Banyasin A and banyasides A and B, three novel modified peptides from a water bloom of the cyanobacterium Nostoc sp

Phylogenetic and molecular characteristics of two Aphanizomenon strains from the Curonian Lagoon, Southeastern Baltic Sea and their biological activities

Polyphasic approach has become a generally accepted method for the classification of cyanobacteria. In this study, we present a detailed characterisation of two strains, KUCC C1 and KUCC C2, isolated from the Curonian Lagoon and classified to the Aphanizomenon genus. Despite phylogenetic similarity, the strains differ with respect to morphology, ultrastructure characteristics, and the metabolite profile. In the KUCC C1 extract, three unknown peptides and eight anabaenopeptins were detected, while KUCC C2 produced one unknown peptide and one aeruginosin. In both strains, a total of eleven pigments were detected. The production of myxoxantophyll, chlorophyll-a, chlorophylide-a, and zeaxanthin was higher in KUCC C2 than in KUCC C1. Extracts from both strains of Aphanizomenon also had different effects in antibacterial, anticancer and enzyme inhibition assays. Comprehensive analyses of Aphanizomenon strains performed in this study showed significant diversity between the isolates from the same bloom sample. These differences should be considered when exploring the ecological significance and biotechnological potential of a given population.

Prephenate decarboxylase: An unexplored branchpoint to unusual natural products

Prephenate decarboxylases are a small family of enzymes which initiate a specialized divergence from the shikimate pathway, where prephenate (2) is decarboxylated without aromatization. In addition to effecting a challenging chemical transformation, prephenate decarboxylases have been implicated in the production of rare specialized metabolites, sometimes directly constructing bioactive warheads. Many of the biosynthetic steps to natural products derived from prephenate decarboxylases remain elusive. Here, we review prephenate decarboxylase research thus far and highlight natural products that may be derived from biosynthetic pathways involving prephenate decarboxylases. We also highlight commonly encountered challenges in the structure elucidation of these natural products. Prephenate decarboxylases are a gateway into understudied biosynthetic pathways which present a high potential for the discovery of novel and bioactive natural products, as well as new biosynthetic enzymes.

Highlights of biosynthetic enzymes and natural products from symbiotic cyanobacteria

Covering: up to 2023Cyanobacteria have long been known for their intriguing repertoire of natural product scaffolds, which are often distinct from other phyla. Cyanobacteria are ecologically significant organisms that form a myriad of different symbioses including with sponges and ascidians in the marine environment or with plants and fungi, in the form of lichens, in terrestrial environments. Whilst there have been several high-profile discoveries of symbiotic cyanobacterial natural products, genomic data is scarce and discovery efforts have remained limited. However, the rise of (meta-)genomic sequencing has improved these efforts, emphasized by a steep increase in publications in recent years. This highlight focuses on selected examples of symbiotic cyanobacterial-derived natural products and their biosyntheses to link chemistry with corresponding biosynthetic logic. Further highlighted are remaining gaps in knowledge for the formation of characteristic structural motifs. It is anticipated that the continued rise of (meta-)genomic next-generation sequencing of symbiontic cyanobacterial systems will lead to many exciting discoveries in the future.

Structural Diversity and Biological Activity of Cyanopeptolins Produced by Nostoc edaphicum CCNP1411

Cyanopeptolins (CPs) are one of the most commonly occurring class of cyanobacterial nonribosomal peptides. For the majority of these compounds, protease inhibition has been reported. In the current work, the structural diversity of cyanopeptolins produced by Nostoc edaphicum CCNP1411 was explored. As a result, 93 CPs, including 79 new variants, were detected and structurally characterized based on their mass fragmentation spectra. CPs isolated in higher amounts were additionally characterized by NMR. To the best of our knowledge, this is the highest number of cyanopeptides found in one strain. The biological assays performed with the 34 isolated CPs confirmed the significance of the amino acid located between Thr and the unique 3-amino-6-hydroxy-2-piperidone (Ahp) on the activity of the compounds against serine protease and HeLa cancer cells.

