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Small metabolic molecules often are chiral and can play important roles in regulating a variety of biological functions, occasionally providing information about the presence and progression of disease. The most ubiquitous class of such small molecules are amino acids. Sensitive and accurate analysis of the less prevalent D-amino acids as free entities or as constituents of peptides can be challenging, particularly when complex physiological matrices are involved. The number of studies involving low-abundance D-amino acids in biological systems has increased significantly over the last decade. Studies involving their presence and importance have become increasingly difficult to ignore. Their relevance in neurological pathologies, cancer, kidney disorders, and more, has advanced. Chiral separations have played and continue to play a central role in these studies. Because enantiomers and epimers have the same exact mass, stereoselective separations are essential. However, sens it ive d e tec tio n is al s o nece ssa r y b ec au s e t ra c e leve l s of the s e analy te s are invol ve d. Mu lt id imens ional separ ation s often provide the best avenue for accurate qualitative and quantitative results. Future developments will involve faster and highly specific routine testing, particularly if these analyses are to enter the clinical realm., Specific small-molecule metabolic biomarkers can be essential tools for detecting and diagnosing diseases and monitoring their progress. Furthermore, they can serve as signaling and activation molecules and can even play [...]

Due to the favorable features obtained through the incorporation of fluorine atom(s), fluorinated drugs are a group with emerging pharmaceutical importance. As their commercial availability is still very limited, to expand the range of possible candidates, new fluorinated tryptophan analogs were synthesized. Control of enantiopurity during the synthesis procedure requires that highly efficient enantioseparation methods be available. In this work, the enantioseparation of seven fluorinated tryptophans and tryptophan was studied and compared systematically to (i) develop analytical methods for enantioselective separations and (ii) explore the chromatographic features of the fluorotrytophans. For enantioresolution, macrocyclic glycopeptide-based selectors linked to core-shell particles were utilized, applying liquid chromatography-based methods. Application of the polar-ionic mode resulted in asymmetric and broadened peaks, while reversed-phase conditions, together with mobile-phase additives, resulted in baseline separation for all studied fluorinated tryptophans. The marked differences observed between the methanol and acetonitrile-containing eluent systems can be explained by the different solvation abilities of the bulk solvents of the applied mobile phases. Among the studied chiral selectors, teicoplanin and teicoplanin aglycone were found to work effectively. Under optimized conditions, baseline separations were achieved within 6 min. Ionic interactions were semi-quantitatively characterized and found to not influence enantiorecognition. Interestingly, fluorination of the analytes does not lead to marked changes in the chromatographic characteristics of the methanol-containing eluents, while larger differences were noticed when the polar but aprotic acetonitrile was applied. Experiments conducted on the influence of the separation temperature indicated that the separations are enthalpically driven, with only one exception. Enantiomeric elution order was found to be constant on both teicoplanin and teicoplanin aglycone-based chiral stationary phases (L < D) under all applied chromatographic conditions. [ABSTRACT FROM AUTHOR]

In many land plants, the stomatal pore opens during the day and closes during the night. Thus, periods of darkness could be effective in decreasing pathogen penetration into leaves through stomata, the primary sites for infection by many pathogens. Pseudomonas syringae pv. tomato (Pst) DC3000 produces coronatine (COR) and opens stomata, raising an intriguing question as to whether this is a virulence strategy to facilitate bacterial infection at night. In fact, we found that (a) biological concentration of COR is effective in opening dark-closed stomata of Arabidopsis thaliana leaves, (b) the COR defective mutant Pst DC3118 is less effective in infecting Arabidopsis in the dark than under light and this difference in infection is reduced with the wild type bacterium Pst DC3000, and (c) cma, a COR biosynthesis gene, is induced only when the bacterium is in contact with the leaf surface independent of the light conditions. These findings suggest that Pst DC3000 activates virulence factors at the pre-invasive phase of its life cycle to infect plants even when environmental conditions (such as darkness) favor stomatal immunity. This functional attribute of COR may provide epidemiological advantages for COR-producing bacteria on the leaf surface.

Analytical and preparative separation techniques, although perceived as less detrimental compared to industrial manufacturing processes, present a substantial concealed environmental threat. Green analytical chemistry has seen major advances in the past five years in terms of proposing metrics for measuring the greenness of separation methods. One such comprehensive measure is the Analytical Method Greenness Score (AMGS), which was used to benchmark current enantiomeric separation methods in the literature. In this work, we propose pragmatic and mathematical strategies to minimize AMGSs in high-performance liquid chromatographic enantioseparations. A case study of more than 456 chromatograms from the enantiomers of 38 proteo- and non-proteogenic amino acids was generated and assessed. A sustainable method of generating carbonated water-based eluents was introduced, and the H2CO3* additive was shown to improve the chromatographic figures of merit (resolution and efficiency) while lowering the AMGS. We show that narrow diameter columns with superficially porous particles reduced the solvent waste 12-fold compared to traditional analyses. The AMGS formula was modified to incorporate the "cycle time" of the chromatograph, which provides a more accurate picture of solvent waste generation in high throughput chemical analyses. Using the principles of mathematical optimization, the AMGS was minimized with respect to flow rate to show that the ideal separation speed differs depending on the solvent composition. The AMGS reached values as low as 1.2 for ultrafast (<15 s) amino acid chiral separations, where 79% was contributed by the cycle time. This AMGS minimization adds a new optimization problem to future method development, with widespread implications for drug development research and other production fields reliant on separation sciences. [ABSTRACT FROM AUTHOR]