Photoaffinity Labels of Daptomycin

Abstract

Daptomycin (Dap) is a cyclic lipodepsipeptide antibiotic that is currently used in the treatment of bacterial infections caused by Staphylococcus aureus including the strains that are methicillin-resistant (MRSA), as well as vancomycin-resistant (VRSA). Although it is known that daptomycin inserts into the membrane of the bacteria causing cell death very few details of its specific mechanism of action have been elucidated. Studies on Dap-resistant bacteria suggest that Dap may interact with specific proteins as well as specific lipids. It is anticipated that a photoaffinity label (PAL) of daptomycin (Dap-PAL) will be useful in determining what bacterial membrane components interact with Dap. The objective of this proposal is to prepare a photoaffinity label of daptomycin. Starting from 4,4’-dimethylbenzophenone, a benzophenone derivative was prepared that contained a 4-aldehyde moiety and a 4’-alkyl tail which contained a terminal alkyne group. This derivative was attached to the Orn residue in Dap via reductive amination to give the desired Dap-PAL. The minimal inhibitory concentration (MIC) of the Dap-PAL with Bacillus subtillus was determined to be 1.5 μg/mL which is only two times greater than the MIC of Dap.