'Upenamide: An unprecedented macrocyclic alkaloid from the Indonesian sponge Echinochalina sp

Selective construction of fused heterocycles by an iridium-catalyzed reductive three-component annulation reaction

Catalytic conversion of ubiquitously distributed but less reactive N-heteroarenes into functional products remains to date a challenge. Here, through an initial pretreatment of N-heteroarenes with alkyl bromide, we describe a syn-selective construction of functional fused heterocycles via iridium catalyzed reductive annulation of N-heteroarenium salts with formaldehyde and cyclic 1,3-diketones or 4-hydroxycoumarins, proceeding with broad substrate scope, good functional group compatibility, readily available feedstocks, and high step and atom efficiency.

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.

Silver Catalyzed Decarbonylative [3 + 2] Cycloaddition of Cyclobutenediones and Formamides

As an important moiety in natural products, N,O-acetal has attracted wide attention in the past few years. An efficient method to construct N,O-acetal has been developed. Using silver catalyst, cyclobutenediones were smoothly converted to the corresponding γ-aminobutenolides in the presence of formamides, in which cyclobutenediones likely proceed with a key decarbonylative [3 + 2] cycloaddition process. In this way, a series of products with varied substituents were isolated in moderate yield and fully characterized.

Still Relevant Today: The Asinger Multicomponent Reaction

The Asinger multicomponent reaction is a versatile synthetic tool which gives access to multiple drug-like scaffolds such as 3-thiazolines. The diversity and easy access of its starting materials, its operational simplicity combined with mild conditions and relatively good yields, renders the Asinger reaction, today more than ever, a cornerstone not only in heterocyclic chemistry and modern synthesis but also in medicinal chemistry. In this review, we perform a thorough analysis of the scope and limitations on the different reaction variants with their starting materials, the three-dimensional solid-state conformations of the Asinger derivatives, and we underline and classify all the major post-modifications that have been described. In addition, we report all the major applications in drug discovery projects.

Recent progress on the total syntheses of macrocyclic diamine alkaloids

This review highlights the progress and challenges in the chemical synthesis of macrocyclic diamine alkaloids since 2006.

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.

Diastereoselective One Pot Five-Component Reaction toward 4-(Tetrazole)-1,3-Oxazinanes

A diastereoselective one pot five-component reaction toward the synthesis of 4-(tetrazole)-1,3-oxazinanes has been reported. The sonication-accelerated, catalyst-free, simple, general and highly time efficient, Asinger-Ugi-tetrazole reaction was used for the synthesis of diverse 4-(tetrazole)-1,3-oxazinanes. The reaction exhibit excellent diastereoselectivity and broad substrate scope.

A concise Diels-Alder strategy leading to congeners of the ABC ring system of the marine alkaloid 'upenamide

A second-generation approach to the BC spirocycle of 'upenamide is reported. Central to the synthesis is an endo selective Diels-Alder reaction between 1-(t-butyldimethylsiloxy)-1,3-butadiene and bromomaleic anhydride followed by a radical mediated allylation of the ring fusion bromide. Functional group manipulation provides three (9-11) advanced synthetic intermediates ready for coupling with the remaining half (DE bicycle) of 'upenamide.

Marine natural products

This review covers the literature published in 2013 for marine natural products (MNPs), with 982 citations (644 for the period January to December 2013) 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 (1163 for 2013), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Direct imine acylation: synthesis of the proposed structures of 'upenamide

The synthesis of the two proposed structures of macrocyclic marine natural product 'upenamide is reported. The key step utilizes direct imine acylation (DIA) with a protected β-hydroxy acid to construct the key tricyclic ABC ring system. The macrocyclization was completed in the final step using a Stille cross-coupling reaction.

Densanins A and B, new macrocyclic pyrrole alkaloids isolated from the marine sponge Haliclona densaspicula

Densanins A (1) and B (2) were isolated from the sponge Haliclona densaspicula. On the basis of spectral data and the Mosher ester method, the complete structures were characterized as hexacyclic diamine alkaloids, which were probably derived from 3-alkylpyridine. Compounds 1 and 2 showed relatively potent inhibitory effects on lipopolysaccharide-induced nitric oxide production in BV2 microglial cells with IC(50) values of 1.05 and 2.14 μM, respectively.

Formation of the BC ring system of upenamide via a Staudinger/aza-Wittig reaction

The BC ring system of upenamide was assembled using a stereoselective Diels-Alder reaction followed by a Staudinger/aza-Wittig/imine hydrolysis reaction. Stereoselective aldol coupling with an aldehyde that incorporates the DE ring system led to an advanced synthetic intermediate en route to the marine alkaloid upenamide.

The First Synthesis of the ABC-Ring System of ‘Upenamide

The first synthetic route to the spirooxaquinolizidinone core (ABC core) of the macrocyclic marine alkaloid 'upenamide (1) has been developed. All five stereocenters were introduced with complete stereocontrol. The hydroxyl group at C-11 was introduced by a regio- and stereoselective SeO(2)-mediated allylic oxidation. The spirocyclic skeleton was formed by a stannous chloride induced deacetalization-bicyclization procedure. Further stereocenters were introduced by an enzymatic desymmetrization and by incorporation of an (S)-malic acid derived building block.

Status and perspective of sponge chemosystematics

In addition to their pharmaceutical applications, sponges are an important source of compounds that are used to elucidate classification patterns and phylogenetic relationships. Here we present a review and outlook on chemosystematics in sponges in seven sections: Secondary metabolites in sponges; Further applications of bioactive compound research in sponges; Sponge chemotaxonomy; Pitfalls of sponge chemotaxonomy; The chemotaxonomic suitability of sponge compounds; Potential synapomorphic markers in sponges; and The future of sponge chemotaxonomy.

Total syntheses of (+)-zampanolide and (+)-dactylolide exploiting a unified strategy

The first total syntheses of (+)-zampanolide (1) and (+)-dactylolide (2), members of a new class of tumor cell growth inhibitory macrolides, have been achieved. Key features of the unified synthetic scheme included the stereocontrolled construction of the cis-2,6-disubstituted tetrahydropyran via a modified Petasis-Ferrier rearrangement, a highly convergent assembly of the macrocyclic domain, and, in the case of zampanolide, a Curtius rearrangement/acylation tactic to install the N-acyl hemiaminal. The complete relative and absolute stereochemistries for both (+)-zampanolide and (+)-dactylolide were also assigned, albeit tentatively in the case of (+)-zampanolide (1).