The Bioconversion of (3RS,E)- and (3RS,Z)-Nerolidol into Oxygenated Products by Streptomyces cinnamonensis. Possible Implications for the Biosynthesis of the Polyether Antibiotic Monensin A??

The ability of the monensin-producing organism Streptomyces cinnamonensis to bioconvert the (E)-and (Z)-isomers of nerolidol (= 3,7,1 1-trimethyldodeca-1,6,10-trien-3-ol) into new oxygenated products has been investigated. When a ³H-labelled racemic form of each sesquiterpene was added to fermentations of S. cinnamonensis, several new ³H-labelled products could be detected. Two products were isolated from bioconversion of (E)-nerolidol, the amide 8 and the 9 (Scheme 2), whereas four products were isolated from the bioconversion of (Z)-nerolidol, the epoxydiol 10 , triols 11 and 12 , and the tetrahydrofuryl alcohol 13 (Scheme 4). Products 9 – 13 were obtained as a 1 : 1 mixture of diastereoisomers, and 12 was shown to arise by the overall anti addition of two OH groups to the trisubstituted (Z)-double bond of (Z)-nerolidol. Both isomers of nerolidol as well as the acetylene 7 are inhibitors of monensin production in shake cultures of S. cinnamonensis.     

Adsorption configuration and local ordering of silicotungstate anions on Ag(100) electrode surfaces

X-ray reflectivity, cyclic voltammetry, and scanning tunneling microscopy (STM) are used to examine the structure of alpha-SiW12O4(4-) or silicotungstic acid (STA) adsorbed on Ag(100) in acid solution. The voltammetry shows that STA passivates the Ag surface relative to electron transfer to a solution redox species. STM images reveal the formation of a series of lattice structures, one of which can be associated with a commensurate ( radical13x radical13)R33.69 degrees structural model. X-ray reflectivity measurements show uniquely that STA orients with its four-fold axis perpendicular to the Ag(100) surface and that the center of the STA molecule is 4.90 A above the top layer of the Ag substrate. Analysis of bond lengths leads to a footprint of STA on Ag(100), in which the four terminal O atoms are located near the hollow sites and have a Ag-O bond length of 2.06 A. This bond length is consistent with a strong covalent interaction between STA and the Ag surface.     

Regioselective and enantiospecific rhodium-catalyzed allylic amination with N-(arylsulfonyl)anilines

[reaction: see text]. The regioselective and enantiospecific rhodium-catalyzed allylic amination of secondary allylic carbonates 1 with N-(arylsulfonyl)anilines provides a convenient process for the construction of arylamines 2. This method, in conjunction with ring-closing metathesis and radical cyclization reactions, allows the direct construction of biologically relevant pharmacophores as exemplified by the construction of dihydroquinoline and dihydrobenzo[b]indoline derivatives.     

Bifurcation to infinitely many sinks

This paper considers one parameter families of diffeomorphisms {F _t } in two dimensions which have a curve of dissipative saddle periodic pointsP _t , i.e.F _t ⁿ (P _t )=P _t and |detDF _t ⁿ (P _t )|<1. The family is also assumed to create new homoclinic intersections of the stable and unstable manifolds ofP _t as the parameter varies throught ₀. Gavirlov and Silnikov proved that if the new homoclinic intersections are created nondegenerately att ₀, then there is an infinite cascade of periodic sinks, i.e. there are parameter valuest _n accumulating att ₀ for which there is a sink of periodn [GS2, Sect. 4]. We show that this result is true for real analytic diffeomorphisms even if the homoclinic intersection is created degenerately. We give computer evidence to show that this latter result is probably applicable to the Hénon map forA near 1.392 andB equal ?0.3. Newhouse proved a related result which showed the existence of infinitely many periodic sinks for a single diffeomorphism which is a perturbation of a diffeomorphism with a nondegenerate homoclinic tangency. We give the main geometric ideas of the proof of this theorem. We also give a variation of a key lemma to show that the result is true for a fixed one parameter family which creates a nondegenerate tangency. Thus under the nondegeneracy assumption, not only is there a cascade of sinks proved by Gavrilov and Silnikov, but also a single parameter valuet* with infinitely many sinks.     

The first enantioselective total synthesis of the anti-Helicobacter pylori agent (+)-spirolaxine methyl ether

The first enantioselective synthesis of the anti-Helicobacter pylori agent (+)-spirolaxine methyl ether has been carried out in a convergent fashion by heterocycle-activated Julia olefination of a spiroacetal-containing sulfone fragment with a phthalide-containing aldehyde fragment. The total synthesis of (+)-spirolaxine methyl ether establishes the absolute stereochemistry of the natural product to be (3R,2'R,5'R,7'R).     

Thermogravimetric investigation of manganese(ii), silver and thorium diliturates

Thermolysis curves for manganese(II), silver and thorium diliturates were obtained. Manganese diliturate precipitated as the octahydrate and dehydrated in two steps. Silver diliturate formed as a monohydrate from aqueous solutions. Thorium diliturate formed as a hydrate containing 20 moles of water and dehydrated in two steps.Methods for the thermogravimetric determination of manganese(II) and thorium by precipitation as the diliturates are suggested.     

CsOH-promoted epoxide ring-opening with phosphines: mild and efficient synthesis of monohydroxyphosphines

A mild and convenient synthesis of monohydroxyphosphines has been achieved by epoxide ring-opening using primary or secondary phosphines in the presence of cesium hydroxide, 4 Å molecular sieves and DMF at room temperature. These reaction conditions were found to be highly regio- and stereoselective producing various monohydroxyphosphines exclusively in moderate to high yields.     

Nitrosyl derivatives of tricobaltcarbon clusters

The nitrosyl clusters PPN[YCCo₃(CO)₇(NO)] (Y = Me, Ph, COOH, (C₅H₅)Fe(C₅H₄)) have been prepared in high yield from the reaction of YCCo₃(CO)₉ with PPN(NO₂) in THF, acetone or acetonitrile. Spectroscopic evidence indicates the structure of the nitrosyl anions is derived from that of YCCo₃(CO)₉ by the replacement of two CO ligands on one cobalt atom by a linear, terminal nitrosyl group. The nitrosyl metallates are extremely sensitive to oxidation and attempts to protonate the anions resulted in the reformation of the parent YCCo₃(CO)₉, molecules. The oxidative electrochemistry of the ferrocene complex, PPN[(C₅H₅)Fe(C₅H₄CCo₃(CO)₇(NO)] is also discussed.