Production of anticancer polyenes through precursor-directed biosynthesis

The biosynthesis of the pyrrolyl moiety of the fungal metabolite rumbrin originates from pyrrole-2-carboxylic acid. In an effort to produce novel derivatives with enhanced biological activity a series of substituted pyrrole-2-carboxylates were synthesised and incubated with the producing organism, Auxarthron umbrinum. Several 4-halo-pyrrole-2-carboxylic acids were incorporated into the metabolite yielding three new derivatives: 3-fluoro-, 3-chloro- and 3-bromo-isorumbrin, which were generated in milligram quantities enabling cytotoxicity assays to be conducted. The 3-chloro- and 3-bromo-isorumbrins had improved activity against HeLa cells compared with rumbrin; 3-bromoisorumbrin also showed dramatically improved activity towards a lung cancer cell line (A549).     

Stereochemical assignment of intermediates in the rifamycin biosynthetic pathway by precursor-directed biosynthesis

Natural and semisynthetic rifamycins are clinically important inhibitors of bacterial DNA-dependent RNA polymerase. Although the polyketide-nonribosomal peptide origin of the naphthalene core of rifamycin B is well established, the absolute and relative configuration of both stereocenters introduced by the first polyketide synthase module is obscured by aromatization of the naphthalene ring. To decode the stereochemistry of the rifamycin polyketide precursor, we synthesized all four diastereomers of the biosynthetic substrate for module 2 of the rifamycin synthetase in the form of their N-acetylcysteamine (SNAC) thioester. Only one diastereomer was turned over in vivo into rifamycin B, thus establishing the absolute and relative configuration of the native biosynthetic intermediates.     

Synthesis of phosphinic analogs of sulfur-containing amino acids

Phosphinic analogs of the key compounds of the metabolism of methionine were synthesized. The compounds obtained were selectively oxidized either at the phosphinic group or at the sulfur-containing fragment. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1360–1363, July, 1999.     

Synthesis of sulfur-containing analogs of the K group vitamins by an electrochemical method

An efficient electrochemical method is proposed for obtaining structural analogues of the K group vitamins (3-alkylthio and 3-arylthio ethers of 2-methyl-1,4-naphthoquninone).N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. M. V. Lomonosov Institute of Fine Chemical Technology, 119899 Moscow. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2605–2608, November, 1992.     

Unusual enniatins produced by the insect pathogenic fungus Verticillium hemipterigenum: isolation and studies on precursor-directed biosynthesis

Two new enniatins H (3) and I (4), whose substituents on 2-hydroxycarboxylic acid moieties were different from those of known compounds, were isolated, together with known enniatins B (1) and B₄ (2), from the insect pathogenic fungus Verticillium hemipterigenum BCC 1449. Structures of these compounds were elucidated by spectroscopic means. Studies on precursor-directed biosynthesis with strain BCC 1449 led to the production and identification of three analogs, enniatins G (5), C (6) and MK1688 (7), as well as the stereochemical elucidation of 3 and 4. Enniatins 1-7 were evaluated for their antiplasmodial and antimycobacterial activities.     

Novel synthesis of heterocyclic spirans by tandem cycloaddition to sulfur-containing heterocumulenes

Novel Ni(C0)₄-promoted tandem cycloadditions of diphenylcyclo- propenone to isothiocyanates and to CS₂ were found to provide new heterocyclic spirans, pyrroline-2-one-5-spiro-5′-thiolene-4′-ones and a thiolene-2-one-5-spiro-5′-thiolene-4′-one, respectively, in moderate yields.     

