Two new bicyclic sulfoxides from Welsh onion

Newly identified bicyclic sulfoxides, welsonins A₁ (1) and A₂ (2), were isolated from acetone extracts of the bulbs of the Welsh onion (Allium fistulosum). In this study, the structures of 1 and 2, which are tetrahydrothiophene-S-oxide derivatives, were characterized by spectroscopic analysis. These compounds appeared to be derived from the coupling of 1-propenyl sulfenic acid and uronic acid. Welsonin A₁ (1) showed the potential to suppress tumor-cell proliferation by inhibiting the polarization of alternatively activated M2 macrophages.