Nodulisporic acids D-F: structure, biological activities, and biogenetic relationships

Antiviral and cytotoxic indole diterpenoids from the antarctic sponge-derived fungus Aspergillus candidus HDN15-152

One new indole diterpenoid, ascandinine T (1), and three known analogues (2-4) were isolated from an Antarctic sponge-derived fungus Aspergillus candidus HDN15-152. The structures, including absolute configurations, were established based on NMR, HRESIMS, and electronic circular dichroism (ECD) calculations. All isolated compounds were tested for antiviral and anticancer activity. Compound 4 displayed antiviral activity against influenza A virus (IAV) of A/PR/8/34(H1N1) strain with an IC50 value of 39.2 μM, while compound 2 showed cytotoxicity against NCI-H446, NCI-H446/EP and L-02 cells with IC50 values ranging from 9.77 to 13.91 μM.

Seco-pimarane diterpenoids and androstane steroids from an endophytic Nodulisporium fungus derived from Cyclosorus parasiticus

Five previously undescribed specialized metabolites, including three 9,11-seco-pimarane diterpenoids, nodulisporenones A-C, and two androstane steroids, nodulisporisterones A and B, together with previously described ergosterol derivatives, dankasterone A and demethylincisterol A₃, were isolated from solid cultures of the endophytic fungus Nodulisporium sp. SC-J597. Their structures including absolute configurations were elucidated by extensive spectroscopic analysis and theoretical calculations of electronic circular dichroism spectra. Among them, nodulisporenones A and B are the first examples of seco-pimarane diterpenoids that is cyclized to form an unprecedented diterpenoid lactone scaffold and nodulisporisterones A and B represent the first normal C₁₉ androstane steroids of fungal origin. Nodulisporisterone B exhibited potent inhibitory effect on the production of NO in LPS-stimulated RAW264.7 macrophages (IC₅₀ = 2.95 μM). This compound, together with the two known ergosterol derivatives, also displayed cytotoxicity against A549, HeLa, HepG2 and MCF-7 cancer cell lines with IC₅₀ values of 5.2-16.9 μM.

Biosynthesis of indole diterpenes: a reconstitution approach in a heterologous host

Covering: 2013 to 2022In this review, we provide an overview elucidating the biosynthetic pathway and heterologous production of fungal indole diterpenes (IDTs). Based on the studies of six IDT biosynthesis, we extracted nature's strategy: (1) two-stage synthesis for the core scaffold and platform intermediates, and (2) late-stage modifications for installing an additional cyclic system on the indole ring. Herein, we describe reconstitution studies applying this strategy to the synthesis of highly elaborated IDTs. We also discuss its potential for future biosynthetic engineering.

The chemical structures and biological activities of indole diterpenoids

Indole diterpenoids (IDTs) are an essential class of structurally diverse fungal secondary metabolites, that generally appear to be restricted to a limited number of fungi, such as Penicillium, Aspergillus, Claviceps, and Epichloe species, etc. These compounds share a typical core structure consisting of a cyclic diterpene skeleton of geranylgeranyl diphosphate (GGPP) and an indole ring moiety derived from indole-3-glycerol phosphate (IGP). 3-geranylgeranylindole (3-GGI) is the common precursor of all IDTs. On this basis, it is modified by cyclization, oxidation, and prenylation to generate a large class of compounds with complex structures. These compounds exhibit antibacterial, anti-insect, and ion channel inhibitory activities. We summarized 204 compounds of IDTs discovered from various fungi over the past 50 years, these compounds were reclassified, and their biological activities were summarized. This review will help to understand the structural diversity of IDTs and provide help for their physiological activities.

