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At least 955 records · Page 53Linked to original sources
PubMed1996

Copper(II) complexes of N2-alkyl-(S)-amino acid amides as chiral selectors for dynamically coated chiral stationary phases in RP-HPLC.

Copper(II) complexes of N2-octyl-(S)-phenylalaninamide (Noc-Phe-NH2), N2-dodecyl-(S)-phenylalaninamide (Ndo-Phe-NH2), and N2-octyl-(S)-norleucinamide (Noc-NLeu-NH2), dynamically adsorbed on a reversed-phase C18 column, were able to perform the direct enantiomeric separation of unmodified amino acids, amino acid amides and esters, hydroxy acids, and dipeptides by elution with aqueous or mixed aqueous-organic solutions containing copper(II) sulphate or acetate. The role played by several parameters in the separation procedure was examined with the copper(II) complex of Noc-Phe-NH2 [concentration of the copper(II) ion in the eluent, pH and eluent polarity, amount of adsorbed selector]. The separation was shown to occur entirely on the stationary phase. The mechanism of chiral discrimination is discussed in terms of the chromatographic parameters and of the structure of the copper(II) complexes in solution and in the solid state. The chiral stationary phase maintained its separation ability for about 3 months. However, the column could be easily restored by recovering the selector with methanol and repeating the loading procedure.

Amides↗
PubMed2001

Crystal structure of a depsipeptide, Boc-(Leu-Leu-Lac)3-Leu-Leu-OEt.

A sequential polydepsipeptide, Boc-(Leu-Leu-Lac)3-Leu-Leu-OEt (1) (Lac = L-lactic acid residue) has been synthesized by the segment condensation method. The sequential unit of 1, -Leu-Leu-Lac-, is consisted of two amino acid residues and one hydroxy acid residue. X-ray diffraction measurement with an imaging plate detector and a direct-methods procedure of Shake-and-Bake successfully revealed the crystal structure of 1. In the solid state, the 11-mer depsipeptide, 1, have clear alpha-helical conformation even with the three ester linkages.

Crystallization↗
PubMed2005

Selective extraction of derivates of p-hydroxy-benzoic acid from plant material by using a molecularly imprinted polymer.

Selective SPE of derivates of p-hydroxybenzoic acid (pHBA) from plant extract of Melissa officinalis is presented using a molecularly imprinted polymer (MIP) made with protocatechuic acid (PA) as template molecule. MIP was prepared with acrylamide as functional monomer, ethylene glycol dimethacrylate as crosslinking monomer and ACN as porogen. MIP was evaluated towards six phenolic acids: PA, gallic acid, pHBA, vanillic acid (VA), gentisic acid (GeA) and syringic acid (SyrA), and then steps of molecularly imprinted SPE (MISPE) procedure were optimized. The best specific binding capacity of MIP was obtained for PA in ACN (34.7 microg/g of MIP). Other tested acids were also bound on MIP if they were dissolved in this solvent. ACN was chosen as solvent for sample application. M. officinalis was extracted into methanol/water (4:1, v/v), the extract was then evaporated to dryness and dissolved in ACN before application on MIP. Water and ACN were used as washing solvents and elution of benzoic acids was performed by means of a mixture methanol/acetic acid (9:1, v/v). pHBA, GA, PA and VA were extracted with recoveries of 56.3-82.1% using this MISPE method. GeA was not determined in plant extract.

Acetic Acid↗
PubMed2001

Inhibitory effect of glycolic acid on ultraviolet-induced skin tumorigenesis in SKH-1 hairless mice and its mechanism of action.

Glycolic acid, an alpha-hydroxy acid derived from fruit and milk sugars, has been used commonly as a cosmetic ingredient since it was discovered to have photoprotective and anti-inflammatory effects and antioxidant effects on ultraviolet (UV)B-irradiated skin. Little is known, however, about the functional role of glycolic acid on UV-induced skin tumorigenesis. In the present study, we examined the effect of glycolic acid on UV (UVA + UVB)-induced skin tumorigenesis and assessed several significant contributing factors in SKH-1 hairless mice. Inbred hairless female mice (15 animals/group) were irradiated for 5 d/wk at a total dose of 74.85 J/cm(2) UVA and 2.44 J/cm(2) UVB for 22 wk. Glycolic acid was applied topically twice a week at a dose of 8 mg/cm(2) immediately after UV irradiation. Glycolic acid reduced UV-induced skin tumor development. The protective effect of glycolic acid was a 20% reduction of skin tumor incidence, a 55% reduction of tumor multiplicity (average number of tumors/mouse), and a 47% decrease in the number of large tumors (larger than 2 mm). Glycolic acid also delayed the first appearance of tumor formation by about 3 wk. The inhibitory effect of glycolic acid on UV-induced tumor development was accompanied by decreased expression of the following UV-induced cell-cycle regulatory proteins: proliferating cell nuclear antigen (PCNA), cyclin D1, cyclin E, and the associated subunits cyclin-dependent kinase 2 (cdk2) and cdk4. In addition, the expression of p38 kinase, jun N-terminal kinase (JNK), and mitogen-activated protein kinase kinase (MEK) also was lower in UV + glycolic acid-treated skin compared with expression in UV-irradiated skin. Moreover, transcription factors activator protein 1 (AP-1) and nuclear factor kappaB (NF-kappaB) activation was significantly lower in UV + glycolic acid-treated skin compared with activation in UV-irradiated skin. These results show that glycolic acid reduced UV-induced skin tumor development. The decreased expression of the cell-cycle regulatory proteins PCNA, cyclin D1, cyclin E, cdk2, and cdk4 and the signal mediators JNK, p38 kinase, and MEK may play a significant role in the inhibitory effect of glycolic acid on UV-induced skin tumor development. In addition, the inhibition of activation of transcription factors AP-1 and NF-kappaB could contribute significantly to the inhibitory effect of glycolic acid.

