Talarolide A, a Cyclic Heptapeptide Hydroxamate from an Australian Marine Tunicate-Associated Fungus, Talaromyces sp. (CMB-TU011)

Total Synthesis of Talarolide A and atrop-Talarolide A: Hydroxamate H-Bond Bridge Stabilization of Cyclic Peptide Conformers Invokes Non-Canonical Atropisomerism

The first total synthesis of the Australian marine tunicate fungus-derived cyclic peptide talarolide A (1) has confirmed the structure previously proposed on the basis of spectroscopic and chemical analyses and re-affirmed the importance of the unique hydroxamate H-bond bridge in ring conformer stabilization. The unexpected co-synthesis of atrop-talarolide A (8) revealed, for the first time, that hydroxamate H-bond bridging in the talarolide framework invokes non-canonical atropisomerism and that talarolides A (1), C (3), and D (4) all exist naturally as atropisomers. These discoveries raise the intriguing prospect that comparable functionalisation of other cyclic peptides, including those with commercial value, could provide ready access to new "unnatural atropisomeric" chemical space, with new and/or improved chemical and biological properties.

Prenylated indole diketopiperazine alkaloids as phosphatase inhibitors from the marine-derived fungus Talaromyces purpureogenus

Six previously undescribed prenylated indole diketopiperazine alkaloids, talaromyines A-F (1-6), were isolated from the marine-derived fungus Talaromyces purpureogenus SCSIO 41517. Their structures including absolute configurations were elucidated on the basis of comprehensive spectroscopic data including NMR, HR-ESI-MS, and electronic circular dichroism calculations, together with chemical analysis of hydrolysates. Compounds 1-5 represent the first example of spirocyclic indole diketopiperazines biosynthesized from the condensation of L-tryptophan and L-alanine. Compounds 2 and 4-5 showed selective inhibitory activities against phosphatases TCPTP and MEG2 with IC50 value of 17.9-29.7 μM, respectively. Compounds 4-5 exhibited mild cytotoxic activities against two human cancer cell lines H1975 and HepG-2.

Separation and Identification of Isoleucine Enantiomers and Diastereomers Using an Original Chiral Resolution Labeling Reagent

D-Amino acids, which are present in small amounts in living organisms, are responsible for a variety of physiological functions. Some bioactive/biomolecular peptides also contain D-amino acids in their sequences; such peptides express different functions than peptides composed only of L-form amino acids. Among the 20 amino acids that make up proteins, threonine (Thr) and isoleucine (Ile) have two chiral carbons and thus have two enantiomers and diastereomers. These stereoisomers have been previously analyzed through HPLC using chiral columns or chiral resolution labeling reagents. However, the separation and identification of these stereoisomers are highly laborious and complicated. Herein, we propose an analytical method for the separation and identification of Ile stereoisomers through LC-MS using our original chiral resolution labeling reagent, 1-fluoro-2,4-dinitrophenyl-5-L-valine-N,N-dimethylethylenediamine-amide (L-FDVDA) and a PBr column packed with pentabromobenzyl-modified silica gel. Twenty DL-amino acids including Thr stereoisomers (41 amino acids including glycine) were separated and identified using C18 column. Ile stereoisomers could be separated using not a C18 column but a PBr column. Additionally, we showed that peptides containing Thr and Ile stereoisomers can be accurately detected through labeling with L-FDVDA.

Characterization of Arthropeptide B, an Antifungal Cyclic Tetrapeptide from Arthrobacter humicola

Disease suppressive composts are known, yet little information on the potential role of specific microbial antagonist within are available. Arthrobacter humicola isolate M9-1A has been obtained from a compost prepared from marine residues and peat moss. The bacterium is a non-filamentous actinomycete with antagonistic activity against plant pathogenic fungi and oomycetes sharing its ecological niche in agri-food microecosystems. Our objective was to identify and characterize compounds with antifungal activity produced by A. humicola M9-1A. Arthrobacter humicola culture filtrates were tested for antifungal activity in vitro and in vivo and a bioassay-guided approach was used to identify potential chemical determinants of its observed activity against molds. The filtrates reduced the development of lesions of Alternaria rot on tomatoes and the ethyl acetate extract inhibited growth of Alternaria alternata. A compound, arthropeptide B [cyclo-(L-Leu, L-Phe, L-Ala, L-Tyr)], was purified from the ethyl acetate extract of the bacterium. Arthropeptide B is a new chemical structure reported for the first time and has shown antifungal activity against A. alternata spore germination and mycelial growth.

