(+)- and (-)-Spiroreticulatine, A Pair of Unusual Spiro Bisheterocyclic Quinoline-imidazole Alkaloids from the South China Sea Sponge Fascaplysinopsis reticulata

Discovery of Anti-Inflammatory Alkaloids from Sponge Stylissa massa Suggests New Biosynthetic Pathways for Pyrrole-Imidazole Alkaloids

Pyrrole-imidazole alkaloids (PIAs) are a class of marine sponge derived natural products which have complex carbon frameworks and broad bioactivities. In this study, four new alkaloids, stylimassalins A-B (1-2), 3, and 5, together with two known compounds (4 and 6), were isolated from Stylissa massa. Compounds 2, 4, and 6 are the C-2 brominated analogues of 1, 3, and 5, respectively. Their structures display three different scaffolds, of which scaffold 1 (compounds 1,2) is new. A new biosynthetic pathway from oroidin, through spongiacidin, to latonduine and scaffold 1 was proposed by our group, in which the C12-N13-cleavaged compounds of spongiacidin (scaffold 2), dubbed seco-spongiacidins (3 and 4), are recognized as a key bridged scaffold, to afford PIA analogues (1,2 and 5,6). An anti-inflammatory evaluation in a zebrafish inflammation model induced by copper sulphate (CuSO4) demonstrated that stylimassalins A and B (1 and 2) could serve as a promising lead scaffold for treating inflammation.

Tagpyrrollins A and B and Tagpyrrollidone A: Three Pyrrole Steroid Analogues with AKR1B1-Targeting Inhibitory Activity from the Sponges Stylissa massa and Pseudospongosorites suberitoides

Pyrrole alkaloids (PAs) are a diverse class of natural products with complex carbon frameworks and broad bioactivities that are usually derived from marine sponges. Stylissa massa and Pseudospongosorites suberitoides are two independent sponges collected from the South China Sea in 2013 and 2018, respectively. We discovered PAs are common constituents in both two sponges; more specifically, S. massa produces pyrrole-imidazole alkaloids, and P. suberitoides contains pyrrolidone alkaloids. In this study, three pyrrole steroid metabolites were obtained. Compounds 1 and 2 are a pair of epimers sharing a new 5/7/5/6/6 pentacyclic structural configuration, and compound 3 has a new rigid 5/6/6 tricyclic structure. Interestingly, their scaffolds all possess a 6/6 bicyclic system on the featured classic pyrrole/pyrrolidone skeletons, so-dubbed tagpyrrollins A and B (1 and 2, respectively) and tagpyrrollidone A (3). From a biosynthetic viewpoint, 4,5-dihydroxypent-2-enal probably plays a crucial role in constructing these pyrrole steroid analogues. Based on our previous study on the inhibitory activity of spongiacidin targeting AKR1B1, a drug target for the treatment of chronic diabetic complications, in this study we found that tagpyrrolin A (1) also exhibits an inhibitory effect against AKR1B1.

Cytotoxic Epipolythiodioxopiperazines from the Deep-Sea-Derived Fungus Exophiala mesophila MCCC 3A00939

Four new aranotin-type epipolythiodioxopiperazines, graphiumins K-N (1-4), along with four known analogues (5-8), were isolated from the deep-sea-derived fungus Exophiala mesophila MCCC 3A00939. Their structures were elucidated by detailed interpretation of NMR and mass spectrometric data. The absolute configuration of the isolates was deduced by a single-crystal X-ray diffraction analysis and the comparisons of experimental electronic circular dichroism (ECD) data with calculated ECD spectra. Graphiumins K (1) and L (2) exhibited cytotoxic activities against the K562, H69AR, and MDA-MB-231 cancer cells with IC50 values ranging from 2.3 to 5.9 μM.

