A Cook's tour is presented of the organosulfur chemistry of the genus Allium, as represented, inter alia, by garlic (Allium sativum L.) and onion (Allium cepa L.). We report on the biosynthesis of the S-alk(en)yl-L-cysteine S-oxides (aroma and flavor precursors) in intact plants and on how upon cutting or crushing the plants these precursors are cleaved by allinase enzymes, giving sulfenic acids—highly reactive organosulfur intermediates. In garlic, 2-propenesulfenic acid gives allicin, a thiosulfinate with antibiotic properties, while in onion 1-propenesulfenic acid rearranges to the sulfine (Z)-propanethial S-oxide, the lachrymatory factor (LF) of onion. Highlights of onion chemistry include the assignment of stereochemistry to the LF and determination of the mechanism of its dimerization; the isolation, characterization, and synthesis of thiosulfinates which most closely duplicate the taste and aroma of the freshly cut bulb, and additional unusual compounds such as zwiebelanes (dithiabicyclo[2.1.1]hexanes), a bis-sulfine (a 1,4-butanedithial S,S′-dioxide), antithrombotic and antiasthmatic cepaenes (α-sulfinyl disulfides), and vic-disulfoxides. Especially noteworthy in the chemistry of garlic are the discovery of ajoene, a potent antithrombotic agent from garlic, and the elucidation of the unique sequence of reactions that occur when diallyl disulfide, which is present in steam-distilled garlic oil, is heated. Reaction mechanisms under discussion include [3, 3]- and [2, 3]-sigma-tropic rearrangements involving sulfur (e.g. sulfoxide-accelerated thio- and dithio-Claisen rearrangements) and cycloadditions involving thiocarbonyl systems. In view of the culinary importance of alliaceous plants as well as the unique history of their use in folk medicine, this survey concludes with a discussion of the physiological activity of the components of these plants: cancer prevention, antimicrobial activity, insect and animal attractive/repulsive activity, olfactory–gustatory–lachrymatory properties, effect on lipid metabolism, platelet aggregation inhibitory activity and properties associated with ajoene. And naturally, comments about onion and garlic induced bad breath and heartburn may not be overlooked.

The Organosulfur Chemistry of the Genus Allium – Implications for the Organic Chemistry of Sulfur

https://onlinelibrary.wiley.com/doi/pdf/10.1002/jps.20578

Pharmaceutical Co-Crystals

Allicin (diallylthiosulfinate) is a defence molecule from garlic (Allium sativum L.) with a broad range of biological activities. Allicin is produced upon tissue damage from the non-proteinogenic amino acid alliin (S-allylcysteine sulfoxide) in a reaction that is catalyzed by the enzyme alliinase. Current understanding of the allicin biosynthetic pathway will be presented in this review. Being a thiosulfinate, allicin is a reactive sulfur species (RSS) and undergoes a redox-reaction with thiol groups in glutathione and proteins that is thought to be essential for its biological activity. Allicin is physiologically active in microbial, plant and mammalian cells. In a dose-dependent manner allicin can inhibit the proliferation of both bacteria and fungi or kill cells outright, including antibiotic-resistant strains like methicillin-resistant Staphylococcus aureus (MRSA). Furthermore, in mammalian cell lines, including cancer cells, allicin induces cell-death and inhibits cell proliferation. In plants allicin inhibits seed germination and attenuates root-development. The majority of allicin's effects are believed to be mediated via redox-dependent mechanisms. In sub-lethal concentrations, allicin has a variety of health-promoting properties, for example cholesterol- and blood pressure-lowering effects that are advantageous for the cardio-vascular system. Clearly, allicin has wide-ranging and interesting applications in medicine and (green) agriculture, hence the detailed discussion of its enormous potential in this review. Taken together, allicin is a fascinating biologically active compound whose properties are a direct consequence of the molecule's chemistry.

https://www.mdpi.com/1420-3049/19/8/12591/pdf

Allicin: Chemistry and Biological Properties

A substantial increase in capillary permeability is a feature of acute inflammation in bacterial infections. The present investigation is part of an attempt to prove an old hypothesis, namely, that this increase in permeability is mediated by histamine. A comparative study was made of histamine, of the histamineliberator 48/80, a condensation product ofp-methoxyphenylethylmethylamine and formaldehyde (Baltzly, Buck, de Beer & Webb, 1949), and of leukotaxine (Menkin, 1936, 1938a, b). In animals with a recently injected vital dye in their blood, the intradermal injection of substances that increase permeability of the blood vessels is followed by an accumulation of dye at the site of injection, presumably due to the passage of an excess of dye-stained plasma into the tissue spaces. When the blood flow and the vascular bed of the skin are relatively constant, differences in the size and intensity of stained areas of skin reflect differences in vascular permeability, and may be used to investigate the properties of substances that increase permeability in this way. Our work was confined to the skin of guinea-pigs, partly because much is already known about skin reactions to toxins and other inflammatory agents, and partly because it is a tissue readily studied in the intact and unanaesthetized animal-an important consideration with phenomena which, like the passage of dye through vascular endothelium, are peculiarly dependent on the state of the blood vessels in the tissue under test.

Johannes S. Buck

Papers

Allicin, the antibacterial principle of Allium sativum: II. determination of the chemical structure

A family of long-acting depressors.

The Antibacterial Principle of Allium sativum. III. Its Precursor and “Essential Oil of Garlic”1

The Preparation of N-Mono-substituted and Unsymmetrically Disubstituted Piperazines

Catalytic reduction of alpha-diketones and their derivatives