Peptides from Marine-Derived Fungi: Chemistry and Biological Activities

Marine natural products are well-recognized as potential resources to fill the pipeline of drug leads to enter the pharmaceutical industry. In this circumstance, marine-derived fungi are one of the unique sources of bioactive secondary metabolites due to their capacity to produce diverse polyketides and peptides with unique structures and diverse biological activities. The present review covers the peptides from marine-derived fungi reported from the literature published from January 1991 to June 2023, and various scientific databases, including Elsevier, ACS publications, Taylor and Francis, Wiley Online Library, MDPI, Springer, Thieme, Bentham, ProQuest, and the Marine Pharmacology website, are used for a literature search. This review focuses on chemical characteristics, sources, and biological and pharmacological activities of 366 marine fungal peptides belonging to various classes, such as linear, cyclic, and depsipeptides. Among 30 marine-derived fungal genera, isolated from marine macro-organisms such as marine algae, sponges, coral, and mangrove plants, as well as deep sea sediments, species of Aspergillus were found to produce the highest number of peptides (174 peptides), followed by Penicillium (23 peptides), Acremonium (22 peptides), Eurotium (18 peptides), Trichoderma (18 peptides), Simplicillium (17 peptides), and Beauveria (12 peptides). The cytotoxic activity against a broad spectrum of human cancer cell lines was the predominant biological activity of the reported marine peptides (32%), whereas antibacterial, antifungal, antiviral, anti-inflammatory, and various enzyme inhibition activities ranged from 7% to 20%. In the first part of this review, the chemistry of marine peptides is discussed and followed by their biological activity.

Talarolides Revisited: Cyclic Heptapeptides from an Australian Marine Tunicate-Associated Fungus, Talaromyces sp. CMB-TU011

Application of a miniaturized 24-well plate system for cultivation profiling (MATRIX) permitted optimization of the cultivation conditions for the marine-derived fungus Talaromyces sp. CMB-TU011, facilitating access to the rare cycloheptapeptide talarolide A (1) along with three new analogues, B-D (2-4). Detailed spectroscopic analysis supported by Marfey's analysis methodology was refined to resolve N-Me-l-Ala from N-Me-d-Ala, l-allo-Ile from l-Ile and l-Leu, and partial and total syntheses of 2, and permitted unambiguous assignment of structures for 1 (revised) and 2-4. Consideration of diagnostic ROESY correlations for the hydroxamates 1 and 3-4, and a calculated solution structure for 1, revealed how cross-ring H-bonding to the hydroxamate moiety influences (defines/stabilizes) the cyclic peptide conformation. Such knowledge draws attention to the prospect that hydroxamates may be used as molecular bridges to access new cyclic peptide conformations, offering the prospect of new biological properties, including enhanced oral bioavailability.

Emerging pharmaceutical therapies of Ascidian-derived natural products and derivatives

In a growing multidrug-resistant environment, the identification of potential new drug candidates with an acceptable safety profile is a substantial crux in pharmaceutical discovery. This review discusses several aspects and properties of approved marine natural products derived from ascidian sources (phylum Chordata, subphylum Tunicata) and/or their deduced analogues including their biosynthetic origin, (bio)chemical preclinical assessments and known efficacy-safety profiles, clinical status in trials, but also translational developments, opportunities and final conclusions. The review also describes the preclinical assessments of a large number of other ascidian compounds that have not been involved in clinical trials yet. Finally, the emerging research on the connectivity of the ascidian hosts and their independent or obligate symbiotic guests is discussed. The review covers the latest information on the topic of ascidian-derived marine natural products over the last two decades including 2022, with the majority of publications published in the last decade.