Quantum-Chemical Study of the Assembly Mechanism of 1-Pyrrolines from N-Benzylaldimines and Arylacetylenes in KOtBu/DMSO Superbasic Medium

By using a quantum-chemical approach, B2PLYP-D2/6-311+G**//B3LYP/6-31+G*, we have carried out a detailed study of the assembly of 1-pyrrolines from N-benzyl-1-phenylmethanimine and phenylacetylene in the superbasic medium KO^tBu/dimethyl sulfoxide (DMSO). In this way, we have considered, both theoretically and experimentally, the mechanisms of the assembly through a concerted and stepwise nucleophilic cycloaddition and have addressed the side processes accompanying the assembly. It is found that the assembly via the concerted cycloaddition is kinetically more favorable than that via the stepwise cycloaddition. At the same time, the reaction of C-vinylation of aldimine with phenylacetylene occurs with a similar activation energy as the concerted cycloaddition and leads to the formation of 2-aza-1,4-pentadiene. The anion of 2-aza-1,4-pentadiene is an intermediate for the side processes leading to the formation of triarylpyridines and 1,3-diarylpropan-1-ones. Triarylpyridines are formed through the concerted cycloaddition of the next phenylacetylene molecule to 2-aza-1,4-pentadiene, while 1,3-diarylpropan-1-ones are formed as a result of the hydrolysis of 2-aza-1,4-pentadienes. It is found out that the mild conditions for the assembly of 1-pyrrolines (60 °C, 15 min) relate to the formation of complexes in the KO^tBu/DMSO superbasic medium, where the anion is readily accessible for the nucleophilic attack by the phenylacetylene molecule.

Four new suomilides isolated from the cyanobacterium Nostoc sp. KVJ20 and proposal of their biosynthetic origin

The suomilide and the banyasides are highly modified and functionalized non-ribosomal peptides produced by cyanobacteria of the order Nostocales. These compound classes share several substructures, including a complex azabicyclononane core, which was previously assumed to be derived from the amino acid tyrosine. In our study we were able to isolate and determine the structures of four suomilides, named suomilide B - E (1-4). The compounds differ from the previously isolated suomilide A by the functionalization of the glycosyl group. Compounds 1-4 were assayed for anti-proliferative, anti-biofilm and anti-bacterial activities, but no significant activity was detected. The sequenced genome of the producer organism Nostoc sp. KVJ20 enabled us to propose a biosynthetic gene cluster for suomilides. Our findings indicated that the azabicyclononane core of the suomilides is derived from prephenate and is most likely incorporated by a proline specific non-ribosomal peptide synthetase-unit.

Chemodivergent photocatalytic access to 1-pyrrolines and 1-tetralones involving switchable C(sp3)–H functionalization

A chemodivergent photocatalytic approach to 1-pyrrolines and 1-tetralones from alkyl bromides and vinyl azides has been developed through chemoselectively controllable intermolecular [3 + 2] and [4 + 2] cyclization. This photoredox-neutral two-component protocol involves intermolecular radical addition and switchable distal C(sp³)–H functionalization enabled by iminyl radical-mediated 1,5-hydrogen atom transfer. Meanwhile, chemoselectivity between C(sp³)–N bond formation and C(sp³)–C(sp²) bond formation is precisely switched by photocatalysts (Ru(bpy)₃(PF₆)₂ vs. fac-Ir(ppy)₃) and additives (base vs. acid).

