GE3, a novel hexadepsipeptide antitumor antibiotic produced by Streptomyces sp. II. Structure determination

Stereoselective Synthesis of a Protected Side Chain of Meliponamycin A

The Matteson homologation was found to be a versatile tool for the construction of the linear polyketide side chain of meliponamycin and related compounds in only four steps. The ester dienolate version of this reaction allowed the introduction of the unsaturated ester moiety in a highly stereoselective fashion. Boronate oxidation/deoxygenation and Sharpless dihydroxylation are additional key steps in the stereoselective construction of this highly functionalized tetrahydropyran ring system, which is characteristic of this substance class.

A Comprehensive Review on Therapeutic Potentials of Natural Cyclic Peptides

Abstract:

Cyclic peptides have emerged as a promising class of organic compounds that possess polypeptide chains with a cyclic ring structure. There is a circular sequence of bonds in which the ring structure is formed via linkage between one end of the peptide bond and the other end with an amide bond or any other chemically stable bonds like ether, thioether, lactone, and disulfide. Generally, the cyclic peptides are isolated from natural resources like invertebrate animals, micro-organisms of marine habitats, and higher plants. These cyclic peptides possess unique structures with diverse pharmacological activities. Now a day, cyclic peptides possess superior therapeutic value due to several reasons such as greater resistance to enzymatic degradation (in vivo) and higher bio-availability. Some of these cyclic peptides are rich in leucine, proline while some have other amino acids as their major constituents. Numerous novel cyclic peptides isolated from natural sources are successfully developed as bioactive products. Recently, cyclic peptides derived from natural resources have attracted attention for exploring their numerous beneficial effects. Moreover, it is reported that natural cyclic peptides exhibit various therapeutic activities like an anthelmintic, ACE inhibitor, anti-tumor, microtubule inhibitor, anti-fungal, anti-malarial, and platelet aggregation inhibiting activity. In this review, various cyclic peptides are reported with structures and biological activities that are isolated from various natural sources. The natural cyclic peptides possess a wide spectrum of biological activities and can become a drug of the future for replacing the existing drugs which develop resistance

Linear Peptides Are the Major Products of a Biosynthetic Pathway That Encodes for Cyclic Depsipeptides

Three new dentigerumycin analogues are produced by Streptomyces sp. M41, a bacterium isolated from a South African termite, Macrotermes natalensis. The structures of the complex nonribosomal peptide synthetase-polyketide synthase (NRPS/PKS) hybrid compounds were determined by 1D- and 2D-NMR spectroscopy, high-resolution mass spectrometry, and circular dichroism (CD) spectroscopy. Both cyclic and linear peptides are reported, and the genetic organization of the NRPS modules within the biosynthetic gene cluster accounts for the observed structural diversity.

Characterization of the aurantimycin biosynthetic gene cluster and enhancing its production by manipulating two pathway-specific activators in Streptomyces aurantiacus JA 4570

Background

Aurantimycin (ATM), produced by Streptomyces aurantiacus JA 4570, is a potent antimicrobial and antitumor antibiotic. Although the chemical structure of ATM is highly distinctive and features a cyclohexadepsipeptide scaffold attached with a C₁₄ acyl side chain, little is known about its biosynthetic pathway and regulatory mechanism.

Results

In this work, we report the identification and characterization of the ATM biosynthetic gene cluster from S. aurantiacus JA 4570. Targeted inactivation of artG, coding for a NRPS enzyme, completely abolished ATM production, thereof demonstrating the target gene cluster (art) is responsible for ATM biosynthesis. Moreover, four NRPS adenylation (A) domains including a freestanding enzyme ArtC have been characterized in vitro, whose substrate specificities are consistent with in silico analysis. Further genetic analysis of the two regulatory genes artB and artX unambiguously suggested both of them play positive roles in ATM biosynthesis, and ATM-A production was thus rationally enhanced to about 2.5 fold via tandem overexpression of artB and artX in S. aurantiacus JA 4570.

Conclusions

These results will provide the basis for the understanding of precise mechanisms for ATM biosynthesis, and open the way for both rational construction of high-production ATM producer and orient-directed generation of designer ATM derivatives via synthetic biology strategies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0559-7) contains supplementary material, which is available to authorized users.