Revision of the genus Fascaplysinopsis, the type species Fascaplysinopsis reticulata (Hentschel, 1912) (Porifera, Dictyoceratida, Thorectidae) and descriptions of two new genera and seven new species

The present study examines the taxonomy of sponge specimens with unique chemistry collectively known as Fascaplysinopsis reticulata (Hentschel, 1912). Examination of Hentschels original species upon which the genus Fascaplysinopsis Bergquist, 1980 was based in conjunction with a comparison with recent Indo-west Pacific collections, using morphological and molecular analyses (ITS and 28S rDNA), revealed extensive variation. Fascaplysinopsis reticulata was found to be a species complex comprising the genus Fascaplysinopsis, as well as two new genera: Skolosachlys gen. nov. and Rubrafasciculus gen. nov. The new species of Fascaplysinopsis described are F. palauensis sp. nov., F. klobos sp. nov. and F. ronquinni sp. nov. The new species of Skolosachlys gen. nov. described herein are: S. enlutea sp. nov. and S. nidus sp. nov. The new species described of Rubrafasciculus gen. nov. includes: R. cerasus sp. nov. and R. fijiensis sp. nov..

Rigidified Bis(sulfonyl)ethylenes as Effective Michael Acceptors for Asymmetric Catalysis: Application to the Enantioselective Synthesis of Quaternary Hydantoins

The catalytic, enantio- and diastereoselective addition of hydantoin surrogates II to "rigidified" vinylidene bis(sulfone) reagents is developed, thus overcoming the inability of commonly employed β-substituted vinylic sulfones to react. Adducts are transformed in enantioenriched 5,5-disubstituted hydantoins through hydrolysis and reductive desulfonylation processes providing new structures for eventual bioassays. Density functional theory studies that rationalize the observed reactivity and stereoselectivity trends are also provided.

Structural Investigation of Aaptourinamine by a Novel Module-Assembly-Based Calculation

Natural products have various and complicated structures, which is still a challenge for elucidating these compounds, especially for those lacking two-dimensional nuclear magnetic resonance (2D NMR) correlations mainly caused by high C/H ratios or proton-deficient and multiple heteroatoms through the conventional structural analytical methods. We reported a novel module-assembly calculation method named Dooerafa, which included constructing the meta-structures by a grafting method based on the crucial and the limited 2D NMR correlations, ring-contraction strategy based on mechanic force field and quantum chemical theory, and self-assemble calculation in Python programming for shaping up the structural candidates along with DFT-GIAO calculation. This new method, verified by a known alkaloid spiroreticulatine with the structure determined by X-ray diffraction, was performed for the structural elucidation of aaptourinamine isolated from marine sponge Aaptos suberitoides, showing us a brand new scaffold of imidazo [4,5,1-ij]pyrrolo [3,2-f]quinolin-7(8H)-one, which has a biosynthetic relationship with the bioactive and structurally unique aaptamine alkaloid.

Demystifying racemic natural products in the homochiral world

Natural products possess structural complexity, diversity and chirality with attractive functions and biological activities that have significantly impacted drug discovery initiatives. Chiral natural products are abundant in nature but rarely occur as racemates. The occurrence of natural products as racemates is very intriguing from a biosynthetic point of view; as enzymes are chiral molecules, enzymatic reactions generating natural products should be stereospecific and lead to single-enantiomer products. Despite several reports in the literature describing racemic mixtures of stereoisomers isolated from natural sources, there has not been a comprehensive review of these intriguing racemic natural products. The discovery of many more natural racemates and their potential enzymatic sources in recent years allows us to describe the distribution and chemical diversity of this 'class of natural products' to enrich discussions on biosynthesis. In this Review, we describe the chemical classes, occurrence and distribution of pairs of enantiomers in nature and provide insights about recent advances in analytical methods used for their characterization. Special emphasis is on the biosynthesis, including plausible enzymatic and non-enzymatic formation of natural racemates, and their pharmacological significance.