Biosynthesis of Nodulisporic Acids: A Multifunctional Monooxygenase Delivers a Complex and Highly Branched Array

Nodulisporic acids (NAs) are structurally complex potent antiinsectan indole diterpenes. We previously reported the biosynthetic gene cluster for these metabolites in Hypoxylon pulicicidum and functionally characterised the first five steps of the biosynthetic pathway. Here we reveal a highly complex biosynthetic array, furnishing multiple end products through expression of cluster components in Penicillium paxilli. We show that seven additional cluster-encoded gene products comprise the biosynthetic machinery that elaborate precursor NAF in this highly branched pathway. The combined action of these enzymes delivers 37 NA congeners including four major end products, NAA, NAA₁ , NAA₂ and NAA₄ . The plethora of intermediates arises due to modification of the carboxylated prenyl tail by a single promiscuous P450 monooxygenase, NodJ, a pivotal branchpoint enzyme which produces four distinct biosynthetic products giving rise to the complex metabolic grid that characterises NA biosynthesis.

The Biosynthesis Related Enzyme, Structure Diversity and Bioactivity Abundance of Indole-Diterpenes: A Review

Indole diterpenes are a large class of secondary metabolites produced by fungi, possessing a cyclic diterpenoid backbone and an indole moiety. Novel structures and important biological activity have made indole diterpenes one of the focuses of synthetic chemists. Although the discovery, identification, structural diversity, biological activity and especially structure–activity relationship of indole diterpenes have been reported in some papers in recent years, they are absent of a systematic and comprehensive analysis, and there is no elucidation of enzymes related to this kind of natural product. Therefore, it is necessary to summarize the relevant reports to provide new perspectives for the following research. In this review, for the first time, the function of related synthases and the structure–activity relationship of indole diterpenes are expounded, and the recent research advances of them are emphasized.

Synthesis of rearranged indole diterpenes of the paxilline type

Covering: up to 2021Rearranged indole diterpenes of the paxilline type comprise a large group of fungal metabolites that possess diverse structural features and potentially useful biological effects. The unique indoloterpenoid motif, which is common to all congeners, was first confirmed by crystallographic studies of paxilline. This family of natural products has fascinated organic chemists for the past four decades and has inspired numerous syntheses and synthetic approaches. The present review highlights efforts that have laid the foundation and introduced new directions to this field of natural product synthesis. The introduction includes a summary of biosynthetic considerations and biological activities, the main body of the manuscript provides a detailed discussion of selected syntheses, and the review concludes with a brief outlook on the future of the field.

Recent advances in the total syntheses of indole diterpenoids

Indole diterpenoids constitute a large family of natural products that are characterized by a hybrid molecular architecture consisting of an indole nucleus and diterpenoid moiety. Their pharmacologically and agriculturally important biological properties as well as intriguing molecular architectures have attracted much attention from many synthetic organic chemists. In 2012, we succeeded in the concise total synthesis of a paspalane-type indole diterpenoid, namely paspalinine, by developing a highly efficient indole ring formation protocol. After the report of this total synthesis, 4 research groups achieved the total syntheses of other paspalane- and nodulisporane-type indole diterpenoids using current state-of-the-art methods. This review summarizes the total syntheses of the paspalane- and nodulisporane-type indole diterpenoids that were described in the last 10 years.

Indole-based alkaloids from Ophiocordyceps xuefengensis

Seven undescribed indole-based alkaloids, xuefengins A-D and xuefenglasins A-C, were isolated from natural Ophiocordyceps xuefengensis, along with six known alkaloids. Their structures were elucidated by comprehensive spectroscopy, with absolute configurations confirmed by comparison with calculated electronic circular dichroism spectra. Eleven of the isolates were tested for cytotoxicity against the U937, NB4, MCF-7, Hep G2, and A549 cancer cell lines. Two compounds exhibited moderate activities, with IC₅₀ values of 2.83-25.68 μM and 1.54-12.16 μM. Further pharmacological studies showed that these two compounds inhibit cell proliferation by inducing apoptosis, and decreasing p38 and caspase-3 levels in A549 cells.

Total synthesis of alkaloids using both chemical and biochemical methods

A chemoenzymatic approach to synthesize structurally complex natural alkaloids (tetrahydroisoquinoline antibiotics, indole diterpenes, and monoterpene indole alkaloids) has been reviewed.