Identification and characterization of the biosynthetic gene cluster of polyoxypeptin A, a potent apoptosis inducer

BACKGROUND

Polyoxypeptin A was isolated from a culture broth of Streptomyces sp. MK498-98 F14, which has a potent apoptosis-inducing activity towards human pancreatic carcinoma AsPC-1 cells. Structurally, polyoxypeptin A is composed of a C₁₅ acyl side chain and a nineteen-membered cyclodepsipeptide core that consists of six unusual nonproteinogenic amino acid residues (N-hydroxyvaline, 3-hydroxy-3-methylproline, 5-hydroxypiperazic acid, N-hydroxyalanine, piperazic acid, and 3-hydroxyleucine) at high oxidation states.

RESULTS

A gene cluster containing 37 open reading frames (ORFs) has been sequenced and analyzed for the biosynthesis of polyoxypeptin A. We constructed 12 specific gene inactivation mutants, most of which abolished the production of polyoxypeptin A and only ΔplyM mutant accumulated a dehydroxylated analogue polyoxypeptin B. Based on bioinformatics analysis and genetic data, we proposed the biosynthetic pathway of polyoxypeptin A and biosynthetic models of six unusual amino acid building blocks and a PKS extender unit.

CONCLUSIONS

The identified gene cluster and proposed pathway for the biosynthesis of polyoxypeptin A will pave a way to understand the biosynthetic mechanism of the azinothricin family natural products and provide opportunities to apply combinatorial biosynthesis strategy to create more useful compounds.

Synthesis and inhibitory effect on fat accumulation of (-)-ternatin derivatives modified in the beta-OH-D-Leu(7) moiety

An efficient synthesis of (-)-ternatin derivatives directed toward their SAR at the beta-OH-D-Leu(7) moiety and their biological activities against 3T3-L1 murine adipocytes are described.

Piperazimycins: cytotoxic hexadepsipeptides from a marine-derived bacterium of the genus Streptomyces

Three potent cancer cell cytotoxins, piperazimycins A-C (1-3), have been isolated from the fermentation broth of a Streptomyces sp., cultivated from marine sediments near the island of Guam. The structures of these cyclic hexadepsipeptides were assigned by a combination of spectral, chemical, and crystallographic methods. The piperazimycins are composed of rare amino acids, including hydroxyacetic acid, alpha-methylserine, gamma-hydroxypiperazic acid, and gamma-chloropiperazic acid. The novel amino acid residues 2-amino-8-methyl-4,6-nonadienoic acid and 2-amino-8-methyl-4,6-decadienoic acid were found as components of piperazimycins A and C, respectively. When screened in the National Cancer Institute's 60 cancer cell line panel, piperazimycin A exhibited potent in vitro cytotoxicity toward multiple tumor cell lines with a mean GI50 of 100 nM.

Low-abundance kutznerides from Kutzneria sp. 744

Five new (5-9) and four known (1-4) kutznerides were isolated from the actinomycete Kutzneria sp. 744. Compounds 1-9 all consisted of a cyclohexadepsipeptide core with the general structure 2-(1-methylcyclopropyl)-D-glycine-(2S,3aR,8aS)-6,7-dichloro-3a-hydroxy-1,2,3,3a,8,8a-hexahydropyrrolo[2,3-b]indole-2-carboxylic acid-3-hydroxy-D-glutamic acid-O-methyl-L-serine-L-piperazic acid-(S)-2-hydroxy-3,3-dimethylbutyric acid. Compounds 5, 6, and 8 contained erythro-3-hydroxy-D-glutamic acid, whereas 7 and 9 contained the threo isomer and the hydroxy acid was present as (S)-2-hydroxy-3-methylbutyric acid in 5 and 7. The piperazic acid was C-5-N unsaturated and 4-hydroxylated in 6, 4-chlorinated in 8, and C-5-N unsaturated in 9. Minimal inhibitory concentrations for bacteria were found down to 6 microM (Staphylococcus aureus and Erwinia carotovora) and for fungi down to 70 microM (Fusarium culmorum). The trichlorinated 2 and 8 showed the highest antimicrobial activity, whereas 6, with a hydroxylated piperazic acid unit, did not show any inhibition of the pathogens at 230 microM.

