Analogs of 11 that varied the linker portion of the aglycone were also synthesized (Fig. ). The connection between the desosamine moiety and the "linker" aromatic ring was shortened (13), lengthened (14), or modified to contain an additional hydroxymethyl group (15). When the new compounds were evaluated in the cell-free transcription/translation fluorescence assay, compound 15 showed greater inhibition than 11b or 11c, reducing of EmEFG fluorescence by approximately 70% (Fig. ). In order to rule out that the possibility that the inhibitors were false positives due to fluorescence quenching, we incubated purified EmGFP with increasing concentrations of the inhibitory compound. No fluorescence quenching was detected, even at inhibitor concentrations above 1 mM. Compounds investigated in this study did not possess intrinsic fluorescence activity in isolation when excited at 480 nm (See Supporting Information). Compound 15 also inhibited bacterial cell growth, with an MIC ≤50 μg/mL against S. aureus 29213, K. pneumoniae 10031,and E. coli strains NB6900 and 25922. The data suggest inhibition of protein synthesis as a possible mechanism of action for 15. While we have not confirmed it experimentally, it is reasonable to postulate that the ribosome, with its highly conserved macrolide binding pocket, is the target for the desosaminyl glycosides described here. The collection of compounds (7, 10-15) was also screened for activity in an assay that monitors binding of a fluorescent antibody to a lysosomal protein (LAMP-1) that is transferred to the cells' plasma membrane upon lytic granule exocytosis. Because the assay is conducted using flow cytometry, it is not necessary to wash away unbound antibody. To initiate the assay, TALL-104 human leukemic cytotoxic T cells are stimulated with beads coated with anti-CD3 antibodies. Compound 14 inhibited exocytosis in a timedependent manner, with > 75% inhibition at a concentration of 10 µM after 24 hour incubation. It does not appear to affect cell viability, assessed via the percentage of cells in the live cell forward scatter vs side scatter gate.