Chemical and biological diversity of new natural products from marine sponges: a review (2009-2018)

Marine sponges are productive sources of bioactive secondary metabolites with over 200 new compounds isolated each year, contributing 23% of approved marine drugs so far. This review describes statistical research, structural diversity, and pharmacological activity of sponge derived new natural products from 2009 to 2018. Approximately 2762 new metabolites have been reported from 180 genera of sponges this decade, of which the main structural types are alkaloids and terpenoids, accounting for 50% of the total. More than half of new molecules showed biological activities including cytotoxic, antibacterial, antifungal, antiviral, anti-inflammatory, antioxidant, enzyme inhibition, and antimalarial activities. As summarized in this review, macrolides and peptides had higher proportions of new bioactive compounds in new compounds than other chemical classes. Every chemical class displayed cytotoxicity as the dominant activity. Alkaloids were the major contributors to antibacterial, antifungal, and antioxidant activities while steroids were primarily responsible for pest resistance activity. Alkaloids, terpenoids, and steroids displayed the most diverse biological activities. The statistic research of new compounds by published year, chemical class, sponge taxonomy, and biological activity are presented. Structural novelty and significant bioactivities of some representative compounds are highlighted. Marine sponges are rich sources of novel bioactive compounds and serve as animal hosts for microorganisms, highlighting the undisputed potential of sponges in the marine drugs research and development.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-022-00132-3.

Natural Enantiomers: Occurrence, Biogenesis and Biological Properties

The knowledge that natural products (NPs) are potent and selective modulators of important biomacromolecules (e.g., DNA and proteins) has inspired some of the world's most successful pharmaceuticals and agrochemicals. Notwithstanding these successes and despite a growing number of reports on naturally occurring pairs of enantiomers, this area of NP science still remains largely unexplored, consistent with the adage "If you don't seek, you don't find". Statistically, a rapidly growing number of enantiomeric NPs have been reported in the last several years. The current review provides a comprehensive overview of recent records on natural enantiomers, with the aim of advancing awareness and providing a better understanding of the chemical diversity and biogenetic context, as well as the biological properties and therapeutic (drug discovery) potential, of enantiomeric NPs.

Penitol A and Penicitols E-I: Citrinin Derivatives from Penicillium citrinum and the Structure Revision of Previously Proposed Analogues

Penitol A (1), a new citrinin derivative with a rare tricyclic spiro skeleton, was isolated from a coral-derived strain of the fungus Penicillium citrinum. In addition, penicitols E-I (2-6), five new citrinin analogues, were coisolated. Their structures were determined by an analysis of 1D/2D NMR and HRESIMS data, statistical DP4+ analyses based on DFT-GIAO NMR calculations, quantum chemistry ECD calculations, and a single-crystal X-ray diffraction study. The structures of penicitol A (7) and two related synthetic intermediates were revised. Biological evaluation results revealed that penitol A (1) exhibited cytotoxic activity against K562 tumor cells, with an IC₅₀ value of 8.8 μM. A proposed route of formation of compounds 1-7 was reported.

New from Old: Thorectandrin Alkaloids in a Southern Australian Marine Sponge, Thorectandra choanoides (CMB-01889)

Thorectandra choanoides (CMB-01889) was prioritized as a source of promising new chemistry from a library of 960 southern Australian marine sponge extracts, using a global natural products social (GNPS) molecular networking approach. The sponge was collected at a depth of 45 m. Chemical fractionation followed by detailed spectroscopic analysis led to the discovery of a new tryptophan-derived alkaloid, thorectandrin A (1), with the GNPS cluster revealing a halo of related alkaloids 1a–1n. In considering biosynthetic origins, we propose that Thorectandrachoanoides (CMB-01889) produces four well-known alkaloids, 6-bromo-1′,8-dihydroaplysinopsin (2), 6-bromoaplysinopsin (3), aplysinopsin (4), and 1′,8-dihydroaplysinopsin (10), all of which are susceptible to processing by a putative indoleamine 2,3-dioxygenase-like (IDO) enzyme to 1a–1n. Where the 1′,8-dihydroalkaloids 2 and 10 are fully transformed to stable ring-opened thorectandrins 1 and 1a–1b, and 1h–1j, respectively, the conjugated precursors 3 and 4 are transformed to highly reactive Michael acceptors that during extraction and handling undergo complete transformation to artifacts 1c–1g, and 1k–1n, respectively. Knowledge of the susceptibility of aplysinopsins as substrates for IDOs, and the relative reactivity of Michael acceptor transformation products, informs our understanding of the pharmaceutical potential of this vintage marine pharmacophore. For example, the cancer tissue specificity of IDOs could be exploited for an immunotherapeutic response, with aplysinopsins transforming in situ to Michael acceptor thorectandrins, which covalently bind and inhibit the enzyme.

