Nazumazoles D-F, Cyclic Pentapeptides That Inhibit Chymotrypsin, from the Marine Sponge Theonella swinhoei

Natural Products That Contain Higher Homologated Amino Acids

This review focuses on discussing natural products (NPs) that contain higher homologated amino acids (homoAAs) in the structure as well as the proposed and characterized biosynthesis of these non-proteinogenic amino acids. Homologation of amino acids includes the insertion of a methylene group into its side chain. It is not a very common modification found in NP biosynthesis as approximately 450 homoAA-containing NPs have been isolated from four bacterial phyla (Cyanobacteria, Actinomycetota, Myxococcota, and Pseudomonadota), two fungal phyla (Ascomycota and Basidiomycota), and one animal phylum (Porifera), except for a few examples. Amino acids that are found to be homologated and incorporated in the NP structures include the following ten amino acids: alanine, arginine, cysteine, isoleucine, glutamic acid, leucine, phenylalanine, proline, serine, and tyrosine, where isoleucine, leucine, phenylalanine, and tyrosine share the comparable enzymatic pathway. Other amino acids have their individual homologation pathway (arginine, proline, and glutamic acid for bacteria), likely utilize the primary metabolic pathway (alanine and glutamic acid for fungi), or have not been reported (cysteine and serine). Despite its possible high potential in the drug discovery field, the biosynthesis of homologated amino acids has a large room to explore for future combinatorial biosynthesis and metabolic engineering purpose.

Highly N-Methylated Peptides from the Antarctic Sponge Inflatella coelosphaeroides Are Active against Plasmodium falciparum

Malaria, caused by the parasite Plasmodium falciparum, continues to threaten much of the world's population, and there is a pressing need for expanding treatment options. Natural products have been a vital source of such drugs, and here we report seven new highly N-methylated linear peptides, friomaramide B (2) and shagamides A-F (3-8) from the marine sponge Inflatella coelosphaeroides, collected in Antarctic waters, which demonstrate activity against three strains of blood-stage P. falciparum. The planar structures of these metabolites were solved by interpreting NMR data, as well as HRESIMS/MS fragmentation patterns, while Marfey's analysis was used to establish the configurations of the amino acids. Reisolation of the previously reported compound friomaramide A (1) allowed us to revise its structure. The panel of isolated compounds allowed establishing structure/activity relationships and provided information for future structure optimization for this class of P. falciparum inhibitory metabolites.

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.

A convenient synthetic route to (2S,4S)-methylproline and its exploration for protein engineering of thioredoxin

4-Substituted prolines, especially 4-fluoroprolines, have been widely used in protein engineering and design. Here, we report a robust and stereoselective approach for the synthesis of (2S,4S)-methylproline starting from (2S)-pyroglutamic acid. Incorporation studies with both (2S,4R)- and (2S,4S)-methylproline into the Trx1P variant of the model protein thioredoxin of E. coli show that the stereochemistry of the 4-methyl group might be a key determinator for successful incorporation during ribosomal synthesis of this protein.

An Overview of Bioactive 1,3-Oxazole-Containing Alkaloids from Marine Organisms

1,3-Oxazole chemicals are a unique class of five-membered monocyclic heteroarenes, containing a nitrogen atom and an oxygen. These alkaloids have attracted extensive attention from medicinal chemists and pharmacologists owing to their diverse arrays of chemical structures and biological activities, and a series of 1,3-oxazole derivatives has been developed into therapeutic agents (e.g., almoxatone, befloxatone, cabotegravir, delpazolid, fenpipalone, haloxazolam, inavolisib). A growing amount of evidence indicates that marine organisms are one of important sources of 1,3-oxazole-containing alkaloids. To improve our knowledge regarding these marine-derived substances, as many as 285 compounds are summarized in this review, which, for the first time, highlights their sources, structural features and biological properties, as well as their biosynthesis and chemical synthesis. Perspective for the future discovery of new 1,3-oxazole compounds from marine organisms is also provided.

