Synthesis and antimicrobial activity of tetrodecamycin partial structures

An efficient synthetic approach to the core structure 5 of the novel polyketide antibiotic tetrodecamycin (1) was developed. This approach features the acid-catalyzed cyclization of a tert-butyldimethylsilyl protected methyl alpha-(gamma-hydroxyacyl) tetronate, leading to the novel tricyclic ring skeleton exhibited by 5, and an efficient strategy for the parallel introduction of the cis-diol and exo-methylene function. In addition to 5, diastereomer 26, analogue 6 and several derivatives (16, 27-29) were prepared and evaluated for their antibacterial activities against Staphylococcus aureus (including MRSA) and Enterococcus faecalis and for their cytotoxic activities against human leukemia cell lines (HL-60, Jurkat T-cells). While compound 5 did not inhibit the growth of the Gram-positive pathogens (MICs >128 microg mL(-1)), analogue 6 and 2-naphthoyl derivative 27 showed promising antibacterial activities with MICs of 4-16 microg mL(-1). Remarkably, the antibacterial activity of these compounds was paralleled by cytotoxicity (IC(50) 10-23 microM). The reactive exo-methylene moiety was shown to be crucial, but not sufficient by its own, for both the antibacterial and the cytotoxic activities.