Nodulisporic acid E biosynthesis: in vivo characterisation of NodD1, an indole-diterpene prenyltransferase that acts on an emindole SB derived indole-diterpene scaffold

Prenylation of aromatic compounds is a key tailoring reaction in biosynthesis of bioactive indole-diterpenes. Here, we identify NodD1 as the enzyme responsible for the bisprenylation of nodulisporic acid F. This prenyltransferase showed a preference for its natural indole-diterpene substrate whereas other related enzymes were not able to catalyse this conversion.

Indole Diterpenoids from an Endophytic Penicillium sp

A chemical investigation of the endophyte Penicillium sp. (strain ZO-R1-1), isolated from roots of the medicinal plant Zingiber officinale, yielded nine new indole diterpenoids (1-9), together with 13 known congeners (10-22). The structures of the new compounds were elucidated by 1D and 2D NMR analysis in combination with HRESIMS data. The absolute configuration of the new natural products 1, 3, and 7 was determined using the TDDFT-ECD approach and confirmed for 1 by single-crystal X-ray determination through anomalous dispersion. The isolated compounds were tested for cytotoxicity against L5178Y, A2780, J82, and HEK-293 cell lines. Compound 1 was the most active metabolite toward L5178Y cells, with an IC₅₀ value of 3.6 μM, and an IC₅₀ against A2780 cells of 8.7 μM. Interestingly, 1 features a new type of indole diterpenoid scaffold with a rare 6/5/6/6/6/6/5 heterocyclic system bearing an aromatic ring C, which is suggested to be important for the cytotoxic activity of this natural product against L5278Y and A2780 cells.

Twelve-Step Asymmetric Synthesis of (-)-Nodulisporic Acid C

A short, enantioselective synthesis of (-)-nodulisporic acid C is described. The route features two highly diastereoselective polycyclizations en route to the terpenoid core and the indenopyran fragment and a highly convergent assembly of a challenging indole moiety. Application of this chemistry allows for a 12-step synthesis of the target indoloterpenoid from commercially available material.

Total Synthesis of (-)-Nodulisporic Acids D, C, and B: Evolution of a Unified Synthetic Strategy

A unified synthetic strategy leading to the total synthesis of (-)-nodulisporic acids D, C, and B is described. Key synthetic transformations include a nickel-chromium-mediated cyclization, an aromatic ring functionalization employing a novel copper-promoted alkylation, a palladium-catalyzed cross-coupling cascade/indole ring construction, and a palladium-mediated regio- and diastereoselective allylic substitution/cyclization reaction, the latter to construct ring D.

Drechmerin H, a novel 1(2), 2(18)-diseco indole diterpenoid from the fungus Drechmeria sp. as a natural agonist of human pregnane X receptor

A novel 1(2), 2(18)-diseco indole diterpenoid, drechmerin H (1), was isolated from the fermentation broth of Drechmeria sp. together with a new indole diterpenoid, 2'-epi terpendole A (3), and a known analogue, terpendole A (2). Their structures were determined by HRESIMS, 1D and 2D NMR, ECD, and X-ray single crystal diffraction analyses as well as quantum chemical calculation. The abosulte configuration of terpendole A (2) was determined for the first time. Compound 1 displayed the significant agonistic effect on pregnane X receptor (PXR) with EC₅₀ value of 134.91 ± 2.01 nM, and its interaction with PXR was investigated by molecular docking. Meantime, a plausible biosynthetic pathway for compounds 1-3 is also discussed in the present work.