Cytotoxic Manoalide-Type Sesterterpenes from the Sponge Luffariella variabilis Collected in the South China Sea

Thirteen new linear terpenes, including 11 rare acyclic manoalide derivatives (1-11), one polyprenylphenol derivative (12), and one polyprenylbenzaldehyde derivative (13), together with three known compounds (14-16) were isolated from the sponge Luffariella variabilis collected in the South China Sea. The planar structures were resolved by NMR and MS analyses, while the absolute configurations were fully elucidated by NOESY experiments, combined with experimental and calculated ECD spectra, acetal formation, empirical rules of ¹H and ¹³C NMR shifts, DP4+ probability analyses, and Mosher's method. Compounds 1-7, 10, and 13 demonstrated cytotoxic activities against several human cancer cell lines with IC₅₀ values ranging from 2 to 10 μM.

Recent Advances on Marine Alkaloids from Sponges

Alkaloids from marine secondary metabolites have received extensive attention from pharmacists in recent years. Miscellaneous alkaloids derived from marine sponges possessed various pharmacological activities including cytotoxicity, antimicrobial, antioxidant, and so on. Herein, we summarized 149 marine alkaloids from sponges based on their structures and bioactivities reported from 2015 to 2020 and analyzed the production environment of marine sponges with rich alkaloids. Moreover, we discussed biosynthesis routes of pyrrole and guanidine alkaloids from marine sponges Agelas and Monanchora. This article will be beneficial for future research on drugs from marine natural products.

Bishomoscalarane Sesterterpenoids from the Sponge Dysidea granulosa Collected in the South China Sea

Granulosane A (1), a new C₂₇ bishomoscalarane sesterterpenoid with a rare 6/6/6/8 tetracyclic skeleton, together with eight additional new C₂₇ bishomoscalarane sesterterpenes (2, 8-14) and five new C₂₆ 20,24-bishomo-25-norscalarane sesterterpenes (3-7), were isolated from the marine sponge Dysidea granulosa collected in the South China Sea. Their structures were elucidated by extensive spectroscopic analysis and quantum chemical calculation methods. Compound 4 showed antiproliferative activities against two cancer cell lines.

Marine Pharmacology in 2014-2015: Marine Compounds with Antibacterial, Antidiabetic, Antifungal, Anti-Inflammatory, Antiprotozoal, Antituberculosis, Antiviral, and Anthelmintic Activities; Affecting the Immune and Nervous Systems, and Other Miscellaneous Mechanisms of Action

The systematic review of the marine pharmacology literature from 2014 to 2015 was completed in a manner consistent with the 1998-2013 reviews of this series. Research in marine pharmacology during 2014-2015, which was reported by investigators in 43 countries, described novel findings on the preclinical pharmacology of 301 marine compounds. These observations included antibacterial, antifungal, antiprotozoal, antituberculosis, antiviral, and anthelmintic pharmacological activities for 133 marine natural products, 85 marine compounds with antidiabetic, and anti-inflammatory activities, as well as those that affected the immune and nervous system, and 83 marine compounds that displayed miscellaneous mechanisms of action, and may probably contribute to novel pharmacological classes upon further research. Thus, in 2014-2015, the preclinical marine natural product pharmacology pipeline provided novel pharmacology as well as new lead compounds for the clinical marine pharmaceutical pipeline, and thus continued to contribute to ongoing global research for alternative therapeutic approaches to many disease categories.

