Previously undescribed antioxidative azocinyl morpholinone alkaloid from red seaweed Gracilaria opuntia with anti-cyclooxygenase and lipoxygenase properties

Natural products with 1,2-oxazine scaffold: occurrence, chemical diversity, bioactivity, synthesis, and biosynthesis

Covering: up to the end of July, 20231,2-Oxazine is a heterocyclic scaffold rarely found in natural products and is characterized by a directly connected N-O bond in a six-membered ring. Since the discovery of geneserine, the first 1,2-oxazine-containing natural product (1,2-oxazine NP) being isolated from Calabar bean (Physostigma venenosum) in 1925, a total of 76 naturally occurring 1,2-oxazine NPs have been isolated and identified from various sources, which have attracted the attention of researchers in the field of natural product chemistry, organic synthesis, biosynthesis, and pharmacology. This review summarizes the chemical family of 1,2-oxazine NPs, focusing on their source organisms, structural diversities, chemical synthesis, and biosynthesis.

Anti-Inflammatory Effects of Bioactive Compounds from Seaweeds, Bryozoans, Jellyfish, Shellfish and Peanut Worms

Inflammation is a defense mechanism of the body in response to harmful stimuli such as pathogens, damaged cells, toxic compounds or radiation. However, chronic inflammation plays an important role in the pathogenesis of a variety of diseases. Multiple anti-inflammatory drugs are currently available for the treatment of inflammation, but all exhibit less efficacy. This drives the search for new anti-inflammatory compounds focusing on natural resources. Marine organisms produce a broad spectrum of bioactive compounds with anti-inflammatory activities. Several are considered as lead compounds for development into drugs. Anti-inflammatory compounds have been extracted from algae, corals, seaweeds and other marine organisms. We previously reviewed anti-inflammatory compounds, as well as crude extracts isolated from echinoderms such as sea cucumbers, sea urchins and starfish. In the present review, we evaluate the anti-inflammatory effects of compounds from other marine organisms, including macroalgae (seaweeds), marine angiosperms (seagrasses), medusozoa (jellyfish), bryozoans (moss animals), mollusks (shellfish) and peanut worms. We also present a review of the molecular mechanisms of the anti-inflammatory activity of these compounds. Our objective in this review is to provide an overview of the current state of research on anti-inflammatory compounds from marine sources and the prospects for their translation into novel anti-inflammatory drugs.

Anti-inflammatory xenicane-type diterpenoid from the intertidal brown seaweed Sargassum ilicifolium

Chemical analysis of the organic extract from intertidal brown seaweed Sargassum ilicifolium (family Sargassaceae) characterised an undescribed xenicane-type diterpenoid sargilicixenicane, elucidated as 3-(17-hydroxy-14-methylhept-13-en-10-yl)-6-methylhexahydro-1H-cyclonona[c]furan-4,19-diyl diacetate (compound 1). The studied compound exhibited prospective free radical quenching potential (IC50 1.2-1.4 mM) in comparison with commercial antioxidant (α-tocopherol, IC50 > 1.40 mM). Attenuation property of sargilicixenicane against pro-inflammatory enzyme, 5-lipoxygenase (IC50 4.70 mM) was comparable with that displayed by the non-steroidal anti-inflammatory agent ibuprofen (IC50 4.51 mM). Greater selectivity index displayed by the studied xenicane-type diterpenoid (1.42) than that exhibited by ibuprofen (0.44) recognised the selective attenuation potential of the former against the inducible cyclooxygenase-2 and 5-lipoxygenase enzymes. Higher electronic parameters (topological polar surface area, 82.06) and balanced hydrophobic-hydrophilic property (octanol-water partition coefficient 2.94) coupled with docking score (-11.17 kcal mol-1) and lower binding energy (-9.61 kcal mol-1) with the active site of 5-lipoxygenase supported the significant anti-inflammatory properties of the studied xenicane-type diterpenoid.

