Biocenversion of cyclohexene derivatives

Summary Bioconversion of new methylcyclohexene derivatives with bulky side chains ending in aromatic or heteroaromatic rings by Streptomyces natalensis and Mycobacterium smegmatis results in monohydroxylation of the cyclohexene ring. Further oxidation of the hydroxyl group into a keto group is effected only with M. smegmatis. The synthesis of the substrates and proof of the structure of the products is given in detail.     

Theoretical investigation on the water-assisted excited-state proton transfer of 7-azaindole derivatives: substituent effect

A systematic study on the first excited-state proton transfer (ESPT) in 2RAI-H₂O (R = OH, OCH₃, CN, NO₂, CHO) complexes in solution were investigated at the TD-M06-2X/6-31 + G(d, p) level. The double proton transfer occurred in an asynchronous but concerted protolysis fashion no matter which substituent R was used at C₂ position in pyrrole ring in the 7AI-H₂O complex. The specific vibrational-mode of ESPT in the model systems was confirmed and contributed to promote the reaction rate by shortening the reaction path. The substituent effects of different groups on the ESPT thermodynamics and kinetics were discussed. It was obvious that the geometries, barrier height, asynchrony, and specific vibration-mode of excited-state proton transfer changed with the different substituent groups.

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Graphical Abstract The distance between two neighboring heavy atoms such as N₁-O₁₁ (R₁) and O₁₁-N₈ (R₂) distances played an important role in the proton transfer reaction. The sum of the N₁-O₁₁ and O₁₁-N₈ distances in the reactant of 2RAI-H₂O (R=H, OH, OCH₃; CN, CHO, NO₂) complexes is in the range of 5.542 Å~5.692 Å and changes along with the substituent group at C₂ position in the pyrrole ring. The ESDPT barrier height and the sum of the N₁-O₁₁ and O₁₁-N₈ distances have a good correlation.

     

In-silico analysis of substituent effect on the static first order hyperpolarizability of electron donating mono substituted Chalcone derivatives

Noncentrosymmetric π conjugated systems with suitable electron donor acceptor groups play a crucial role in material NLO activity. The influence of an electron donating mono substituent at the para position of the phenylene ring of chalcone was investigated as a resource for second harmonic generation. The geometrical optimization of 11 electron donating group substituted chalcones were performed using density functional theory at the B3LYP/6-311G(d,p) level and compared with experimental geometrical parameters of five reported chalcones. All the derivatives are transparent to visible radiation as shown by the electronic absorption spectra investigated by the TDDFT-CAM B3LYP/6-311G(d,p) method, and the maximum absorption wavelength was due to the π_PhB?→?π* transition. The first order hyperpolarizability β_tot, calculated using the CAM B3LYP/6-311G(d,p) method, increases with the electron donating ability of the substituent, and the largest β_tot was observed for dimethylamino substituent. The Hammett substituent constant (σ_p) shows good linear correlation with β, λ_max, and E_gap in the ground state. The Brown constant (σ_p⁺) was better correlated indicating the polarization of carbonyl group in the excited state. Frontier molecular orbitals also reveal the valence electron excitation. Correlation of σ_p with various parameters was analyzed to assess the property interrelationship with electronic reorganization in the molecule. The electronic structures of molecular fragments were described in terms of natural bond orbital analysis, which shows intramolecular interactions.     

Density functional studies of the substituent effect on absorption and emission properties of 1, 8-naphthalimide derivatives

Using TD-PBE1PBE/6-31G* and TD-B3LYP/6-31G* approaches, we calculated the absorption and emission spectra of 1,8-naphthalmide derivatives in gas-phase. The geometric structures optimized by HF/6-31G* and B3LYP/6-31G* models and the absorption and emission maxima were in good agreement with existed experimental measurements. It was also found that the lowest singlet states corresponded mainly to the electronic transition from the highest occupied orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO). Intramolecular charge transfer occurred between substituents and naphthalimic rings. Study also showed that most compounds with low absorption excitation energies had low vertical ionization potentials. Finally, the delocalization electronic energies between substituents and naphthalimic rings of isomers were investigated to obtain further sight into their stability.     