Emerging Marine Immunomodulatory Small-molecules (2010- Present)

Background:

Immunomodulation-based therapy has achieved a breakthrough in the last decade, which stimulates the passion of searching for potential immunomodulatory substances in recent years.

Objective:

Marine natural products are a unique source of immunomodulatory substances. This paper summarized the emerging marine natural small-molecules and related synthesized derivatives with immunomodulatory activities to provide readers an overview of these bioactive molecules and their potential in immunomodulation therapy.

Conclusion:

An increasing number of immunomodulatory marine small-molecules with diverse intriguing structure-skeletons were discovered. They may serve as a basis for further studies of marine natural products for their chemistry, related mechanism of action and structure- activity relationships.

New Antimalarial and Antimicrobial Tryptamine Derivatives from the Marine Sponge Fascaplysinopsis reticulata

Chemical study of the CH₂Cl₂-MeOH (1:1) extract of the sponge Fascaplysinopsis reticulata collected in Mayotte highlighted three new tryptophan derived alkaloids, 6,6′-bis-(debromo)-gelliusine F (1), 6-bromo-8,1′-dihydro-isoplysin A (2) and 5,6-dibromo-8,1′-dihydro-isoplysin A (3), along with the synthetically known 8-oxo-tryptamine (4) and the three known molecules from the same family, tryptamine (5), (E)-6-bromo-2′-demethyl-3′-N-methylaplysinopsin (6) and (Z)-6-bromo-2′-demethyl-3′-N-methylaplysinopsin (7). Their structures were elucidated by 1D and 2D NMR spectra and HRESIMS data. All compounds were evaluated for their antimicrobial and their antiplasmodial activities. Regarding antimicrobial activities, the best compounds are (2) and (3), with minimum inhibitory concentration (MIC) of 0.01 and 1 µg/mL, respectively, towards Vibrio natrigens, and (5), with MIC values of 1 µg/mL towards Vibrio carchariae. In addition the known 8-oxo-tryptamine (4) and the mixture of the (E)-6-bromo-2′-demethyl-3′-N-methylaplysinopsin (6) and (Z)-6-bromo-2′-demethyl-3′-N-methylaplysinopsin (7) showed moderate antiplasmodial activity against Plasmodium falciparum with IC₅₀ values of 8.8 and 8.0 µg/mL, respectively.

Aplysinopsin-type and Bromotyrosine-derived Alkaloids from the South China Sea Sponge Fascaplysinopsis reticulata

Seven pairs of new oxygenated aplysinopsin-type enantiomers, (+)- and (-)-oxoaplysinopsins A‒G (1‒7), two new bromotyrosine-derived alkaloids, subereamollines C and D (18 and 19), together with ten known compounds (8‒17) were isolated from the Xisha Islands sponge Fascaplysinopsis reticulata. The planar structures were determined by extensive NMR and MS spectroscopic data. Each of the optically pure enantiomers was achieved by chiral HPLC separation. The absolute configurations were assigned by the quantum chemical calculation methods. Compound 19 showed cytotoxicity against Jurkat cell lines with IC₅₀ value of 0.88 μM. Compounds 2, 16 and 17 showed tyrosine phosphatase 1B (PTP1B) inhibition activity with IC₅₀ value ranging from 7.67 to 26.5 μM, stronger than the positive control of acarbose and 1-deoxynojirimycin. A structural activity relationship for the aplysinopsin-type enantiomers were observed in PTP1B inhibition activity of 2 and cytotoxicity of 3 that the dextrorotary (+)-2 and (+)-3 showed stronger activity than the levorotary (-)-2 and (-)-3.

Copper-Mediated N-Arylations of Hydantoins

A set of two broadly applicable procedures for the N-arylation of hydantoins is reported. The first one relies on the use of stoichiometric copper(I) oxide under ligand- and base-free conditions and enables a clean regioselective arylation at the N³ nitrogen atom, while the second one is based on the use of catalytic copper(I) iodide and trans- N, N'-dimethylcyclohexane-1,2-diamine and promotes arylation at the N¹ nitrogen atom. Importantly, the combination of these two procedures affords a straightforward entry to diarylated hydantoins.

