A new antibiotic SF-2370 produced by Actinomadura

Chemistry and biology of specialized metabolites produced by Actinomadura

Covering: up to the end of 2022In recent years rare Actinobacteria have become increasingly recognised as a rich source of novel bioactive metabolites. Actinomadura are Gram-positive bacteria that occupy a wide range of ecological niches. This review highlights about 230 secondary metabolites produced by Actinomadura spp., reported until the end of 2022, including their bioactivities and selected biosynthetic pathways. Notably, the bioactive compounds produced by Actinomadura spp. demonstrate a wide range of activities, including antimicrobial, antitumor and anticoccidial effects, highlighting their potential in various fields.

The synthesis of biologically active indolocarbazole natural products

Covering: up to 2020The indolocarbazoles, in particular indolo[2,3-a]pyrrolo[3,4-c]carbazole derivatives, are an important class of natural products that exhibit a wide range of biological activities. There has been a plethora of synthetic approaches to this family of natural products, leading to advances in chemical methodology, as well as affording access to molecular scaffolds central to protein kinase drug discovery programmes. In this review, we compile and summarise the synthetic approaches to the indolo[2,3-a]pyrrolo[3,4-c]carbazole derivatives, spanning the period from their isolation in 1980 up to 2020. The selected natural products include indolocarbazoles not functionalised at indolic nitrogen, pyranosylated indolocarbazoles, furanosylated indolocarbazoles and disaccharideindolocarbazoles.

Chemistry and Properties of Indolocarbazoles

The indolocarbazoles are an important class of nitrogen heterocycles which has evolved significantly in recent years, with numerous studies focusing on their diverse biological effects, or targeting new materials with potential applications in organic electronics. This review aims at providing a broad survey of the chemistry and properties of indolocarbazoles from an interdisciplinary point of view, with particular emphasis on practical synthetic aspects, as well as certain topics which have not been previously accounted for in detail, such as the occurrence, formation, biological activities, and metabolism of indolo[3,2- b]carbazoles. The literature of the past decade forms the basis of the text, which is further supplemented with older key references.

Synthetic Applications and Methodological Developments of Donor-Acceptor Cyclopropanes and Related Compounds

Donor-acceptor cyclopropanes are convenient precursors to reactive and versatile 1,3-dipoles, and have found application in the synthesis of a variety of carbo- and heterocyclic scaffolds. This perspective review details our laboratory's use of donor-acceptor cyclopropanes as intermediates toward the total synthesis of various natural products. We also discuss our work in the development of novel cycloadditions and rearrangements of donor-acceptor cyclopropanes and aziridines, as well as an example of an aryne insertion proceeding via fragmentation of a transient donor-acceptor cyclobutane.

Indolocarbazole natural products: occurrence, biosynthesis, and biological activity

The indolocarbazole family of natural products, including the biosynthetically related bisindolylmaleimides, is reviewed (with 316 references cited). The isolation of indolocarbazoles from natural sources and the biosynthesis of this class of compounds are thoroughly reviewed, including recent developments in molecular genetics, enzymology and metabolic engineering. The biological activities and underlying modes of action displayed by natural and synthetic indolocarbazoles is also presented, with an emphasis on the development of analogs that have entered clinical trials for its future use against cancer or other diseases.

Astonishing diversity of natural surfactants: 2. Polyether glycosidic ionophores and macrocyclic glycosides

Polyether glycosidic ionophores and macrocyclic glycosides are of great interest, especially for the medicinal and pharmaceutical industries. These biologically active natural surfactants are good prospects for the future chemical preparation of compounds useful as antibiotics, anticancer agents, or in industry. More than 300 interesting and unusual natural surfactants are described in this review article, including their chemical structures and biological activities.

The synthesis of bioactive indolocarbazoles related to K-252a

A range of functionalised indolocarbazoles, related to the natural product K-252a, have been prepared, starting from a readily available bridged cyclopentene. Sequences of transformations, involving initial hydroboration-oxidation to give a ketone, or by dihydroxylation and cyclic sulfate formation, enable the preparation of diverse indolocarbazole products. Issues of imide nitrogen protection for the indolocarbazole, and opportunities for asymmetric desymmetrisation of key intermediates were also explored. A novel chiral lithium amide base mediated transformation of a cyclic sulfate intermediate gave the anticipated ketone product in up to 87% ee. A number of compounds, in the form of unprotected imide substituted indolocarbazoles, were screened for biological activity and were found to be potent inhibitors of a number of kinase enzymes.