Indole diterpenoids from the endophytic fungus Drechmeria sp. as natural antimicrobial agents

A fungal strain, Drechmeria sp., was isolated from the root of Panax notoginseng. Totally, seven new indole diterpenoids, drechmerins A-G (1-7), were isolated from the fermentation broth of Drechmeria sp. together with four known analogues (8-11). Their structures were determined on the basis of 1D and 2D NMR and electronic circular dichroism (ECD) spectroscopic analyses as well as theoretical calculations. All the isolated compounds were evaluated for their antimicrobial activities against Candida albicans, Staphylococcus aureus, Bacillus cereus, B. subtillis, Pseudomonas aeruginosa, and Klebsiella pneumonia, respectively. Drechmerin B (2) displayed antimicrobial activity against C. albicans with an MIC value of 12.5 μg/mL. Molecular docking was used to investigate interactions of peptide deformylase with compounds 1-3, 5-7, 9, and 10.

Draft Genome Sequence of the Filamentous Fungus Hypoxylon pulicicidum ATCC 74245

Hypoxylon pulicicidum strain MF5954 (ATCC 74245) (formerly classified as Nodulisporium sp.) is a filamentous fungal species known for its production of the secondary metabolite nodulisporic acid A. We present here the 41.5-Mb draft genome sequence for this organism.

Total synthesis of architecturally complex indole terpenoids: strategic and tactical evolution

Indole terpenes have attracted the interests of synthetic chemists due to their complex architectures and potent biological activities. Examples of total syntheses of several indole terpenes were reviewed in this article to honor Professor KC Nicolaou.

Biosynthesis of Shearinine: Diversification of a Tandem Prenyl Moiety of Fungal Indole Diterpenes

The late-stage biosynthetic pathway of the indole diterpene shearinine involving four enzymatic reactions (JanQDOJ) was elucidated by an efficient heterologous expression system using Aspergillus oryzae. Key oxidative cyclization, forming a characteristic A/B bicyclic shearinine core by flavoprotein oxidase, was studied using a substrate analogue and a buffer containing H₂¹⁸O. These experimental data provided evidence that JanO catalyzes two-step oxidation via a hydroxylated product and that the JanO reaction involves the hydride-transfer mechanism.

Copper-catalyzed intramolecular aryl-bicyclization of diynes with diaryliodonium salts via vinyl cations

A novel protocol for the synthesis of polycyclic compounds from linear diynes and diaryliodonium salts has been realized.

A Practical, Multi-gram Synthesis of (±)-Herbindole A, (±)-Herbindole B, and (±)-Herbindole C from a Common Intermediate via 6,7-Indole Aryne Cycloaddition and Pd(0)-Catalyzed Cross-Coupling Reactions

A practical, multi-gram 10-step synthesis of racemic herbindole A, B, and C from a common intermediate is described. The key step features a remarkably regioselective C-7 metal-halogen exchange and elimination from a Bartoli-generated N-t-butyldimethylsilyl-4,6,7-tribromo-5-methylindole scaffold to afford the 6,7-indole aryne. Cycloaddition with cyclopentadiene, oxidative cleavage, and Fujimoto reduction gave a common intermediate from which all three herbindoles were readily derived. A final Pd(0)-catalyzed Negishi and Stille cross-coupling reaction at the C-4 bromide afforded each of the herbindoles on a multigram scale.

Total Synthesis of (-)-Nodulisporic Acid D

A convergent total synthesis of the architecturally complex indole diterpenoid (-)-nodulisporic acid D has been achieved. Key synthetic transformations include vicinal difunctionalization of an advanced α,β-unsaturated aldehyde to form the E,F-trans-fused 5,6-ring system of the eastern hemisphere and a cascade cross-coupling/indolization protocol leading to the CDE multisubstituted indole core.

Drugs and drug intermediates from fungi: Striving for greener processes

There is an ever-increasing demand of newer and improved drugs from biological sources to cater to the bio-pharmaceutical sector. Among various other resources, fungal species have an immense contribution owing to their potential to carry out the bio-transformations and drug synthesis in diverse conditions and in an eco-friendly manner. Advancement in the biotechnological processes has accelerated the process. Genome sequence information of various fungal species has opened newer avenues for improved and faster drug targeting and designing. The review highlights the production of pharmaceutical drugs and drug intermediates like antibiotics, anti-cancer, anti-cholesterol, anti-diabetic, immunosuppressant, anti-anxiety, anti-virals and many other drugs from fungus. Many of these have been commercialized and there are many more which are either in research or in clinical trial phase. There is a need to exploit and explore the vast biota of fungi in the hope of discovering untapped therapeutic uses of the earth's countless species of fungus.