Animals↗
PubMed1994

Identification and characterization of O-biotinylated hydroxy amino acid residues in peptides.

Recent findings have indicated that certain hydroxyl groups of peptides have enhanced intrinsic chemical reactivity and can be O-acylated by N-hydroxysuccinimide esters of biotin. Analytical procedures are described for the identification of O-acylated derivatives of seryl, threonyl, and tyrosyl residues after reaction with the N-hydroxysuccinimide ester of biotin containing the extended spacer arm 6-aminohexanoic acid. The identification and chemical characterization of O-biotinylated residues included amino acid analysis, peptide sequence determination, and mass spectrometric analysis. The application of these analytical procedures provided unequivocal identification of O-biotinylated residues for a number of peptides investigated. In a separate study, we also show that O-biotinylated amino-terminal seryl residues occurring after proteolysis of peptides or proteins can rapidly undergo an O-->N acyl shift resulting in blockage of sequence analysis by the Edman degradation procedure.

Amino Acid Sequence↗
PubMed1990

Development of a new quantitative method for detection of endotoxin by fluorescence labeling of 3-hydroxy fatty acid.

New quantitative method for the detection of minute amounts of endotoxin has been developed using 3-hydroxytetradecanoic acid as a chemical marker. After converting 3-hydroxytetradecanoic acid to methyl ester, it was coupled with a fluorescent probe, anthracene-9-carboxyl chloride, obtained by chlorization of 9-anthroic acid with oxalyl chloride. The resulting ester was isolated by HPLC on silica column. The purified product, methyl-3-0-(9-carboxy-anthracenyl) tetradecanoate (M/Z 462), was highly responsive to a fluorescence spectrophotometer, showing maximum emission with excitation wavelength at 257 nm and emission wavelength at 458 nm in dichloromethane, the limit of detection being as little as 10 f mol. Using this method it is currently possible to detect Salmonella abortus equi endotoxin in aqueous solution at a level of 100 pg.

Anthracenes↗
PubMed1980

Evolutionary constraints in the mechanism of flavin catalysis.

Analysis of the possible evolution of flavin catalysis in succinate dehydrogenase suggests as the ultimate state an active site that bears one or more acid functions and uses the enediol form of the substrate rather than the carbanion as a nucleophile. In the case of flavoenzyme catalyzed oxidation of fatty acylCoA, alpha-amino acids and alpha-hydroxy acids evolution to a similar mechanism seems to be blocked.

Acyl Coenzyme A↗
PubMed1993

15-Hydroxy-eicosatetraenoic acid has minor anti-inflammatory properties in colitis.

This study was performed to determine whether 15-HETE, which is the major metabolite of arachidonic acid (AA) in inflamed and normal human colonic tissue, has pro- or anti-inflammatory properties. To investigate these effects, 15-HETE (100 micrograms/kg/day) was administered rectally to mice with colitis induced by dextran sodium sulphate (DSS). Colons were removed and examined macroscopically and histologically and specimens were incubated with [14C]-AA and stimulated with A23187. Exogenous eicosanoids were separated by HPLC; the endogenously formed mediators were measured by radioimmunoassay. DSS produced a marked diffuse inflammatory response in the colon, associated with a raised inflammation score (mean 7.6 vs. < 0.5) and a significant increase in endogenously formed metabolites PGE2, LTB4 and 12-HETE. 15-HETE treatment resulted in a slight decrease in inflammation score (6.4 vs. 7.6) and a slight, but not significant, decrease in endogenous LTB4.

Animals↗
PubMed1992

Interleukin-8 stimulates the formation of 15-hydroxy-eicosatetraenoic acid by human neutrophils in vitro.

Interleukin-8 (IL-8), is a potent activator of polymorphonuclear leukocyte (PMN) functions including chemotaxis, superoxide anion production, and enzyme release and it is also chemotactic for lymphocytes. Additionally, it has recently been shown that IL-8 stimulates the formation of 5-lipoxygenase (LO) products of arachidonic acid (AA) by human PMNs. The purpose of the present study was to determine whether IL-8 also might affect the formation of 15-LO products from AA. Purified PMNs in phosphate buffered saline were preincubated with and without exogenous AA (10(-5)-10(-4) M) for 10 min. Then IL-8 was added in biologically relevant concentrations ranging from 0.1 to 100 ng/ml and incubation was carried out for 5 min at 37 degrees C. Lipids were then extracted from supernatants, and eicosanoids were determined by quantitative RP-HPLC. Compared with unstimulated cells, IL-8 resulted in a dose dependent increase in both LTB4 and 15-HETE (up to 125% and 40% at 100 ng/ml, respectively). This increase in eicosanoid formation required the presence of exogenous AA. These results indicate that IL-8 is both a potent stimulator of 5-LO activity and of 15-LO activity. LTB4 can induce both inflammation and contribute to hyperproliferation in the skin. 15-HETE in contrast has the ability to inhibit the effects induced by LTB4. Because IL-8 is able to stimulate both LTB4 and 15-HETE formation, the effect of IL-8 as a putative regulator of inflammatory processes may be dependent on the relative stimulation of 5-LO and 15-LO.

Chromatography, High Pressure Liquid↗