Fluoroalkyl chloroformates in treating amino acids for gas chromatographic analysis

A sensitive liquid chromatography-tandem mass spectrometry method for determination biomarkers of monoamine neurotransmitter disorders in cerebrospinal fluid

BACKGROUND

Cerebrospinal fluid (CSF) monoamine neurotransmitters, their precursors and metabolites are essential biomarkers in the diagnosis and follow-up of monoamine neurotransmitter disorders (MNDs). However, their extra low concentrations and potential instability challenge the detection method. Here, we present a method that enables simultaneous quantification of these biomarkers.

METHOD

With propyl chloroformate /n-propanol, 16 biomarkers in 50 μL of CSF were derivatized in situ within seconds under an ambient temperature. The derivatives were extracted by ethyl acetate and separated by a reverse phase column followed by mass spectrometric detection. The method was fully validated. Optimal conditions for standard solution preparation and storage, as well as CSF sample handling, were investigated. CSF samples from 200 controls and 16 patients were analyzed.

RESULTS

The derivatization reaction stabilized biomarkers and increased sensitivity. Most biomarkers were quantifiable in concentrations between 0.02 and 0.50 nmol/L that were sufficient to measure their endogenous concentrations. The intra- and inter-day imprecision were < 15% for most analytes, and accuracy ranged from 90.3% to 111.6%. The stability study showed that standard stock solutions were stable at -80 °C for six years when prepared in the protection solutions; Analytes in CSF samples were stable for 24 h on wet ice and at least two years at -80 °C; But repeated freeze-thaw should be avoided. With this method, age-dependent reference intervals for each biomarker in the pediatric population were established. Patients with MNDs were successfully identified.

CONCLUSION

The developed method is valuable for MNDs diagnosis and research, benefiting from its advantages of sensitivity, comprehensiveness, and high throughput.

Monitoring of circulating amino acids in patients with pancreatic cancer and cancer cachexia using capillary electrophoresis and contactless conductivity detection

Branched chain amino acids (BCAAs), alanine and glutamine are determined in human plasma by capillary electrophoresis with contactless conductivity detection (CE/C⁴ D). The baseline separation of five amino acids from other plasma components is achieved on the short capillary effective length of 18 cm in 3.2 mol/L acetic acid with addition of 13% v/v methanol as background electrolyte. Migration times range from 2.01 min for valine to 2.84 min for glutamine, and LODs for untreated plasma are in the interval 0.7-0.9 μmol/L. Sample treatment is based on the addition of acetonitrile to only 15 μL of plasma and supernatant is directly subjected to CE/C⁴ D. Circulating amino acids are measured in patients with pancreatic cancer and cancer cachexia during oral glucose tolerance test. It is shown that patients with pancreatic cancer and cancer cachexia syndrome exhibit low basal circulating BCAAs and glutamine levels and loss of their insulin-dependent suppression.

The Importance of Time and Place: Nutrient Composition and Utilization of Seasonal Pollens by European Honey Bees (Apis mellifera L.)

Simple Summary

Honey bees rely on pollen and nectar to provide nutrients to support their yearly colony cycle. Specifics of the cycle differ among geographic regions as do the species of flowering plants and the nutrients they provide. We examined responses of honey bees from two different queen lines fed pollens from locations that differed in floral species composition and yearly colony cycles. We detected differences between the queen lines in the amount of pollen they consumed and the size of their hypopharyngeal glands (HPG). There were also seasonal differences between the nutrient composition of pollens. Spring pollens collected from colonies in both locations had higher amino and fatty acid concentrations than fall pollens. There also were seasonal differences in responses to the pollens consumed by bees from both queen lines. Bees consumed more spring than fall pollen, but digested less of it so that bees consumed more protein from fall pollens. Though protein consumption was higher with fall pollen, HPG were larger in spring bees.