Kettapeptin: Isolation, Structure Elucidation and Activity of a New Hexadepsipeptide Antibiotic from a Terrestrial Streptomyces sp

The ethyl acetate extract of the Streptomyces sp. isolate GW99/1572 exhibited significant biological activity against Gram-positive bacteria and delivered kettapeptin (1), a new hexadepsipeptide antibiotic of the azinothricin type. The structure was elucidated by various 1D and 2D NMR techniques, mass spectrometry and by comparison of the NMR data with those of closely related antibiotics. The absolute configuration of the compound was derived by crystal structure analysis and by comparison with the optical rotation data of related compounds.

Kutznerides 1-4, depsipeptides from the actinomycete Kutzneria sp. 744 inhabiting mycorrhizal roots of Picea abies seedlings

Bioassay-guided fractionation of culture supernatants of the actinomycete Kutzneria sp. 744 resulted in the isolation of four new depsipeptides (1-4). Structure analysis revealed the general structure: cyclo[2-(1-methylcyclopropyl)-D-glycine-(2S,3aR,8aS)-6,7-dichloro-3a-hydroxy-1,2,3,3a,8,8a-hexahydropyrrolo[2,3-b]indole-2-carboxylic acid-3-hydroxy-D-glutamic acid-O-methyl-L-serine-L-piperazic acid-(S)-2-hydroxy-3,3-dimethylbutanoic acid]. The 3-hydroxy-d-glutamic acid was present as its threo-isomer in 1 and 2 and as its erythro-isomer in 3 and 4. The piperazic acid was modified to its (R)-4-chloro analogue in 2 and to its C-5/N unsaturated analogue in 4. Compounds 1-4 displayed moderate spore germination inhibiting activity against several common root-rotting fungi.

Lipase TL-mediated kinetic tesolution of 5-benzyloxy-1-tert-butyldimethylsilyloxy-2-pentanol at low temperature: concise asymmetric synthesis of both enantiomers of a piperazic acid derivative

Lipase TL-mediated kinetic resolution of (+/-)-5-benzyloxy-1-tert-butyldimethylsilyloxy-2-pentanol (5) at low temperature proceeded to give the corresponding (S)-alcohol 5 and (R)-acetate 6 in quantitative yields with high enantiomeric purity. The addition of bases such as pyridine, DMAP, 2,4- and 2,6-lutidines, or triethylamine considerably enhanced the rate of kinetic resolution. The alcohol (S)-5 and the acetate (R)-6 were converted to piperazic acid derivatives (R)- and (S)-3, respectively, via the intramolecular Mitsunobu reaction as a key step.

Polyoxypeptins A and B Produced by Streptomyces: Apoptosis-Inducing Cyclic Depsipeptides Containing the Novel Amino Acid (2S,3R)-3-Hydroxy-3-methylproline

Potent apoptosis-inducing peptides, polyoxypeptins A (1) and B (2) were isolated from the culture broth of Streptomyces sp. by solvent extraction and column chromatography. Structural elucidation of 1 by MS and NMR analyses revealed that it is a cyclic hexadepsipeptide having a novel amino acid and a previously unrecognized N-acyl side chain. The depsipeptide consisted of 3-hydroxyleucine, N-hydroxyvaline, N-hydroxyalanine, piperazic acid, 5-hydroxyhexahydropiperazine-3-carboxylic acid, and an unusual and hitherto unreported amino acid, 3-hydroxy-3-methylproline. Alanine and valine obtained from the hydrolyzate of 1 were both in the L-configuration as concluded from chiral TLC analysis. Then, the absolute structure of 1 was determined with the relative structure obtained from X-ray crystallographic analysis, and the new amino acid was isolated and confirmed to be (2S,3R)-3-hydroxy-3-methylproline (3). MS and NMR of 2 exhibited that it is a monodeoxy compound of 1. Stereochemistry of 2 was determined by degradation studies. Both 1 and 2 at a concentration of about 0.1 &mgr;g/mL induced early cell death, nuclear fragmentation, and internucleosomal DNA scission, all of which are characteristic of apoptosis, in human pancreatic carcinoma AsPC-1 cells.