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At least 523 records · Page 29Linked to original sources
PubMed1996

Flagellar proteins of motile spores of Actinomycetes.

Flagella of some of the actinoplanete genera were purified and the molecular sizes of their flagellin subunits compared by SDS-PAGE analysis to flagellins of cells of other bacteria. Several species of Actinoplanes have a major flagellar protein of subunit sizes of 42-43 kDa and a lesser amount of a second protein, possibly a minor flagellin subunit, of 60 kDa. The flagellar protein sizes of other actinoplanetes ranged from 32-43 kDa (major) and 48-58 kDa (minor). Antibodies formed against the 42-kDa protein of A. rectilineatus showed cross-reactivity in Western blots against flagellar proteins of spores of other Actinoplanes species, two species of Dactylosporangium and an Ampullariella species. Cross-reactivity was also observed with motile cells of two other actinomycetes, Arthrobacter atrocyaneus and a Geodermatophilus species, and with Bacillus subtilis. No cross-reactivity was observed with Escherichia coli or Planomonospora parontospora flagellar proteins. The amino acid composition and partial N-terminal sequence of the 42-kDa flagellar protein of A. rectilineatus was compared to literature data for other bacterial flagellins and found to be most similar to B. subtilis 168.

Actinomycetales↗
PubMed1995

Synthesis of (+)-dynemicin A and analogs of wide structural variability: establishment of the absolute configuration of natural dynemicin A.

BACKGROUND: Dynemicin A is an exceedingly potent antitumor antibiotic derived from microbial fermentation that cleaves double-stranded B-form DNA in vitro in the presence of activating factors such as NADPH or glutathione. Because of the structural complexity, high reactivity, and scarcity of natural dynemicin A, it has not been feasible to modify the structure to any significant extent. Previous studies have not determined the absolute configuration of the natural product. RESULTS: A multistep route for the preparation of enantiomerically pure, synthetic dynemicin A was developed. The absolute configuration of natural dynemicin was determined by comparing the synthetic drug with dynemicin A derived from fermentation. The route that was developed is highly convergent, as the result of a late-stage coupling reaction that combines two complex synthetic fragments, and has been shown to provide access to non-natural dynemicins of wide structural variability by modifications of these fragments. In this way, several nonnatural dynemicins, unavailable by any other means, were synthesized and shown to have DNA-cleaving activity in the presence of glutathione or NADPH. CONCLUSIONS: Enantiomerically pure dynemicin A is now available by laboratory synthesis. The natural, (+)-enantiomer of dynemicin A is shown to possess the 2S, 3S, 4S, 7R, 8R configuration. A wide variety of heretofore unavailable, active analogs of dynemicin A have been prepared and are found to produce subtle variations in sequence specificity of DNA cleavage compared to the natural product and, of potentially greater significance, display variations in the efficiency of DNA cleavage as a function of the activating agent.

Anthraquinones↗
PubMed1998

The crystal structure of an intramolecular trans-sialidase with a NeuAc alpha2-->3Gal specificity.

BACKGROUND: Intramolecular trans-sialidase from leech (Macrobdella decora) is a unique enzyme which cleaves the terminal neuraminic acid (NeuAc) residue from sialoglycoconjugates, releasing 2, 7-anhydro-neuraminic acid (2,7-anhydro-NeuAc). It is the first enzyme found to exhibit strictly specific cleavage of NeuAc alpha2-->3Gal linkages in sialoglycoconjugates. The release of 2,7-anhydro-NeuAc instead of NeuAc implies a unique mechanism, in which the sialosyl linkage is transferred within the sialoglycoconjugate rather than hydrolyzed. The aims of the structural study were to gain structural insight into the strict specificity and unique mechanism of this unusual enzyme. RESULTS: . The 2.0 A crystal structure of recombinant leech intramolecular trans-sialidase has been solved by multiple isomorphous replacement. The 1.8 A structure of the enzyme in complex with 2-deoxy-2, 3-didehydro-NeuAc was also solved. The refined model comprising residues 81-769 has a catalytic beta-propeller domain (C), a N-terminal lectin-like domain (II) and an irregular beta-stranded domain (III) inserted into the catalytic domain. The structure reveals several possible carbohydrate-binding features: domain II has a concave face, like that of other sialidases, and there is a suitable surface charge distribution at the domain III-C interface. CONCLUSIONS: Structural comparisons showed closer evolutionary relationships to bacterial sialidases than to viral neuraminidases. Mainchain and sidechain atoms around Thr593 make the glycerol-binding pocket incapable of accommodating an extended equatorial 6-glycerol group, implying that the 6-glycerol group of the reaction intermediate may occupy an axial position, which is also required by the catalytic mechanism. The steric hindrance introduced by the bulky sidechain of Trp734 above the 2-carboxylate group may explain the lack of water involvement in the cleavage reaction and the substrate specificity.