Red Seaweed-Derived Compounds as a Potential New Approach for Acne Vulgaris Care

Acne vulgaris (AV) is a chronic skin disease of the pilosebaceous unit affecting both adolescents and adults. Its pathophysiology includes processes of inflammation, increased keratinization, sebum production, hormonal dysregulation, and bacterial Cutibacterium acnes proliferation. Common AV has been treated with antibiotics since the 1960s, but strain resistance has emerged and is of paramount concern. Macroalgae are known producers of substances with bioactive properties, including anti-viral, antibacterial, antioxidant, and anti-inflammatory properties, among several others. In particular, red algae are rich in bioactive compounds such as polysaccharides, phenolic compounds, lipids, sterols, alkaloids, and terpenoids, conferring them antioxidant, antimicrobial, and anti-inflammatory activities, among others. Thus, the exploration of compounds from marine resources can be an appealing approach to discover new treatment options against AV. The aim of this work is to provide an overview of the current knowledge of the potentialities of red macroalgae in the treatment of AV by reviewing the main therapeutic targets of this disease, and then the existence of compounds or extracts with bioactive properties against them.

Redox Modifications in the Biosynthesis of Alchivemycin A Enable the Formation of Its Key Pharmacophore

Redox enzymes play a critical role in transforming nascent scaffolds into structurally complex and biologically active natural products. Alchivemycin A (AVM, 1) is a highly oxidized polycyclic compound with potent antimicrobial activity and features a rare 2H-tetrahydro-4,6-dioxo-1,2-oxazine (TDO) ring system. The scaffold of AVM has previously been shown to be biosynthesized by a hybrid polyketide synthase-nonribosomal peptide synthetase (PKS-NRPS) pathway. In this study, we present a postassembly secondary metabolic network involving six redox enzymes that leads to AVM formation. We characterize this complex redox network using in vivo gene deletions, in vitro biochemical assays, and one-pot enzymatic total synthesis. Importantly, we show that an FAD-dependent monooxygenase catalyzes oxygen insertion into an amide bond to form the key TDO ring in AVM, an unprecedented function of flavoenzymes. We also show that the TDO ring is essential to the antimicrobial activity of AVM, likely through targeting the β-subunit of RNA polymerase. As further evidence, we show that AvmK, a β-subunit of RNA synthase, can confer self-resistance to AVM via target modification. Our findings expand the repertoire of functions of flavoenzymes and provide insight into antimicrobial and biocatalyst development based on AVM.

Discovery of natural anti-inflammatory alkaloids: Potential leads for the drug discovery for the treatment of inflammation

Inflammation is an adaptive response of the immune system to tissue malfunction or homeostatic imbalance. Corticosteroids and non-steroidal anti-inflammatory drugs (NSAIDs) are frequently applied to treat varieties of inflammatory diseases but are associated with gastrointestinal, cardiovascular, and kidney side effects. Developing more effective and less toxic agents remain a challenge for pharmaceutical chemist due to the complexity of the different inflammatory processes. Alkaloids are widely distributed in plants with diverse anti-inflammatory activities, providing various potential lead compounds or candidates for the design and discovery of new anti-inflammatory drug candidates. Therefore, re-examining the anti-inflammatory alkaloid natural products is advisable, bringing more opportunities. In this review, we summarized and described the recent advances of natural alkaloids with anti-inflammatory activities and possible mechanisms in the period from 2009 to 2020. It is hoped that this review of anti-inflammatory alkaloids can provide new ideas for researchers engaged in the related fields and potential lead compounds for the discovery of anti-inflammatory drugs.