Evaluating precursor-directed biosynthesis towards novel erythromycins through in vitro studies on a bimodular polyketide synthase

Background: Modular polyketide synthases (PKSs) catalyse the biosynthesis of complex polyketides using a different set of enzymes for each successive cycle of chain extension. Directed biosynthesis starting from synthetic diketides is a potentially valuable route to novel polyketides. We have used a purified bimodular derivative of the erythromycin-producing polyketide synthase (DEBS 1-TE) to study chain extension starting from a variety of diketide analogues and, in some cases, from the alternative acyl-CoA thioester substrates.Results: Chain initiation in vitro by DEBS 1-TE module 2 using a synthetic diketide analogue as a substrate was tolerant of significant structural variation in the starter unit of the synthetic diketide, but other changes completely abolished activity. Interestingly, a racemic β-keto diketide was found to be reduced in situ on the PKS and utilised in place of its more complex hydroxy analogue as a substrate for chain extension. The presence of a diketide analogue strongly inhibited chain initiation via the loading module. Significantly higher concentrations of diketide N-acetylcysteamine analogues than their corresponding acyl-CoA thioesters are required to achieve comparable yields of triketide lactones.Conclusions: Although a broad range of variation in the starter residue is acceptable, the substrate specificity of module 2 of a typical modular PKS in vitro is relatively intolerant of changes at C-2 and C-3. This will restrict the usefulness of approaches to synthesise novel erythromycins using synthetic diketides in vivo. The use of synthetic β-keto diketides in vivo deserves to be explored.     

Generating rapamycin analogues by directed biosynthesis: starter acid substrate specificity of mono-substituted cyclohexane carboxylic acids

We report a convenient synthesis of 4-fluorocyclohexanoic acid, and an insight into the rules governing acceptance of starter acid analogues in the precursor-directed biosynthesis of rapamycin.     

Engineered biosynthesis of geldanamycin analogs for Hsp90 inhibition

Geldanamycin, a polyketide natural product, is of significant interest for development of new anticancer drugs that target the protein chaperone Hsp90. While the chemically reactive groups of geldanamycin have been exploited to make a number of synthetic analogs, including 17-allylamino-17-demethoxy geldanamycin (17-AAG), currently in clinical evaluation, the "inert" groups of the molecule remain unexplored for structure-activity relationships. We have used genetic engineering of the geldanamycin polyketide synthase (GdmPKS) gene cluster in Streptomyces hygroscopicus to modify geldanamycin at such positions. Substitutions of acyltransferase domains were made in six of the seven GdmPKS modules. Four of these led to production of 2-desmethyl, 6-desmethoxy, 8-desmethyl, and 14-desmethyl derivatives, including one analog with a four-fold enhanced affinity for Hsp90. The genetic tools developed for geldanamycin gene manipulation will be useful for engineering additional analogs that aid the development of this chemotherapeutic agent.     

Novel polymer electrolytes prepared by copolymerization of ionic liquid monomers

Ionic liquid monomer couples were prepared by the neutralization of 1‐vinylimidazole with vinylsulfonic acid or 3‐sulfopropyl acrylate. These ionic liquid monomer couples were viscous liquid at room temperature and showed low glass transition temperature (Tg) at ?83 °C and ?73 °C, respectively. These monomer couples were copolymerized to prepare ion conductive polymer matrix. Thus prepared ionic liquid copolymers had no carrier ions, and they showed very low ionic conductivity of below 10^?9 S cm^?1. Equimolar amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to imidazolium salt unit was then added to generate carrier ions in the ionic liquid copolymers. Poly(vinylimidazolium‐co‐vinylsulfonate) containing equimolar LiTFSI showed the ionic conductivity of 4 × 10^?8 S cm^?1 at 30 °C. Advanced copolymer, poly(vinylimidazolium‐co‐3‐sulfopropyl acrylate) which has flexible spacer between the anionic charge and polymer main chain, showed the ionic conductivity of about 10^?6 S cm^?1 at 30 °C, which is 100 times higher than that of copolymer without spacer. Even an excess amount of LiTFSI was added, the ionic conductivity of the copolymer kept this conductivity. This tendency is completely different from the typical polyether systems. Copyright © 2002 John Wiley & Sons, Ltd.     

Novel magnetic functionalities of Prussian blue analogs

Cyano-bridged bimetal assemblies demonstrate novel magnetic functionalities, particularly Prussian blue analogs, which have unique properties. In this perspective, we describe a charge-transfer phase transition, reversible photomagnetism, second harmonic generation and magnetization-induced second harmonic generation, ferroelectric ferromagnetism, humidity-sensitive magnetism, high ionic conductivity, and a coupling effect (which we named spin-ionics) between ionic conduction and magnetic ordering with Prussian blue analogs.     

