Properties and production of valienamine and its related analogues

Diversification of Simple Arenes into Complex (Amino)cyclitols

Highly oxygenated cyclohexanes, including (amino)cyclitols, are featured in natural products possessing a notable range of biological activities. As such, these building blocks are valuable tools for medicinal chemistry. While de novo synthetic strategies have provided access to select compounds, challenges including stereochemical density and complexity have hindered the development of a general approach to (amino)cyclitol structures. This work reports the use of arenophile chemistry to access dearomatized intermediates which are amenable to diverse downstream transformations. Practical guidelines were developed for the synthesis of natural and non-natural (amino)cyclitols from simple arenes through a series of strategic functionalization events.

Carbohydrate-based drugs launched during 2000-2021

Carbohydrates are fundamental molecules involved in nearly all aspects of lives, such as being involved in formating the genetic and energy materials, supporting the structure of organisms, constituting invasion and host defense systems, and forming antibiotics secondary metabolites. The naturally occurring carbohydrates and their derivatives have been extensively studied as therapeutic agents for the treatment of various diseases. During 2000 to 2021, totally 54 carbohydrate-based drugs which contain carbohydrate moities as the major structural units have been approved as drugs or diagnostic agents. Here we provide a comprehensive review on the chemical structures, activities, and clinical trial results of these carbohydrate-based drugs, which are categorized by their indications into antiviral drugs, antibacterial/antiparasitic drugs, anticancer drugs, antidiabetics drugs, cardiovascular drugs, nervous system drugs, and other agents.

Drug/Lead Compound Hydroxymethylation as a Simple Approach to Enhance Pharmacodynamic and Pharmacokinetic Properties

Hydroxymethylation is a simple chemical reaction, in which the introduction of the hydroxymethyl group can lead to physical–chemical property changes and offer several therapeutic advantages, contributing to the improved biological activity of drugs. There are many examples in the literature of the pharmaceutical, pharmacokinetic, and pharmacodynamic benefits, which the hydroxymethyl group can confer to drugs, prodrugs, drug metabolites, and other therapeutic compounds. It is worth noting that this group can enhance the drug’s interaction with the active site, and it can be employed as an intermediary in synthesizing other therapeutic agents. In addition, the hydroxymethyl derivative can result in more active compounds than the parent drug as well as increase the water solubility of poorly soluble drugs. Taking this into consideration, this review aims to discuss different applications of hydroxymethyl derived from biological agents and its influence on the pharmacological effects of drugs, prodrugs, active metabolites, and compounds of natural origin. Finally, we report a successful compound synthesized by our research group and used for the treatment of neglected diseases, which is created from the hydroxymethylation of its parent drug.

Efficient production of valinomycin by the soil bacterium, Streptomyces sp. ZJUT-IFE-354

A novel strain with antifungal activity against Sclerotinia sclerotiorum was isolated from soil, and identified as Streptomyces sp. ZJUT-IFE-354 using morphological and 16S rDNA sequence analysis. The bioactive metabolite produced by strain ZJUT-IFE-354 was identified and characterized as valinomycin by spectroscopic and chemical methods. The yield of valinomycin was 191.26 mg/L from the culture of Streptomyces sp. ZJUT-IFE-354, which was the highest yield to our knowledge. The in vitro antifungal activity of valinomycin against S. sclerotiorum was investigated as 0.056 ± 0.012 (EC₅₀) and 0.121 ± 0.023 μg/mL (EC₉₅), respectively, which was approximately 10.696- and 30.960-fold more active than that of carbendazim. The results from scanning electron microscopy, cell membrane permeability, and _D-sorbitol and ergosterol assay indicated that valinomycin exerted the antifungal activity probably by increasing permeability of fungal cell membrane, leading to mycelial electrolyte leakage, and eventually resulting in the death of S. sclerotiorum. Thus, valinomycin may be a promising antifungal agent to control S. sclerotiorum.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03055-5.

