Stereochemical Control in Microbial Reduction. Part 10. Asymmetric Reduction of Alkyl 3-Methyl-2-Oxobutanoate with Immobilized Bakers' Yeast in Hexane

Esters of 3-methyl-2-oxobutanoic acid are reduced with bakers' yeast by three methods: free bakers' yeast in water, immobilized bakers' yeast in water, and immobilized bakers' yeast in hexane. Although (R)-hydroxy esters are obtained in all cases, the enantiomeric excess varies from 3% (reduction of the methyl ester with free bakers' yeast in water) to 93% (reduction of the butyl ester with immobilized bakers' yeast in hexane) depending on the structure of substrate and on the reaction conditions. The mechanism of the present stereochemical control is discussed.     

Metabolites of Cercospora. Taiwapyrone,an α-pyrone of unusual structure from Cercospora taiwanensis

(+)-Mellein (1), cis-3S,4S-4-hydroxymellein (3), and taiwapyrone (4), a new α-pyrone, have been isolated from the mycelium of Cercospora taiwanensis, grown on potato-agar. The structure and absolute configuration of (3) and (4) have been elucidated.     

Effect of Vegetable Extracts on the Transepithelial Permeability of the Human Intestinal Caco-2 Cell Monolayer

The Effect of vegetable extracts on intestinal epithelial permeability was investigated by using Caco-2 cell monolayers as the model system. Among 32 kinds of vegetable samples, the extract of sweet pepper is considered to have contained certain substances that could modulate the tight junction permeability.     

湛江高桥红树林沉积物放线菌多样性及其中一株链霉菌产生的germicidins类化合物的鉴定

【目的】从3种红树林植物根际沉积物中分离和鉴定放线菌,进行抑菌活性初筛获得目标菌株并研究其次级代谢产物。【方法】使用5种培养基对红树林植物根际沉积物放线菌进行分离,采用16S rRNA基因序列比对的方法研究沉积物中的放线菌多样性,结合抑菌活性筛选获得目标菌株后进行放大规模发酵和分离鉴定次级代谢产物,根据生物合成基因簇定位和分析对化合物的生物合成途径进行推导。【结果】从3种红树林植物根际沉积物中分离得到放线菌49株,包括链霉菌属(Streptomyces)31株、小单孢菌属(Micromonospora)14株、小双孢菌属(Microbispora)、链孢子囊菌属(Streptosporangium)、野野村氏菌属(Nonomuraea)和糖单孢菌属(Saccharomonospora)各1株。获得粗浸膏抑菌活性较好的菌株Streptomyces sp. SCSIO 40067,从中分离鉴定了6个α-吡喃酮类化合物：germicidin A–C、germicidin I和isogermicidin A–B,并首次报道了germicidin A的晶体结构。从菌株SCSIO 40067基因组...     

Substituent Effect on the Absolute Stereochemistry of the Asymmetric Reduction of Fluorine-Containing β-Diketones by Bakers' Yeast

Fluorine-containing β-diketones (la-d) were reduced by free bakers' yeast (FBY) and immobilized baker yeast (IMBY) in water, to give optically-active fluorinated β-hydroxyketones (2a-d). It was found that the reaction is highly regioselective, and that the stereochemistry of the reduction is controlled by the R substituent.     

Stereoselectivity of the aliphatic hydroxylation of 6-n-propylchromone-2-carboxylic acid in rat and guinea pig

Following administration of 6-n-propylchromone-2-carboxylic acid (6-n-PCCA) (500 μmol/kg) to male rats, three metabolic products were detected and isolated from the 0–24 h urine. All were identified as resulting from oxidation exclusively along the 6-n-propyl moiety. Some 66% of the dose was excreted in the 0–24 h urine, 55% of which was 6-PCCA, with 15% as (6-1′-hydroxypropyl)chromone-2-carboxylic acid (6-1′-HPCCA), 22% as 6-(2′-hydroxypropyl)chromone-2-carboxylic acid (6-2′-HPCCA), and 4% as (6-3′-carboxypropyl)chromone-2-carboxylic acid (6-3′-CPCCA). Derivatization of the methyl esters of the hydroxylated metabolities with S-α-methoxy-α-(trifuloromethyl)-phenylacetyl chloride (Mosher's reagent) allowed the evaluation of urinary enantiomeric composition by HPLC and assignment of their absolute configurations by NMR. This was found to be 90:10 (R/S) for 6-2′-HPCCA, and 7:93 (R/S) for 6-1′-HPCCA. When rats were dosed with the racemic 1′- and 2-hydroxy metabolites; no stereoselective metabolism or excretion was observed. Administration of 6-n-PCCA to male guinea pigs revealed that this species was unable to metabolise this compound. © 1993 Wiley-Liss, Inc.     