Abstract

Honey bee colonies have a yearly cycle that is supported nutritionally by the seasonal progression of flowering plants. In the spring, colonies grow by rearing brood, but in the fall, brood rearing declines in preparation for overwintering. Depending on where colonies are located, the yearly cycle can differ especially in overwintering activities. In temperate climates of Europe and North America, colonies reduce or end brood rearing in the fall while in warmer climates bees can rear brood and forage throughout the year. To test the hypothesis that nutrients available in seasonal pollens and honey bee responses to them can differ we analyzed pollen in the spring and fall collected by colonies in environments where brood rearing either stops in the fall (Iowa) or continues through the winter (Arizona). We fed both types of pollen to worker offspring of queens that emerged and open mated in each type of environment. We measured physiological responses to test if they differed depending on the location and season when the pollen was collected and the queen line of the workers that consumed it. Specifically, we measured pollen and protein consumption, gene expression levels (hex 70, hex 110, and vg) and hypopharyngeal gland (HPG) development. We found differences in macronutrient content and amino and fatty acids between spring and fall pollens from the same location and differences in nutrient content between locations during the same season. We also detected queen type and seasonal effects in HPG size and differences in gene expression between bees consuming spring vs. fall pollen with larger HPG and higher gene expression levels in those consuming spring pollen. The effects might have emerged from the seasonal differences in nutritional content of the pollens and genetic factors associated with the queen lines we used.

A chiral GC-MS method for analysis of secondary amino acids after heptafluorobutyl chloroformate & methylamine derivatization

L-amino acids (L-AAs) play different important roles in the physiology of all living organisms. Their chiral counterparts, D-amino acids (D-AAs) are increasingly being recognized as essential molecules in many biological systems. Secondary amino acids with cyclic structures, such as prolines, exhibit conformational rigidity and thus unique properties in the structural and protein folding. Despite their widespread occurrence, much less attention was paid to their chiral analysis, particularly when the minor, typically D-enantiomer, is present in low amounts in a complex biological matrix. In this paper, a cost-effective, chiral GC-MS method is described for capillary Chirasil-L-Val separation of nine cyclic secondary amino acid enantiomers with four-, five-, and six-membered rings, involving azetidine-2-carboxylic acid, pipecolic acid, nipecotic acid, proline, isomeric cis/trans 3-hydroxy, 4-hydroxyproline, and cis/trans-5-hydroxy-L-pipecolic acid in the excess of its enantiomeric antipode. The sample preparation involves in-situ derivatization with heptafluorobutyl chloroformate, simultaneous liquid-liquid micro-extraction into isooctane followed by amidation of the arising low-polar derivatives with methylamine, an evaporation step, re-dissolution, and final GC-MS analysis. The developed method was used for analyses of human biofluids, biologically active peptides containing chiral proline constituents, and collagen.

Heptafluorobutyl Chloroformate-Based Sample Preparation Protocol for Nonchiral and Chiral Amino Acid Analysis by Gas Chromatography-Mass Spectrometry

Gas chromatography (GC) is a commonly used technique in amino acid analysis (AAA). However, one of the requirements of the application of GC for AAA is a need for the polar analytes to be converted into their volatile, thermally stable derivatives. In the last two decades, alkyl chloroformates (RCFs) have become attractive derivatization reagents. The reagents react immediately with most amino acid functional groups in aqueous matrices, and the process can easily be coupled with liquid-liquid extraction of the resulting less polar derivatives into immiscible organic phase. Here we describe a simple protocol for in situ derivatization of amino acids with heptafluorobutyl chloroformate (HFBCF) followed by subsequent chiral as well as nonchiral GC/MS (mass spectrometric) analysis on a respective nonpolar fused silica and an enantioselective Chirasil-Val capillary column.

