Biosynthetic Implications Research Articles

Total Synthesis of the Norcembranoid Scabrolide B and Its Transformation into Sinuscalide C, Ineleganolide, and Horiolide.

It was recognized only recently that the sister norcembranoids scabrolides A and B have notably different carbotricyclic scaffolds. Therefore, our synthesis route leading to scabrolide A could not be extended to its sibling. Rather, a conceptually new approach had to be devised that relied on a challenging intramolecular alkenylation of a ketone to forge the congested central cycloheptene ring at the bridgehead enone site; the required cyclization precursor was attained by a lanthanide-catalyzed Mukaiyama-Michael addition. The dissonant 1,4-oxygenation pattern was then installed by allylic rearrangement/oxidation of the enone, followed by suprafacial 1,3-transposition. Synthetic scabrolide B was transformed into sinuscalide C by dehydration and into ineleganolide by base-mediated isomerization/oxa-Michael addition, which has potential biosynthetic implications; under basic conditions, the latter compound converts into horiolide by an intricate biomimetic cascade.

Crossiellidines A-F, Unprecedented Pyrazine-Alkylguanidine Metabolites with Broad-Spectrum Antibacterial Activity from Crossiella sp.

Crosiellidines are intriguing pyrazine-alkylguanidine metabolites isolated from the minor actinomycete genus Crossiella. Their structures present an unprecedented 2-methoxy-3,5,6-trialkyl pyrazine scaffold and uncommon guanidine prenylations, including an exotic O-prenylated N-hydroxyguanidine moiety. The novel substitution pattern of the 2-methoxypyrazine core inaugurates a new class of naturally occurring pyrazine compounds, the biosynthetic implications of which are discussed herein. Isotopic feeding and genome analysis allowed us to propose a biosynthetic pathway from arginine. The crossiellidines exhibited remarkable, broad-spectrum antibacterial activity.

Discovery of pentaene polyols by the activation of an enediyne gene cluster: biosynthetic implications for 9-membered enediyne core structures.

The identification and characterization of enediyne polyketide synthases (PKSEs) revealed that PKSE-bound polyene is a common intermediate, while its subsequent tailoring steps to enediyne cores remain obscure. Herein, we report pentaene polyols 5-7 and cinnamic acid derivatives 8 and 9 biosynthesized from an activated enediyne biosynthetic gene cluster in Streptomyces sp. CB02130. The C-1027 pksE could partially complement production of these polyene polyols in a CB02130 mutant where the native pksE is inactivated. The yields of 5-7 were improved by increasing the cellular pool of l-Phe through either gene inactivation of a prephenate dehydrogenase WlsPDH or supplementation of l-Phe. A flexible ammonia lyase WlsC4 is responsible for biosynthesis of 8 and 9 from l-Phe. The co-localization of wlsPDH and PKSE gene cassette supports their close evolutionary relationships and an enediyne genome mining strategy using WlsPDH. These findings not only provide a facile approach to activate silent enediyne BGCs, but suggest that a polyene epoxide intermediate may be formed for construction of 9-membered enediyne macrocycles.

Total syntheses of spiroviolene and spirograterpene A: a structural reassignment with biosynthetic implications.

The recent natural product isolates spiroviolene and spirograterpene A are two relatively non-functionalized linear triquinane terpenes with a large number of structural homologies. Nevertheless, three significant areas of structural disparity exist based on their original assignments, one of which implies a key stereochemical divergence early in their respective biosyntheses. Herein, using two known bicyclic ketone intermediates, a core Pd-catalyzed Heck cyclization sequence, and several chemoselective transformations, we describe concise total syntheses of both natural product targets and propose that the structure of spiroviolene should be reassigned. As a result, these natural products possess greater homology than previously anticipated.

Chemoenzymatic, biomimetic total synthesis of (-)-rugulosin B, C and rugulin analogues and their biosynthetic implications.

Herein, we report the chemoenzymatic synthesis of a heterodimeric (-)-rugulosin B, homodimeric (-)-rugulosin C, and several rugulin analogues in three to four steps starting from anthraquinones. This work supports dimerization between variously substituted putative monomeric intermediates during the biosynthesis of naturally occurring (+)-rugulosin B and C.

Structure Determination, Functional Characterization, and Biosynthetic Implications of Nybomycin Metabolites from a Mining Reclamation Site-Associated Streptomyces.

