The attachment of lipids to C-or N-terminally positioned lysine side-chain amino groups increases the activity of a short synthetic (Arg-Trp) 3 antimicrobial peptide significantly, making these peptides even active against pathogenic Gram-negative bacteria. Thus, a peptide with strong activity against S. aureus (1.1−2 μM) and good activity against A. baumannii and P. aeruginosa (9−18 μM) was identified. The most promising peptide causes 50% hemolysis at 285 μM and shows some selectivity against human cancer cell lines. Interestingly, the increased activity of ferrocenoylated peptides is mostly due to the lipophilicity of the organometallic fragment.

By taking a systematic approach several short organometallic AMP conjugates were discovered which have very low hemolytic activity but virtually the same antimicrobial activity against MRSA as that of vancomycin.

High systemic toxicity of antimicrobial peptides (AMPs) limits their clinical application to the treatment of topical infections; in parenteral systemic application of AMPs the problem of hemolysis is one of the first to be tackled. We now show that the selectivity of lipidated short synthetic AMPs can be optimized substantially by reducing their hemolytic activity without affecting their activity against methicillin resistant Staphylococcus aureus (MRSA). In order to identify the optimized peptides, two sets of 32 diastereomeric H-(D)Arg-WRWRW-(L)Lys(C(O)CnH2n+1)-NH2 (n = 7 or 9) peptides were prepared using a split-split procedure to perform a systematic L-to-D exchange scan on the central WRWRW-fragment. Compared to the all-L C8-lipidated lead sequence, diastereomeric peptides had very similar antibacterial properties, but were over 30 times less hemolytic. We show that the observed hemolysis and antibacterial activity is affected by both differences in lipophilicity of the different peptides and specific combinations of L- and D-amino acid residues. This study identified several peptides that can be used as tools to precisely unravel the origin of hemolysis and thus help to design even further optimized nontoxic very active short antibacterial peptides.

Selected molybdenum sulfur compounds with the formulas (M)[Mo2O2S4L] where (Et4N)2(1), L=S4(2-), (Et4N)(2), L=Cp, (3), L=DMF, K(5), L=serine, M=Et4N(+), K(+), Na(+) and [Mo2O2S2L2] where Na2(4), L=cysteine, and (6), L=threonine, were prepared and subjected to cytotoxicity studies in vitro. The results were analyzed to rank the compounds according to their relative cytotoxicity and to correlate the observed toxicity to specific composition. The results guide future efforts to synthesize highly water soluble, non-toxic, compounds. Strong correlation was observed between toxicity and cation selection, as well as selection of biocompatible ligands combined with alkali metal salts. The most toxic compound analyzed showed about 50 times less cytotoxicity than the cisplatin reference compound in HT-29 cells. Preliminary results from in vivo data agree with the ranking obtained in vitro.