The Outstanding Chemodiversity of Marine-Derived Talaromyces

Fungi in the genus Talaromyces occur in every environment in both terrestrial and marine contexts, where they have been quite frequently found in association with plants and animals. The relationships of symbiotic fungi with their hosts are often mediated by bioactive secondary metabolites, and Talaromyces species represent a prolific source of these compounds. This review highlights the biosynthetic potential of marine-derived Talaromyces strains, using accounts from the literature published since 2016. Over 500 secondary metabolites were extracted from axenic cultures of these isolates and about 45% of them were identified as new products, representing a various assortment of chemical classes such as alkaloids, meroterpenoids, isocoumarins, anthraquinones, xanthones, phenalenones, benzofurans, azaphilones, and other polyketides. This impressive chemodiversity and the broad range of biological properties that have been disclosed in preliminary assays qualify these fungi as a valuable source of products to be exploited for manifold biotechnological applications.

Spirocyclic polyketides from the marine fungus Talaromyces sp. CX11

Three new spirocyclic polyketides, talaromyacins A - C, were identified from the endophytic fungus Talaromyces sp. CX11. Their structures including absolute configurations were determined by extensive spectroscopic analysis, Snatzke's method and quantum chemical calculations. Talaromyacin A is identical to the known sequoiamonascin A, for which a structural revision is required.

Research advances in the structures and biological activities of secondary metabolites from Talaromyces

The genus Talaromyces belongs to the phylum Ascomycota of the kingdom Fungi. Studies have shown that Talaromyces species yield many kinds of secondary metabolites, including esters, terpenes, steroids, alkaloids, polyketides, and anthraquinones, some of which have biological activities such as anti-inflammatory, bacteriostatic, and antitumor activities. The chemical constituents of fungi belonging to the genus Talaromyces that have been studied by researchers over the past several years, as well as their biological activities, are reviewed here to provide a reference for the development of high-value natural products and innovative uses of these resources.

Two New Cytotoxic Decalin Derivatives from Marine-Derived Fungus Talaromyces sp

Two new decalin derivatives named fusarielins O (1) and P (2), together with seven known compounds (3-9) were isolated from the crude extract of the marine-derived fungus Talaromyces sp. The planar structures of the new compounds were elucidated by comprehensive spectroscopic analyses of NMR and HR-ESI-MS. The absolute configuration of 1 was assigned by Snatzke's method and comparison of experimental and calculated electronic circular dichroism (ECD) spectra. Compounds 1-9 were evaluated for their cytotoxic activities against three tumor cell lines and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities.

Digyalipopeptide A, an antiparasitic cyclic peptide from the Ghanaian Bacillus sp. strain DE2B

During the continued isolation of different bacteria from highly diverse, low human activity environments in Ghana and the subsequent characterization and biological activity studies of their secondary metabolites, we found both Gram-positive and Gram-negative Bacillus strains to be ubiquitous and widespread. One of such strains, the Ghanaian novel Bacillus sp. strain DE2B was isolated from rhizosphere soils collected from the Digya National Park in Ghana. Chromatographic purifications of the fermented culture extract of the strain DE2B, led to the isolation of a cyclic lipopeptide, digyalipopeptide A (1). Using 1D and 2D NMR data, mass spectrometry sequence tagging, advanced Marfey's analysis, and the GNPS molecular networking we solved the full structure of digyalipopeptide A (1). We found that compound 1 is a member of a somewhat homologous series of peptides produced as a mixture by the strain containing the same amino acid sequence in the cyclic peptide backbone but differing only by the length of aliphatic fatty acid side chains. When tested against Trypanosoma brucei subsp. brucei strain GUTat 3.1 and Leishmania donovani (Laveran and Mesnil) Ross (D10), digyalipopeptide A (1) gave IC₅₀ values of 12.89 µM (suramin IC₅₀ 0.96 µM) and 4.85 µM (amphotericin B IC₅₀ 4.87 µM), respectively. Furthermore, digyalipopeptide A (1) produced IC₅₀ values of 10.07 µM (ampicillin IC₅₀ 0.18 µM) and 10.01 µM (ampicillin IC₅₀ 1.53 µM) for Staphylococcus aureus and Shigella sonnei, respectively. The selectivity and toxicity profile of compound 1 was investigated using normal cell lines, macrophages RAW 264.7. When tested against normal macrophages, compound 1 gave an IC₅₀ value of 71.32 μM. Selectivity indices (SI) were obtained by calculating the ratio of the IC₅₀ in RAW 264.7 to the IC₅₀ in the respective microbe and neglected parasite. In the presence of RAW 264.7 cell lines, compound 1 was particularly selective towards Leishmania donovani (Laveran and Mesnil) Ross (D10) with an SI value of 14.71. The bioactivity studies conducted confirm the role of these cyclic lipopeptides as defense chemicals in their natural environment and their ability to be biologically active across different species.