We report the isolation and characterization of three new nybomycins (nybomycins B-D, 1-3) and six known compounds (nybomycin, 4; deoxynyboquinone, 5; α-rubromycin, 6; β-rubromycin, 7; γ-rubromycin, 8; and [2α(1E,3E),4β]-2-(1,3-pentadienyl)-4-piperidinol, 9) from the Rock Creek (McCreary County, KY) underground coal mine acid reclamation site isolate Streptomyces sp. AD-3-6. Nybomycin D (3) and deoxynyboquinone (5) displayed moderate (3) to potent (5) cancer cell line cytotoxicity and displayed weak to moderate anti-Gram-(+) bacterial activity, whereas rubromycins 6-8 displayed little to no cancer cell line cytotoxicity but moderate to potent anti-Gram-(+) bacterial and antifungal activity. Assessment of the impact of 3 or 5 cancer cell line treatment on 4E-BP1 phosphorylation, a predictive marker of ROS-mediated control of cap-dependent translation, also revealed deoxynyboquinone (5)-mediated downstream inhibition of 4E-BP1p. Evaluation of 1-9 in a recently established axolotl embryo tail regeneration assay also highlighted the prototypical telomerase inhibitor γ-rubromycin (8) as a new inhibitor of tail regeneration. Cumulatively, this work highlights an alternative nybomycin production strain, a small set of new nybomycin metabolites, and previously unknown functions of rubromycins (antifungal activity and inhibition of tail regeneration) and also provides a basis for revision of the previously proposed nybomycin biosynthetic pathway.

Direct and Metal-Catalyzed Photochemical Dimerization of the Phthalide (Z)-Ligustilide Leading to Both [2 + 2] and [4 + 2] Cycloadducts: Application to Total Syntheses of Tokinolides A-C and Riligustilide.

Synthetically derived (Z)-ligustilide (1) has been subjected to photochemically-promoted dimerization processes under a range of conditions. By such means, varying distributions of the dimeric natural products tokinolides A-C (4, 3, and 6, respectively) and riligustilide (5) as well certain related (isomeric) compounds have been obtained. The structures of three of them have been confirmed by single-crystal X-ray analysis. The biosynthetic implications of the outcomes of this study are discussed.

Asymmetric Synthesis of Natural cis-Dihydroarenediols Using Tetrahydroxynaphthalene Reductase and Its Biosynthetic Implications.

Asymmetric reduction of hydroxynaphthoquinones to secondary metabolites, (3 S,4 R)-3,4,8- and (2 S,4 R)-2,4,8-trihydroxy-1-tetralone, a putative biosynthetic diketo intermediate and a probable natural analogue, (3 S,4 R)-7-acetyl-3,4,8-trihydroxy-6-methyl-3,4-dihydronaphthalene-1(2 H)-one, using NADPH-dependent tetrahydroxynaphthalene reductase (T4HNR) of Magnaporthe grisea is described. This work implies the involvement of T4HNR or related enzymes during the (bio)synthesis of other dihydroarenediols by reduction of the hydroxynaphthoquinone scaffold containing substrates.

The biosynthetic implications of late-stage condensation domain selectivity during glycopeptide antibiotic biosynthesis.

Non-ribosomal peptide synthesis is a highly important biosynthetic pathway for the formation of many secondary metabolites of medical relevance. Due to the challenges associated with the chemical synthesis of many of the products of these assembly lines, understanding the activity and selectivity of non-ribosomal peptide synthetase (NRPS) machineries is an essential step towards the redesign of such machineries to produce new bioactive peptides. Whilst the selectivity of the adenylation domains responsible for amino acid activation during NRPS synthesis has been widely studied, the selectivity of the essential peptide bond forming domains - known as condensation domains - is not well understood. Here, we present the results of a combination of in vitro and in vivo investigations into the final condensation domain from the NRPS machinery that produces the glycopeptide antibiotics (GPAs). Our results show that this condensation domain is tolerant for a range of peptide substrates and even those with unnatural stereochemistry of the peptide C-terminus, which is in contrast to the widely ascribed role of these domains as a stereochemical gatekeeper during NRPS synthesis. Furthermore, we show that this condensation domain has a significant preference for linear peptide substrates over crosslinked peptides, which indicates that the GPA crosslinking cascade targets the heptapeptide bound to the final module of the NRPS machinery and reinforces the role of the unique GPA X-domain in this process. Finally, we demonstrate that the peptide bond forming activity of this condensation domain is coupled to the rate of amino acid activation performed by the subsequent adenylation domain. This is a significant result with implications for NRPS redesign, as it indicates that the rate of amino acid activation of modified adenylation domains must be maintained to prevent unwanted peptide hydrolysis from the NRPS due to a loss of the productive coupling of amino acid selection and peptide bond formation. Taken together, our results indicate that assessing condensation domain activity is a vital step in not only understanding the biosynthetic logic and timing of NRPS-mediated peptide assembly, but also the rules which redesign efforts must obey in order to successfully produce functional, modified NRPS assembly lines.