Stereoselective synthesis of a 4-⍺-glucoside of valienamine and its X-ray structure in complex with Streptomyces coelicolor GlgE1-V279S

Glycoside hydrolases (GH) are a large family of hydrolytic enzymes found in all domains of life. As such, they control a plethora of normal and pathogenic biological functions. Thus, understanding selective inhibition of GH enzymes at the atomic level can lead to the identification of new classes of therapeutics. In these studies, we identified a 4-⍺-glucoside of valienamine (8) as an inhibitor of Streptomyces coelicolor (Sco) GlgE1-V279S which belongs to the GH13 Carbohydrate Active EnZyme family. The results obtained from the dose-response experiments show that 8 at a concentration of 1000 µM reduced the enzyme activity of Sco GlgE1-V279S by 65%. The synthetic route to 8 and a closely related 4-⍺-glucoside of validamine (7) was achieved starting from readily available D-maltose. A key step in the synthesis was a chelation-controlled addition of vinylmagnesium bromide to a maltose-derived enone intermediate. X-ray structures of both 7 and 8 in complex with Sco GlgE1-V279S were solved to resolutions of 1.75 and 1.83 Å, respectively. Structural analysis revealed the valienamine derivative 8 binds the enzyme in an E₂ conformation for the cyclohexene fragment. Also, the cyclohexene fragment shows a new hydrogen-bonding contact from the pseudo-diaxial C(3)-OH to the catalytic nucleophile Asp 394 at the enzyme active site. Asp 394, in fact, forms a bidentate interaction with both the C(3)-OH and C(7)-OH of the inhibitor. In contrast, compound 7 disrupts the catalytic sidechain interaction network of Sco GlgE1-V279S via steric interactions resulting in a conformation change in Asp 394. These findings will have implications for the design other aminocarbasugar-based GH13-inhibitors and will be useful for identifying more potent and selective inhibitors.

Genome-based classification of the Streptomyces violaceusniger clade and description of Streptomyces sabulosicollis sp. nov. from an Indonesian sand dune

A polyphasic study was designed to determine the taxonomic provenance of a strain, isolate PRKS01-29^T, recovered from an Indonesian sand dune and provisionally assigned to the Streptomyces violaceusniger clade. Genomic, genotypic and phenotypic data confirmed this classification. The isolate formed an extensively branched substrate mycelium which carried aerial hyphae that differentiated into spiral chains of rugose ornamented spores, contained LL-as the wall diaminopimelic acid, MK-9 (H₆, H₈) as predominant isoprenologues, phosphatidylethanolamine as the diagnostic phospholipid and major proportions of saturated, iso- and anteiso- fatty acids. Whole-genome sequences generated for the isolate and Streptomyces albiflaviniger DSM 41598^T and Streptomyces javensis DSM 41764^T were compared with phylogenetically closely related strains, the isolate formed a branch within the S. violaceusniger clade in the resultant phylogenomic tree. Whole-genome sequences data showed that isolate PRKS01-29^T was most closely related to the S. albiflaviniger strain but was distinguished from the latter and from other members of the clade using combinations of phenotypic properties and average nucleotide identity and digital DNA:DNA hybridization scores. Consequently, it is proposed that isolate PRKS01-29^T (= CCMM B1303^T = ICEBB-02^T = NCIMB 15210^T) should be classified in the genus Streptomyces as Streptomyces sabulosicollis sp. nov. It is also clear that streptomycetes which produce spiral chains of rugose ornamented spores form a well-defined monophyletic clade in the Streptomyces phylogenomic tree., the taxonomic status of which requires further study. The genome of the type strain of S. sabulosicollis contains biosynthetic gene clusters predicted to produce new natural products.

Stereoselective syntheses of 3-aminocyclooctanetriols and halocyclooctanetriols

The efficient synthesis of two new stereoisomeric 3-aminocyclooctanetriols and their new halocyclitol derivatives starting from cis,cis-1,3-cyclooctadiene are reported. Reduction of cyclooctene endoperoxide, obtained by photooxygenation of cis,cis-1,3-cyclooctadiene, with zinc yielded a cyclooctene diol followed by acetylation of the hydroxy group, which gave dioldiacetate by OsO₄/NMO oxidation. The cyclooctane dioldiacetate prepared was converted to the corresponding cyclic sulfate via the formation of a cyclic sulfite in the presence of catalytic RuO₄. The reaction of this cyclic sulfate with a nucleophilic azide followed by the reduction of the azide group provided the target, 3-aminocyclooctanetriol. The second key compound, bromotriol, was prepared by epoxidation of the cyclooctenediol with m-chloroperbenzoic acid followed by hydrolysis with HBr(g) in methanol. Treatment of bromotriol with NaN₃ and the reduction of the azide group yielded the other desired 3-aminocyclooctanetriol. Hydrolysis of the epoxides with HCl(g) in methanol gave stereospecifically new chlorocyclooctanetriols.

