Structure and absolute configuration of 3-alkylpiperidine alkaloids from an Indonesian sponge of the genus Halichondria

A Soft Spot for Chemistry-Current Taxonomic and Evolutionary Implications of Sponge Secondary Metabolite Distribution

Marine sponges are the most prolific marine sources for discovery of novel bioactive compounds. Sponge secondary metabolites are sought-after for their potential in pharmaceutical applications, and in the past, they were also used as taxonomic markers alongside the difficult and homoplasy-prone sponge morphology for species delineation (chemotaxonomy). The understanding of phylogenetic distribution and distinctiveness of metabolites to sponge lineages is pivotal to reveal pathways and evolution of compound production in sponges. This benefits the discovery rate and yield of bioprospecting for novel marine natural products by identifying lineages with high potential of being new sources of valuable sponge compounds. In this review, we summarize the current biochemical data on sponges and compare the metabolite distribution against a sponge phylogeny. We assess compound specificity to lineages, potential convergences, and suitability as diagnostic phylogenetic markers. Our study finds compound distribution corroborating current (molecular) phylogenetic hypotheses, which include yet unaccepted polyphyly of several demosponge orders and families. Likewise, several compounds and compound groups display a high degree of lineage specificity, which suggests homologous biosynthetic pathways among their taxa, which identifies yet unstudied species of this lineage as promising bioprospecting targets.

Marine-Derived Macrocyclic Alkaloids (MDMAs): Chemical and Biological Diversity

The curiosity and attention that researchers have devoted to alkaloids are due to their bioactivities, structural diversity, and intriguing chemistry. Marine-derived macrocyclic alkaloids (MDMAs) are considered to be a potential source of drugs. Trabectedin, a tetrahydroisoquinoline derivative, has been approved for the treatment of metastatic soft tissue sarcoma and ovarian cancers. MDMAs displayed potent activities that enabled them to be used as anticancer, anti-invasion, antimalarial, antiplasmodial, and antimicrobial. This review presents the reported chemical structures, biological activities, and structure-activity relationships of macrocyclic alkaloids from marine organisms that have been published since their discovery until May 2020. This includes 204 compounds that are categorized under eight subclasses: pyrroles, quinolines, bis-quinolizidines, bis-1-oxaquinolizidines, 3-alkylpiperidines, manzamines, 3-alkyl pyridinium salts, and motuporamines.

Marine Natural Products from Indonesian Waters

Natural products are primal and have been a driver in the evolution of organic chemistry and ultimately in science. The chemical structures obtained from marine organisms are diverse, reflecting biodiversity of genes, species and ecosystems. Biodiversity is an extraordinary feature of life and provides benefits to humanity while promoting the importance of environment conservation. This review covers the literature on marine natural products (MNPs) discovered in Indonesian waters published from January 1970 to December 2017, and includes 732 original MNPs, 4 structures isolated for the first time but known to be synthetic entities, 34 structural revisions, 9 artifacts, and 4 proposed MNPs. Indonesian MNPs were found in 270 papers from 94 species, 106 genera, 64 families, 32 orders, 14 classes, 10 phyla, and 5 kingdoms. The emphasis is placed on the structures of organic molecules (original and revised), relevant biological activities, structure elucidation, chemical ecology aspects, biosynthesis, and bioorganic studies. Through the synthesis of past and future data, huge and partly undescribed biodiversity of marine tropical invertebrates and their importance for crucial societal benefits should greatly be appreciated.

Alkylidene Dihydropyridines As Synthetic Intermediates: Model Studies toward the Synthesis of the Bis(piperidine) Alkaloid Xestoproxamine C

Results of model studies demonstrating a stereoselective synthetic route to tricyclic analogues of the bis(piperidine) alkaloid xestoproxamine C are presented. Dearomatization of a tricyclic pyridine derivative to afford an alkylidene dihydropyridine (anhydrobase) intermediate followed by catalytic heterogeneous hydrogenation was used to install the correct relative stereochemistry about the bis(piperidine) ring system. Other key features of these model studies include development of an efficient ring-closing metathesis procedure to prepare macrocyclic derivatives of 3,4-disusbstituted pyridines, intramolecular cyclizations of alkylidene dihydropyridines to establish pyridine-substituted pyrrolidines and piperidines, successful homologation of pyridine-4-carboxaldehydes using formaldehyde dimethyl thioacetal monoxide (FAMSO), and application of B-alkyl Suzuki coupling to assemble substituted pyridines.