Anabaenopeptins from Nostoc edaphicum CCNP1411

Cyanobacteria of the Nostoc genus belong to the most prolific sources of bioactive metabolites. In our previous study on Nostoc edaphicum strain CCNP1411, the occurrence of cyanopeptolins and nostocyclopeptides was documented. In the current work, the production of anabaenopeptins (APs) by the strain was studied using genetic and chemical methods. Compatibility between the analysis of the apt gene cluster and the structure of the identified APs was found. Three of the APs, including two new variants, were isolated as pure compounds and tested against four serine proteases and carboxypeptidase A (CPA). The in vitro enzymatic assays showed a typical activity of this class of cyanopeptides, i.e., the most pronounced effects were observed in the case of CPA. The activity of the detected compounds against important metabolic enzymes confirms the pharmaceutical potential of anabaenopeptins.

Discovery of varlaxins, new aeruginosin-type inhibitors of human trypsins

Low-molecular weight natural products display vast structural diversity and have played a key role in the development of novel therapeutics. Here we report the discovery of novel members of the aeruginosin family of natural products, which we named varlaxins. The chemical structures of varlaxins 1046A and 1022A were determined using a combination of mass spectrometry, analysis of one- and two-dimensional NMR spectra, and HPLC analysis of Marfey's derivatives. These analyses revealed that varlaxins 1046A and 1022A are composed of the following moieties: 2-O-methylglyceric acid 3-O-sulfate, isoleucine, 2-carboxy-6-hydroxyoctahydroindole (Choi), and a terminal arginine derivative. Varlaxins 1046A and 1022A differ in the cyclization of this arginine moiety. Interestingly, an unusual α-D-glucopyranose moiety derivatized with two 4-hydroxyphenylacetic acid residues was bound to Choi, a structure not previously reported for other members of the aeruginosin family. We sequenced the complete genome of Nostoc sp. UHCC 0870 and identified the putative 36 kb varlaxin biosynthetic gene cluster. Bioinformatics analysis confirmed that varlaxins belong to the aeruginosin family of natural products. Varlaxins 1046A and 1022A strongly inhibited the three human trypsin isoenzymes with IC₅₀ of 0.62-3.6 nM and 97-230 nM, respectively, including a prometastatic trypsin-3, which is a therapeutically relevant target in several types of cancer. These results substantially broaden the genetic and chemical diversity of the aeruginosin family and provide evidence that the aeruginosin family is a source of strong inhibitors of human serine proteases.

Potent Inhibitor of Human Trypsins from the Aeruginosin Family of Natural Products

Serine proteases regulate many physiological processes and play a key role in a variety of cancers. Aeruginosins are a family of natural products produced by cyanobacteria that exhibit pronounced structural diversity and potent serine protease inhibition. Here, we sequenced the complete genome of Nodularia sphaerocarpa UHCC 0038 and identified the 43.7 kb suomilide biosynthetic gene cluster. Bioinformatic analysis demonstrated that suomilide belongs to the aeruginosin family of natural products. We identified 103 complete aeruginosin biosynthetic gene clusters from 12 cyanobacterial genera and showed that they encode an unexpected chemical diversity. Surprisingly, purified suomilide inhibited human trypsin-2 and -3, with IC₅₀ values of 4.7 and 11.5 nM, respectively, while trypsin-1 was inhibited with an IC₅₀ of 104 nM. Molecular dynamics simulations suggested that suomilide has a long residence time when bound to trypsins. This was confirmed experimentally for trypsin-1 and -3 (residence times of 1.5 and 57 min, respectively). Suomilide also inhibited the invasion of aggressive and metastatic PC-3M prostate cancer cells without affecting cell proliferation. The potent inhibition of trypsin-3, together with a long residence time and the ability to inhibit prostate cancer cell invasion, makes suomilide an attractive drug lead for targeting cancers that overexpress trypsin-3. These results substantially broaden the genetic and chemical diversity of the aeruginosin family and suggest that aeruginosins may be a source of selective inhibitors of human serine proteases.