Rapid and Sensitive Determination of Branched-Chain Amino Acids in Human Plasma by Capillary Electrophoresis with Contactless Conductivity Detection for Physiological Studies

Capillary electrophoresis (CE) with contactless conductivity detection (C⁴D) represents a strong tool for determining amino acids in clinical samples. This chapter provides detailed instructions for CE/C⁴D determination of the branched-chain amino acids (BCAAs) valine, isoleucine, and leucine in human plasma, which can be readily employed in physiological studies. Baseline separation of all the BCAAs is achieved on a short separation length equal to 18 cm in optimized background electrolyte consisting of 3.2 M acetic acid dissolved in 20% v/v methanol with addition of 1.0% v/v INST-coating solution. The analysis time does not exceed 3 min and the limit of detection is 0.4 μM for all BCAAs. The pretreatment of human plasma is very simple and is based on fourfold plasma dilution by acetonitrile and subsequent filtration. Only 50 μL of plasma is used for the analysis. The high sensitivity of the CE/C⁴D method is achieved by injecting a large volume of sample, combined with application of negative pressure to flush the acetonitrile zone out of the capillary.

Connecting the nutrient composition of seasonal pollens with changing nutritional needs of honey bee (Apis mellifera L.) colonies

Free-ranging herbivores have yearly life cycles that generate dynamic resource needs. Honey bee colonies also have a yearly life cycle that might generate nutritional requirements that differ between times of brood rearing and colony expansion in the spring and population contraction and preparation for overwintering in the fall. To test this, we analyzed polyfloral mixes of spring and fall pollens to determine if the nutrient composition differed with season. Next, we fed both types of seasonal pollens to bees reared in spring and fall. We compared the development of brood food glands (i.e., hypopharyngeal glands - HPG), and the expression of genes in the fat body between bees fed pollen from the same (in-season) or different season (out-of-season) when they were reared. Because pathogen challenges often heighten the effects of nutritional stress, we infected a subset of bees with Nosema to determine if bees responded differently to the infection depending on the seasonal pollen they consumed. We found that spring and fall pollens were similar in total protein and lipid concentrations, but spring pollens had higher concentrations of amino and fatty acids that support HPG growth and brood production. Bees responded differently when fed in vs. out of season pollen. The HPG of both uninfected and Nosema-infected spring bees were larger when they were fed spring (in-season) compared to fall pollen. Spring bees differentially regulated more than 200 genes when fed in- vs. out-of-season pollen. When infected with Nosema, approximately 400 genes showed different infection-induced expression patterns in spring bees depending on pollen type. In contrast, HPG size in fall bees was not affected by pollen type, though HPG were smaller in those infected with Nosema. Very few genes were differentially expressed with pollen type in uninfected (4 genes) and infected fall bees (5 genes). Pollen type did not affect patterns of infection-induced expression in fall bees. Our data suggest that physiological responses to seasonal pollens differ between bees reared in the spring and fall with spring bees being significantly more sensitive to pollen type especially when infected with Nosema. This study provides evidence that seasonal pollens may provide levels of nutrients that align with the activities of honey bees during their yearly colony cycle. The findings are important for the planning and establishment of forage plantings to sustain honey bees, and in the development of seasonal nutritional supplements fed to colonies when pollen is unavailable.

Simultaneous analysis of the non-canonical amino acids norleucine and norvaline in biopharmaceutical-related fermentation processes by a new ultra-high performance liquid chromatography approach

In this study, a precise and reliable ultra-high performance liquid chromatography (UHPLC) method for the simultaneous determination of non-canonical (norvaline and norleucine) and standard amino acids (aspartic acid, glutamic acid, serine, histidine, glycine, threonine, arginine, tyrosine, methionine, valine, phenylalanine, isoleucine, leucine) in biopharmaceutical-related fermentation processes was established. After pre-column derivatization with ortho-phthaldialdehyde and 2-mercaptoethanol, the derivatives were separated on a sub-2 μm particle C18 reverse-phase column. Identification and quantification of amino acids were carried out by fluorescence detection. To test method feasibility on standard HPLC instruments, the assay was properly transferred to a core-shell particle C18 reverse-phase column. The limits of detection showed excellent sensitivity by values from 0.06 to 0.17 pmol per injection and limits of quantification between 0.19 and 0.89 pmol. In the present study, the newly established UHPLC method was applied to a recombinant antibody Escherichia coli fermentation process for the analysis of total free amino acids. We were able to specifically detect and quantify the unfavorable amino acids in such complex samples. Since we observed trace amounts of norvaline and norleucine during all fermentation phases, an obligatory process monitoring should be considered to improve quality of recombinant protein drugs in future.

