Allostreptopyrroles A-E, β-alkylpyrrole derivatives from an actinomycete Allostreptomyces sp. RD068384

Five new β-alkylpyrrole derivatives, allostreptopyrroles A-E (1-5), were isolated from the culture broth of Allostreptomyces RD068384. Their structures were elucidated by 1D and 2D NMR spectroscopic analyses, HRESIMS, and chemical derivatization. The absolute configurations of compounds 2 and 3 were predicted by comparison of experimental and calculated specific rotation data. Compounds 1-5 are the first examples of natural pyrroles substituted by formyl and carboxyl functionalities. Compounds 1, 4, and 5 showed cytotoxicity against Kasumi-1 human acute myeloblastic leukemia cells with IC50 values of 103, 105, and 105 μM, respectively, which are less active than the anticancer agent cisplatin, with an IC50 value of 70 μM.

Synthesis and anti-tumor activities in human leukemia-derived cells of polyenylpyrroles with a methyl group at the conjugated polyene terminus

To develop novel drugs for treating T-cell acute lymphoblastic leukemia (T-ALL) and acute myeloid leukemia (AML) which are highly malignant hematological tumors, a series of analogs having a polyenylpyrrole structure of natural compounds (rumbrin and auxarconjugatin B) were synthesized and investigated their structure-activity relationships (SAR) of in vitro anti-T-ALL and anti-AML activities. We obtained three findings: (1) introduction of a methyl group at the conjugated polyene terminus enhanced anti-T-ALL activity, (2) analogs with a 3-chloropyrrole moiety had even higher selectivity for T-ALL cells, and (3) some analogs were effective against AML-derived cells. Among the studied compounds, 3-chloro-2-(8-ethoxycarbonylnona-1,3,5,7-tetraenyl) pyrrole 4e was the most promising candidate of T-ALL- and AML-treating drug. This study provides useful structural information for designing novel drugs treating T-ALL and AML.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Production of Multiple Talaroenamines from Penicillium malacosphaerulum via One-Pot/Two-Stage Precursor-Directed Biosynthesis

Nineteen new talaroenamine derivatives, talaroenamines F1-F19 (1-19), were isolated from the Yellow River wetland derived Penicillium malacosphaerulum HPU-J01 by use of a one-pot/two-stage precursor-directed biosynthesis approach. During this approach, the initial precursor p-methylaniline was first used as a carrier to capture the biologically synthesized cyclohexanedione to produce talaroenamine F, and then the other aniline derivatives were employed to replace the p-methylaniline fragment of talaroenamine F to generate the final products. LC-MS analysis showed that only four compounds (2, 8, 10, and 12) could be produced by the traditional precursor-directed biosynthesis in which the aniline precursors were added simultaneously. Compound 14 was cytotoxic against the K562 cell line with an IC₅₀ value of 2.2 μM. This work demonstrated the one-pot/two-stage precursor-directed biosynthesis could improve substrate acceptance leading to the production of diverse talaroenamines.

Precursor-Directed Biosynthesis of Talaroenamine Derivatives Using a Yellow River Wetland-Derived Penicillium malacosphaerulum

Precursor-directed biosynthesis was used to introduce selected aniline derivatives into the talaroenamine pathway, which had recently been defined from a Yellow River wetland-derived Penicillim malacosphaerulum HPU-J01. The known talaroenamine B (1) and six previously undescribed talaroenamine derivatives, talaroenamines F-K (2-7), were generated and structurally characterized. The aniline derivatives are introduced via nonenzymatic addition to the reactive intermediate cyclohexanedione. Compound 2 was active against Bacillus cereus with an MIC value of 0.85 μg/mL.

Synthesis of polyenylpyrrole derivatives with selective growth inhibitory activity against T-cell acute lymphoblastic leukemia cells

T-cell acute lymphoblastic leukemia (T-ALL) is a hardly curable disease with a high relapse rate. 20 analogs were synthesized based on the structures of two kinds of fungi-derived polyenylpyrrole products (rumbrin (1) and auxarconjugatin-B (2)) to suppress the growth of T-ALL-derived cell line CCRF-CEM and tested for growth-inhibiting activity. The octatetraenylpyrrole analog gave an IC₅₀ of 0.27 μM in CCRF-CEM cells, while it did not affect Burkitt lymphoma-derived cell line Raji and the cervical cancer cell line HeLa, or the oral cancer cell line HSC-3 (IC₅₀ > 10 μM). This compound will be a promising compound for developing T-ALL-specific drugs.