Phytoplankton of the Curonian Lagoon as a New Interesting Source for Bioactive Natural Products. Special Impact on Cyanobacterial Metabolites

The bioprospecting of marine and brackish water systems has increased during the last decades. In this respect, microalgae, including cyanobacteria, and their metabolites are one of the most widely explored resources. Most of the bioactive compounds are isolated from ex situ cultures of microorganisms; however, analysis of field samples could also supply valuable information about the metabolic and biotechnological potential of microalgae communities. In this work, the activity of phytoplankton samples from the Curonian Lagoon was studied. The samples were active against antibiotic resistant clinical and environmental bacterial strains as well as against serine proteases and T47D human breast adenocarcinoma cells. No significant effect was found on Daphnia magna. In addition, using LC-MS/MS, we documented the diversity of metabolites present in field samples. A list of 117 detected cyanopeptides was presented. Cyanopeptolins constituted the largest class of cyanopeptides. As complex bloom samples were analyzed, no link between the observed activity and a specific sample component can be established. However, the results of the study showed a biotechnological potential of natural products from the Curonian Lagoon.

The structure and biosynthesis of heinamides A1-A3 and B1-B5, antifungal members of the laxaphycin lipopeptide family

Laxaphycins are a family of cyclic lipopeptides with synergistic antifungal and antiproliferative activities. They are produced by multiple cyanobacterial genera and comprise two sets of structurally unrelated 11- and 12-residue macrocyclic lipopeptides. Here, we report the discovery of new antifungal laxaphycins from Nostoc sp. UHCC 0702, which we name heinamides, through antimicrobial bioactivity screening. We characterized the chemical structures of eight heinamide structural variants A1-A3 and B1-B5. These variants contain the rare non-proteinogenic amino acids 3-hydroxy-4-methylproline, 4-hydroxyproline, 3-hydroxy-d-leucine, dehydrobutyrine, 5-hydroxyl β-amino octanoic acid, and O-carbamoyl-homoserine. We obtained an 8.6-Mb complete genome sequence from Nostoc sp. UHCC 0702 and identified the 93 kb heinamide biosynthetic gene cluster. The structurally distinct heinamides A1-A3 and B1-B5 variants are synthesized using an unusual branching biosynthetic pathway. The heinamide biosynthetic pathway also encodes several enzymes that supply non-proteinogenic amino acids to the heinamide synthetase. Through heterologous expression, we showed that (2S,4R)-4-hydroxy-l-proline is supplied through the action of a novel enzyme LxaN, which hydroxylates l-proline. 11- and 12-residue heinamides have the characteristic synergistic activity of laxaphycins against Aspergillus flavus FBCC 2467. Structural and genetic information of heinamides may prove useful in future discovery of natural products and drug development.

Base-Catalyzed [3 + 2] Cycloaddition of N-Benzyl Ketimines to Arylacetylenes Followed by Oxidation: A One-Pot Access to Polyarylated 2H-Pyrroles via Intermediate Pyrrolines

N-Benzyl ketimines undergo [3 + 2] cycloaddition with arylacetylenes in the KOBu^t/DMSO solution to 2,3,5-triarylpyrrolines, which are oxidized (chloranil, DDQ) in situ to 2,3,5-triaryl-2H-pyrroles in 53-71% yields. The intermediate 1-pyrrolines can be isolated in 31-91% yields and separately oxidized to the corresponding 2H-pyrroles.

Beyond Microcystins: Cyanobacterial Extracts Induce Cytoskeletal Alterations in Rice Root Cells

Microcystins (MCs) are cyanobacterial toxins and potent inhibitors of protein phosphatases 1 (PP1) and 2A (PP2A), which are involved in plant cytoskeleton (microtubules and F-actin) organization. Therefore, studies on the toxicity of cyanobacterial products on plant cells have so far been focused on MCs. In this study, we investigated the effects of extracts from 16 (4 MC-producing and 12 non-MC-producing) cyanobacterial strains from several habitats, on various enzymes (PP1, trypsin, elastase), on the plant cytoskeleton and H₂O₂ levels in Oryza sativa (rice) root cells. Seedling roots were treated for various time periods (1, 12, and 24 h) with aqueous cyanobacterial extracts and underwent either immunostaining for α-tubulin or staining of F-actin with fluorescent phalloidin. 2,7-dichlorofluorescein diacetate (DCF-DA) staining was performed for H₂O₂ imaging. The enzyme assays confirmed the bioactivity of the extracts of not only MC-rich (MC+), but also MC-devoid (MC−) extracts, which induced major time-dependent alterations on both components of the plant cytoskeleton. These findings suggest that a broad spectrum of bioactive cyanobacterial compounds, apart from MCs or other known cyanotoxins (such as cylindrospermopsin), can affect plants by disrupting the cytoskeleton.