Preparation of enantiopure Wieland-Miescher ketone and derivatives by the MalphaNP acid method: substituent effect on the HPLC separation

Enantiopure Wieland-Miescher ketone (4, W-M ketone) and derivatives were prepared by the enantioresolution with 2-methoxy-2-(1-naphthyl)propionic acid (MalphaNP acid 1). Various racemic derivatives of 4 were esterified with acid (S)-(+)-1 yielding diastereomeric MalphaNP esters, which were separated by HPLC on silica gel. It was clarified that the HPLC separation of diastereomers depended on the substituent of the derivatives, leading to the working hypothesis that MalphaNP acid esters of alcohols with less polar and more bulky aliphatic substituents are more effectively separated. The best separation was obtained in the case of tert-butyldimethylsilyl (TBDMS) ether derivative (12a/12b): separation factor alpha=1.80, and resolution factor, Rs=1.30. The (1)H NMR spectra of separated MalphaNP esters showed anomalously large magnetic anisotropy effects, from which their absolute configurations were determined. Solvolysis or reduction of the separated MalphaNP esters yielded alcohols, which were converted to enantiopure W-M ketones 4. The results thus provided another route for preparation of enantiopure ketones (8aR)-(-)-4 and (8aS)-(+)-4.     

Electronic and steric substituent effects on the fluorescence emission of 2-pyrazoline derivatives

A series of substituted 2-pyrazolines were synthesized, and the steric and electronic effects of substituents on the C₃- and C₅-positions of the heterocyclic ring on their fluorescent ability were investigated. Two different conjugative intramolecular charge transfer (ICT) and intramolecular charge transfer through space (spiro-conjugation) affect the fluorescence intensity of these compounds. The extent of the ICT process and spiro-conjugation depends on the electronic nature of the additional substitution and its position on the attached aryl rings. In addition, the effects of the concentration and the solvent polarity on the fluorescence emission were studied. Density functional theory (DFT) calculations were carried out to gain insight into the geometric, electronic, and spectroscopic properties of the pyrazoline derivatives. The results of both experimental and computational studies explain the effects of the geometrical orientation of the C₃- and C₅-aryl rings toward the heterocyclic ring and also the electronic nature of their additional substitutions on the fluorescence intensity.     

Glycine origin of the methyl substituent on C7'-N of octodiose for the biosynthesis of apramycin

Apramycin is unique in the aminoglycoside family due to its octodiose moiety. However, either the biosynthesis process or the precursors involved are largely unknown. Addition of glycine, as well as serine or threonine, to the Streptomyces tenebrabrius UD2 fermentation medium substantially increases the production of apramycin with little effect on the growth of mycelia, indicating that glycine and/or serine might be involved in the biosynthesis of apramycin. The 13C-NMR analysis of [2-13C] glycine-fed (25% enrichment) apramycin showed that glycine specifically and efficiently incorporated into the only N-CH3 substituent of apramycin on the C7' of the octodiose moiety. We noticed that the in vivo concentration of S-adenosyl methionine increased in parallel with the addition of glycine, while the addition of methione in the fermentation medium significantly decreased the productivity of apramycin. Therefore, the methyl donor function of glycine is proposed to be involved in the methionine cycle but methionine itself was proposed to inhibit the methylation and methyl transfer processes as previously reported for the case of rapamycin. The 15N NMR spectra of [2-13C,15N]serine labeled apramycin indicated that serine may also act as a limiting precursor contributing to the -NH2 substituents of apramycin.     

Metabolism and bioconversion of chromene derivatives inAgeratina adenophora (Asteraceae)

Seedlings ofAgeratina adenophora accumulate the chromenes demethoxyencecalin, encecalin and demethylencecalin. More than 80% of the total chromenes within the seedling are confined to the leaves where they are stored within the mesophyll. Metabolism of the chromenes during development of the seedlings was subjected to analysis by high-performance liquid chromatography. The accumulation kinetics obtained, as well as feeding experiments with non-radioactive chromenes, showed the bioconversion of these compounds to proceed from demethoxyencecalin via hydroxylation yielding demethylencecalin, followed by methylation yielding encecalin. Inhibitor studies with glyphosate indicate that the chromenes arise from precursors derived from the shikimic-acid pathway.Abbreviation HPLC high-performance liquid chromatography     

Understanding the substituent effect on the acidity of alcohols and para-substituted phenols

We carried out Hartree–Fock (HF) and density functional theory calculations on the conjugated bases of phenols and alcohols for 23 compounds and analysed their acid–base behaviour using molecular orbital (MO) energies and their dependence on solvent effects. Despite the well-known correlation between highest-occupied MO (HOMO) energies and proton affinity (PA), we observed that HOMO energies are inadequate to describe the acid–base behaviour of these compounds. Therefore, we established a criterion to identify the best frontier MO for describing PA values and also to understand why the HOMO approach fails. The MO that fits our criterion provided very good correlations with PA values, much better than those obtained by the HOMO energies. Since the frontier MOs are those which drive the acid–base reactions in each compound, they were called frontier effective-for-reaction MOs, or FERMOs. By using the FERMO concept, the reactions that are HOMO driven, and those that are not, can be better explained, independent of the calculation method used, since both HF and Kohn–Sham methodologies lead to the same FERMO.     