A Validamycin Shunt Pathway for Valienamine Synthesis in Engineered Streptomyces hygroscopicus 5008

Valienamine is the key functional component of many natural glycosidase inhibitors, including the crop protectant validamycin A and the clinical antidiabetic agent acarbose. Due to its important biomedical activity, it is also the prominent lead compound for the exploration of therapeutic agents, such as the stronger α-glucosidase inhibitor voglibose. Currently, the main route for obtaining valienamine is a multistep biosynthetic process involving the synthesis and degradation of validamycin A. Here, we established an alternative, vastly simplified shunt pathway for the direct synthesis of valienamine based on an envisioned non-natural transamination in the validamycin A producer Streptomyces hygroscopicus 5008. We first identified candidate aminotransferases for the non-natural ketone substrate valienone and conducted molecular evolution in vitro. The WecE enzyme from Escherichia coli was verified to complete the envisioned step with >99.9% enantiomeric excess and was further engineered to produce a 32.6-fold more active mutant, VarB, through protein evolution. Subsequently, two copies of VarB were introduced into the host, and the new shunt pathway produced 0.52 mg/L valienamine after a 96-h fermentation. Our study thus illustrates a dramatically simplified alternative shunt pathway for valienamine production and introduces a promising foundational platform for increasing the production of valienamine and its valuable N-modified derivatives for use in pharmaceutical applications.

Chain-Branched Polyhydroxylated Octahydro-1H-Indoles as Potential Leads against Lysosomal Storage Diseases

Here, the synthesis and glycosidase inhibition properties of the two first known 3-ethyloctahydro-1H-indole-4,5,6-triols are reported. This study shows the transformation of d-glucose into polyhydroxylated 1-(2-nitrocyclohexane) acetaldehydes, followed by a protocol involving the formation of the azacyclopentane ring. Results of inhibitory potency assays and docking calculations show that at least one of them could be a lead for optimization in the search for compounds that behave like folding chaperones in lysosomal storage diseases.

Recent advances in the Overman rearrangement: synthesis of natural products and valuable compounds

This review documents the reports since 2005 on the Overman rearrangement, an important C–N bond forming reaction that has been profoundly used in the synthesis of natural products, synthetic intermediates, building blocks and valuable compounds.

Biosynthesis and Biological Activity of Carbasugars

The first synthesis of carbasugars, compounds in which the ring oxygen of a monosaccharide had been replaced by a methylene moiety, was described in 1966 by Professor G. E. McCasland’s group. Seven years later, the first true natural carbasugar (5a-carba-R-D-galactopyranose) was isolated from a fermentation broth of Streptomyces sp. MA-4145. In the following decades, the chemistry and biology of carbasugars have been extensively studied. Most of these compounds show interesting biological properties, especially enzymatic inhibitory activities, and, in consequence, an important number of analogues have also been prepared in the search for improved biological activities. The aim of this review is to give coverage on the progress made in two important aspects of these compounds: the elucidation of their biosynthesis and the consideration of their biological properties, including the extensively studied carbapyranoses as well as the much less studied carbafuranoses.

Building Bridges: Biocatalytic C-C-Bond Formation toward Multifunctional Products

Carbon-carbon bond formation is the key reaction for organic synthesis to construct the carbon framework of organic molecules. The review gives a selection of biocatalytic C-C-bond-forming reactions which have been investigated during the last 5 years and which have already been proven to be applicable for organic synthesis. In most cases, the reactions lead to products functionalized at the site of C-C-bond formation (e.g., α-hydroxy ketones, aminoalcohols, diols, 1,4-diketones, etc.) or allow to decorate aromatic and heteroaromatic molecules. Furthermore, examples for cyclization of (non)natural precursors leading to saturated carbocycles are given as well as the stereoselective cyclopropanation of olefins affording cyclopropanes. Although many tools are already available, recent research also makes it clear that nature provides an even broader set of enzymes to perform specific C-C coupling reactions. The possibilities are without limit; however, a big library of variants for different types of reactions is required to have the specific enzyme for a desired specific (stereoselective) reaction at hand.