Cyanopeptolins with Trypsin and Chymotrypsin Inhibitory Activity from the Cyanobacterium Nostoc edaphicum CCNP1411

Cyanopeptolins (CPs) are one of the most frequently occurring cyanobacterial peptides, many of which are inhibitors of serine proteases. Some CP variants are also acutely toxic to aquatic organisms, especially small crustaceans. In this study, thirteen CPs, including twelve new variants, were detected in the cyanobacterium Nostoc edaphicum CCNP1411 isolated from the Gulf of Gdańsk (southern Baltic Sea). Structural elucidation was performed by tandem mass spectrometry with verification by NMR for CP962 and CP985. Trypsin and chymotrypsin inhibition assays confirmed the significance of the residue adjacent to 3-amino-6-hydroxy-2-piperidone (Ahp) for the activity of the peptides. Arginine-containing CPs (CPs-Arg²) inhibited trypsin at low IC₅₀ values (0.24⁻0.26 µM) and showed mild activity against chymotrypsin (IC₅₀ 3.1⁻3.8 µM), while tyrosine-containing CPs (CPs-Tyr²) were selectively and potently active against chymotrypsin (IC₅₀ 0.26 µM). No degradation of the peptides was observed during the enzyme assays. Neither of the CPs were active against thrombin, elastase or protein phosphatase 1. Two CPs (CP962 and CP985) had no cytotoxic effects on MCF-7 breast cancer cells. Strong and selective activity of the new cyanopeptolin variants makes them potential candidates for the development of drugs against metabolic disorders and other diseases.

A Genetic and Chemical Perspective on Symbiotic Recruitment of Cyanobacteria of the Genus Nostoc into the Host Plant Blasia pusilla L

Liverwort Blasia pusilla L. recruits soil nitrogen-fixing cyanobacteria of genus Nostoc as symbiotic partners. In this work we compared Nostoc community composition inside the plants and in the soil around them from two distant locations in Northern Norway. STRR fingerprinting and 16S rDNA phylogeny reconstruction showed a remarkable local diversity among isolates assigned to several Nostoc clades. An extensive web of negative allelopathic interactions was recorded at an agricultural site, but not at the undisturbed natural site. The cell extracts of the cyanobacteria did not show antimicrobial activities, but four isolates were shown to be cytotoxic to human cells. The secondary metabolite profiles of the isolates were mapped by MALDI-TOF MS, and the most prominent ions were further analyzed by Q-TOF for MS/MS aided identification. Symbiotic isolates produced a great variety of small peptide-like substances, most of which lack any record in the databases. Among identified compounds we found microcystin and nodularin variants toxic to eukaryotic cells. Microcystin producing chemotypes were dominating as symbiotic recruits but not in the free-living community. In addition, we were able to identify several novel aeruginosins and banyaside-like compounds, as well as nostocyclopeptides and nosperin.