Sarcoglaucins A-I, new antifouling cembrane-type diterpenes from the South China Sea soft coral Sarcophyton glaucum

Nine new cembrane diterpenes, named sarcoglaucins A-I (1–9) along with three known analogues, trochelioid (10), 7α-hydroxy-Δ⁸⁽¹⁹⁾-deepoxysarcophine (11), and (−)-sartrochine (12), were isolated from the soft coral Sarcophyton glaucum collected at Xisha Islands in the South China Sea.

Isolation and Absolute Configurations of Diversiform C17, C21 and C25 Terpenoids from the Marine Sponge Cacospongia sp

Chemical investigation of MeOH extract of a South China Sea sponge Cacospongia sp. yielded 15 terpenoids belonging to three different skeleton-types, including the unusual C₁₇γ-lactone norditerpenoids (1–3), the rare C₂₁ pyridine meroterpenoid (7), and the notable C₂₅ manoalide-type sesterterpenoids (4–6, 8–10). Compounds 1–5 were initially obtained as enantiomers, and were further separated to be optically pure compounds (1a, 1b, 2a, 2b, 3a-r, 3b-r, 4a, 4b, 5a and 5b) by chiral HPLC, with a LiAlH₄ reduction aid for 3. Compounds 3a/3b (a pair of inseparable enantiomers), 4a, 5a, 6, and 7 were identified as new compounds, while 1a/1b and 2a/2b were obtained from a natural source and were determined for their absolute configurations for the first time. This is also the first time to encounter enantiomers of the well-known manoalide-type sesterterpenoids from nature. The structures with absolute configurations of the new compounds were unambiguously determined by comprehensive methods including HR-ESI-MS and NMR data analysis, optical rotation comparison, experimental and calculated electronic circular dichroism (ECD), and Mo₂(OAc)₄ induced circular dichroism (ICD) methods. The cytotoxicity of the isolates against selected human tumor cell lines was evaluated, however, the tested compounds showed no activity against selected cell lines.

Metabolites from the Paracel Islands Soft Coral Sinularia cf. molesta

Five new oxygenated sesquiterpenes, molestins A–D (1, 3–5) and epi-gibberodione (2), three new cyclopentenone derivatives, ent-sinulolides C, D, and F ((+)-9–(+)-11), one new butenolide derivative, ent-sinulolide H ((+)-13), and one new cembranolide, molestin E (14), together with 14 known related metabolites (6–8, (–)-9–(–)-11, (±)-12, (–)-13, 15–19) were isolated from the Paracel Islands soft coral Sinularia cf. molesta. The structures and absolute configurations were elucidated based on comprehensive spectroscopic analyses, quantum chemical calculations, and comparison with the literature data. Compound 5 is the first example of a norsesquiterpene with a de-isopropyl guaiane skeleton isolated from the genus Sinularia. Molestin E (14) exhibited cytotoxicities against HeLa and HCT-116 cell lines with IC₅₀ values of 5.26 and 8.37 μM, respectively. Compounds 4, 5, and 8 showed significant inhibitory activities against protein tyrosine phosphatase 1B (PTP1B) with IC₅₀ values of 218, 344, and 1.24 μM, respectively.