Indole diterpenoids and isocoumarin from the fungus, Aspergillus flavus, isolated from the prawn, Penaeus vannamei

Two new indole-diterpenoids (1 and 2) and a new isocoumarin (3), along with the known β-aflatrem (4), paspalinine (5), leporin B (6), α-cyclopiazonic acid (7), iso-α-cyclopiazonic acid (8), ditryptophenaline (9), aflatoxin B₁ (10), 7-O-acetylkojic acid (11) and kojic acid (12), were isolated from the fermentation broth of the marine-derived fungus, Aspergillus flavus OUCMDZ-2205. The structures of Compounds 1–12 were elucidated by spectroscopic analyses, quantum ECD calculations and the chemical method. New Compound 1 exhibited antibacterial activity against Staphylococcus aureus with a MIC value of 20.5 μM. Both new Compounds 1 and 2 could arrest the A549 cell cycle in the S phase at a concentration of 10 μM. Compound 1 showed PKC-beta inhibition with an IC₅₀ value of 15.6 μM. In addition, the absolute configurations of the known compounds, 4–6 and leporin A (6a), were also determined for the first time.

A fungal prenyltransferase catalyzes the regular di-prenylation at positions 20 and 21 of paxilline

A putative indole diterpene biosynthetic gene cluster composed of eight genes was identified in a genome database of Phomopsis amygdali, and from it, biosynthetic genes of fusicoccin A were cloned and characterized. The six genes showed significant similarities to pax genes, which are essential to paxilline biosynthesis in Penicillium paxilli. Recombinants of the three putative prenyltransferase genes in the cluster were overexpressed in Escherichia coli and characterized by means of in vitro experiments. AmyG is perhaps a GGDP synthase. AmyC and AmyD were confirmed to be prenyltransferases catalyzing the transfer of GGDP to IGP and a regular di-prenylation at positions 20 and 21 of paxilline, respectively. AmyD is the first know example of an enzyme with this function. The Km values for AmyD were calculated to be 7.6 ± 0.5 μM for paxilline and 17.9 ± 1.7 μM for DMAPP at a kcat of 0.12 ± 0.003/s.

Regiospecificities and prenylation mode specificities of the fungal indole diterpene prenyltransferases AtmD and PaxD

We recently reported the function of paxD, which is involved in the paxilline (compound 1) biosynthetic gene cluster in Penicillium paxilli. Recombinant PaxD catalyzed a stepwise regular-type diprenylation at the 21 and 22 positions of compound 1 with dimethylallyl diphosphate (DMAPP) as the prenyl donor. In this study, atmD, which is located in the aflatrem (compound 2) biosynthetic gene cluster in Aspergillus flavus and encodes an enzyme with 32% amino acid identity to PaxD, was characterized using recombinant enzyme. When compound 1 and DMAPP were used as substrates, two major products and a trace of minor product were formed. The structures of the two major products were determined to be reversely monoprenylated compound 1 at either the 20 or 21 position. Because compound 2 and β-aflatrem (compound 3), both of which are compound 1-related compounds produced by A. flavus, have the same prenyl moiety at the 20 and 21 position, respectively, AtmD should catalyze the prenylation in compound 2 and 3 biosynthesis. More importantly and surprisingly, AtmD accepted paspaline (compound 4), which is an intermediate of compound 1 biosynthesis that has a structure similar to that of compound 1, and catalyzed a regular monoprenylation of compound 4 at either the 21 or 22 position, though the reverse prenylation was observed with compound 1. This suggests that fungal indole diterpene prenyltransferases have the potential to alter their position and regular/reverse specificities for prenylation and could be applicable for the synthesis of industrially useful compounds.

