Figure 4. Distances between an antibiotic and the bacterial cell wall.

(A) Chemical schematic of the S. aureus peptidoglycan, highlighting the unique bridge-link and crosslink sites that are often targeted in REDOR experiments through the use of selective D-[1-¹³C]Ala, [¹⁵N]Gly, and L-[ε-¹⁵N]Lys labeling. (B) Chemical structure of [¹⁹F]oritavancin. (C) ¹³C{¹⁹F} REDOR dephasing (ΔS/S₀) as a function of the dipolar evolution time, t, for complexes of [¹⁹F]oritavancin with peptidoglycan isolated from S. aureus whole cells grown on media containing D-[1-¹³C]alanine. The binding site occupancy of [¹⁹F]oritavancin complexed to cell walls was either 33% (open circles) or 16% (closed circles), wherein 2 µmol antibiotic was bound to 20 or 40 mg, respectively, of isolated peptidoglycan (dry mass). The calculated cell wall dephasing (solid lines) assumed a Gaussian distribution of distances for isolated ¹³C-¹⁹F pairs centered at 7.6 Å with a width of 1.5 Å. The dashed line also provides a reasonable fit to the data. Spectra were obtained on a 500 MHz spectrometer. Figure adapted from Kim et al.³⁵