Synthesis and evaluation of hydroxymethylaminocyclitols as glycosidase inhibitors

Four series of C7N aminocyclitol analogues of glucose were synthesized by stereocontrolled epoxide opening of hydroxyl protected forms of the cyclohexane epoxides cyclophellitol and 1,6-epi-cyclophellitol. The resulting hydroxymethyl substituted aminocyclitols were tested as glycosidase inhibitors. Cyclitols having an amino group in an α configuration at a position equivalent to the anomeric in the sugar were found to be low micromolar inhibitors of the α-glucosidase from baker's yeast with Ki's near to 2 μM. On the other hand, N-octyl aminocyclitols having the nitrogen substituents in an α or β configuration were found to be good inhibitors of recombinant β-glucocerebrosidase with Ki values between 8.3 and 17 μM, and also inhibited lysosomal β-glucosidase activity in live cells at low-micromolar concentrations. A computational docking study suggests a differential binding among the different series of β-glucocerebrosidase inhibitors. In agreement with the experimental results, the binding poses obtained indicate that the presence of an alkyl lipid substituent in the inhibitor mimicking one of the lipid chains in the substrate is critical for potency. In contrast, the matching of hydroxymethyl substituents in the aminocyclitols and the parent glucosylceramide does not seem to be strictly necessary for potent inhibition, indicating the risk of simplifying structural analogies in sugar mimetic design.

Synthesis of 4-membered carbasugars by way of stereoselective SmI2-mediated aldehyde-alkene cyclization

A stereodivergent synthesis of the first examples of 4-membered carbasugars has been achieved from vitamin C by way of an efficient intramolecular SmI2-mediated aldehyde-alkene coupling. In this key step, cylobutanes with four contiguous asymmetric centers are generated with a high level of stereocontrol.

A convenient synthesis of N-linked diglycose derivatives based on one-pot tandem Staudinger/aza-Wittig/reduction and biological evaluation

A series of novel N-linked diglycose derivatives 9 and 10 were conveniently and directly synthesized based on the key step of one-pot tandem Staudinger/aza-Wittig/reduction reaction from the azido sugar and sugar-derived aldehyde followed by deprotection. The biological activities against glycosidases (α-amylase, α-glucosidase, and β-glucosidase) and HIV-RT and antitumor activity of these compounds were preliminarily evaluated.

Cloning, expression and medium optimization of validamycin glycosyltransferase from Streptomyces hygroscopicus var. jinggangensis for the biotransformation of validoxylamine A to produce validamycin A using free resting cells

Validamycin A is widely used to control Basidiomycetes, which causes sheath blight disease in rice, potatoes, vegetables, and other crops as well as dumping-off disease in vegetable seedlings, cotton, sugar beets, and other plants. In order to improve the content of validamycin A in the commercial products, valG from Streptomyces hygroscopicus was successfully cloned into Escherichia coli BL21(DE3) and was directly employed as the biocatalyst in the biotransformation from validoxylamine A to validamycin A with the existence of d-cellobiose using the free resting cells in the present study. The fermentation medium was optimized through single factor experiment and response surface method. With the optimized medium, which contained lactose 4.7g/L, yeast extract 49.5g/L, ammonium chloride 2.7g/L, potassium phosphate buffer solution 110mL/L, Ca(2+) 0.0352g/L, the biomass yield and enzyme activity reached 5.5g/L and 1.49U/mL, respectively, which were nearly twice higher than those with initial medium.

A chiron approach to aminocytitols by Petasis-Borono-Mannich reaction: formal synthesis of (+)-conduramine E and (-)-conduramine E

A chiron approach to a stereoselective route for the synthesis of aminocytitols from carbohydrates is described. The formal synthesis of (+)-conduramine E and (-)-conduramine E was achieved by utilizing this strategy. The key features of the synthetic strategy include one-pot three-component Petasis-Borono-Mannich reaction to introduce the syn-β-amino alcohol functionality of conduramine E and ring-closing metathesis to construct its carbocyclic core. The present synthetic approach paves the way for stereoselective synthesis of several conduramines starting from carbohydrates.