Talaromydien a and talaroisocoumarin A, new metabolites from the marine-sourced fungus Talaromyces sp. ZZ1616

New talaromydien A (1) and talaroisocoumarin A (2), together with nine known compounds (3 - 11), were isolated from a culture of the marine-derived Talaromyces sp. ZZ1616 in potato dextrose broth medium. Structures of the new compounds were elucidated based on their HRESIMS data, NMR spectroscopic analyses, the modified Mosher's method, ECD, ¹³C NMR and optical rotation calculations. Talaroisocoumarin A showed antimicrobial activities with MIC values of 36.0 μg/mL against methicillin-resistant Staphylococcus aureus, 32.0 μg/mL against Escherichia coli, and 26.0 μg/mL against Candida albicans.

Methods in Microbial Biodiscovery

This review presents an account of the microbial biodiscovery methodology developed and applied in our laboratory at The University of Queensland, Institute for Molecular Bioscience, with examples drawn from our experiences studying natural products produced by Australian marine-derived (and terrestrial) fungi and bacteria.

Roussoelins A and B: two phenols with antioxidant capacity from ascidian-derived fungus Roussoella siamensis SYSU-MS4723

Ascidian-derived microorganisms are a significant source of pharmacologically active metabolites with interesting structural properties. When discovering bioactive molecules from ascidian-derived fungi, two new phenols, roussoelins A (1) and B (2), and ten known polyketides (3-12) were isolated from the ascidian-derived fungus Roussoella siamensis SYSU-MS4723. The planar structure of compounds 1 and 2 was established by analysis of HR-ESIMS and NMR data. The conformational analysis of the new compounds was assigned according to coupling constants and selective gradient NOESY experiments, and absolute configurations were completed by the modified Mosher's method. Among the isolated compounds, 1, 2, and 9 showed moderate antioxidant capacity.

Graphical abstract

Two new bioactive polyphenols from the soft coral-derived fungus Talaromyces sp. SCSIO 041201

Two new polyphenols, talaversatilis A (1) and B (2), together with fifteen known compounds (3-17) were isolated from the extract of the culture broth of a soft coral-derived fungus Talaromyces sp. SCSIO 041201. The structures of these compounds were elucidated by the extensive analyses of spectroscopic data and by comparison with the reported literature. Antifouling and antibacterial activities of all purified compounds were tested and evaluated. Compounds 5 and 6 showed antifouling activity towards Bugula neritina larva, with LC₅₀ values of 3.86 μg/mL and 3.05 μg/mL, respectively. Compounds 7, 8, 10 and 13 exhibited significant antibacterial activities against E. coli, MRSA, S. aureus and E. faecalis, with MIC values ranging from 0.45 to 15.6 μg/mL.

Structure-Property Relationship Study of N-(Hydroxy)Peptides for the Design of Self-Assembled Parallel β-Sheets

The design of novel and functional biomimetic foldamers remains a major challenge in creating mimics of native protein structures. Herein, we report the stabilization of a remarkably short β-sheet by incorporating N-(hydroxy)glycine (Hyg) residues into the backbone of peptides. These peptide-peptoid hybrids form unique parallel β-sheet structures by self-assembly upon hydrogenation. Our spectroscopic and crystallographic data suggest that the local conformational perturbations induced by N-(hydroxy)amides are outweighed by a network of strong interstrand hydrogen bonds.

Talascortenes A-G, Highly Oxygenated Diterpenoid Acids from the Sea-Anemone-Derived Endozoic Fungus Talaromyces scorteus AS-242

Eight new diterpenoid acids, namely, talascortenes A-G (1-7) and 5α,9β-dihydroxyisocupressic acid (8), with four different carbon skeletons, were isolated and identified from the endozoic fungal strain Talaromyces scorteus AS-242 that was obtained from the inner fresh tissue of a deep sea Cerianthus sp. sea anemone. The structures of the new compounds were elucidated by detailed interpretation of NMR and mass spectrometric data. X-ray crystallographic analysis of compounds 1-5 and 7 confirmed their structures and absolute configurations. Compounds 1-8 showed inhibitory activities against several human, aquatic, and plant pathogens with MIC values ranging from 1 to 32 μg/mL.