Nodulisporisteriods A and B, the first 3,4-seco-4-methyl-progesteroids from Nodulisporium sp

Two new 4-methyl-progesteroids, nodulisporisteriod A (1) and nodulisporisteriod B (2), were isolated from the extract of an endolichenic fungal strain Nodulisporium sp. (No. 65-17-2-1), along with two related metabolites, demethoxyviridin (3) and inoterpene B (4). Their structures were determined by detailed spectroscopic analyses, X-ray crystallographic analysis and comparison of the NMR data with those of the closely related compounds previously reported. Nodulisporisteriod A (1) and nodulisporisteriod B (2) possess new carbon skeletons, which are the first cases of fission at C-3,4 in 4-methyl-progesteroids. A hypothetical biosynthetic pathway for 1 and 2 was proposed. Moreover, the Aβ42 aggregation inhibitory activities of 1-4 were evaluated using standard thioflavin T (ThT) fluorescence assay with epigallocatechin gallate (EGCG) as positive control. Demethoxyviridin (3) displayed anti-Aβ42 aggregation activity with IC50 value of 13.4μM.

Total Synthesis of (±)-Cis-Trikentrin B via Intermolecular 6,7-Indole Aryne Cycloaddition and Stille Cross-Coupling

An efficient total synthesis of the annulated indole natural product (±)-cis-trikentrin B was accomplished by means of a regioselectively generated 6,7-indole aryne cycloaddition via selective metal-halogen exchange from a 5,6,7-tribromoindole. The unaffected C-5 bromine was subsequently used for a Stille cross-coupling to install the butenyl side chain and complete the synthesis. This strategy provides rapid access into the trikentrins and the related herbindoles, and represents another application of this methodology to natural products total synthesis. The required 5,6,7-indole aryne precursor was prepared using the Leimgruber-Batcho indole synthesis.

Hypoxylon pulicicidum sp. nov. (Ascomycota, Xylariales), a pantropical insecticide-producing endophyte

BACKGROUND

Nodulisporic acids (NAs) are indole diterpene fungal metabolites exhibiting potent systemic efficacy against blood-feeding arthropods, e.g., bedbugs, fleas and ticks, via binding to arthropod specific glutamate-gated chloride channels. Intensive medicinal chemistry efforts employing a nodulisporic acid A template have led to the development of N-tert-butyl nodulisporamide as a product candidate for a once monthly treatment of fleas and ticks on companion animals. The source of the NAs is a monophyletic lineage of asexual endophytic fungal strains that is widely distributed in the tropics, tentatively identified as a Nodulisporium species and hypothesized to be the asexual state of a Hypoxylon species.

METHODS AND RESULTS

Inferences from GenBank sequences indicated that multiple researchers have encountered similar Nodulisporium endophytes in tropical plants and in air samples. Ascomata-derived cultures from a wood-inhabiting fungus, from Martinique and closely resembling Hypoxylon investiens, belonged to the same monophyletic clade as the NAs-producing endophytes. The hypothesis that the Martinique Hypoxylon collections were the sexual state of the NAs-producing endophytes was tested by mass spectrometric analysis of NAs, multi-gene phylogenetic analysis, and phenotypic comparisons of the conidial states. We established that the Martinique Hypoxylon strains produced an ample spectrum of NAs and were conspecific with the pantropical Nodulisporium endophytes, yet were distinct from H. investiens. A new species, H. pulicicidum, is proposed to accommodate this widespread organism.

CONCLUSIONS AND SIGNIFICANCE

Knowledge of the life cycle of H. pulicicidum will facilitate an understanding of the role of insecticidal compounds produced by the fungus, the significance of its infections in living plants and how it colonizes dead wood. The case of H. pulicicidum exemplifies how life cycle studies can consolidate disparate observations of a fungal organism, whether from environmental sequences, vegetative mycelia or field specimens, resulting in holistic species concepts critical to the assessment of the dimensions of fungal diversity.

