Synthesis of antitumor 6-alkylidenepenicillanate sulfones and related 3-alkylidene-2-azetidinones

6-Alkylidenepenicillanate sulfoxides and sulfones were synthesized on the base of 6-oxopenicillanate esters. The targeted splitting of their thiazolidine ring led to the formation of 3-alkylidene substituted 4-heteryldithio and 4-methylsulfonyl azetidin-2-ones. Some of mono and bicyclic β-lactams revealed potent cytotoxic properties towards monolayer tumor cells in <10-μM concentrations.