Anti-Proliferative Potential of Secondary Metabolites from the Marine Sponge Theonella sp.: Moving from Correlation toward Causation

Marine sponges have been recognized as a rich source of potential anti-proliferative metabolites. Currently, there are two sponge-derived anti-cancer agents (a macrolide and a nucleoside) isolated from the Porifera phylum, suggesting the great potential of this sponge as a rich source for anti-neoplastic agents. To search for more bioactive metabolites from this phylum, we examined the EtOAc extract of Theonella sp. sponge. We isolated seven compounds (1–7), including four 4-methylene sterols (1–4), two nucleosides (5 and 6), and one macrolide (7). Among them, theonellasterol L (1) was identified for the first time, while 5′-O-acetyl-2′-deoxyuridine (5) and 5′-O-acetylthymidine (6) were the first identified deoxyuridine and thymidine derivatives from the sponge Theonella sp. These structures were elucidated based on their spectroscopic data. The anti-proliferation activity of compounds 1–7 against the MCF-7, MDA-MB-231, T-47D, HCT-116, DLD-1, K562, and Molt 4 cancer cell lines was determined. The results indicated that the 14-/15-oxygenated moiety played an important role in the antiproliferative activity and the macrolide derivatives dominated the anti-proliferative effect of the sponge Theonella sp. The in silico analysis, using a chemical global positioning system for natural products (ChemGPS-NP), indicated an anti-proliferative mode of actions (MOA) suggesting the potential applications of the isolated active metabolites as anti-proliferative agents.

Marine Pharmacology in 2016-2017: Marine Compounds with Antibacterial, Antidiabetic, Antifungal, Anti-Inflammatory, Antiprotozoal, Antituberculosis and Antiviral Activities; Affecting the Immune and Nervous Systems, and Other Miscellaneous Mechanisms of Action

The review of the 2016-2017 marine pharmacology literature was prepared in a manner similar as the 10 prior reviews of this series. Preclinical marine pharmacology research during 2016-2017 assessed 313 marine compounds with novel pharmacology reported by a growing number of investigators from 54 countries. The peer-reviewed literature reported antibacterial, antifungal, antiprotozoal, antituberculosis, and antiviral activities for 123 marine natural products, 111 marine compounds with antidiabetic and anti-inflammatory activities as well as affecting the immune and nervous system, while in contrast 79 marine compounds displayed miscellaneous mechanisms of action which upon further investigation may contribute to several pharmacological classes. Therefore, in 2016-2017, the preclinical marine natural product pharmacology pipeline generated both novel pharmacology as well as potentially new lead compounds for the growing clinical marine pharmaceutical pipeline, and thus sustained with its contributions the global research for novel and effective therapeutic strategies for multiple disease categories.

Heteroaryl Rings in Peptide Macrocycles

This Review is devoted to the chemistry of macrocyclic peptides having heterocyclic fragments in their structure. These motifs are present in many natural products and synthetic macrocycles designed against a particular biochemical target. Thiazole and oxazole are particularly common constituents of naturally occurring macrocyclic peptide molecules. This frequency of occurrence is because the thiazole and oxazole rings originate from cysteine, serine, and threonine residues. Whereas other heteroaryl groups are found less frequently, they offer many insightful lessons that range from conformational control to receptor/ligand interactions. Many options to develop new and improved technologies to prepare natural products have appeared in recent years, and the synthetic community has been pursuing synthetic macrocycles that have no precedent in nature. This Review attempts to summarize progress in this area.

