dereplicate hits and to prioritise a set of 29 sponge samples for future chemical investigation. Overall, these results indicate that a range of sponge species from Australian waters represents a rich source of natural compounds with nematocidal or nematostatic properties. Our plan now is to focus on in-depth chemical investigations of the sample set prioritised herein.

Anti-prion and α-Synuclein Aggregation Inhibitory Sterols from the Sponge Lamellodysidea cf. chlorea

In a study aimed at identifying new anti-prion compounds we screened a library of 500 Australian marine invertebrate derived extracts using a yeast-based anti-prion assay. This resulted in an extract from the subtropical sponge Lamellodysidea cf. chlorea showing potent anti-prion activity. The bioassay-guided investigation of the sponge extract led to the isolation of three new bioactive polyoxygenated steroids, lamellosterols A-C (1-3). These sterols were all isolated in low yield, and their structures elucidated by extensive NMR and MS data analysis. Lamellosterols A-C displayed potent anti-prion activity against the [PSI⁺] yeast prion (EC₅₀s of 12.7, 13.8, and 9.8 μM, respectively). Lamellosterol A (1) was further shown to bind to the Parkinson's disease implicated amyloid protein, α-synuclein, and to significantly inhibit its aggregation. Our findings indicate that these polyoxygenated sterol sulfates may be useful compounds to study mechanisms associated with neurodegenerative diseases.

Comatulins A-E, Taurine-Conjugated Anthraquinones from the Australian Crinoid Comatula rotalaria

Chemical investigations of two specimens of the Australian crinoid Comatula rotalaria afforded five new taurine-conjugated anthraquinones, comatulins A-E (1-5), together with 11 known marine natural products (6-16). The chemical structures of all the compounds were elucidated by detailed spectroscopic and spectrometric data analysis. The first X-ray crystal structure of a crinoid-derived acyl anthraquinone, rhodocomatulin 5,7-dimethyl ether (8), is reported here. Compounds 1, 2, 6-13, and two additional naphthopyrone derivatives, 17 and 18, were evaluated for their ability to inhibit HIV-1 replication in vitro; none of the compounds were active at 100 μM. Furthermore, compounds 1, 2, 6-10, 14, 15, 17, and 18 were screened for nematocidal activity against exsheathed third-stage larvae of Hemonchus contortus, a highly pathogenic parasite nematode of ruminants. Compound 17, known as 6-methoxycomaparvin 5,8-dimethyl ether, showed an inhibitory effect on larval motility (IC₅₀ = 30 μM) and development (IC₅₀ = 31 μM) and induced the eviscerated (Evi) phenotype.

Identification of Fromiamycalin and Halaminol A from Australian Marine Sponge Extracts with Anthelmintic Activity against Haemonchus contortus

There is an urgent need to discover and develop new anthelmintics for the treatment of parasitic nematodes of veterinary importance to circumvent challenges linked to drug resistant parasites. Being one of the most diverse natural ecosystems, the marine environment represents a rich resource of novel chemical entities. This study investigated 2000 extracts from marine invertebrates, collected from Australian waters, for anthelmintic activity. Using a well-established in vitro bioassay, these extracts were screened for nematocidal activity against Haemonchus contortus — a socioeconomically important parasitic nematode of livestock animals. Extracts (designated Mu-1, Ha-1 and Ha-2) from two marine sponges (Monanchora unguiculata and Haliclona sp.) each significantly affected larvae of H. contortus. Individual extracts displayed a dose-dependent inhibition of both the motility of exsheathed third-stage larvae (xL3s) and the development of xL3s to fourth-stage larvae (L4s). Active fractions in each of the three extracts were identified using bioassay-guided fractionation. From the active fractions from Monanchora unguiculata, a known pentacyclic guanidine alkaloid, fromiamycalin (1), was purified. This alkaloid was shown to be a moderately potent inhibitor of L4 development (half-maximum inhibitory concentration (IC₅₀) = 26.6 ± 0.74 µM) and L4 motility (IC₅₀ = 39.4 ± 4.83 µM), although it had a relatively low potency at inhibiting of xL3 motility (IC₅₀ ≥ 100 µM). Investigation of the active fractions from the two Haliclona collections led to identification of a mixture of amino alcohol lipids, and, subsequently, a known natural product halaminol A (5). Anthelmintic profiling showed that 5 had limited potency at inhibiting larval development and motility. These data indicate that fromiamycalin, other related pentacyclic guanidine alkaloids and/or halaminols could have potential as anthelmintics following future medicinal chemistry efforts.

