Synthesis and Reactions of 3‐Oxobutyl Isothiocyanate (OB ITC)

Synthetic and mechanistic study on the conjugate isothiocyanation of enones with trimethylsilyl isothiocyanate

Alkyl isothiocyanates (R-NCS) have pharmacological applications and provide a synthetic handle to various functional groups including thioureas. There are however few methods to access alkyl isothiocyanates through the creation of the C-N bond. We have developed a simple approach for the conjugate isothiocyanation of enones by trimethylsilyl isothiocyanate (TMSNCS), which proceeds through the 1,4-addition of the weak isothiocyanate nucleophile to activated enones in the absence of external promoters. This method avoids the direct use of highly toxic acids and bases, produces β-isothiocyanato carbonyl products in yields of 87-98% under mild conditions (less than 6 hours at 0 °C), and displays wide functional group tolerance. Density functional theory calculations highlighted competing cationic and anionic mechanisms, where the enone activation by the TMSNCS reagent is accelerated in protic solvents. The selective formation of the isothiocyanate vs. thiocyanate isomers is explained by the thermodynamically-controlled nature of the reaction in which only the conjugate isothiocyanation is exergonic.

Antibacterial activity and mode of action of selected glucosinolate hydrolysis products against bacterial pathogens

Plants contain numerous components that are important sources of new bioactive molecules with antimicrobial properties. Isothiocyanates (ITCs) are plant secondary metabolites found in cruciferous vegetables that are arising as promising antimicrobial agents in food industry. The aim of this study was to assess the antibacterial activity of two isothiocyanates (ITCs), allylisothiocyanate (AITC) and 2-phenylethylisothiocyanate (PEITC) against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Listeria monocytogenes. The antibacterial mode of action was also characterized by the assessment of different physiological indices: membrane integrity, intracellular potassium release, physicochemical surface properties and surface charge. The minimum inhibitory concentration (MIC) of AITC and PEITC was 100 μg/mL for all bacteria. The minimum bactericidal concentration (MBC) of the ITCs was at least 10 times higher than the MIC. Both AITC and PEITC changed the membrane properties of the bacteria decreasing their surface charge and compromising the integrity of the cytoplasmatic membrane with consequent potassium leakage and propidium iodide uptake. The surface hydrophobicity was also non-specifically altered (E. coli and L. monocytogenes become less hydrophilic; P. aeruginosa and S. aureus become more hydrophilic). This study shows that AITC and PEITC have strong antimicrobial potential against the bacteria tested, through the disruption of the bacterial cell membranes. Moreover, phytochemicals are highlighted as a valuable sustainable source of new bioactive products.

Enzymatic inhibition by allyl isothiocyanate and factors affecting its antimicrobial action against Escherichia coli O157:H7

Allyl isothiocyanate (AIT) is derived from the glucosinolate sinigrin found in plants of the family Brassicaceae. It is a well-recognized antimicrobial agent against a variety of organisms, including foodborne pathogens such as Escherichia coli O157:H7. The efficiency of this natural agent in reducing E. coli O157:H7 numbers in food products have been reported. However, few have examined the mechanism by which AIT, and perhaps most of the isothiocyanates, kill E. coli O157:H7. In the present report, AIT showed greater antimicrobial activity at low pH values. For example, at pH 4.5 and 5.5 the MIC was 25 microL/L, while at pH 8.5, 500 microL/L was required to inhibit bacterial growth. This mustard-derived compound exhibited a high decomposition rate in water at 37 degrees C. Its degradation profile contained 3 major products and of these, diallylthiourea represented the largest ( approximately 80%) component. The decomposition products did not show antimicrobial activity towards E. coli O157:H7, even when combined with a sub-lethal dose of AIT (10 microL/L). AIT may only be antimicrobial in its original form and any further degradation in water is undesirable. AIT interactions with thioredoxin reductase and acetate kinase were also subjects of this study. AIT at 10 to 100 microL/L was able to significantly inhibit both enzymes, but only 1 microL/L was needed to decrease the activity of thioredoxin reductase. From these results, it can be postulated that: 1) AIT is a more effective antimicrobial at low pH values and its degradation reduces this activity; 2) decomposition products in water might not participate in the antimicrobial action of AIT; and 3) AIT seems to have a multi-targeted mechanism of action, perhaps inhibiting several metabolic pathways and damaging cellular structures.

Effect of free-SH containing compounds on allyl isothiocyanate antimicrobial activity against Escherichia coli O157:H7

Escherichia coli O157:H7 contamination is a significant meat safety issue in many countries. Allyl isothiocyanate (AIT) is a natural compound found to limit the survival of E. coli O157:H7 and other pathogens in meat and meat products. In the present study, it was found that glutathione and cysteine naturally present in meat can interfere with AIT antimicrobial activity. Spectroscopy, HPLC, and LC-MS were used to confirm that glutathione was able to react with AIT and formed a conjugate with no or low bactericidal activity against the tested organisms. The same reaction also occurred at pH values of 4.9 and 5.8 at 25 and 4 degrees C, respectively, which broadly represent storage conditions in raw beef (pH 5.8) and during fermented sausage (pH 4.9) manufacture. Reactions observed help to explain reduction in antimicrobial potency of AIT in food (meat) systems.