Fungi: outstanding source of novel chemical scaffolds

A large number of remarkable studies on the secondary metabolites of fungi have been conducted in recent years. This review gives an overview of one hundred and sixty-seven molecules with novel skeletons and their bioactivities that have been reported in seventy-nine articles published from 2013 to 2017. Our statistical data showed that endophytic fungi and marine-derived fungi are the major sources of novel bioactive secondary metabolites.

Origins and Bioactivities of Natural Compounds Derived from Marine Ascidians and Their Symbionts

Marine ascidians are becoming important drug sources that provide abundant secondary metabolites with novel structures and high bioactivities. As one of the most chemically prolific marine animals, more than 1200 inspirational natural products, such as alkaloids, peptides, and polyketides, with intricate and novel chemical structures have been identified from ascidians. Some of them have been successfully developed as lead compounds or highly efficient drugs. Although numerous compounds that exist in ascidians have been structurally and functionally identified, their origins are not clear. Interestingly, growing evidence has shown that these natural products not only come from ascidians, but they also originate from symbiotic microbes. This review classifies the identified natural products from ascidians and the associated symbionts. Then, we discuss the diversity of ascidian symbiotic microbe communities, which synthesize diverse natural products that are beneficial for the hosts. Identification of the complex interactions between the symbiont and the host is a useful approach to discovering ways that direct the biosynthesis of novel bioactive compounds with pharmaceutical potentials.

Trivirensols: Selectively Bacteriostatic Sesquiterpene Trimers from the Australian Termite Nest-Derived Fungus Trichoderma virens CMB-TN16

The termite nest-derived fungus Trichoderma virens CMB-TN16 cultivated on rice-based media produced seven new first-in-class trimeric sesquiterpenes, trivirensols A-G (11-17). Structures inclusive of absolute configurations were assigned by detailed spectroscopic analysis and biosynthetic considerations. Although trivirensols exhibit no cytotoxicity to mammalian carcinoma cells, selected examples are bacteriostatic against vancomycin-resistant Enterococcus faecalis (VRE). Structure-activity relationship (SAR) investigations combined with in situ chemical stability studies documented bacteriostatic activity for trivirensols A (11) and B (12) and the co-metabolite divirensols A (4), B (5), and G (10), all of which share a common terminal butenolide. Significantly, SAR studies also revealed bacteriostatic activity for trivirensols C (13) and G (17) and the co-metabolite divirensol C (6), all of which share a common hydrated butenolide terminal. Of note, when exposed to VRE cell cultures, the hydrated butenolides 6, 13, and 17 undergo rapid in situ dehydration to corresponding butenolides, suggesting hydrated butenolides are a pro-drug form of the butenolide VRE bacteriostatic pharmacophore.

A new fusicoccane diterpene and a new polyene from the plant endophytic fungus Talaromyces pinophilus and their antimicrobial activities

A new fusicoccane diterpene, pinophicin A (1), and a new polyene, pinophol A (2), were isolated from the plant endophytic fungus Talaromyces pinophilus obtained from the aerial parts of Salvia miltiorrhiza. The structures and relative configurations of 1-2 were determined by the analysis of extensive spectroscopic data, chemical method, and comparison with known compounds. Compound 2 exhibited weak antibacterial activity against Bacterium paratyphosum B with an MIC value of 50 μg/mL.

Divirensols: Sesquiterpene Dimers from the Australian Termite Nest-Derived Fungus Trichoderma virens CMB-TN16

A chemical investigation of the Australian termite nest-derived fungus Trichoderma virens CMB-TN16 yielded the known sesquiterpene gliocladic acid (1), together with two new acetylated analogues, 3-acetylgliocladic acid (2) and 14-acetylgliocladic acid (3), and seven new dimeric congeners, divirensols A-G (4-10). All metabolites were identified by detailed spectroscopic analysis, supported by biosynthetic considerations, and were assessed for antibacterial and cytotoxic properties. The divirensols are examples of an exceptionally rare class of dimeric sesquiterpene, likely linked via a highly convergent biosynthetic pathway. HPLC-DAD-MS analysis of the crude fungal extract detected ions attributed to putative monomeric biosynthetic precursors.