From Synthetic Simplified Marine Metabolite Analogues to New Selective Allosteric Inhibitor of Aurora B Kinase

Significant inhibition of Aurora B was achieved by the synthesis of simplified fragments of benzosceptrins and oroidin belonging to the marine pyrrole-2-aminoimidazoles metabolites isolated from sponges. Evaluation of kinase inhibition enabled the discovery of a synthetically accessible rigid acetylenic structural analogue EL-228 (1), whose structure could be optimized into the potent CJ2-150 (37). Here we present the synthesis of new inhibitors of Aurora B kinase, which is an important target for cancer therapy through mitosis regulation. The biologically oriented synthesis yielded several nanomolar inhibitors. The optimized compound CJ2-150 (37) showed a non-ATP competitive allosteric mode of action in a mixed-type inhibition for Aurora B kinase. Molecular docking identified a probable binding mode in the allosteric site "F" and highlighted the key interactions with the protein. We describe the improvement of the inhibitory potency and specificity of the novel scaffold as well as the characterization of the mechanism of action.

Fluorinated Analogues of Desferrioxamine B from Precursor-Directed Biosynthesis Provide New Insight into the Capacity of DesBCD

The siderophore desferrioxamine B (DFOB, 1) native to Streptomyces pilosus is biosynthesized by the DesABCD enzyme cluster. DesA-mediated decarboxylation of l-lysine gives 1,5-diaminopentane (DP) for processing by DesBCD. S. pilosus culture medium was supplemented with rac-1,4-diamino-2-fluorobutane ( rac-FDB) to compete against DP to generate fluorinated analogues of DFOB, as agents of potential clinical interest. LC-MS/MS analysis identified fluorinated analogues of DFOB with one, two, or three DP units (binary notation: 0) exchanged for one (DFOA-F₁[001] (2), DFOA-F₁[010] (3), DFOA-F₁[100] (4)), two (DFOA-F₂[011] (5), DFOA-F₂[110] (6), DFOA-F₂[101] (7)), or three (DFOA-F₃[111] (8)) rac-FDB units (binary notation: 1). The two sets of constitutional isomers 2-4 and 5-7 arose from the position of the substrates in the N-acetyl, internal, or amine-containing regions of the DFOB trimer. N-Acetylated fluorinated DFOB analogues were formed where the rac-FDB substrate was positioned in the amine region ( e.g., N-Ac-DFOA-F₁[001] (2a)). Other analogues contained two hydroxamic acid groups and three amide bonds. Experiments using rac-FDB, R-FDB, or S-FDB showed a similar species profile between rac-FDB and R-FDB. These data are consistent with the following. (i) DesB can act on rac-FDB. (ii) DesC can act directly on rac-FDB. (iii) The products of DesBC or DesC catalysis of rac-FDB can undergo a second round of DesC catalysis at the free amine. (iv) DesD catalysis of these products gives N, N'-diacetylated compounds. (v) A minimum of two hydroxamic acid groups is required to form a viable DesD-substrate(s) precomplex. (vi) One or more DesBCD-catalyzed steps in DFOB biosynthesis is enantioselective. This work has provided a potential path to access fluorinated analogues of DFOB and new insight into its biosynthesis.

Pyrrole Derivatives and Diterpene Alkaloids from the South China Sea Sponge Agelas nakamurai

Two pairs of new non-brominated racematic pyrrole derivatives, (±)-nakamurine D (1) and (±)-nakamurine E (2), two new diterpene alkaloids, isoagelasine C (16) and isoagelasidine B (21), together with 13 known pyrrole derivatives ((±)-3 - 15), five known diterpene alkaloids (17 - 20, 22) were isolated from the South China Sea sponge Agelas nakamurai. The racemic mixtures, compounds 1 - 4, were resolved into four pairs of enantiomers, (+)-1 and (-)-1, (+)-2 and (-)-2, (+)-3 and (-)-3, and (+)-4 and (-)-4, by chiral HPLC. The structures and absolute configurations were elucidated on the basis of comprehensive spectroscopic analyses, quantum chemical calculations, quantitative measurements of molar rotations, application of van't Hoff's principle of optical superposition, and comparison with the literature data. The NMR and MS data of compound 3 are reported for the first time, as the structure was listed in SciFinder Scholar with no associated reference. These non-brominated pyrrole derivatives were found in this species for the first time. Compound 18 showed valuable cytotoxicities against HL-60, K562, and HCT-116 cell lines with IC₅₀ values of 12.4, 16.0, and 19.8 μm, respectively. Compounds 16 - 19, 21, and 22 showed potent antifungal activities against Candida albicans with MIC values ranging from 0.59 to 4.69 μg/ml. Compounds 16 - 19 exhibited moderate antibacterial activities against Proteusbacillus vulgaris (MIC values ranging from 9.38 to 18.75 μg/ml).