Acanthocyclamine A From the Indonesian Marine Sponge Acanthostrongylophora ingens

A new 3-alkylpiperidine compound (–)-acanthocyclamine A (1) has been obtained from the methanolic extract of Acanthostrongylophora ingens (order Haplosclerida, family Petrosiidae) collected from Wakatobi Marine National Park in South East Sulawesi, Indonesia. The structure of 1 was investigated by extensive 1D- and 2D-NMR experiments. The absolute configuration of 1 was established by X-ray crystallography from anomalous dispersion effects using Cu radiation as C2 (R), C3 (R), C7 (R), and C9 (R). A plausible biosynthetic scheme leading to 1 is presented, and compared with the biosynthetic pathway proposed for the manzamine alkaloids.

Discovery of a new class of immunosuppressants from Trichothecium roseum co-inspired by cross-kingdom similarity in innate immunity and pharmacophore motif

The limited selection of immunosuppressants in the clinic hampers the efficient management of immune disorders such as rejections after organ transplantations. However, the search for new immunosuppressive compounds remains random and creates inevitably financial and laborious wastes. Herein, we present an immunity-inspired discovery strategy that rationally allows an efficient identification of immunosuppressive compounds from the endophyte culture, as exemplified by the new peptide trichomide A. This compound exerts its immunosuppressive action more selectively than cyclosporin A. It was found that trichomide A decreases the expression of Bcl-2, increases the expression of Bax, and has a small or negligible effect on the expressions of p-Akt, CD25, and CD69. Our study strengthens the idea that the cross-kingdom similarity in immunity among living things could provide a shorter route towards the identification of natural products valuable for the development of new immunosuppressants.

Psammaplysin derivatives from the Balinese marine sponge Aplysinella strongylata

Twenty-one new psammaplysin derivatives (4-24) exhibiting a variety of side chains, as well as six previously known psammaplysins, were identified from the Indonesian marine sponge Aplysinella strongylata. The double bond on the side chain of the fatty acid-containing psammaplysins was located by GC-MS analysis of the fatty acid methyl esters and their pyrrolidide derivatives. HPLC and Mosher ester studies confirmed that the isolated metabolites possessing a 19-OH substituent were mixtures of diastereomers. Selected compounds (4, 5, 7, 8, 12, 18, and 22) were screened for in vitro activity against chloroquine-sensitive (3D7) P. falciparum malaria parasites. Of the new psammaplysins, 19-hydroxypsammaplysin E (4) showed the best antimalarial activity, with an IC(50) value of 6.4 μM.

Marine natural products

Covering: 2010. Previous review: Nat. Prod. Rep., 2011, 28, 196. This review covers the literature published in 2010 for marine natural products, with 895 citations (590 for the period January to December 2010) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1003 for 2010), together with the relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

3,4'-Linked bis(piperidines) related to the haliclonacyclamine class of marine alkaloids: synthesis using crossed-aldol chemistry and preliminary biological evaluations

Compounds 2-5, incorporating various elements of the 3,4'-bis(piperidine) core associated with the sponge-derived alkaloid haliclonacyclamine A (HA, 1), have been prepared through, inter alia, aldol-type reactions of N-substituted piperidin-4-ones and certain derivatives. Screening of these compounds in various assays, including an ecological one, reveals that compound 5 exhibits allelochemical properties similar to those associated with HA itself.

Xestoproxamines A-C from Neopetrosia proxima. Assignment of absolute stereostructure of bis-piperidine alkaloids by integrated degradation-CD analysis

The complete stereostructures of xestoproxamines A-C, from the Bahamian sponge Neopetrosia proxima, were assigned from spectroscopic analysis, including MS, 2D NMR, and integrated degradation-CD analysis. Two new CD application protocols are described for defining absolute configuration: one for allylic methyl groups in branched chains and a second for the heterocyclic core bis-piperidine with specific applicability to other members of this class alkaloids--known for their stereoheterogeneity--and tertiary cyclic amines in general.

Neopetrosiamine A, biologically active bis-piperidine alkaloid from the Caribbean sea sponge Neopetrosia proxima

A new tetracyclic bis-piperidine alkaloid, neopetrosiamine A (1), has been extracted from the marine sponge Neopetrosiaproxima collected off the west coast of Puerto Rico. The structure of compound 1 was elucidated by analysis of spectroscopic data coupled with careful comparisons of its (1)H and (13)C NMR data with those of a well-known 3-alkylbis-piperidine alkaloid model. The new alkaloid displayed strong in vitro cytotoxic activity against a panel of cancer cell lines as well as in vitro inhibitory activity against the pathogenic microbes Mycobacterium tuberculosis and Plasmodium falciparum.