Synthesis, Modeling, and In Vitro Activity of (3‘S)-epi-K-252a Analogues. Elucidating the Stereochemical Requirements of the 3‘-Sugar Alcohol on trkA Tyrosine Kinase Activity

Utilizing our recently published semisynthetic approach to the (3'S)-K-252a diastereomer, we report the first synthesis of the (3'R)-10 diastereomer and a set of related epimers, with the goal of defining the stereochemical role of the 3'-sugar hydroxyl group on trkA tyrosine kinase activity and selectivity. (3'R)-10 displayed potent trkA inhibitory activity with an IC50 value of 4 nM. The corresponding deshydroxy epimer (3'S)-14 was 7-fold more potent than its 3'R counterpart (natural stereochemistry) with a trkA IC50 value of 3 nM and demonstrated >280-fold selectivity over PKC (IC50 = 850 nM). In cells, (3'S)-14 displayed potent inhibition of trkA autophosphorylation with an IC50 < 10 nM. Molecular modeling studies revealed that the 3'-OH, due to the inverted geometry, forms significant H-bonding interactions with Glu27 and Arg195, an interaction that is not attainable with the natural isomers.

Synthesis and kinase inhibitory activity of 3'-(S)-epi-K-252a

The 3'-epi diastereomer of K-252a was synthesized with the goal of evaluating the stereochemical requirements of the 3'-sugar alcohol on kinase inhibitory activity. Inverting the 3'-alcohol resulted in a 20 nM inhibitor of VEGFR2 and a 1 nM inhibitor of TrkA tyrosine kinase.

Efficient syntheses of novel C2'-alkylated (+/-)-K252a analogues

Recent efforts in our laboratories have resulted in a synthetic approach toward C2'-alkylated K252a analogues via extension of a K252a cyclofuranosylation strategy. The bis-indole-N-glycosidic coupling of 6-N-(3,4-dimethoxybenzyl)-staurosporinone (21) with a number of highly functionalized carbohydrates has given access to previously unattainable, biologically relevant analogues.

Effect of staurosporine derivatives on protein kinase activity and vinblastine accumulation in mouse leukaemia P388/ADR cells

Inhibition by staurosporine derivatives of cyclic AMP-dependent protein kinase (A-kinase) and protein kinase C (C-kinase), and drug resistance has been investigated. The substitution of an acetyl or an ethoxycarbonyl group for the amine N-ethoxycarbonyl-7-oxostaurosporine moiety on the tetrahydropyran ring of staurosporine decreased inhibition of both protein kinases, but increased selectivity for C-kinase by further modification of the lactam moiety to the imide (NA-382). The activities of SF-2370 on protein kinases were decreased by decarboxylation and hydroxyalkylation. These staurosporine derivatives enhanced accumulation of vinblastine in adriamycin-resistant P388 (P388/ADR) cells in a dose-dependent manner. The potency for the drug accumulation of these compounds was correlated with their inhibitory activity on the drug efflux, but was not correlated with their activity on protein kinases. Staurosporine and NA-382, with high potency for vinblastine accumulation, inhibited the photolabelling of [3H]azidopine on 140 kDa P-glycoprotein in the plasma membrane. The tetrahydrofuran compounds and NA-357, which had low potency for the drug accumulation, hardly interacted with azidopine on P-glycoprotein. Most of these compounds were highly cytotoxic by themselves, and only NA-382 was less cytotoxic among them and completely reversed the vinblastine-resistance of P388/ADR cells at a non-cytotoxic concentration. These results suggest that staurosporine derivatives can enhance drug accumulation and inhibit drug resistance through their direct action on the P-glycoprotein.

K-252 compounds: modulators of neurotrophin signal transduction

K-252 compounds, which share a common polyaromatic aglycon structure, are rather general and potent inhibitors of various protein kinases, including protein kinase C and tyrosine-specific protein kinases, and possibly act by interfering at or near the ATP binding site. However, chemical modifications in their sugar moiety can result in high specificity of the inhibitory action and, furthermore, can induce other stimulatory and inhibitory effects on nerve cells. These compounds are of particular interest because, in intact cells, they inhibit the actions of NGF and other neurotrophins without diminishing comparable actions of other growth factors. This effect seems to reflect a direct inhibitory action on trk neurotrophin receptor proteins. At concentrations lower than those necessary to inhibit neurotrophin actions, K-252a and K-252b have been shown to potentiate the stimulatory effects of NT-3 on different neurons in culture and on PC12 cells. The structural requirements for this effect seem to be different from those for the inhibition of neurotrophin actions. These findings raise the possibility of development of compounds of high selectivity, able to inhibit or potentiate the transduction mechanisms of individual neurotrophins, and identify K-252a and K-252b as lead compounds for the development of such selective molecules. Specific inhibitors and stimulators of neurotrophins would be valuable tools to investigate biological functions of the neurotrophins in vitro and in vivo. Furthermore, it is possible that, in the future, highly selective drugs with agonistic or antagonistic actions on neurotrophin mechanisms could become therapeutically useful in the treatment of neurological disease and injury.