Morphologic, Phylogenetic and Chemical Characterization of a Brackish Colonial Picocyanobacterium (Coelosphaeriaceae) with Bioactive Properties

Despite their cosmopolitan distribution, knowledge on cyanobacteria in the family Coelosphaeriaceae is limited. In this study, a single species culture of a coelosphaeran cyanobacterium isolated from a brackish rock pool in the Baltic Sea was established. The strain was characterized by morphological features, partial 16S rRNA sequence and nonribosomal oligopeptide profile. The bioactivity of fractionated extracts against several serine proteases, as well as protein-serine/threonine phosphatases was studied. Phylogenetic analyses of the strain suggested a close relationship with Snowella litoralis, but its morphology resembled Woronichinia compacta. The controversial morphologic and phylogenetic results demonstrated remaining uncertainties regarding species division in this cyanobacteria family. Chemical analyses of the strain indicated production of nonribosomal oligopeptides. In fractionated extracts, masses and ion fragmentation spectra of seven possible anabaenopeptins were identified. Additionally, fragmentation spectra of cyanopeptolin-like peptides were collected in several of the fractions. The nonribosomal oligopeptide profile adds another potential identification criterion in future inter- and intraspecies comparisons of coelosphaeran cyanobacteria. The fractionated extracts showed significant activity against carboxypeptidase A and trypsin. Inhibition of these important metabolic enzymes might have impacts at the ecosystem level in aquatic habitats with high cyanobacteria densities.

A comprehensive review of glycosylated bacterial natural products

A systematic analysis of all naturally-occurring glycosylated bacterial secondary metabolites reported in the scientific literature up through early 2013 is presented. This comprehensive analysis of 15 940 bacterial natural products revealed 3426 glycosides containing 344 distinct appended carbohydrates and highlights a range of unique opportunities for future biosynthetic study and glycodiversification efforts.

Total synthesis of the putative structure of the proposed Banyasin A

The first total synthesis of four possible isomers of a molecule possessing the configuration proposed for Banyasin A is described. The structure synthesized appears to be different from that of the natural product.

Direct arginine modification in native peptides and application to chemical probe development

An efficient method for the direct labeling of the Arg guanidinium group in native peptides is reported. This straightforward procedure allows modifying the arginine moiety in peptides with various reporter groups, such as fluorophores, biotin, etc., under mild conditions in an operationally simple procedure. The scope of this method tolerates various functionalized amino acids such as His, Ser, Trp, Tyr, Glu, etc., while the only limitations uncovered so far are restricted to cysteine and free amine residues. The utility of this late-stage diversification method was demonstrated in direct labeling of leuprolide, a clinically used drug, for distribution monitoring in Daphnia, and in labeling of microcystin, a cyanobacterial toxin.

Nostosins, Trypsin Inhibitors Isolated from the Terrestrial Cyanobacterium Nostoc sp. Strain FSN

Two new trypsin inhibitors, nostosin A (1) and B (2), were isolated from a hydrophilic extract of Nostoc sp. strain FSN, which was collected from a paddy field in the Golestan Province of Iran. Nostosins A (1) and B (2) are composed of three subunits, 2-hydroxy-4-(4-hydroxyphenyl)butanoic acid (Hhpba), L-Ile, and L-argininal (1) or argininol (2). Nostosins A (1) and B (2) exhibited IC50 values of 0.35 and 55 μM against porcine trypsin, respectively, suggesting that the argininal aldehyde group plays a crucial role in the efficient inhibition of trypsin. Molecular docking of nostosin A (1) (449 Da), leupeptin (426 Da, IC50 0.5 μM), and spumigin E (610 Da, IC50 < 0.1 μM) with trypsin suggested prominent binding similarity between nostosin A (1) and leupeptin but only partial binding similarity with spumigin E. The number of hydrogen bonds between ligands and trypsin increased according to the length and size of the ligand molecule, and the docking affinity values followed the measured IC50 values. Nostosin A (1) is the first highly potent three-subunit trypsin inhibitor with potency comparable to the known commercial trypsin inhibitor leupeptin. These findings expand the known diversity of short-chain linear peptide protease inhibitors produced by cyanobacteria.