Novel one-pot syntheses of sulfur-containing polymers from a bifunctional five-membered cyclic dithiocarbonate

Novel one-pot syntheses of sulfur-containing polymers from a bifunctional five-membered cyclic dithiocarbonate ( 1a ) were carried out. Polythiourethanes were obtained by the polyaddition of 4,4′-methylenebis(phenyl isocyanate), tolylene 2,6-diisocyanate, and hexamethylene diisocyanate with a dithiol ( 2a ) obtained by the reaction of 1a and benzylamine under mild conditions. Polythioesters were also obtained by the polycondensation of terephthaloyl and succinyl chlorides with 2a . Further, polythioether was obtained by the polycondensation of α,α′-dibromo-p-xylene with 2a . © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1189–1195, 1998     

Novel soraphens from precursor directed biosynthesis

Six novel halogenated soraphen analogues have been isolated from the wild-type producing organism using precursor directed biosyntheses; the best 'delivery vehicle' for the novel starter acids was cinnamate but ortho substituents were not tolerated by the soraphen PKS.     

Effect of α-tocopherol and its sulfur-containing analogs on radiation-induced chemical transformations of hexane and ethanol

A series of sulfur-containing structural analogs of α-tocopherol was synthesized, and their effect on the formation of molecular products of ethanol and hexane radiolysis under aerated and deaerated conditions was studied. The O-H bond dissociation enthalpies (BDEs) were calculated for the compounds containing hydroxyl groups. It was found that α-tocopherol and its analogs have the most significant effect on the radiolysis of ethanol and hexane under air-free conditions when the products are formed in the reactions of carbon-centered radicals. The probability of the reaction of the test compounds with alkyl radicals increases with a decrease in the BDE for the OH groups present in these compounds. The carbonyl group in compounds (IV-VIII) makes them efficient oxidants of α-hydroxyalkyl radicals, thus resulting in a change in the product composition for the ethanol radiolysis in presence of these compounds.     

Novel sulfur-containing amidecrownophanes: synthesis via tandem Claisen rearrangement and an unpredicted mercuration

Two novel sulfur-containing amidecrownophanes, 3a (N₂S) and 3b (N₂S₂), were synthesized by diacyl chloride-diamine sulfide coupling reactions followed by the tandem Claisen rearrangement of macrocycles 2a and 2b as precursors, respectively. The reactivity of the titled macrocycles with some transition and heavy metal ions was examined. The most salient feature of the reactions is the mercurated dihydrobenzofuran 4 derived from 3b and Hg(OAc)₂. The X-ray crystal structures of 4 as well as 2a and 2b were revealed.     

Directed biosynthesis of alkaloid analogs in the medicinal plant Catharanthus roseus

Terpene indole alkaloids are plant natural products with diverse structures and biological activities. A highly branched biosynthetic pathway is responsible for the production of approximately 130 different alkaloids in Madagascar periwinkle (C. roseus) from a common biosynthetic intermediate derived from tryptamine. Although numerous biosynthetic pathways can incorporate unnatural starting materials to yield novel natural products, it was not clear how efficiently the complex, eukaryotic TIA pathway could utilize unnatural substrates to make new alkaloids. This work demonstrates that the TIA biosynthetic machinery can be used to produce novel alkaloid structures and also highlights the potential of this pathway for future metabolic engineering efforts.     

Novel regulation of aflatoxin B1 biosynthesis in Aspergillus flavus by piperonal

The present study investigated its inhibitory role in aflatoxin (AF) biosynthesis. Treating only AFB1- and B2-producing Aspergillus flavus with piperonal completely inhibited AFB1 production with high sclerotial formation, resulting in 20-fold higher AFG2 production. On the other hand, benzodioxole and eugenol suppressed AFB1 production without AFG formation, while methyleugenol showed potent inhibition of AFB1 production with slight production of AFG1. These results indicate that natural products may change aflatoxin biosynthesis, and highlight a novel regulation of AFG2 production by piperonal. It is the first report for chemical regulation on AFG2 production in non-AFG producing-aspergilli.