Isolation of a new indoxyl alkaloid, Amoenamide B, from Aspergillus amoenus NRRL 35600: Biosynthetic implications and correction of the structure of Speramide B

A new prenylated indoxyl alkaloid, Amoenamide B (1), was isolated from Aspergillus amoenus NRRL 35600 along with Asperochramide A (2). Although many prenylated oxindole alkaloids, containing bicyclo[2.2.2]diazaoctane cores, have been isolated from the fungus of the genera Aspergillus and Penicillium to date, 1 is the fourth compound with the indoxyl unit containing the cores. During the structure elucidation of 1, we found that the planar structure matched to that of Speramide A (3), isolated from A. ochraceus KM007, but the reported structure of 3 was incorrect and turned out to be that of Taichunamide H (4), recently isolated from A. versicolor HDN11-84.

Rapid Generation of Molecular Complexity by Chemical Synthesis: Highly Efficient Total Synthesis of Hexacyclic Alkaloid (-)-Chaetominine and Its Biosynthetic Implications.

The efficiency becomes a key issue in today's natural product total synthesis. While biomimetic synthesis is one of the most elegant strategies to achieve synthetic efficiency and thus to approach the ideal synthesis, most biogenetic pathways are unknown or unconfirmed. In this account, we demonstrate, through the shortest and also the most efficient asymmetric total syntheses of the hexacyclic alkaloid (-)-chaetominine to date, that on the basis of biogenetic thinking, one can develop quite efficient bio-inspired total synthesis, which in turn serves to suggest and chemically validate plausible biosynthetic routes for the natural product. The synthetic strategy thus developed is also inspiring for the development of other synthetic methods and efficient total synthesis of other natural products.

Chemical Transformations of the Fungal Meroterpenoid Dhilirolide A Reveal Skeletal Degradation and Rearrangement Reactions with Biosynthetic Implications.

Treatment of the fungal meroterpenoid dhilirolide A (1) with either sodium azide or perchloric acid results in conversion of the dhilirane carbon skeleton of 1 to the 14,15-dinordhilirane carbon skeleton of the products 5-7, with and without concomitant transfer of an acetyl residue to form a C-9 acetate ester. The discovery of these transformations, which are vinylogous retro-Claisen-type condensations, suggests an efficient biogenetic route to 14,15-dinordhiliranes such as dhilirolide K (3).

ORF7 from Amycolatopsis orientalis catalyzes decarboxylation of Nδ-methylarginine and amine oxidation of arginine: Biosynthetic implications

A key step in the biosynthesis of the polyene polyketide ECO-0501 by Amycolatopsis orientalis ATCC 43491 is thought to involve oxidative decarboxylation of arginine or Nδ-methylarginine to the corresponding primary amide. This reaction is the centerpiece of a recently identified biosynthetic cassette that generates 4-guanidinobutyryl thioesters to serve as starter units for polyketide synthesis. We examined the reaction of ORF7, the predicted ECO-0501 biosynthetic decarboxylase, with arginine, and saw no evidence of decarboxylation. Instead, we observed exclusive amine oxidation to generate 2-oxoarginine, with a kcat/KM,Arg of 5.6×106M−1s−1, typical of values measured for physiological amino acid decarboxylases. In contrast, when ORF7 was incubated with Nδ-methylarginine, we observed exclusive decarboxylation to generate 4-(N1-methylguanidino)butyramide. These differing reactive pathways provide insight into the biosyntheses of guanidinobutyryl-derived polyketides and demonstrate the biosynthetic versatility of arginine-processing decarboxylases. In addition, it suggests that ORF7 may be an incisive model system for dissecting the determinants of flavoprotein-catalyzed oxidase and monooxygenase modes of reactivity.

ChemInform Abstract: Complexity Generation by Chemical Synthesis: A Five‐Step Synthesis of (‐)‐Chaetominine from L‐Tryptophan and Its Biosynthetic Implications.

AbstractChaetominine (I) is prepared in five steps with an overall yield of 23.2%.

5‐Aminopenta‐2,4‐dienals: Synthesis, Activation towards Nucleophiles, Molecular Modeling and Biosynthetic Implications in Relation to the Manzamine Alkaloids

AbstractSubstituted 5‐aminopentadienals and glutaconaldehydes are key elements postulated in the biosynthesis of the diverse class of manzamine‐type alkaloids. The activation of 5‐aminopentadienals into electrophilic iminium salts and their subsequent reactivity towards various nucleophiles has permitted the synthesis of a series of unsaturated compounds sometimes accompanied by cascades of rearrangements. Molecular modeling of these systems carried out using DFT calculations of HOMO/LUMO was in agreement with the experimental results indicating that strong electrophilic agents, such as POCl3 are required to turn 5‐aminopentadienals into electrophiles. New examples of glutaconaldehyde reactivity, especially towards pyridinium salts, are presented and biosynthetic considerations are kept in mind throughout this study.