Short chain α-pyrones capable of potentiating penicillin G against Pseudomonas aeruginosa

The dramatic increase in bacterial resistance over the past three decades has greatly reduced the effectiveness of nearly all clinical antibiotics, bringing infectious disease to the forefront as a dire threat to global health. To combat these infections, adjuvant therapies have emerged as a way to reactivate known antibiotics against resistant pathogens. Herein, we report the evaluation of simplified α-pyrone adjuvants capable of potentiating penicillin G against Pseudomonas aeruginosa, a Gram-negative pathogen whose multidrug-resistant strains have been labeled by the Centers for Disease Control and Prevention as a serious threat to public health.     

Neuroprotective effects of extract of Acanthopanax senticosus harms on SH-SY5Y cells overexpressing wild-type or A53T mutant α-synuclein

Extract of Acanthopanax senticosus harms (EAS) has been shown to have neuroprotective effects on dopaminergic neurons in Parkinson's disease (PD) mice model. α-Synuclein is a key player in the pathogenesis of PD, the elevated level of which is deleterious to dopaminergic neurons, and enhancing its clearance might be a promising strategy for treating PD. To assess the potential of EAS in this regard, we investigated its effect on the SH-SY5Y cells overexpressing wild-type α-synuclein (WT-α-Syn) or A53T mutant α-synuclein (A53T-α-Syn), and the implicated pathway it might mediate. After treatment with EAS, the changes of α-synuclein, caspase-3, parkin, phospho-protein kinase B (Akt), phospho-glycogen synthase kinase 3 beta (GSK3β), and phospho-microtubule-associated protein tau (Tau) in WT-α-Syn or A53T-α-Syn transgenic cells were reverted back to near normal levels, demonstrated by the western blotting and quantitative real-time PCR outcomes. The neuroprotective effects of EAS may be able to protect WT-α-Syn or A53T-α-Syn transgenic SH-SY5Y cells from α-synuclein overexpression and toxicity. Therefore, we speculate that EAS might be a promising candidate for prevention or treatment of α-synuclein-related neurodegenerative disorders such as PD.     

Biocatalytic synthesis of chiral N-(2-hydroxyalkyl)-acrylamides

Abstract

The preparation of a series of novel chiral N-(2-hydroxylalkyl)-acrylamides through a lipase-catalyzed resolution of racemic alkanolamines is described. The absolute stereochemistry and enantiomeric excess of the products were determined by a modified Mosher's method. The method was validated for this particular case by the synthesis of an enantiomerically pure product. Moreover, the stereoselective behavior of the lipase in this reaction is discussed.     

New Plant Growth Retardants

Phosphatidylcholine hydroperoxide was assayed with phospholipase A₂ and glutathione peroxidase, based on fluorometry with N(9-acridinyl)maleimide. The hydroperoxide was poorly reduced by glutathione peroxidase, and was converted by phospholipase A₂ into reactable forms of glutathione peroxidase. A linear relationship was found between hydroperoxides assayed by the enzymatic and chemical methods in the range from 0.05 to 5.0 nmol with 0.5 to 1.5 mg of the sample. The hydroperoxides of fatty acids, triacylglycerol and phosphatidylcholine were assayed in their mixtures and in commercial lecithins.     

Zur konfiguration des cyanglycosides holocalin

From its behaviour on GLC holocalin possesses the (R)-configuration in the chiral centre of its aglycone; consequently the diastereomeric glycoside zierin belongs to the (S)-series.     

Effect of increased gene dosage expression on the α-interferon receptors in Down's syndrome

The gene coding for the α,β-interferon (α,β-IFN) receptor is localized to chromosome 21. Cells from patients with Down's syndrome contain an extra chromosome 21, and thereby an expected 1.5-times increase in the number of genes located to this chromosome and in consequence a 1.5-times increase in cell surface α-IFN receptors. Actual measurements of these by competition binding experiments with human recombinant α-IFN on peripheral blood mononuclear cells (PBMC) from patients with Down's syndrome resulted in a mean of 1.69, which is in accordance to the theoretical 1.50, but slightly overestimated due to the calculation method. The increased gene dosage of the α-IFN receptor was quantitatively verified by Southern blot-hybridizations. Further characterization of α-IFN receptor binding showed insignificant differences in dissociation constants among patients and healthy individuals.