Marine natural products

Covering: January to December 2017This review covers the literature published in 2017 for marine natural products (MNPs), with 740 citations (723 for the period January to December 2017) 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 (1490 in 477 papers for 2017), 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. Geographic distributions of MNPs at a phylogenetic level are reported.

Biological and Chemical Diversity of Ascidian-Associated Microorganisms

Ascidians are a class of sessile filter-feeding invertebrates, that provide unique and fertile niches harboring various microorganisms, such as bacteria, actinobacteria, cyanobacteria and fungi. Over 1000 natural products, including alkaloids, cyclic peptides, and polyketides, have been isolated from them, which display diverse properties, such as antibacterial, antifungal, antitumor, and anti-inflammatory activities. Strikingly, direct evidence has confirmed that ~8% of natural products from ascidians are actually produced by symbiotic microorganisms. In this review, we present 150 natural products from microorganisms associated with ascidians that have been reported up to 2017.

Talaropeptides A-D: Structure and Biosynthesis of Extensively N-methylated Linear Peptides From an Australian Marine Tunicate-Derived Talaromyces sp

An Australian marine tunicate-derived fungus, Talaromyces sp. CMB-TU011 was subjected to a program of analytical microbioreactor (MATRIX) cultivations, supported by UHPLC-QTOF profiling, to reveal conditions for producing a new class of extensively N-methylated 11-12 residue linear peptides, talaropeptides A-D (2-5). The structures for 2-5, inclusive of absolute configurations, were determined by a combination of detailed spectroscopic and chemical (e.g., C₃ and C₁₈ Marfey's) analyses. We report on the biological properties of 2-5, including plasma stability, as well as antibacterial, antifungal and cell cytotoxicity. The talaropeptide mega non-ribosomal peptide synthetase (NRPS) is described, as second only in size to that for the fungus-derived immunosuppressant cyclosporine (an 11-residue extensively N-methylated cyclic peptide).

Natural Cyclic Peptides as an Attractive Modality for Therapeutics: A Mini Review

Peptides are important biomolecules which facilitate the understanding of complex biological processes, which in turn could be serendipitous biological targets for future drugs. They are classified as a unique therapeutic niche and will play an important role as fascinating agents in the pharmaceutical landscape. Until now, more than 40 cyclic peptide drugs are currently in the market, and approximately one new cyclopeptide drug enters the market annually on average. Interestingly, the majority of clinically approved cyclic peptides are derived from natural sources, such as peptide antibiotics and human peptide hormones. In this report, the importance of cyclic peptides is discussed, and their role in drug discovery as interesting therapeutic biomolecules will be highlighted. Recently isolated naturally occurring cyclic peptides from microorganisms, sponges, and other sources with a wide range of pharmacological properties are reviewed herein.

Total synthesis of the proposed structure of talarolide A

The proposed structure of talarolide A, a cycloheptapeptide featuring a hydroxamate moiety within the peptide backbone, was successfully synthesized.

Structural Diversity and Biological Activities of Fungal Cyclic Peptides, Excluding Cyclodipeptides

Cyclic peptides are cyclic compounds formed mainly by the amide bonds between either proteinogenic or non-proteinogenic amino acids. This review highlights the occurrence, structures and biological activities of fungal cyclic peptides (excluding cyclodipeptides, and peptides containing ester bonds in the core ring) reported until August 2017. About 293 cyclic peptides belonging to the groups of cyclic tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-, undeca-, dodeca-, tetradeca-, and octadecapeptides as well as cyclic peptides containing ether bonds in the core ring have been isolated from fungi. They were mainly isolated from the genera Aspergillus, Penicillium, Fusarium, Acremonium and Amanita. Some of them were screened to have antimicrobial, antiviral, cytotoxic, phytotoxic, insecticidal, nematicidal, immunosuppressive and enzyme-inhibitory activities to show their potential applications. Some fungal cyclic peptides such as the echinocandins, pneumocandins and cyclosporin A have been developed as pharmaceuticals.