Amino Acid Sequence↗
PubMed2004

Total synthesis of (+)-SCH 351448.

Total synthesis of SCH 351448 was accomplished employing the ring-closing olefin metathesis reaction for the preparation of the 28-membered macrodiolide.

Crystallography, X-Ray↗
PubMed2003

Total synthesis of (+)-macquarimicin A.

The first total synthesis of (+)-macquarimicin A (1), a novel inhibitor of neutral sphingomyelinase (N-SMase) with antiinflammatory activity, has been accomplished. The present work determined the absolute configuration of (+)-1 and revised the C(2)-C(3) geometry to be Z. The synthesis features a transannular Diels-Alder reaction, which constructed the tetracyclic framework stereoselectively, and a convergent and efficient synthetic pathway, which afforded (+)-macquarimicin A (1) in 27 steps (longest linear sequence) with 9.9% overall yield.

Macrolides↗
PubMed2004

Characterization of tylM3/tylM2 and mydC/mycB pairs required for efficient glycosyltransfer in macrolide antibiotic biosynthesis.

The heterologous expression of tylM3 and mydC, two homologous genes of previously unknown function, along with genes encoding their respective partner glycosyltransferases, tylM2 and mycB, and the necessary sugar biosynthesis genes significantly enhances the glycosyltransferase activity in the engineered Streptomyces venezuelae host in which the native glycosyltransferase, desVII, has been inactivated. Both glycosyltransferases accept the endogenous 12-membered macrolide, 10-deoxymethynolide, or the exogenously fed 16-membered macrolide, tylactone. Five new compounds were generated using this expression system. This work suggests that the 13 other known TylM3/MydC/DesVIII homologues found in macrolide and anthracycline antibiotic clusters likely function as glycosyltransferase auxiliary proteins as well. These findings will greatly assist endeavors to generate new natural products in these pathways in a combinatorial fashion.

Anti-Bacterial Agents↗
PubMed2001

Synthetic study of macquarimicins: highly stereoselective construction of the AB-ring system.

The highly stereoselective synthesis of the AB-ring system of macquarimicins, a novel class of microbial metabolites with inhibitory activity for neutral sphingomyelinase, has been achieved. The present synthesis features the highly stereocontrolled construction of the cis-tetrahydroindan structure via the intramolecular Diels-Alder reaction of an (E,Z,E)-1,6,8-nonatriene derived from D-glyceraldehyde acetonide. Reaction: see text.

Anti-Bacterial Agents↗
PubMed2002

Synthesis of the C1-C21 (C1'-C21') fragment of the dimeric polyketide natural product SCH 351448.

[structure: see text] A convergent, stereoselective assembly of the C1-C21 (C1'-C21') fragment of SCH 351448, a 28-membered bis-lactone natural product, has been developed. A highly efficient approach to this fragment assembles 75% of the carbon skeleton and all the stereochemical elements present in the natural product. In addition, an interesting boron ligand effect on the diastereoselectivity of a key aldol reaction with methyl ketone-derived enolborinates is reported.

Anticholesteremic Agents↗
PubMed2005

A concise synthesis of (+)-SCH 351448.

[structure: see text] We describe a highly convergent synthetic approach to the natural product (+)-SCH 351448 (1)-a hexane-soluble heptacoordinate monosodium salt of a C(2)-symmetrical macrocyclic dilactone. Our approach implements a photochemical acylation as the key step to combine two nearly identical but orthogonal C1-C29 fragments, followed by a base-induced intramolecular acylation and deprotection to yield the natural product.

Lactones↗
PubMed2006

Enantioselective total synthesis of (+)-SCH 351448.

[structure: see text] A stereoselective synthesis of SCH 351448 has been completed. Twelve of the fourteen stereogenic centers were established through chiral enolate reactions, and six key C-C bonds were formed by metathesis reactions.

Lactones↗