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.     

Synthesis and near infrared luminescence of a tetrametallic Zn2Yb2 architecture from a trinuclear Zn3L2 Schiff base complex

Near infrared luminescence is observed in tetrametallic [Zn2Yb2L2(mu-OH)2Cl4].2MeCN which is obtained from the Zn3 Schiff-base complex [Zn3L2(NO3)2].MeOH, (H2L =N,N'-bis(5-bromo-3-methoxysalicylidene)propylene-1,3-diamine).     

Thermochemistry and metastable energy release for the dissociation [C3H7]+ → [C3H5]+ + H2

The reverse activation energy, E_rev, for the dissociation [C₃H₇]⁺ → [C₃H₅]⁺ + H₂ has been determined as 0.24 ± 0.06 eV from measurements of the AP of [C₃H₅]+ produced by electron-impact from thermally generated sec-C₃H₇ radicals. The energy release observed in the corresponding metastable dissociation is 0.21 ± 0.01 eV, indicating that virtually all of E_rev is partitioned as translational Kinetic energy of the fragmentation products. The metastable ion peak shape is also discussed with respect to the evaluation of the energy release.     

Metastable ion studies. IV—thermochemistry and ion structures among fragmenting [C3H6]+· ions

Metastable ion peak shapes, dimensions and relative abundances have been measured for the three fragmentations [C₃H₆]⁺· → [C₃H₄]⁺· + H₂, [C₃H₆]⁺· → [C₃H₅]⁺ + H· and [C₃H₆]⁺· → [C₃H₃]⁺ + H₂ + H·. [C₃H₆]⁺· ions were derived from propene, cyclopropane, tetrahydrofuran, cyclohexanone, 2-methyl but-1-ene and cis-pent-2-ene. Activation energies for these fragmentations have been evaluated. Three daughter ion dissociations ([C₃H₅]⁺ → [C₃H₃]⁺ + H₂, [C₃H₅]⁺ → [C₃H₄]⁺· + H· and [C₃H₄]⁺· → [C₃H₃]⁺ + H·) have been similarly examined. Ion structures have been determined and the metastable energy releases have been correlated with the thermochemical data. It is concluded that the molecular ions of propene and cyclopropane become structurally indistinguishable prior to fragmentation and that differences in their metastable ion characteristics can be ascribed wholly to internal energy differences; the latter can be correlated with the photoelectron spectra of the isomers. The pathway for the consecutive fragmentation which generates the metastable ion peak (m/e 42 → m/e.39) has been shown to be It is likewise concluded that fragmentating [C₃H₆]⁺· ions generated from the various precursor molecules are also structurally indistinguishable and cannot be classified with either molecular ion of the isomeric C₃H₆ hydrocarbons.     

Synthesis of ((t)Bu3SiNH)2ClW triple bond WCl(NHSi(t)Bu3)2 and its degradation via NH bond activation.

Treatment of NaW2Cl7(THF)5 with 4 equiv of (t)Bu3SiNHLi afforded the C2 W(III) dimer [((t)Bu3SiNH)2WCl]2 (1, d(W triple bond W) = 2.337(2) A), which is a rare, primary amide M2X4Y2 species. Its degradation provided evidence of NH bond activation by the ditungsten bond. Addition of 2 equiv of (t)Bu3SiNHLi or TlOSi(t)Bu3 to 1 yielded H2 and hydride ((t)Bu3SiN)2((t)Bu3SiNH)WH (2, d(WH) = 1.67(3) A) or ((t)Bu3SiN)2((t)Bu3SiO)WH (3). Thermolysis (60 degrees C, 16 h) of 1 in py gave ((t)Bu3SiN)2WHCl(py) (4-py, 40-50%), ((t)Bu3SiN)2WCl2(py) (6-py, 10%), and ((t)Bu3SiN)2HW(mu-Cl)(mu-H)2W(NSi(t)Bu3)py2 (5-py2, 5%), whereas thermolysis in DME produced ((t)Bu3SiN)2WCl(OMe) (7, 30%), ((t)Bu3SiN)2WCl2 (6, 20%), and ((t)Bu3SiN)2HW(mu-Cl)(mu-H)2W(NSi(t)Bu3)DME (5-DME, 3%). Compound 7 was independently produced via thermolysis of 4-py and DME (-MeOEt, -py), and THF and ethylene oxide addition to hydride 2 gave ((t)Bu3SiN)2((t)Bu3SiNH)WO(n)Bu (8) and ((t)Bu3SiN)2((t)Bu3SiNH)WOEt (9), respectively. Dichloride 6 was isolated from SnCl4 treatment of 1 with the loss of H2. Sequential NH bond activations by the W2 core lead to "((t)Bu3SiN)2WHCl" (4) and subsequent thermal degradation products. Thermolysis of 1 in the presence of H2C=CH(t)Bu and PhC triple bond CPh trapped 4 and generated ((t)Bu3SiN)2W((neo)Hex)Cl (10) and a approximately 6:1 mixture of ((t)Bu3SiN)2WCl(cis-CPh=CPhH) (11-cis) and ((t)Bu(3)SiN)2WCl(trans-CPh=CPhH) (11-trans), respectively. Thermolysis of the latter mixture afforded ((t)Bu3SiNH)((t)Bu3SiN)WCl(eta2-PhCCPh) (12) as the major constituent. Alkylation of 1 with MeMgBr produced ((t)Bu3SiN)2W(CH3)2 (13), as did addition of 2 equiv of MeMgBr to 6. X-ray crystal structure determinations of 1, 2, 5-py2, 6-py, 11-trans, and 12 confirmed spectroscopic identifications. A general mechanism that features a sequence of NH activations to generate 4, followed by chloride metathesis, olefin insertion, etc., explains the formation of all products.     