Application of 6,7-indole aryne cycloaddition and Pd(0)-catalyzed Suzuki-Miyaura and Buchwald-Hartwig cross-coupling reactions for the preparation of annulated indole libraries

The construction of an unprecedented class of an indole-based library, namely, a 6,7-annulated-4-substituted 93-member indole library, using a strategic combination of 6,7-indolyne cycloaddition and cross-coupling reactions under both Suzuki-Miyaura and Buchwald-Hartwig conditions is described. This work represents the first example of library development that employs the indole aryne methodology. Annulated indoles, with the exception of only a few biologically active natural products (i.e., the trikentrins, herbindoles, teleocidins, and nodulisporic acids), have no representation in the PubChem or MLSMR databases. These structural entities are therefore predicted to have unique chemical property space characteristics and a high probability of exhibiting interesting biological activity.

Discovery of the development candidate N-tert-butyl nodulisporamide: a safe and efficacious once monthly oral agent for the control of fleas and ticks on companion animals

Nodulisporic acid A (1) is a structurally complex fungal metabolite that exhibits systemic efficacy against fleas via modulation of an invertebrate specific glutamate-gated ion channel. In order to identify a nodulisporamide suitable for monthly oral dosing in dogs, a library of 335 nodulisporamides was examined in an artificial flea feeding system for intrinsic systemic potency as well as in a mouse/bedbug assay for systemic efficacy and safety. A cohort of 66 nodulisporamides were selected for evaluation in a dog/flea model; pharmacokinetic analysis correlated plasma levels with flea efficacy. These efforts resulted in the identification of the development candidate N-tert-butyl nodulisporamide (3) as a potent and efficacious once monthly oral agent for the control of fleas and ticks on dogs and cats which was directly compared to the topical agents fipronil and imidacloprid, with favorable results obtained. Multidose studies over 3 months confirmed the in vivo ectoparasiticidal efficacy and established that 3 lacked overt mammalian toxicity. Tissue distribution studies in mice using [(14)C]-labeled 3 indicate that adipose beds serve as ligand depots, contributing to the long terminal half-lives of these compounds.

Indole diterpene synthetic studies. Total synthesis of (+)-nodulisporic acid F and construction of the heptacyclic cores of (+)-nodulisporic acids A and B and (-)-nodulisporic acid D

A first-generation strategy for construction of (+)-nodulisporic acids A (1) and B (2) is described. The strategy entails union of the eastern and western hemisphere subtargets via the indole synthesis protocol developed in our laboratory. Subsequent elaboration of rings E and F, however, revealed the considerable acid instability of the C(24) hydroxyl, thereby preventing further advancement. Nonetheless, preparation of the heptacyclic core of (+)-nodulisporic acids A and B, the total synthesis of (+)-nodulisporic acid F, the simplest member of the nodulisporic acid family, and elaboration of the heptacyclic core of (-)-nodulisporic acid D were achieved.

Indole Diterpenoid Synthetic Studies. Construction of the Heptacyclic Core of (−)-Nodulisporic Acid D

[structure: see text] Construction of the heptacyclic core of (-)-nodulisporic acid D, a representative member of a recently discovered class of architecturally complex, ectoparasiticidal indole alkaloids, has been achieved. The modular synthetic strategy comprises an expedient, stereocontrolled synthesis of a tricyclic western hemisphere, in conjunction with union of an eastern hemisphere, exploiting the 2-substituted indole synthetic protocol introduced and developed in our laboratory.

Indole Diterpenoid Synthetic Studies. The Total Synthesis of (+)-Nodulisporic Acid F

[structure: see text] A stereocontrolled total synthesis of (+)-nodulisporic acid F, the simplest member of a family of novel ectoparasiticidal agents, has been achieved. Highlights of the effective modular synthetic strategy include anionic union of a tricyclic lactone with o-toluidine via our 2-substituted indole synthetic protocol, an optimized C-ring construction protocol, and a late-stage installation of the alpha,beta-unsaturated carboxylic acid side chain via the B-alkyl Suzuki-Miyaura cross-coupling tactic.