Onion blend mixed with honey and vinegar is sometimes used as an antidiabetic agent and to control blood pressure. Moreover, it is known to exibit anticarcinogenic activities via enzymatic inhibition, enzymatic induction, and apoptosis. In addition, it possesses the following properties: antiinflammatory, antioxidant, antimicrobial, antifungal, and antiparasitic properties. Further, it plays a role in the prevention of cardiovascular diseases. Wagner et al. isolated thiosulphinates and α-sulphinyldisulphides from the chloroform extract of onion. However, these were not genuine constituents and were volatile and unstable. They also obtained novel biologically active 2,3-dimethyl-5,6- tithiabicyclo[2.1.1] hexane 5-oxide. In order to develop natural healthy foods that can prevent and combat the above diseases, we tried to isolate a stable substance from the acetone extract of onion. Onions were roughly chopped and soaked in acetone for 3 days at room temperature. The filtrate was evaporated at 40℃ in vacuo to yield a residue, which was subjected to Diaion HP-20 and then repeatedly dhromatographed on silica gel to give a small amount of a new compound named onionin A (1). The positive HR-FAB-MS of 1 showed peaks due to [M+Na]^+ and [C_6H_<11>OS]^+ at m/z 243.0489 (Calcd for C_9H_<16>O_2S_2Na, 243.0489), 70%, and at m/z 131.0525 [Calcd for C_6H_<11>OS, 131.0531], base peak, respectiely. The ^1H- and ^<13>C-NMR spectra and various 2D-NMR techniques revealed the structure of 1 as shown in Fig. 4. It is known that inhibition of M2 macrophage polarization suppresses tumor cell proliferation. We then examined the inhibitoy effect of 1, a new compound isolated from onion, on CD163 expression, M2 macrophage marker, by a Cell noncompetitive enzyme-linked immunosorbent assay (Cell-ELISA). As a result, 1 significantly inhibited CD13 expression. This result suggests that onionin A (1) has a potential to suppress tumor cell proliferation by inhibition of M2 macrophage polarization.