In situ derivatization-liquid liquid extraction as a sample preparation strategy for the determination of urinary biomarker prolyl-4-hydroxyproline by liquid chromatography-tandem mass spectrometry

Polar analytes that possess protic functional groups have often been treated with alkyl chloroformates to decrease their polarity and increase their volatility prior to gas chromatography-mass spectrometry analysis. This derivatization reaction has two distinct advantages. It proceeds smoothly in aqueous media, and the desired reaction products are efficiently separated from interfering ionic components by their extraction into a water-immiscible organic phase. In the present work, the derivatization-liquid liquid sample preparation was examined in detail for analysis of a potential urinary dipeptide biomarker L-prolyl-4-L-hydroxyproline (PHP) by downstream liquid chromatography coupled to electrospray mass spectrometry. PHP was treated with a series of alkyl and fluoroalkyl chloroformates in aqueous media, and the detected reaction products were investigated. Smooth conversion of PHP into the N-isobutyloxycarbonyl isobutyl ester was accomplished by the coupled action of isobutanol, isobutyl chloroformate and the pyridine catalyst. This derivative afforded a highest detector response from all the derivatized forms examined, including the nonderivatized PHP. A simple isocratic elution on a common RP-C18 HPLC column coupled with tandem mass spectrometry, and use of the synthesized heptadeuterated analog (D7-PHP) as an internal standard, enabled validation of the method and determination of PHP in human urine in less than 5 min. The in situ derivatization-liquid liquid extraction has thus been demonstrated to be a useful sample preparation strategy for the analysis of polar metabolites by liquid chromatography-tandem mass spectrometry in the complex urine matrix.

Heptafluorobutyl chloroformate-based sample preparation protocol for chiral and nonchiral amino acid analysis by gas chromatography

Gas chromatography (GC) is a commonly used technique in amino acid analysis (AAA). However, one of the requirements of the application of GC for AAA is a need for the polar analytes to be converted into their volatile, thermally stable derivatives. In the last two decades, alkyl chloroformates have become attractive derivatization reagents. The reagents react immediately with most amino acid functional groups in aqueous matrices and the process can easily be coupled with liquid-liquid extraction of the resulting less-polar derivatives into immiscible organic phase. Here, we describe a simple protocol for in situ derivatization of amino acids with heptafluorobutyl chloroformate followed by subsequent chiral as well as nonchiral GC/mass spectrometric analysis on a respective nonpolar fused silica and an enantioselective Chirasil-Val capillary column.

Advances in amino acid analysis

Amino acids are important targets for metabolic profiling. For decades, amino acid analysis has been accomplished by either cation-exchange or reversed-phase liquid chromatography coupled to UV absorbance or fluorescence detection of pre-column or post-column-derivatized amino acids. Recent years have seen great progress in the development of direct-infusion or hyphenated mass spectrometry in the analysis of free amino acids in physiological fluids, because mass spectrometry not only matches optical detection in sensitivity, but also offers superior selectivity. The advent of cryo-probes has also brought NMR spectroscopy within the detection limits required for the analysis of free amino acids. But there is still room for further improvement, including expansion of the analyte spectrum, reduction of sample preparation and analysis time, automation, and synthesis of affordable isotope standards.

Gas chromatographic analysis of amino acid enantiomers in Carbetocin peptide hydrolysates after fast derivatization with pentafluoropropyl chloroformate

A novel sample preparation protocol for gas chromatographic (GC) analysis of amino acid enantiomers in peptides was developed. It comprises traditional acid hydrolysis, a novel treatment of the analytes with a fluoroalkyl chloroformate and GC/FID separation of enantiomers on a chiral capillary column. The major improvements consist in that the derivatization step proceeds in organic-aqueous media within seconds and the amino acid derivatives are volatile enough to suit the temperature range of the chiral Chirasil-Val capillary column. The approach was found beneficial for chiral analysis of pharmaceutically important Carbetocin peptide.