Toward the Synthesis and Improved Biopotential of an N-methylated Analog of a Proline-Rich Cyclic Tetrapeptide from Marine Bacteria

An N-methylated analog of a marine bacteria-derived natural proline-rich tetracyclopeptide was synthesized by coupling the deprotected dipeptide fragments Boc-l-prolyl-l-N-methylleucine-OH and l-prolyl-l-N-methylphenylalanine-OMe. A coupling reaction was accomplished utilizing N,N'-Dicyclohexylcarbodidimde (DCC) and 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC·HCl) as coupling agents and Triethylamine (TEA) or N-methylmorpholine (NMM) as the base in the presence of the racemization suppressing agent. This was followed by the cyclization of the linear tetrapeptide fragment under alkaline conditions. The structure of the synthesized cyclooligopeptide was confirmed using quantitative elemental analysis, FTIR (Fourier-transform infrared spectroscopy), ¹H NMR (Nuclear magnetic resonance spectroscopy), 13C NMR, and mass spectrometry. From the bioactivity results, it was clear that the newly synthesized proline-rich tetracyclopeptide exhibited better anthelmintic potential against Megascoplex konkanensis, Pontoscotex corethruses, and Eudrilus eugeniae at a concentration of 2 mg/mL as well as improved antifungal activity against pathogenic dermatophytes Trichophyton mentagrophytes and Microsporum audouinii at a concentration of 6 μg/mL, as compared to non-methylated tetracyclopeptide. Moreover, N-methylated tetracyclopeptide displayed significant activity against pathogenic Candida albicans.

Swinhoeisterols from the South China Sea Sponge Theonella swinhoei

Swinhoeisterols C-F (1-4), four new steroids having a rearranged 6/6/5/7 ring system, were isolated from the Xisha sponge Theonella swinhoei, together with the known analogue swinhoeisterol A (5). Their structures were determined based on spectroscopic analysis, TDDFT-ECD and optical rotation calculations, and biogenetic correlations. In an in vitro assay, compound 1 showed an inhibitory effect on (h)p300 with an IC₅₀ value of 8.8 μM, whereas compounds 2-4 were not active.

Marine natural products

Covering: 2016. Previous review: Nat. Prod. Rep., 2017, 34, 235-294This review covers the literature published in 2016 for marine natural products (MNPs), with 757 citations (643 for the period January to December 2016) 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 (1277 in 432 papers for 2016), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included.

Marine natural product peptides with therapeutic potential: Chemistry, biosynthesis, and pharmacology

The oceans are a uniquely rich source of bioactive metabolites, of which sponges have been shown to be among the most prolific producers of diverse bioactive secondary metabolites with valuable therapeutic potential. Much attention has been focused on marine bioactive peptides due to their novel chemistry and diverse biological properties. As summarized in this review, marine peptides are known to exhibit various biological activities such as antiviral, anti-proliferative, antioxidant, anti-coagulant, anti-hypertensive, anti-cancer, antidiabetic, antiobesity, and calcium-binding activities. This review focuses on the chemistry and biology of peptides isolated from sponges, bacteria, cyanobacteria, fungi, ascidians, and other marine sources. The role of marine invertebrate microbiomes in natural products biosynthesis is discussed in this review along with the biosynthesis of modified peptides from different marine sources. The status of peptides in various phases of clinical trials is presented, as well as the development of modified peptides including optimization of PK and bioavailability.

First Total Synthesis and Biological Screening of a Proline-Rich Cyclopeptide from a Caribbean Marine Sponge

A natural heptacyclopeptide, stylissamide G (7), previously isolated from the Bahamian marine sponge Stylissa caribica from the Caribbean Sea, was synthesized via coupling of the tetrapeptide l-phenylalanyl-l-prolyl-l-phenylalanyl-l-proline methyl ester with the tripeptide Boc-l-leucyl-l-isoleucyl-l-proline, followed by cyclization of the linear heptapeptide fragment. The structure of the synthesized cyclooligopeptide was confirmed using quantitative elemental analysis, FT-IR, ¹H NMR, ¹³C NMR and mass spectrometry. Results of pharmacological activity studies indicated that the newly synthesized cycloheptapeptide displayed good anthelmintic potential against Megascoplex konkanensis, Pontoscotex corethruses and Eudrilus eugeniea at 2 mg/mL and in addition, potent antifungal activity against pathogenic Candida albicans and dermatophytes Trichophyton mentagrophytes and Microsporum audouinii at a concentration of 6 μg/mL.