Marine Alkaloids with Anti-Inflammatory Activity: Current Knowledge and Future Perspectives

Alkaloids are nitrogenous compounds with various biological activities. Alkaloids with anti-inflammatory activity are commonly found in terrestrial plants, but there are few records of the identification and characterization of the activity of these compounds in marine organisms such as fungi, bacteria, sponges, ascidians, and cnidarians. Seaweed are a source of several already elucidated bioactive compounds, but few studies have described and characterized the activity of seaweed alkaloids with anti-inflammatory properties. In this review, we have gathered the current knowledge about marine alkaloids with anti-inflammatory activity and suggest future perspectives for the study and bioprospecting of these compounds.

Bioactive compounds in seaweeds: An overview of their biological properties and safety

Seaweeds are among the significant currently exploited marine plant resources which are gaining full applications in culinary, cosmetic, pharmaceutical, and biotechnological processes. Much attention has been devoted to seaweeds based on their proven health benefits and is considered as a rich source of structurally different bioactive metabolites for the discovery of novel functional food-based pharmacophores/drugs. Nonetheless, there is still a dearth of updated compilation and analysis of the in-depth pharmacological activities of these compounds. This review, therefore, aims to provide a piece of up-to-date detailed information on the major compounds isolated from various seaweed species together with their in-vitro and in-vivo biological properties. These compounds were found to possess broad pharmacological properties and inhibitory enzyme activities against critical enzymes involved in the aetiology of noncommunicable diseases. However, their toxicity, clinical efficacy, mechanisms of action, and interaction with conventional foods, are still less explored and require more attention in future studies.

Metabolites from Marine Microorganisms, Micro, and Macroalgae: Immense Scope for Pharmacology

Marine organisms produce a large array of natural products with relevance in drug discovery. These compounds have biological activities such as antioxidant, antibacterial, antitumor, antivirus, anticoagulant, anti-inflammatory, antihypertensive, antidiabetic, and so forth. Consequently, several of the metabolites have made it to the advanced stages of clinical trials, and a few of them are commercially available. In this review, novel information on natural products isolated from marine microorganisms, microalgae, and macroalgae are presented. Given due research impetus, these marine metabolites might emerge as a new wave of promising drugs.

First report of spiro-compounds from marine macroalga Gracilaria salicornia: prospective natural anti-inflammatory agents attenuate 5-lipoxygenase and cyclooxygenase-2

The inflammation pathology is an orchestrated biological process and the dual inhibition of pro-inflammatory enzymes 5-lipoxygenase and cyclooxygenase-2 has been found to be an effective approach against inflammation. This study involves the characterisation of two previously undescribed spiro[5.5]undecanes, 3-(hydroxymethyl)-7-(methoxymethyl)-3,11-dimethyl-9-oxospiro[5.5]undec-4-en-10-methylbutanoate (1) and 4-ethoxy-11,11-dimethyl-7-methylene-8-(propionyloxy)spiro[5.5]undec-2-en-10⁴,10⁶-dihydroxytetrahydro-2H-pyran-10-carboxylate (2) with potential anti-inflammatory properties, from seaweed Gracilaria salicornia by extensive-spectroscopic-experiments. These metabolites recorded prospective bioactivities against 5-lipoxygenase (IC₅₀ < 2.80 mM), whereas their selectivity indices were significantly greater (∼1) than ibuprofen (0.89) (p < 0.05), which attributed selective anti-inflammatory potencies of the studied spiro[5.5]undecane derivatives against inducible cyclooxygenase-2 than constitutive cyclooxygenase-1. Radical scavenging potential of spiro[5.5]undec-2-en-10⁴,10⁶-dihydroxytetrahydro-2H-pyran-10-carboxylate analogue (2) against oxidants, 2,2-diphenyl-1-picrylhydrazyl and 2,2'-azino-bis-3 ethylbenzothiozoline-6-sulfonic acid were found to be greater (IC₅₀ < 1.25 mM) than commercial standard, α-tocopherol (IC₅₀ 1.42-1.79 mM). The greater hydrogen-bonding interactions and binding affinity of 2 (-10.13 kcal/mol) with 5-LOX appropriately corroborated its prospective anti-inflammatory activity.