Core-Shell Metal-Organic Frameworks/Molecularly Imprinted Nanoparticles as Absorbents for the Detection of Pyrraline in Milk and Milk Powder.

A novel core-shell metal-organic framework coated with a dummy template molecularly imprinted polymer (MOF@DMIP) was synthesized by one-pot bulk polymerization for the detection of pyrraline in food samples. The pyrraline analogue pyrrolidine-3-carboxylic acid was used as the template because of its lower cost, and MIL-101 was used as the MOF core owing to its numerous inherent advantages, including high chemical and hydrothermal stabilities. MIL-101@DMIP was used to detect trace pyrraline in foods by solid-phase extraction combined with high-performance liquid chromatography. It exhibited the advantages of faster mass transport, excellent sensitivity, and selectivity. Under optimum conditions, the detection limit of this system was 40.7 µg L-1, and a linear range was from 5 × 10-7 to 2 × 10-3 mol L-1, within relative standard deviations of 4.46-6.87%. The recoveries ranged from 92.23 to 103.87%, indicating the excellent ability of the prepared MIL-101@DMIP to recognize pyrraline in complex food matrices and its potential for application in pyrraline detection.

Identification of AGE-precursors and AGE formation in glycation-induced BSA peptides.

The glycation of BSA leads to protein/peptide modifications that result in the formation of AGEs. AGEs react with the amino groups of N-terminal amino acid residues, particularly arginine and lysine residues. Enhanced AGE formation exists in the blood and tissues of diabetics, as well as in aging and other disorders. The Identification of AGEs is of great importance. Mass spectrometry has been applied to identify and structurally elucidate AGEs. Here, we report on the identification of AGE- peptides and AGE-precursors based on relative mass changes as a result of specific AGE formation. HPLC-ESIMS, ESI-MS/MS, and the Mascot database were used. The relative mass changes due to the specific type of AGE formation were added to the identified peptides followed by a manual search of the glycated samples, which resulted in the identification of seven peptides for the formation of five AGEs, namely CML, pyrraline, imidazolone A, imidazolone B, and AFGP. Four glycated peptides (FPK, ECCDKPLLEK, IETMR, and HLVDEPQNLIK) were identified in the formation of AGE-precursors.

[Studies on the chemical constituents of the ethyl acetate portion of Nervilia fordii].

OBJECTIVE: To study the chemical constituents of the ethyl acetate portion in the herb of Nervilia fordii from guangxi. METHODS: The constituents were separated and purified by using column chromatography with silica gel. These compounds were identified by their physical and spectral data. RESULTS: Five compounds were isolated and identified as norleucine (crystal I), 24 (S/beta)-dihydrocycloeucalenol-(E)-p-hydroxy cinnamate (crystal II) , rhamnocitrin (crystal III), rhamnazin (crystal IV), daucosterol (crystal V). CONCLUSION: Compounds I , II, III, IV, V were isolated from this plant for the first time.

Norleucine, a natural occurrence in a novel ergot alkaloid gamma-ergokryptinine.

A novel natural peptide ergot alkaloid gamma-ergokryptinine containing norleucine has been isolated from ergot sclerotia of the field-growing parasitic fungus Claviceps purpurea CCM 8059. Its structure was deduced from the NMR and mass spectral data. The final structural proof was provided by the crystal structure determination, which is the first X-ray structure of a natural Nle-containing secondary metabolite. The conformations of three ergopeptinines: gamma-ergokryptinine, ergoladinine, and alpha-ergokryptinine were compared.

First evidence for accumulation of protein-bound and protein-free pyrraline in human uremic plasma by mass spectrometry.

Glucose-derived advanced glycation end products (AGEs) cross-link proteins and cause various biological tissue damage. One of them, pyrraline [epsilon-2-(formyl-5-hydroxymethyl-pyrrol-1-yl) -L-norleucine], has been demonstrated by utilizing antibody to accumulate in plasma and sclerosed matrix of diabetic individuals, suggesting responsibility for diabetic complications. To elucidate the involvement of pyrraline in uremia, we examined the pyrraline levels in patients with chronic renal failure by a mass spectrometric approach. Here we show that protein-free pyrraline as well as pyrraline with binding protein are significantly increased in non-diabetic uremic plasma compared to healthy subjects. Our results suggest that circulating pyrraline could be a substance contributing to complications in uremia.

The presence of a glucose-derived Maillard reaction product in the human lens.