Complexity generation by chemical synthesis: a five-step synthesis of (−)-chaetominine from l-tryptophan and its biosynthetic implications

We demonstrated, for the first time, that on the basis of chemistry principles, the hexacyclic peptidyl alkaloid (−)-chaetominine (1) can be synthesized in a straightforward manner from L-Trp. The approach features the efficient generation of molecular complexity via a tandem C3/C14 syn-selective epoxidation (dr = 3:2)–annulative ring-opening reaction and a regioselective epimerization at C14. The successful production of (−)-chaetominine (1) from L-Trp could be helpful for revealing how the configuration of L-tryptophan becomes inverted in the biosynthetic pathway of (−)-chaetominine (1).

Particular behavior of ‘C 6C 2 units’ in the Chichibabin pyridine synthesis and biosynthetic implications

Several aspects of the unusual behavior of C 6C 2 aldehydes and amines during the formation of pyridiniums in analogy with the historical Chichibabin pyridine synthesis are clarified in this Letter. Interesting biosynthetic consequences are also discussed within two classes of polycyclic alkaloids of marine origin.

ChemInform Abstract: Novel Tryptophan Metabolites, Chromoazepinone A (I), B (II) and C (III), Produced by a Blocked Mutant of Chromobacterium violaceum, the Biosynthetic Implications and the Biological Activity of Chromoazepinone A and B.

ChemInformVolume 41, Issue 49 Natural Products ChemInform Abstract: Novel Tryptophan Metabolites, Chromoazepinone A (I), B (II) and C (III), Produced by a Blocked Mutant of Chromobacterium violaceum, the Biosynthetic Implications and the Biological Activity of Chromoazepinone A and B. Takaaki Mizuoka, Takaaki Mizuoka Dep. Appl. Biol. Chem., Fac. Agric., Niigata Univ., Ikarashi, Niigata 950-21, JapanSearch for more papers by this authorKazufumi Toume, Kazufumi Toume Dep. Appl. Biol. Chem., Fac. Agric., Niigata Univ., Ikarashi, Niigata 950-21, JapanSearch for more papers by this authorMasami Ishibashi, Masami Ishibashi Dep. Appl. Biol. Chem., Fac. Agric., Niigata Univ., Ikarashi, Niigata 950-21, JapanSearch for more papers by this authorTsutomu Hoshino, Tsutomu Hoshino Dep. Appl. Biol. Chem., Fac. Agric., Niigata Univ., Ikarashi, Niigata 950-21, JapanSearch for more papers by this author Takaaki Mizuoka, Takaaki Mizuoka Dep. Appl. Biol. Chem., Fac. Agric., Niigata Univ., Ikarashi, Niigata 950-21, JapanSearch for more papers by this authorKazufumi Toume, Kazufumi Toume Dep. Appl. Biol. Chem., Fac. Agric., Niigata Univ., Ikarashi, Niigata 950-21, JapanSearch for more papers by this authorMasami Ishibashi, Masami Ishibashi Dep. Appl. Biol. Chem., Fac. Agric., Niigata Univ., Ikarashi, Niigata 950-21, JapanSearch for more papers by this authorTsutomu Hoshino, Tsutomu Hoshino Dep. Appl. Biol. Chem., Fac. Agric., Niigata Univ., Ikarashi, Niigata 950-21, JapanSearch for more papers by this author First published: 11 November 2010 https://doi.org/10.1002/chin.201049207Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume41, Issue49December 7, 2010 RelatedInformation

Conformational Studies on Rotenoid and Its Biosynthetic Implications

The conformational studies for three rotenone isomers, using a simple rotenoids model has been analyzed by DFT method in B3LYP level of theory and 6-31G∗ basis set to obtain energy. This study shows how a systematic theoretical conformational analysis contributes to understanding molecular level of chemical processes. The gas phase structures are discussed based on thermodynamic values. The results supported that the biological effects of rotenone can be a consequence of conformational restriction and cis preference. The significance of these results is identifying the rotenone toxicity mechanism.

Novel tryptophan metabolites, chromoazepinone A, B and C, produced by a blocked mutant of Chromobacterium violaceum, the biosynthetic implications and the biological activity of chromoazepinone A and B

Chromobacterium violaceum produces tryptophan metabolites, purple pigments of violacein and deoxyviolacein. A blocked mutant was prepared with N-methyl-N'-nitrosoguanidine to gain insights into the biosynthetic mechanisms of the pigments. Five tryptophan metabolites were isolated: three novel compounds, named chromoazepinone A, B and C and two known compounds, chromopyrrolic acid and arcyriarubin A. The structure determinations of the three novel compounds are described. The biosynthetic pathways of these metabolites are proposed on the basis of the findings about violacein biosynthesis. Chromoazepinone A and B were found to have an interesting effect of inhibition of Wnt signal transcriptional activity, which is implicated in the formation of numerous tumors when aberrantly activated.