Capillasterin A, a Novel Pyrano[2,3-f]chromene from the Australian Crinoid Capillaster multiradiatus

Capillasterin A (1), a novel pyrano[2,3-f]chromene, together with seven known naphthopyrones including comaparvin (2), TMC-256C1 (3), 6-methoxycomaparvin-5- methyl ether (4), 5,8-dihydroxy-6-methoxy-2-propyl-4H-naphtho[2,3-b]pyran-4-one (5), 5,8-dihydroxy-6,10-dimethoxy-2-propyl-4H-naphtho[2,3-b]pyran-4-one (6), TMC-256A1 (7) and 6-methoxycomaparvin (8) were isolated from an EtOH/H₂O extract from the Australian crinoid Capillaster multiradiatus. The structures of all the compounds were determined by detailed spectroscopic (1D/2D NMR and MS) data analysis. This is the first report of a natural product that contains the pyrano[2,3-f]chromene skeleton. Compounds 2–6 were observed to display moderate inhibition of in vitro HIV-1 replication in a T cell line with EC₅₀ values ranging from 7.5 to 25.5 µM without concomitant cytotoxicity.

Rhodocomatulin-Type Anthraquinones from the Australian Marine Invertebrates Clathria hirsuta and Comatula rotalaria

Chemical investigations of an Australian sponge, Clathria hirsuta, from the Great Barrier Reef, have resulted in the isolation of two known anthraquinones, rhodocomatulin 5,7-dimethyl ether (1) and rhodocomatulin 7-methyl ether (2). Additionally, four new anthraquinone metabolites, 6-methoxyrhodocomatulin 7-methyl ether, 3-bromo-6-methoxy-12-desethylrhodocomatulin 7-methyl ether, 3-bromo-6-methoxyrhodocomatulin 7-methyl ether, and 3-bromorhodocomatulin 7-methyl ether (3-6), were also isolated and characterized. This is the first report of the rhodocomatulin-type anthraquinones from a marine sponge, as 1 and 2 were previously isolated from the marine crinoid genus Comatula. An additional chemical investigation of the marine crinoid Comatula rotalaria enabled the isolation of further quantities of 1 and 2, as well as two additional new crinoid metabolites, 12-desethylrhodocomatulin 5,7-dimethyl ether and 12-desethylrhodocomatulin 7-methyl ether (7 and 8). An NMR spectroscopic analysis of compounds 7 and 8 provided further insight into the rhodocomatulin planar structure and, together with the successful implementation of DFT-NMR calculations, confirmed that the rhodocomatulin metabolites existed as para rather than ortho quinones.

Two new desma-less species of Theonella Gray, 1868 (Demospongiae: Astrophorida: Theonellidae), from the Great Barrier Reef, Australia,and a re-evaluation of one species assigned previously to Dercitus Gray, 1867

Extensive surveys of the biodiversity on the seafloor of the inter-reef regions of the Great Barrier Reef, Australia, have resulted in the collection of large numbers of sponges, many of which are likely new to science. Identification of these sponges, however, was made difficult by the absence in some specimens of key diagnostic characters, such as megascleres. We used an integrated approach to the taxonomy of these sponges, incorporating morphological examination by SEM, analysis of DNA sequence data (using the COI barcoding fragment of mtDNA) and preliminary studies of the chemistry of the sponges, to describe the new species, which were found to contain no native spicules other than acanthose microrhabds. Here, we propose two new species of Theonella Gray, 1868: Theonella deliqua n. sp. (found in association with a single unidentified species of siliquariid mollusc) and Theonella maricae n. sp. from the Great Barrier Reef. Further, we propose the new combination of Theonella xantha (Sutcliffe, Hooper and Pitcher 2010) n. comb. for another microrhabd-only-bearing species. On the basis of our gene trees, we recognise Theonella (and Theonellidae Lendenfeld, 1903) within Astrophorida Sollas, 1887. We discuss the potential for chemotaxonomic and DNA-based insights into the origins and radiation of species of Theonella and explore the evolutionary significance of the reduced morphology of the three additional species recognised here.

Trikentramides A-D, indole alkaloids from the Australian sponge Trikentrion flabelliforme

Chemical investigations of two specimens of Trikentrion flabelliforme collected from Australian waters have resulted in the identification of four new indole alkaloids, trikentramides A-D (9-12). The planar chemical structures for 9-12 were established following analysis of 1D/2D NMR and MS data. The relative configurations for 9-12 were determined following the comparison of (1)H NMR data with data previously reported for related natural products. The application of a quantum mechanical modeling method, density functional theory, confirmed the relative configurations and also validated the downfield carbon chemical shift observed for one of the quaternary carbons (C-5a) in the cyclopenta[g]indole series. The indole-2,3-dione motif present in trikentramides A-C is rare in nature, and this is the first report of these oxidized indole derivatives from a marine sponge.