Novel Aeruginosin-865 from Nostoc sp. as a potent anti-inflammatory agent

Aeruginosin-865 (Aer-865), isolated from terrestrial cyanobacterium Nostoc sp. Lukešová 30/93, is the first aeruginosin-type peptide containing both a fatty acid and a carbohydrate moiety, and is the first aeruginosin to be found in the genus Nostoc. Mass spectrometry, chemical and spectroscopic analysis as well as one- and two-dimensional NMR and chiral HPLC analysis of Marfey derivatives were applied to determine the peptidic sequence: D-Hpla, D-Leu, 5-OH-Choi, Agma, with hexanoic and mannopyranosyl uronic acid moieties linked to Choi. We used an AlphaLISA assay to measure the levels of proinflammatory mediators IL-8 and ICAM-1 in hTNF-α-stimulated HLMVECs. Aer-865 showed significant reduction of both: with EC50 values of (3.5±1.5) μg mL(-1) ((4.0±1.7) μM) and (50.0±13.4) μg mL(-1) ((57.8±15.5) μM), respectively. Confocal laser scanning microscopy revealed that the anti-inflammatory effect of Aer-865 was directly associated with inhibition of NF-κB translocation to the nucleus. Moreover, Aer-865 did not show any cytotoxic effect.

Bromine- and chlorine-containing aeruginosins from Microcystis aeruginosa bloom material collected in Kibbutz Geva, Israel

Five new natural products, aeruginosins GE686 (1), GE766 (2), GE730 (3), GE810 (4), and GE642 (5), were isolated along with four known aeruginosins, 98C, 101, KY642, and DA688, from bloom material of the cyanobacterium Microcystis aeruginosa collected from a fish pond in Kibbutz Geva, Israel, in August 2007. Their structures were elucidated by a combination of various spectroscopic techniques, primarily NMR and MS, while the absolute configurations of the stereogenic centers were determined by Marfey's and chiral-phase HPLC methods. Two of the new aeruginosins, aeruginosins GE686 (1) and GE766 (2), contain the unprecedented d-m-Br-m'-Cl-p-hydroxyphenyllactic acid derivative. The structures and biological activities of the five new metabolites are described.

SAR analysis and bioactive potentials of freshwater and terrestrial cyanobacterial compounds: a review

Freshwater and terrestrial cyanobacteria resemble the marine forms in producing divergent chemicals such as linear, cyclic and azole containing peptides, alkaloids, cyclophanes, terpenes, lactones, etc. These metabolites have wider biomedical potentials in targeting proteases, cancers, parasites, pathogens and other cyanobacteria and algae (allelopathy). Among the various families of non-marine cyanobacterial peptides reported, many of them are acting as serine protease inhibitors. While the micropeptin family has a preference for chymotrypsin inhibition rather than other serine proteases, the aeruginosin family targets trypsin and thrombin. In addition, cyanobacterial compounds such as scytonemide A, lyngbyazothrins C and D and cylindrocyclophanes were found to inhibit 20S proteosome. Apart from proteases, metabolites blocking the other targets of cancer pathways may exhibit cytotoxic effect. Colon and rectum, breast, lung and prostate are the worst affecting cancers in humans and are deduced to be inhibited by both peptidic and non-peptidic compounds. Moreover, the growth of infections causing parasites such as Plasmodium, Leishmania and Trypanosoma are well controlled by peptides: aerucyclamides A-D, tychonamides and alkaloids: nostocarboline and calothrixins. Likewise, varieties of cyanobacterial compounds tend to inhibit serious infectious disease causing bacterial, fungal and viral agents. Interestingly, portoamides, spiroidesin, nostocyclamide and kasumigamide are the allelopathic peptides determined to suppress the growth of toxic cyanobacteria and nuisance algae. Thus cyanobacterial compounds have a broad bioactive spectrum; the analysis of SAR studies will not only assist to find out the mode of action but also reveal bioactive key components. Thereby, developing the drugs bearing these bioactive skeletons to treat various illnesses is wide open.