The effect of prostaglandins on the bioconversion of arachidonic acid in cervical tissue in early human pregnancy

The aim of the present study was to investigate in late first trimester and early second trimester patients whether whole cell homogenates of cervical tissue incubated with 14C-arachidonic acid was affected by pretreatment for 12 to 14 hours with PGE2 and 9-deoxo- 16,16-dimethyl-9-methylene PGE2 (9-methylene PGE2). After extraction, purification and separation, identification of the compounds found during incubation was achieved using radio-gas liquid chromatography and gas-liquid chromatography-mass spectrometry. Treatment with 9-methylene PGE2 accomplished a reduced production of 14C-labelled PGF2 alpha, -PGE2 and TxB2, while pretreatment with PGE2 induced increase in the production of 14C-6-keto-PGF1 alpha when cervical tissue homogenates were compared with specimens obtained from non-pretreated patients. Recently we reported a significantly increased formation of so far unidentified metabolite(s) in homogenates of human cervical tissue specimens obtained at or near term when compared with corresponding specimens obtained during early pregnancy. With both types of prostaglandin pretreatment there was a tendency of increased formation of these metabolites. It seems possible that the influence on the biochemistry of cervical tissue induced by PGE2 and 9-methylene PGE2 is mediated via the endogenous arachidonic acid cascade towards non-prostaglandin compound(s).     

Regioselective bioconversion of colchicine and thiocolchicine into their corresponding 3-demethyl derivatives

A variety of plant cell cultures and microbial soil isolates were screened for their ability to specifically demethylate colchicine at the C-3 position. Among all plant cell cultures tested, the newly established Colchicum variegatum culture was the only one able to demethylate colchicine, however unspecifically, yielding a mixture of 3-demethylcolchicine and 2-demethylcolchicine. In contrast, two bacterial strains were found among more than 500 isolates tested which expressed higgly regio-specific demethylation activity exclusively at C-3 of colchicine. The bioconversion product of the microorganisms, 3-demethylcolchicine, was completely excreted into the medium. The specific C-3 bioconversion of colchicine as well as of thiocolchicine by one of these strains, Bacillus IND-B 375, was characterized in function of substrate concentration and incubation time.     

Prostaglandin H synthase kinetics. The effect of substituted phenols on cyclooxygenase activity and the substituent effect on phenolic peroxidatic activity.

A series of p- and m-substituted phenols were examined for their effect on the cyclooxygenase activity of prostaglandin H synthase in 0.1 M phosphate buffer at pH 8.0 and 25.0 +/- 0.1 degrees C. A biphasic response was observed. At low concentrations phenols stimulate, but at higher concentrations inhibit, cyclooxygenase activity. Both enhancement and inhibition are increased by phenolic substituents which are electron-donating, quantified by Hammett sigma constants, and hydrophobic, quantified by Hantsch tau constants. The same series of substituted phenols was also reacted with compound II of prostaglandin H synthase at 4.0 +/- 0.5 degrees C. The compound II data fit the Hammett rho sigma equation; no hydrophobicity factors are required. Phenols inhibit cyclooxygenase activity by interfering with the binding of arachidonic acid to compound I and by competing directly with arachidonic acid as reducing substrates for compound I. Phenols stimulate cyclooxygenase activity by acting as reducing substrates for compound II, thereby accelerating the peroxidatic cycle. Phenols also protect the enzyme from self-catalyzed inactivation, most likely by removing the free radical of prostaglandin G2 by reducing it to prostaglandin G2. Kinetic parameters Km and kcat for cyclooxygenase activity were determined in the presence of phenols. Identical values of Km (15.3 +/- 0.5 mM) and kcat (89 +/- 2 s-1) were obtained regardless of which phenol was employed. Therefore these represent the true Km and kcat values for cyclooxygenase activity.