Cytotoxic components from the Xisha sponge Fascaplysinopsis reticulata

A new dolabellane diterpenoid, clavirolide H (1), together with eleven known compounds, including two dolabellane diterpenoid (2 and 3), a rare cavernosine-type C₁₇ γ-lactone terpenoid (4), a diketopiperazine (5) and seven sterols (6-12), were isolated from the Xisha sponge Fascaplysinopsis reticulata. Their structures were elucidated by extensive spectroscopic analysis, and the four types of compounds of the above isolates were reported from the genus Fascaplysinopsis for the first time. Selected compounds 1, 4-6 and 9-12 were evaluated for cytotoxic activities against K562, HL-60, Hela, HCT-116, A549, L-02 and BEL-7402 cell lines. Compounds 4-6 and 10-12 showed potent cytotoxicitives against HL-60 with IC₅₀ values ranging from 8.8 to 12.4 μM. Compounds 4 and 5 exhibited weak cytotoxic activities against HeLa with IC₅₀ of 20.7 and 27.4 μM, and 5 also has moderate cytotoxicity against HCT-116 with IC₅₀ of 16.3 μM.[Figure: see text].

Design and Synthesis of Polycycles, Heterocycles, and Macrocycles via Strategic Utilization of Ring-Closing Metathesis

In this perspective, we summarize new synthetic approaches for the construction of various polycyclic compounds involving ring-closing metathesis as a key step. In this regard, we used ring-closing metathesis in combination with other popular reactions like Suzuki-Miyaura coupling, Claisen rearrangement, Fischer indolization, Grignard addition, Diels-Alder reaction, and [2+2] cycloaddition reaction etc. To this end, a variety of functional molecules such as α-amino acids, cyclophanes, heterocycles, propellanes, spirocycles, and macrocycles have been prepared. The strategies developed and the molecules prepared here play a key role in designing new materials and also act as lead compounds in drug design. The strategies and tactics developed here are useful to design polycycles, macrocycles, and heterocycles of diverse ring systems.

Bidirectional Synthesis of Di- tert-butyl (2 S,6 S,8 S)- and (2 R,6 R,8 R)-1,7-Diazaspiro[5.5]undecane-2,8-dicarboxylate and Related Spirodiamines

Efficient syntheses of both enantiomers of a spirodiamine diester from (l)- and (d)-aspartic acid are described. The key transformation was the conversion of Boc-protected tert-butyl aspartate into the derived aldehyde, two-directional Horner-Wadsworth-Emmons olefination, hydrogenation, and selective acid-catalyzed Boc-deprotection and spirocyclization. An alternative, two-directional approach to derivatives of 1,7-diazaspiro[5.5]undecane is described.

Natural Products Research in China From 2015 to 2016

This review covers the literature published by chemists from China during the 2015-2016 on natural products (NPs), with 1,985 citations referring to 6,944 new compounds isolated from marine or terrestrial microorganisms, plants, and animals. The emphasis is on 730 new compounds with a novel skeleton or/and significant bioactivity, together with their source organism and country of origin.

Biologically active quinoline and quinazoline alkaloids part II

To follow-up on our prior Part I review, this Part II review summarizes and provides updated literature on novel quinoline and quinazoline alkaloids isolated during the period of 2009-2016, together with the biological activity and the mechanisms of action of these classes of natural products. Over 200 molecules with a broad range of biological activities, including antitumor, antiparasitic and insecticidal, antibacterial and antifungal, cardioprotective, antiviral, anti-inflammatory, hepatoprotective, antioxidant, anti-asthma, antitussive, and other activities, are discussed. This survey should provide new clues or possibilities for the discovery of new and better drugs from the original naturally occurring quinoline and quinazoline alkaloids.

Synthesis and Reactions of Benzannulated Spiroaminals: Tetrahydrospirobiquinolines

An efficient two-step synthesis of symmetrical and unsymmetrical tetrahydrospirobiquinolines from o-azidobenzaldehydes is reported. A novel series of tetrahydrospirobiquinolines was prepared by sequential double-aldol condensation with acetone, cyclopentanone, and cyclohexanone to form the corresponding o,o'-diazido-dibenzylidene-acetone, -cyclopentanone, and -cyclohexanone derivatives, respectively, and hydrogenation-spirocyclization. The spirodiamines were further derivatized by electrophilic aromatic bromination, Suzuki coupling, and N-alkylation, all of which proceeded with preservation of the spirocyclic core.