Microbial degradation of fluorinated drugs: biochemical pathways, impacts on the environment and potential applications

Since the discovery over 60 years ago of fluorocortisone's biological properties (9-α-Fluoro derivatives of cortisone and hydrocortisone; Fried J and Sabo EF, J Am Chem Soc 76: 1455-1456, 1954), the number of fluorinated drugs has steadily increased. With the improvement in synthetic methodologies, this trend is likely to continue and will lead to the introduction of new fluorinated substituents into pharmaceutical compounds. Although the biotransformation of organofluorine compounds by microorganisms has been well studied, specific investigations on fluorinated drugs are relatively few, despite the increase in the number and variety of fluorinated drugs that are available. The strength of the carbon-fluorine bond conveys stability to fluorinated drugs; thus, they are likely to be recalcitrant in the environment or may be partially metabolized to a more toxic metabolite. This review examines the research done on microbial biotransformation and biodegradation of fluorinated drugs and highlights the importance of understanding how microorganisms interact with this class of compound from environmental, clinical and biotechnological perspectives.

Synthesis, antitumor activity, and mechanism of action of 6-acrylic phenethyl ester-2-pyranone derivatives

Based on the scaffolds of caffeic acid phenethyl ester (CAPE) as well as bioactive lactone-containing compounds, 6-acrylic phenethyl ester-2-pyranone derivatives were synthesized and evaluated against five tumor cell lines (HeLa, C6, MCF-7, A549, and HSC-2). Most of the new derivatives exhibited moderate to potent cytotoxic activity. Moreover, HeLa cell lines showed higher sensitivity to these compounds. In particular, compound showed potent cytotoxic activity (IC50 = 0.50-3.45 μM) against the five cell lines. Further investigation on the mechanism of action showed that induced apoptosis, arrested the cell cycle at G2/M phases in HeLa cells, and inhibited migration through disruption of the actin cytoskeleton. In addition, ADMET properties were also calculated in silico, and compound showed good ADMET properties with good absorption, low hepatotoxicity, and good solubility, and thus, could easily be bound to carrier proteins, without inhibition of CYP2D6. A structure-activity relationship (SAR) analysis indicated that compounds with ortho-substitution on the benzene ring exhibited obviously increased cytotoxic potency. This study indicated that compound is a promising compound as an antitumor agent.

Recent advances in combinatorial biosynthesis for drug discovery

Because of extraordinary structural diversity and broad biological activities, natural products have played a significant role in drug discovery. These therapeutically important secondary metabolites are assembled and modified by dedicated biosynthetic pathways in their host living organisms. Traditionally, chemists have attempted to synthesize natural product analogs that are important sources of new drugs. However, the extraordinary structural complexity of natural products sometimes makes it challenging for traditional chemical synthesis, which usually involves multiple steps, harsh conditions, toxic organic solvents, and byproduct wastes. In contrast, combinatorial biosynthesis exploits substrate promiscuity and employs engineered enzymes and pathways to produce novel “unnatural” natural products, substantially expanding the structural diversity of natural products with potential pharmaceutical value. Thus, combinatorial biosynthesis provides an environmentally friendly way to produce natural product analogs. Efficient expression of the combinatorial biosynthetic pathway in genetically tractable heterologous hosts can increase the titer of the compound, eventually resulting in less expensive drugs. In this review, we will discuss three major strategies for combinatorial biosynthesis: 1) precursor-directed biosynthesis; 2) enzyme-level modification, which includes swapping of the entire domains, modules and subunits, site-specific mutagenesis, and directed evolution; 3) pathway-level recombination. Recent examples of combinatorial biosynthesis employing these strategies will also be highlighted in this review.

Precursor-directed biosynthesis of micacocidin derivatives with activity against Mycoplasma pneumoniae

Micacocidin is a promising natural product for the treatment of Mycoplasma pneumoniae infections. In the biosynthesis of this antibiotic, a fatty acid-AMP ligase (FAAL) activates the starter unit hexanoic acid as acyl-adenylate and forwards it to an iteratively acting polyketide synthase. Biochemical analysis of the FAAL revealed an extended substrate tolerance, thereby opening the door for the modification of a micacocidin residue that is barely accessible via semisynthesis. A total of six new analogues were generated by precursor-directed biosynthesis in this study and profiled against M. pneumoniae.