Effects of NA0344, a new smooth muscle relaxant, on the actin-myosin-ATP interaction and myosin light chain phosphorylation in vitro

1. Effects of antibiotic NA0344, a smooth muscle relaxant, on phosphorylation of myosin light chain (MLC, 20 kDa) were compared with those on actin-myosin-ATP interaction using native actomyosin preparation containing MLC kinase activity. 2. MLC kinase was shown to be the site of action of NA0344. 3. NA0344 inhibited the interaction and phosphorylation with IC50 = 7.5 x 10(-6) and 1.6 x 10(-5) M, respectively. 4. The discrepancy between the inhibitory effects is explained that myosin is in an active form when myosin is fully phosphorylated. 5. However, the inhibitory effects of NA0359 and NA0362, analogs of NA0344, on the phosphorylation were similar to or more effective than those on the interaction, which cannot be explained by the active form hypothesis. 6. Plausible explanations for the discrepancies are discussed.

Potent and Specific Inhibitors of Protein Kinase C of Microbial Origin

Potent and specific inhibitors of protein kinase C have been found in streptomyces and fungi: Staurosporine, an alkaloid from Streptomyces sp., is the most potent inhibitor of protein kinases with an IC50 in the nanomolar range. UCN-01 (7-hydroxy staurosporine), isolated from Streptomyces sp., is a selective inhibitor of protein kinase C with antitumor activity. Calphostin, isolated from the fungus Cladosporium cladosporioides, specifically inhibits protein kinase C (IC50 = 0.05 microM) without inhibiting other protein kinases. Microbial metabolites appear to be a promising source of inhibitors that target signal transduction pathways of eukaryotes.

Antihypertensive compounds with potent protein kinases inhibitory activity

A new indorocarbazole antibiotic SF2370 has been found in the culture broth of Actinomadura sp.; it has also been found to have the activities of antihypertension and diuresis. Derivatives of SF2370, NA0344, NA0345 and NA0346, when injected (0.1-1 mg/kg i.v.) significantly lowered the blood pressure of anesthetized normotensive rats and showed a long lasting antihypertensive action. In the case of p.o. administration to conscious restrained SHRs, measurement of blood pressure by the plethysmographic method indicated that 10 mg/kg of the compounds was enough to lower the blood pressure; the antihypertensive activities were found to remain more than 12 hrs after oral administration. By studying of the mode of antihypertensive action, these compounds dose dependently relaxed the isolated aortic preparation contracted by norepinephrine. In addition, it was found that protein kinase C activity of mice brain was inhibited by the compounds; the IC50 values were in the range of 0.062-0.20 microM. Moreover, a superprecipitation of actomyosin from smooth muscle of chicken gizzard was inhibited by the compounds, having an IC50 values of 0.31-0.72 microM.

The effect of K-252a, a potent microbial inhibitor of protein kinase, on activated cyclic nucleotide phosphodiesterase

K-252a, an indole carbazol compound of microbial origin, inhibited activation of bovine brain phosphodiesterase induced by calmodulin (CaM), sodium oleate, or limited proteolysis with almost equal potency. Kinetic analysis revealed that the CaM-activated phosphodiesterase (CaM-PDE) was competitively inhibited by K-252a with respect to CaM. On the other hand, inhibition of the trypsin-activated phosphodiesterase was competitive with respect to cyclic AMP. Addition of a lower amount of phosphatidylserine or sodium oleate to the reaction medium was efficacious in attenuating the inhibition of the CaM-PDE by W-7, compound 48/80, or calmidazolium but, in contrast, had no effect on the inhibition by K-252a. Furthermore, CaM-independent systems such as [3H]nitrendipine receptor binding or Na+ + K+-ATPase were influenced less by K-252a compared with W-7, compound 48/80 and calmidazolium. In conclusion, K-252a is an inhibitor of CaM-dependent cyclic nucleotide phosphodiesterase and it appears that it inhibits the enzyme not only via CaM antagonism but possibly also by interfering with the enzyme.