Pyrrole Derivatives and Diterpene Alkaloids from the South China Sea Sponge Agelas nakamurai

Two pairs of new non-brominated racematic pyrrole derivatives, (±)-nakamurine D (1) and (±)-nakamurine E (2), two new diterpene alkaloids, isoagelasine C (16) and isoagelasidine B (21), together with 13 known pyrrole derivatives ((±)-3 - 15), five known diterpene alkaloids (17 - 20, 22) were isolated from the South China Sea sponge Agelas nakamurai. The racemic mixtures, compounds 1 - 4, were resolved into four pairs of enantiomers, (+)-1 and (-)-1, (+)-2 and (-)-2, (+)-3 and (-)-3, and (+)-4 and (-)-4, by chiral HPLC. The structures and absolute configurations were elucidated on the basis of comprehensive spectroscopic analyses, quantum chemical calculations, quantitative measurements of molar rotations, application of van't Hoff's principle of optical superposition, and comparison with the literature data. The NMR and MS data of compound 3 are reported for the first time, as the structure was listed in SciFinder Scholar with no associated reference. These non-brominated pyrrole derivatives were found in this species for the first time. Compound 18 showed valuable cytotoxicities against HL-60, K562, and HCT-116 cell lines with IC₅₀ values of 12.4, 16.0, and 19.8 μm, respectively. Compounds 16 - 19, 21, and 22 showed potent antifungal activities against Candida albicans with MIC values ranging from 0.59 to 4.69 μg/ml. Compounds 16 - 19 exhibited moderate antibacterial activities against Proteusbacillus vulgaris (MIC values ranging from 9.38 to 18.75 μg/ml).

Marine natural products

Covering: 2015. Previous review: Nat. Prod. Rep., 2016, 33, 382-431This review covers the literature published in 2015 for marine natural products (MNPs), with 1220 citations (792 for the period January to December 2015) 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 (1340 in 429 papers for 2015), 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.

Alkaloids and polyketides from the South China Sea sponge Agelas aff. nemoechinata

New pyrrole alkaloids, diterpene-adenine alkaloids with cytotoxic activity, and polyketides were isolated from the South China Sea sponge Agelas aff. nemoechinata.

Structural Analysis of Natural Products

Current mass spectrometry, nuclear magnetic resonance spectroscopy, and X-ray diffraction are presented as structure elucidation tools for analytical chemistry of natural products. Discovering new molecular entities combined with dereplication of known organic compounds represent prerequisites for biological assays and for respective applications as pharmaceuticals or molecular markers. Liquid chromatography is briefly addressed with respect to its use in mass spectrometry- and nuclear magnetic resonance-based metabolomics studies.

Emergence of diversity and stereochemical outcomes in the biosynthetic pathways of cyclobutane-centered marine alkaloid dimers

A deep-sea dive into the ecology and chemistry of surprising cyclobutanes from marine invertebrates.

Bioactive Hydantoin Alkaloids from the Red Sea Marine Sponge Hemimycale arabica

In the course of our continuing efforts to identify bioactive secondary metabolites from Red Sea marine invertebrates, we have investigated the sponge Hemimycale arabica. The antimicrobial fraction of an organic extract of the sponge afforded two new hydantoin alkaloids, hemimycalins A and B (2 and 3), together with the previously reported compound (Z)-5-(4-hydroxybenzylidene)imidazolidine-2,4-dione (1). The structures of the compounds were determined by extensive 1D and 2D NMR (COSY, HSQC and HMBC) studies and high-resolution mass spectral determinations. Hemimycalins A (2) and B (3) represent the first examples of the natural N-alkylated hydantoins from the sponge Hemimycale arabica. Compounds 1-3 displayed variable antimicrobial activities against E. coli, S. aureus, and C. albicans. In addition, compound 1 displayed moderate antiproliferative activity against the human cervical carcinoma (HeLa) cell line. These findings provide further insight into the chemical diversity as well as the biological activity of this class of compounds.

Hot off the press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as sigillin A from Ceratophysella sigillata.