Recent development of two chitinase inhibitors, Argifin and Argadin, produced by soil microorganisms

Chitin, the second most abundant polysaccharide in nature, occurs in fungi, some algae and many invertebrates, including insects. Thus, chitin synthesis and degradation could represent specific targets for fungicides and insecticides. Chitinases hydrolyze chitin into oligomers of N-acetyl-D-glucosamine at key points in the life cycles of organisms, consequently, chitinase inhibitors have become subject of increasing interest. This review covers the development of two chitinase inhibitors of natural origin, Argifin and Argadin, isolated from the cultured broth of microorganisms in our laboratory. In particular, the practical total synthesis of these natural products, the synthesis of lead compounds via computer-aided rational molecular design, and discovery methods that generate only highly-active compounds using a kinetic target(chitinase)-guided synthesis approach (termed in situ click chemistry) are described.

Mirabamides A-D, depsipeptides from the sponge Siliquariaspongia mirabilis that inhibit HIV-1 fusion

Four new cyclic depsipeptides termed mirabamides A-D (1-4) have been isolated from the marine sponge Siliquariaspongia mirabilis and shown to potently inhibit HIV-1 fusion. Their structures were elucidated by NMR and ESIMS, and absolute stereochemistry of the amino acids was determined using advanced Marfey's methods and NMR. Mirabamides contain two new entities, including 4-chlorohomoproline in 1-3 and an unusual glycosylated amino acid, beta-methoxytyrosine 4'-O-alpha-L-rhamnopyranoside (in 1, 2, and 4), along with a rare N-terminal aliphatic hydroxy acid. These elements proved to be useful for anti-HIV structure-activity relationship studies. Mirabamide A inhibited HIV-1 in neutralization and fusion assays with IC50 values between 40 and 140 nM, as did mirabamides C and D (IC50 values between 140 nM and 1.3 microM for 3 and 190 nM and 3.9 microM for 4), indicating that these peptides can act at the early stages of HIV-1 entry. The potent activity of depsipeptides containing the glycosylated beta-OMe Tyr unit demonstrates that beta-OMe Tyr itself is not critical for activity. Mirabamides A-C inhibited the growth of B. subtilis and C. albicans at 1-5 microg/disk in disk diffusion assays.

Biosynthesis and structure of aeruginoside 126A and 126B, cyanobacterial peptide glycosides bearing a 2-carboxy-6-hydroxyoctahydroindole moiety

Aeruginosins represent a group of peptide metabolites isolated from various cyanobacterial genera and from marine sponges that potently inhibit different types of serine proteases. Members of this family are characterized by the presence of a 2-carboxy-6-hydroxyoctahydroindole (Choi) moiety. We have identified and fully sequenced a NRPS gene cluster in the genome of the cyanobacterium Planktothrix agardhii CYA126/8. Insertional mutagenesis of a NRPS component led to the discovery and structural elucidation of two glycopeptides that were designated aeruginoside 126A and aeruginoside 126B. One variant of the aglycone contains a 1-amino-2-(N-amidino-Delta(3)-pyrrolinyl)ethyl moiety at the C terminus, the other bears an agmatine residue. In silico analyses of the aeruginoside biosynthetic genes aerA-aerI as well as additional mutagenesis and feeding studies allowed the prediction of enzymatic steps leading to the formation of aeruginosides and the unusual Choi moiety.

The value of natural products to future pharmaceutical discovery

Natural products have provided considerable value to the pharmaceutical industry over the past half century. In particular, the therapeutic areas of infectious diseases and oncology have benefited from numerous drug classes derived from natural product sources. Unfortunately, pharmaceutical companies have significantly decreased activities in natural product discovery during the past several years. Biotechnology companies working in the fields of combinatorial biosynthesis, genetic engineering and metagenomic approaches to identify novel natural product lead molecules have had limited success. Despite what appears to be a slow death of natural product discovery research, many new and interesting molecules with biological activity have been published in the past few years. If natural product materials continue to be tested for desirable therapeutic activities, we believe that significant progress in identifying new antibiotics, oncology therapeutics and other useful medicines will be made.