Efficient Reagent-Saving Method for the N‑Terminal Labeling of Bioactive Peptides with Organometallic Carboxylic Acids by Solid-Phase Synthesis

Labeling of biomolecules with organometallic moieties holds great promise as a tool for chemical biology and for the investigation of biochemical signaling pathways. Herein, we report a robust and reproducible synthetic strategy for the synthesis of ruthenocenecarboxylic acid, giving the acid in 53% overall yield. This organometallic label was conjugated via solid-phase peptide synthesis in near-quantitative yield to a number of different biologically active peptides, using only 1 equiv of the acid and coupling reagents, thereby avoiding wasting the precious organometallic acid. This optimized method of stoichiometric N-terminal acylation was then also successfully applied to conjugating ferrocenecarboxylic acid and a novel organometallic Re^I(CO)₃ complex, showing the generality of the synthetic procedure

Efficient Reagent-Saving Method for the N‑Terminal Labeling of Bioactive Peptides with Organometallic Carboxylic Acids by Solid-Phase Synthesis

Labeling of biomolecules with organometallic moieties holds great promise as a tool for chemical biology and for the investigation of biochemical signaling pathways. Herein, we report a robust and reproducible synthetic strategy for the synthesis of ruthenocenecarboxylic acid, giving the acid in 53% overall yield. This organometallic label was conjugated via solid-phase peptide synthesis in near-quantitative yield to a number of different biologically active peptides, using only 1 equiv of the acid and coupling reagents, thereby avoiding wasting the precious organometallic acid. This optimized method of stoichiometric N-terminal acylation was then also successfully applied to conjugating ferrocenecarboxylic acid and a novel organometallic Re^I(CO)₃ complex, showing the generality of the synthetic procedure

Synthesis, Antimicrobial Activity, and Membrane Permeabilizing Properties of C‑Terminally Modified Nisin Conjugates Accessed by CuAAC

Functionalization of the lantibiotic nisin with fluorescent reporter molecules is highly important for the understanding of its mode of action as a potent antimicrobial peptide. In addition to this, multimerization of nisin to obtain multivalent peptide constructs and conjugation of nisin to bioactive molecules or grafting it on surfaces can be attractive methods for interference with bacterial growth. Here, we report a convenient method for the synthesis of such nisin conjugates and show that these nisin derivatives retain both their antimicrobial activity and their membrane permeabilizing properties. The synthesis is based on the Cu­(I)-catalyzed alkyne–azide cycloaddition reaction (CuAAC) as a bioorthogonal ligation method for large and unprotected peptides in which nisin was C-terminally modified with propargylamine and subsequently efficiently conjugated to a series of functionalized azides. Two fluorescently labeled nisin conjugates together with a dimeric nisin construct were prepared while membrane insertion as well as antimicrobial activity were unaffected by these modifications. This study shows that C-terminal modification of nisin does not deteriorate biological activity in sharp contrast to N-terminal modification and therefore C-terminally modified nisin analogues are valuable tools to study the antibacterial mode of action of nisin. Furthermore, the ability to use stoichiometric amounts of the azide containing molecule opens up possibilities for surface tethering and more complex multivalent structures

Main Phenolic Compounds of the Melanin Biosynthesis Pathway in Bruising-Tolerant and Bruising-Sensitive Button Mushroom (Agaricus bisporus) Strains

Browning is one of the most common postharvest changes in button mushrooms, which often results in economic losses. Phenolic compounds, which are associated with browning, were extracted from the nonbruised and bruised skin tissue of various button mushrooms with a sulfite-containing solution and analyzed with UHPLC-PDA-MS. In total, 34 phenolic compounds were detected. Only small differences in the total phenolic content between bruising-tolerant and -sensitive strains were observed. The contents of γ-l-glutaminyl-4-hydroxybenzene (GHB) and γ-l-glutaminyl-3,4-dihydroxybenzene (GDHB) correlated with bruising sensitivity; for example, <i>R</i>² values of 0.85 and 0.98 were found for nonbruised brown strains, respectively. In nonbruised skin tissue of the strains with brown caps, the GHB and GDHB contents in sensitive strains were on average 20 and 15 times higher, respectively, than in tolerant strains. GHB and GDHB likely participate in the formation of brown GHB–melanin, which seemed to be the predominant pathway in bruising-related discoloration of button mushrooms

Main Phenolic Compounds of the Melanin Biosynthesis Pathway in Bruising-Tolerant and Bruising-Sensitive Button Mushroom (Agaricus bisporus) Strains

Browning is one of the most common postharvest changes in button mushrooms, which often results in economic losses. Phenolic compounds, which are associated with browning, were extracted from the nonbruised and bruised skin tissue of various button mushrooms with a sulfite-containing solution and analyzed with UHPLC-PDA-MS. In total, 34 phenolic compounds were detected. Only small differences in the total phenolic content between bruising-tolerant and -sensitive strains were observed. The contents of γ-l-glutaminyl-4-hydroxybenzene (GHB) and γ-l-glutaminyl-3,4-dihydroxybenzene (GDHB) correlated with bruising sensitivity; for example, <i>R</i>² values of 0.85 and 0.98 were found for nonbruised brown strains, respectively. In nonbruised skin tissue of the strains with brown caps, the GHB and GDHB contents in sensitive strains were on average 20 and 15 times higher, respectively, than in tolerant strains. GHB and GDHB likely participate in the formation of brown GHB–melanin, which seemed to be the predominant pathway in bruising-related discoloration of button mushrooms