Low-energy fragmentations of five isomeric [H3, C,N, O2] +· ions

The low-energy fragmentation characteristics of the [H₃,C,N,O₂]^+· isomers [H₃CNO₂]^+· (a), [H₂C?N(O)OH]^+· (b), [H₃CONO]^+· (c), [HC(O)NHOH]^+· (d) and [HC(OH)?NOH]^+· (e) were studied in detail by metastable ion mass spectrometry. In agreement with most earlier observations, appearance energy measurements established the potential energy surface of the isomers a, b and c, showing the intricate interrelations between them. It was concluded that a isomerizes into b prior to fragmentation by loss of ^·OH and H₂O and into c before loss of ^·H and H₃CO^· moreover, the reverse reactions do not take place on the metastable time-frame. The dominant metastable process for isomers d and e (obtained via HCN loss from glyoxime) was generation of [H₂NOH]^+·. For isomer e this process was proposed to involved a rate-determining isomerization into d. It was concluded that isomers d and e do not intercommunicate with ions a, b and c prior to fragmentation. Neutralization-reionization mass spectrometry indicated that the enol form of formohydroxamic acid as well as the keto counterpart are stable in the gas phase.     

Effects of Adsorbed Polyaniline on Redox Process on MoO3 Surface

The effects exhibited by adsorbed conducting polyaniline on the redox process on a molybdenum oxide surface were studied. Thermogravimetric results indicate a 4% polyaniline deposition. Cyclic voltammograms of the adsorbed polymer on MoO3 show that polyaniline exerts remarkable effects on the molybdenum blue oxidation-reduction process, with oxidation and reduction potentials of 0.33 and 0.18 V, respectively. This effect strongly enhances the electrode response, and can be used as an important tool in qualitative and/or quantitative determinations of molybdenum in solution as well as in any substrate. Copyright 1999 Academic Press.     

CCR5 antagonists: 3-(pyrrolidin-1-yl)propionic acid analogues with potent anti-HIV activity

[reaction: see text] A novel approach to alpha,alpha-disubstituted-beta-amino acids (beta(2,2)-amino acids) was employed in the synthesis of a series of 3-(pyrrolidin-1-yl)propionic acids possessing high affinity for the CCR5 receptor and potent anti-HIV activity. The rat pharmacokinetics for these new analogues featured higher bioavailabilities and lower rates of clearance as compared to cyclopentane 1.     

Solid-state vibrational spectroscopy: Part VI. An infrared and raman spectroscopic study of transition metal(II)4-methylpyridine complexes

Infrared (4000–200 cm^?1) and Raman (3500–300 cm^?1 ) spectra are reported for metal(II) halide and thiocyanate 4-methylpyridine complexes of the following stoichiometries: (MX₂(4-Mepy)₂) {M = Mn, Co, Cu or Zn, X = Cl or Br; M = Mn, Ni or Zn, X = NCS}; (MX₂(4-Mepy)₄) {M = Mn, Fe, Co or Ni, X = Cl or Br; M = Mn, Fe, Co, W or Cu, X = NCS}. For a given series of isomorphous complexes there is a correlation between the sum of the differences between the liquid and ligand values of the ν₁, ν₂, ν₃, ν₄, ν₅, ν₆, ν₇, ν₈, ν₉, ν₁₀, ν₁₂, ν₁₃ and ν₁₄ modes of 4-methylpyridine and the strength of the metal-nitrogen bond. Comparison of the shift values of pyridine and 4-methylpyridine complexes supports the suggestion that, unlike the situation in the pyridine complexes, back-donation from the metal to the ligand is unimportant in the 4-methylpyridine complexes.