Pyrraline is an advanced Maillard reaction product formed by the non-enzymatic reaction initiated by glucose with lysine residues on proteins. This reaction involves an intermediate, 3-deoxyglucosone, concentration of which is shown to be elevated in plasma and lenses during diabetes. Bovine lens alpha crystallins incubated with 3-deoxyglucosone showed that pyrraline formation was a major modification and its quantification by two different methods revealed time-dependent accumulation. Pyrraline was quantified in normal, senile cataractous and diabetic lenses. Although a wide variation was observed, the mean value in cataractous lenses (mean +/- S.E.: 48.4 +/- 12.67 pmol/mg protein) was higher than in age-matched normal lenses (30.9 +/- 10.26 pmol). Surprisingly, in diabetic lenses, the mean value was lower than normal lenses (28.4 +/- 15.3 pmol). These results suggest that glucose-specific advanced Maillard products occur in the human lens and such modifications may play a role in lens aging and cataract formation.

Optical enrichment of dansyl-rac-amino acids by formation of crystalline inclusion complexes with cyclodextrins.

Optical enrichment from racemic dansyl-leucine, dansyl-norleucine, and dansyl-phenylalanine with both beta- and gamma-cyclodextrins in water is reported. Initial crystallization yielded the dansyl-L-Leucine isomer complexed in excess with beta-cyclodextrin with an optical purity of 62-78% depending on experimental conditions. The optical purities obtained for L-norleucine and L-phenylalanine were 71 and 64%, respectively. The optical purity can be increased with continued recrystallization. The dansyl-D-leucine isomer was obtained in the mother liquor with an optical purity of 54-93% depending on experimental conditions. The optical purities obtained for D-norleucine and D-phenylalanine were 72 and 58%. The optical purity of the isomer depended on the molar ratio of host:guest and the pH value of the solution. Optimum enrichment of both enantiomers was achieved with host:guest ratios of 2:1 and 3:1. Although maximum crystalline yield of the dansyl-leucine/CD inclusion complex was obtained at a pH of 3.5, optical purity of both enantiomers was less than that obtained at other pHs. The influence of the molar ratio of host:guest and the pH value of the solution are discussed. This method is suitable for large-scale enantiomeric separations.

beta-methylnorleucine, an antimetabolite produced by Serratia marcescens.

An amino acid was formed by alpha-aminobutyrate-resistant mutants of Serratia marcescens grown in a medium containing norvaline. This amino acid was identified as erythro-beta-methyl-L-norleucine [(2S,3S)-2-amino-3-methylhexanoic acid] by instrumental analyses. beta-Methylnorleucine inhibited the growth of several bacteria in synthetic medium.

Beta-hydroxynorleucine: separation of its isomers and biological studies.

Separation of the four isomers of beta-hydroxynorleucine was accomplished by partition column chromatography and asymmetric enzymatic hydrolysis of the N-chloroacetyl derivatives. From these, the corresponding N-chloroacetyl derivatives were made. The purity and configuration of each isomer of the free acid and N-chloroacetylated derivative were ascertained by: (a) paper chromatography in five solvent systems, (b) elemental analysis, (c) Van Slyke nitrous acid determination of alpha-carbonyl carbon, and (d) Van Slyke ninhydrin determination of alpha-carbonyl carbon, and (e) optical rotation. Comparison of the rate of enzymatic hydrolysis by hog renal acylase I of the N-chloroacetyl derivative of the L-isomers of each diastereomer showed that the acyl B isomer is a better substrate than the acyl A isomer, where A denotes the faster moving diastereomer and B denotes the slower moving diastereomer in a defined chromatographic solvent system. Microbiological assay using Lactobacillus casei in a system selected for screening for possible antitumor activity indicated that while none of the isomers as free amino acids had any growth inhibitory action, the N-acylated isomers showed modest but significant activity. The N-chloroacetyl derivative of the D-enantiomorph of diastereomer B exhibited the greatest growth inhibitory activity, showing about twice the activity of the other three isomers.

The chemistry of the collagen cross-links. The characterization of fraction C, a possible artifact produced during the reduction of collagen fibres with borohydride.

The present paper describes the isolation and identification of a major radioactive component of borotritide-reduced collagen, previously designated Fraction C. The derived structure for the compound confirms that it is identical with the ;post-histidine' component described by Tanzer et al. (1973) and given the trivial name histidino-hydroxymerodesmosine. Detailed studies of the effects of acid pH on the formation of Fraction C after borohydride reduction demonstrated the apparent lability of the non-reduced form, thus confirming our previous findings (Bailey & Lister, 1968). Inhibition of the formation of this component by the acid treatment appears to be due to protonation of the histidine imidazole group. Since the only new component formed on reduction of the acid-treated fibres was the reduced aldol condensation product, these results indicate that neither the histidine nor the hydroxylysine residues can be involved in covalent linkage with the aldol condensation product in the native fibre. It is suggested therefore that the proposed non-reduced aldimine form of Fraction C does not exist as an intermolecular cross-link in vivo. Thus the presence of histidino-hydroxymerodesmosine as a tetrafunctional cross-link in reduced collagen fibres is a result of a base-catalysed reaction promoted by the borohydride-reduction procedure and this component must therefore be considered as an artifact.